Sequential ethane filling induced structural transitions in a flexible–robust metal–organic framework for ethylene purification

Domain: neuroscience
Published: 2026-04-08
Editorial outcome: minor_revision

Abstract
The preferential identification of inert ethane molecules and the corresponding pore-filling mechanism are fundamentally challenging. Although flexible metal–organic frameworks are considered promising candidates to enhance ethane selectivity, their gate-opening pressures for ethane and ethylene are usually similar, which limits further improvement in their separation performance. Here, we report a flexible–robust metal–organic framework, TYUT-18, whose binary pore system combined with the flexible deformation of the framework produces significantly different gate-opening pressures for ethane (0.18 bar) and ethylene (0.48 bar) at 298 K, effectively reducing competitive adsorption in the same pore and improving overall separation efficiency, and achieves the purification of ultra-high purity ethylene (99.995%) with a separation productivity of 15.7 L kg-1. More importantly, we have systematically elucidated the dynamic filling behaviour of ethane molecules in the flexible–robust framework system, a process of preferentially occupying the large pore cavities then filling into the small ones was uncovered using a combination of extensive single-crystal X-ray diffraction studies and density functional theory calculations. The evolution of this sequential guest-filling mechanism demonstrated the merit of binary pore networks for challenging gas separation tasks and thereby offers valuable insights for the design of highly selective separation materials.

Introduction
Ultra-high purity ethylene (C2H4) is a critical feedstock in the petrochemical industry, which is extensively employed during the production of special type high-end polyolefins, including metallocene polyethylene, ultrahigh molecular weight polyethylene fibre, and others, with a typical purity requirement exceeding 99.995%1-3. Currently, the critical purification of ultra-high purity C2H4 in industry is predominantly achieved using an energy-intensive multistage distillation process4-7. Therefore, there is an urgent need to develop highly selective adsorbents capable of the targeted removal of trace ethane (C2H6), thereby markedly simplifying the current industrial purification process and minimizing energy consumption8-10.

Metal–organic frameworks (MOFs) have emerged as promising candidates for the efficient separation of C2H4/C2H6 due to their highly tuneable architectures and versatile functionalization strategies11-18. However, the preferential recognition of the relatively inert and larger C2H6 molecules from high-concentration C2H4 mixtures remains a major challenge19-21. In general, robust MOFs offer excellent structural stability, while their inherent porous structures often make it difficult to simultaneously achieve both a high C2H6 adsorption capacity and high selectivity6,7,22-27. Flexible MOF with rich supramolecular interactions can achieve the selective recognition of specific gas molecules via the “gate-opening” effect, while they have defects such as closely gate-opening pressures and low adsorption capacity under low-pressure conditions28-32. In contrast, flexible–robust MOFs combine the structural advantages of their robust pore cavities and flexible pore windows, which are expected to achieve high adsorption capacity at low pressure and improved separation selectivity33-38.

Subsequently, we successfully synthesized a flexible–robust MOF, TYUT-17, which achieves high C2H6 adsorption capacity (62.6 cm3 g-1) and C2H6/C2H4 selectivity (6.4) under low-pressure conditions (0.1 bar)19. Nevertheless, its single pore structure concentrates the flexible response and molecular recognition function within the same pore, causing C2H6 and C2H4 molecules to exhibit similar pore-opening behaviours during adsorption, resulting in competitive adsorption within the same pore.

We propose engineering two distinct pore cavities (large and small) within the framework in order to overcome the inherent simple recognition mechanism of single pore systems. Within this system, the large pores facilitate the initial preferential adsorption of C2H6, which gives sufficient gas uptakes at low pressure region, while the small pores highly match the cross-section of C2H6, allowing their precise capture via the gating effect (Fig. 1), providing extra recognition selectivity. Despite the great potential of such flexible framework systems, their effective implementation requires a comprehensive understanding of the dynamic adsorption behaviour of C2H6 in binary pore system MOFs, particularly their sequential filling and reversible release mechanisms39-42. For a long time, chemists have used X-ray diffraction and other techniques in order to identify the adsorption sites of C2H6 within MOFs, while the specific pore-filling process remains poorly understood41,43-50. Notably, Yaghi et al. combined in situ gas-loading single-crystal X-ray diffraction (SCXRD) with density functional theory (DFT) calculations to systematically elucidate the filling mechanism of water molecules in MOF-30351, establishing a research paradigm for probing filling pathways of guest molecules in robust porous materials at the molecular scale52. Subsequently, through in situ gas-loading SCXRD analysis and DFT calculations at different temperatures, Kitagawa et al. systematically elucidated the sequential filling mechanism of C2 gas in flexible–robust MOFs and its correlation with framework flexibility, greatly advancing the understanding of the sequential adsorption behavior of guest molecules in flexible-robust MOFs38. Based on this, we further expanded our research perspective to pressure-mediated effects to reveal the sequential adsorption behavior of C2H6 molecules in flexible–robust MOFs under different pressures and their corresponding structural responses.

Herein, we have synthesized a flexible–robust MOF, Zn(L1)(L2), referred to as TYUT-18 (TYUT: Taiyuan University of Technology, L1: 1,3-di(4-carboxyphenyl)benzene, L2: 1,4-bis(4-pyridyl)benzene), which features a binary pore system that combines the structural advantages of large pore cavities for rapid adsorption and small pore cavities for selective gate-opening responses. TYUT-18 exhibits a pronounced difference in gate-opening pressures for C2H6 (0.18 bar) and C2H4 (0.48 bar), and enables the purification of C2H4 to an ultra-high purity level (99.995%). Furthermore, we have clearly discovered the dynamic pore-filling behaviour of C2H6 molecules in flexible–robust MOF combining SCXRD and DFT calculations, which followed the principle of first occupying the large pores and then filling the small pores. This study provides a theoretical basis for the rational design of next-generation materials for efficient C2H6-selective materials.

Results
Synthesis and Structural Determination

Single crystals of TYUT-18 were successfully synthesized via the self-assembly of zinc nitrate with two organic ligands, 1,3-di(4-carboxyphenyl)benzene (L1) and 1,4-bis(4-pyridyl)benzene (L2) (Fig. 2a and Supplementary Fig. 1). In situ SCXRD studies revealed the single-crystal to single-crystal (sc-sc) transformation of guest-loaded TYUT-18 (α) (CCDC 2407210, Supplementary Data 1 and 9) to guest-free TYUT-18 (β) (CCDC 2412958, Supplementary Data 2 and 10) after the activation process.

SCXRD analysis revealed that the structure of TYUT-18 (α) consisted of a three-dimensional (3D) framework composed of Zn paddle-wheel secondary building units (SBUs) and organic ligands, which formed a porous architecture with a binary pore system. The L1 ligand resided in the equatorial plane, forming pore cavity A (6.5 Å), whereas the L2 ligand occupied the axial coordination site and formed pore cavity B (4.8 Å) with L1 ligand. The pore size and adsorption properties of TYUT-18 were evaluated using N2 adsorption/desorption isotherms at 77 K (Supplementary Fig. 2). The Brunauer-Emmett-Teller (BET) specific surface area of TYUT-18 was calculated to be 636.3 m2 g-1 and the pore size distribution exhibited binary pores of 6.5 Å and 4.8 Å. The crystal belonged to the monoclinic C12/c1 space group. Guest-free TYUT-18 (β) could be obtained by heating the guest-loaded TYUT-18 (α) crystal at 423 K for 12 h. Although its space group remained unchanged, the cell parameters changed significantly, which indicated that TYUT-18 underwent a structural transformation after removing the guest molecules (Supplementary Table 2). We can also observe the phase transition from TYUT-18 (β) to TYUT-18 (α), powder X-ray diffraction (PXRD) results showed a clearly diffraction peak position shifted after the activation process (Supplementary Fig. 3). Thermogravimetric analysis (TGA) confirmed that the 21.5% weight loss observed below 573 K, which could be attributed to the complete removal of the N, N-dimethylformamide (DMF) solvent molecules (Supplementary Fig. 4). Scanning electron microscopy (SEM) images revealed that the material retained its intact lamellar morphology throughout the activation and adsorption processes (Supplementary Fig. 5), thereby further confirming its structural stability.

It is noteworthy that TYUT-18 displayed multidimensional structural flexibility, encompassing ligand rotation and dynamic modulation of the bond angle between the ligand and metal node (Fig. 2b). Rotation of the benzene ring in the L1 ligand during the α to β phase transition (Supplementary Fig. 6), which was accompanied by changes in the bond angles, altered the dimensions of pore cavity A from 5.3 Å × 6.4 Å to 4.8 Å × 7.9 Å (Fig. 2c). Simultaneously, rotation of the benzene ring and pyridine ring in the L2 ligand shifted its corresponding bond angles from 120.2° and 121.0° to 123.5° and 119.1°, respectively (Fig. 2d). Furthermore, ligand rotation modulated the bond angle between the ligand and metal node: In TYUT-18 (α), ∠L1-SBU-L2 ranged from 69.98° to 110.02°, whereas in TYUT-18 (β) it ranged from 63.84° to 116.16° (Supplementary Fig. 7). The neatly arrayed benzene rings and exposed oxygen atoms in pore cavity A created an aromatic-rich environment with a pore diameter of 6.4 Å, which permitted C2H6 to preferentially occupy it at low pressure, thereby imparting a higher initial adsorption capacity for C2H6. In addition, the 4.8 Å pore diameter of cavity B is highly matched with the cross-section of a C2H6 molecule, further triggering a preferential gate-opening effect for C2H6. The synergistic effect of the binary pore system and dynamic structural responsiveness ultimately led to typical step-shaped adsorption behaviour during the C2H6 adsorption process.

Gas sorption analysis

Subsequently, we systematically studied the gas adsorption behaviour of TYUT-18. The adsorption isotherms of C2H6 and C2H4 on TYUT-18 were measured at 273, 298 K and 313 K (Fig. 2e and Supplementary Fig. 8). The isotherm obtained for C2H6 exhibited a significant step-shaped feature with an adsorption capacity of 21.3 cm3 g-1 at 0.1 bar and 298 K, which could be attributed to the preferential occupation of large pore cavity A. As the pressure increased to 0.18 bar, the adsorption capacity rapidly increased to 35.6 cm3 g-1, accompanied by a phase transition from the β to α phase. When the pressure was further increased to 0.5 bar, the flexible pores were fully opened, and the adsorption capacity of TYUT-18 for C2H6 reached 59.7 cm3 g-1, which was significantly better than most reported flexible C2H6-selective MOFs, such as NKPOC-DS (43.7 cm3 g-1)44, ZIF-7 (35.4 cm3 g-1)28, FJI-W-66 (23.9 cm3 g-1)53 and IITKGP-39 (11.3 cm3 g-1)32, and second only to TYUT-17 (66.9 cm3 g-1)19 (Fig. 2f). Furthermore, compared to most reported robust C2H6-selective MOFs, TYUT-18 exhibits a moderately high C2H6 adsorption capacity (Supplementary Fig. 9). Subsequently, the saturated adsorption capacity at 1 bar reached 67.9 cm3 g-1. In contrast, the adsorption isotherm obtained for C2H4 did not show obvious step-shaped feature; its structural phase transition occurred and was delayed until 0.48 bar, corresponding to an uptake of 43.5 cm3 g-1. The saturated uptake at 1 bar reached 60.0 cm3 g-1. At the same time, at 298 K and 1 bar, the C2H6/C2H4 uptake ratio of TYUT-18 reached 1.13 (Fig. 2g), which was better than most reported flexible C2H6-selective MOFs, such as ZIF-7 (1.04)28, FJI-W-66 (1.02)53, NTU-101-NH2 (1.03)31 and TYUT-17 (1.09)19, and second only to IITKGP-39 (1.47)32. When comparing with the robust C2H6-selective MOFs, although the uptake ratio of TYUT-18 is not outstanding, TYUT-18 still exhibits excellent separation performance, which may be closely related to its flexible mechanism (Supplementary Fig. 9). Upon heating to 313 K, both gases exhibited delayed phase transition pressures with C2H4 showing a more sluggish response compared to C2H6. The uptake at 1 bar decreased to 57.9 cm3 g-1 for C2H6 and 50.2 cm3 g-1 for C2H4 (Supplementary Fig. 8). Our results indicated that TYUT-18 was highly sensitive to C2H6 due to its binary pore system and reversible structural transition, thereby enabling the highly selective capture of C2H6.

We conducted in situ gas-loaded variable pressure PXRD experiments to systematically study the structural transformation mechanism of TYUT-18 induced by C2H6 and C2H4 under different pressure conditions. For C2H6 adsorption, during the large-pore filling stage, the PXRD pattern of TYUT-18 at a pressure of 0.13 bar retained the characteristic features of the β phase, as shown in Figs. 3a and 3b. Upon increasing the pressure to 0.18 bar, the framework underwent a phase transition and entered the small-pore filling stage, as evidenced by the gradual disappearance of the β phase diffraction peaks at 2θ = 8.2°, 14.1° and 22.7°, and the emergence of new peaks corresponding to the α phase at 2θ = 9.1° and 14.8°. Concurrently, the diffraction intensities at 2θ = 21.2°, 23.6° and 25.7° were markedly enhanced, further confirming the structural transformation from the β to α phase. During C2H6 desorption, the PXRD pattern reverted to the β phase when the pressure decreased to 0.13 bar, thereby confirming the reversible nature of the phase transformation in TYUT-18 under a C2H6 atmosphere. In contrast, in situ variable-pressure PXRD analysis of C2H4 at 298 K (Figs. 3d and 3e) revealed that a significantly higher pressure threshold was required to induce a phase transition compared to C2H6. A phase transition from the β to α phase was observed in the PXRD pattern when the pressure reached 0.48 bar. During desorption, the structure reverted to the β phase as the pressure decreased to 0.05 bar. These results well demonstrate that C2H6 could more effectively trigger the reversible phase transition in TYUT-18 at lower pressure, which was consistent with the distinct adsorption behaviours of C2H6 and C2H4 observed in our isothermal adsorption studies. Furthermore, the contour plot of in situ PXRD patterns (Figs. 3c and 3f) clearly depicts the dynamic structural evolution of TYUT-18 in C2H6 and C2H4 atmospheres that occurs with changes in pressure, demonstrating its preferential recognition ability for C2H6 and reversible structural phase transition behaviour during the adsorption-desorption process.

The isosteric heat of adsorption (Qst) serves as a key indicator of the interaction strength between the adsorbent and adsorbate. Accordingly, we calculated the Qst values for C2H6 and C2H4 in TYUT-18 using the Clausius–Clapeyron equation (Supplementary Fig. 10 and 11). At zero coverage, the Qst values for C2H6 and C2H4 were 28.6 and 24.1 kJ mol-1, respectively, which confirmed the stronger binding affinity of TYUT-18 toward C2H6. Moreover, the moderate Qst value not only favoured the selective adsorption of C2H6, but also enabled efficient material regeneration under ambient conditions (Supplementary Fig. 12). In addition, kinetic measurements demonstrated that TYUT-18 exhibited excellent mass transfer characteristics (Supplementary Figs. 13–15 and Supplementary Table 6). At 298 K, with a pressurization rate of 100 mbar min-1, both C2H6 and C2H4 reached adsorption equilibrium in TYUT-18 within approximately 10 minutes. This adsorption equilibrium time is shorter than that of Cu(Qc) (13 minutes), MAF-7 (15 minutes), TYUT-12 (18 minutes) and ZIF-7 (40 minutes) (Supplementary Figs. 16 and 17). And due to the preferential flexible response of TYUT-18 to C2H6, its diffusion time constant (1.77 × 10-2 min-1) is greater than that of C2H4 (1.27 × 10-2 min-1). Desorption experiments further showed that both C2H6 and C2H4 could be completely desorbed from TYUT-18 within 10 minutes. This excellent kinetic behaviour could be attributed to the synergistic effect of a binary pore system and dynamic structural response mechanism in TYUT-18; the binary pore system constructs multi-level precise recognition sites and the reversible configuration regulation in the framework adsorption process reduces the diffusion resistance and accelerates the diffusion of the guest molecules. In summary, TYUT-18 combined high C2H6 selectivity adsorption, moderate adsorption heat, and fast adsorption kinetics, offering advantages for energy-efficient separation processes and demonstrates strong potential for industrial applications.

Gas-loaded SCXRD and computational simulation studies

These excellent thermodynamic and kinetic adsorption properties prompted an in-depth investigation into the adsorption mechanism. The dynamic pore filling mechanism of hydrocarbon molecules in the binary pore system was clearly elucidated using SCXRD analysis on TYUT-18 (Fig. 4 and Supplementary Table 3). The results revealed that C2H6 molecules followed the dynamic adsorption-desorption order of preferentially occupying the larger pore cavities then filling the small ones in TYUT-18. During the initial stage of adsorption, the C2H6 molecules preferentially and symmetrically occupied large pore cavity A, maintaining the β phase and forming TYUT-18(β)•0.25C2H6 (CCDC 2449695, Supplementary Data 3 and 11). When the adsorbed C2H6 in cavity A reached saturation, it triggered a phase transition from the β to α phase. Subsequently, the remaining C2H6 molecules sequentially filled small cavity B and reached thermodynamic saturation, thereby forming TYUT-18(α)•3C2H6 (CCDC 2473904, Supplementary Data 5 and 13). The desorption process followed the same sequence as the adsorption process. Initially, the C2H6 molecules in pore cavity A were first desorbed, while the framework remained in the α phase, forming TYUT-18(α)•1C2H6 (CCDC 2449696, Supplementary Data 4 and 12). Subsequently, the C2H6 molecules in pore cavity B were removed and the framework gradually returned to the TYUT-18 (β) phase. This process was accompanied by significant structural dynamics: the unit cell parameters along the a-axes and b-axes underwent significant changes and the L1 and L2 ligands underwent rotations, resulting in fine-tuning of the overall framework geometry; the L1 ligand angle change was particularly pronounced. Similarly, the dynamic filling mechanism of C2H4 in TYUT-18 was elucidated using a combination of in situ PXRD, in situ SCXRD, and Rietveld structure refinement (Supplementary Figs. 18–20 and Supplementary Tables 4 and 5). The adsorption–desorption sequence of C2H4 was similar to that of C2H6. The C2H4 molecules initially preferentially occupied pore cavity A (β phase). When the adsorbed C2H4 in cavity A reached saturation, the framework underwent a phase transition to the α phase. Subsequently, the C2H4 molecules filled pore cavity B until equilibrium was established. During desorption, the C2H4 in pore cavity A were first removed (maintaining the α phase), followed by gradual desorption of the C2H4 in pore cavity B, causing the framework to return to the β phase. A systematic elucidation of the dynamic adsorption sequence of C2H6 and C2H4 not only deepens our understanding of the adsorption mechanisms governing flexible MOFs, but also provides an important theoretical basis for their structural design and functional optimization.

We systematically analysed the adsorption interactions of the three gas-loaded single crystal structures in order to further elucidate how the TYUT-18 pore chemical environment regulated the C2H6 adsorption process: TYUT-18(β)•0.25C2H6, TYUT-18(α)•3C2H6, and TYUT-18(α)•1C2H6 (Fig. 5). In TYUT-18(β)•0.25C2H6, each C2H6 molecule resided within pore cavity A, establishing four C–H···π interactions (3.33–3.70 Å) and seven C–H···H van der Waals interactions (2.88–3.97 Å) with the benzene ring of ligand L1, along with two C–H···O interactions (3.11 Å and 2.97 Å) with the exposed O atoms (Fig. 5a). In TYUT-18(α)•3C2H6, the C2H6 molecules were distributed across both pore cavities A and B. Within pore cavity A, each C2H6 molecule formed five C–H···π interactions (3.27–3.95 Å) and nine C–H···H van der Waals interactions (2.70–3.98 Å) with ligand L1, together with one C–H···O interaction (3.31 Å) with the exposed O atom (Fig. 5c). Within pore cavity B, each C2H6 molecule formed four C–H···π interactions (3.33–3.93 Å) and fifteen C–H···H van der Waals interactions (2.33–3.86 Å) with the benzene rings in ligands L1 and L2, and one C–H···N interaction (3.93 Å) with the N atom of ligand L2 (Fig. 5b). In TYUT-18(α)•1C2H6, each C2H6 molecule was located within pore cavity B, establishing three C–H···π interactions (3.31–3.70 Å) and sixteen C–H···H van der Waals contacts (2.90–3.60 Å) with the benzene rings in ligands L1 and L2, together with one C–H···N interaction (3.82 Å) involving the nitrogen atom of ligand L2 (Fig. 5d). These observations demonstrated that the C2H6 molecules were bound to the framework through multiple weak interactions across various C2H6-loaded states. Similarly, our structural analysis of the C2H4-loaded single crystals [TYUT-18(β)•1C2H4 (Supplementary Data 7), TYUT-18(α)•2C2H4 (Supplementary Data 8), and TYUT-18(α)•0.25C2H4 (CCDC 2449694, Supplementary Data 6 and 14)] revealed that the C2H4 molecules in pore cavities A and B engaged in fewer C–H···π, C–H···N, and C–H···O interactions when compared to C2H6 with longer interaction distances and correspondingly weaker binding strengths (Supplementary Fig. 21). This disparity clearly demonstrated that TYUT-18 exhibited a higher binding affinity toward C2H6, thereby clarifying the potential reasons for preferential adsorption of C2H6 in C2H6/C2H4 separation.

The in situ gas-loading SCXRD analysis presented above indicates that TYUT-18 exhibits sequential adsorption behaviour, preferentially occupying the large pore cavities before filling the smaller ones. Subsequently, we performed DFT calculations and Monte Carlo simulations in order to elucidate this behaviour. In our model, the deformation energy (Edef) is defined as the energy difference between the closed-pore (β) and open-pore (α) states in the absence of guest molecules, whereas the interaction energy (Eint) represents the energy reduction resulting from guest-host interactions due to the intrinsic flexibility of TYUT-1840,54. Supplementary Fig. 22 shows the Eint of C2H6 adsorption within the small pores is comparatively higher (-25.84 kJ mol-1). However, the Edef required for transition from the β phase to the α phase is ~18.79 kJ mol-1. Under low-pressure conditions, C2H6 is preferentially adsorbed in the deformation-free large pores of the β phase (-17.90 kJ mol-1). As the large pores gradually reach saturation, the cumulative energy released from subsequent adsorption into the small pores surpasses Edef, thereby inducing a structural transition from the β to α phase, which initiates filling of the small pores. This energy balance explains the order of large pore adsorption followed by small pore filling observed in our experimental isotherms. In contrast, the Eint of C2H4 adsorption during this process is weaker (-11.96 kJ mol-1 within the large pores and -19.28 kJ mol-1 within the small pores), rendering framework deformation more challenging under identical conditions and necessitating, which necessitates higher pressures to trigger the α to β phase transition (Supplementary Fig. 23). When considering that TYUT-18 reverts to the α phase upon saturation, DFT calculations were performed on the geometrically optimized TYUT-18 (α) framework in order to identify the adsorption sites. Supplementary Fig. 24 shows the C2H6 molecules form more and stronger van der Waals forces and hydrogen bond interactions with TYUT-18 than C2H4, which is consistent with our in situ gas-loading SCXRD analysis results.

Dynamic breakthrough experiments

Given the preferential recognition and high absorption of C2H6 by TYUT-18, we performed further fixed-bed breakthrough experiments in order to assess its performance under realistic dynamic separation conditions. Breakthrough tests were conducted at 298 K and 313 K using a gas flow rate of 2 mL min-1 with 50/50 and 10/90 (v/v) C2H6/C2H4 mixtures, respectively (Fig. 6 and Supplementary Fig. 26). The breakthrough curve show that C2H4 passed through the column first and C2H6 was retained in the bed due to its preferential adsorption by TYUT-18. In the C2H6/C2H4 (v/v = 50/50) system, TYUT-18 achieved a maximum separation time of 18 min g-1 at 298 K and high purity C2H4 (>99.99%) could be collected within this time interval, which demonstrated its excellent selective separation ability for C2H6 (Fig. 6a). In addition, compared to the previously reported single pore flexible-robust TYUT-17 (Supplementary Fig. 25), TYUT-18 exhibits a significantly shorter co-adsorption time under the same dynamic breakthrough conditions, indicating that the synergistic effect of its binary porous structure and flexibility effectively weakens the competitive adsorption behaviour of C2H4 under dynamic conditions. This shortens the overall separation cycle, thereby improving its overall separation efficiency. Furthermore, their desorption curves (Supplementary Figs. 27) show that both C2H6 and C2H4 can achieve complete desorption and regeneration within 8 min g-1 at 298 K. When the temperature increased to 313 K, TYUT-18 could still maintain its good separation performance for the C2H6/C2H4 mixture (v/v = 50/50), indicating the effectiveness of its flexible adsorption mechanism over a wide temperature range. Based on the above results, we further investigated the separation ability of TYUT-18 in a C2H6/C2H4 (v/v = 10/90) mixture. Fig. 6b and Supplementary Fig. 26 show TYUT-18 achieved separation times of 28 min g-1 and 22 min g-1 at 298 K and 313 K, respectively, and high purity C2H4 (>99.99%) could be collected within these time intervals, which demonstrated its excellent separation ability. To verify the separation capability of TYUT-18 for low-concentration C2H6 impurities, we conducted separation experiments using C2H6/C2H4 mixtures with volume ratios of 5/95 and 1/99 (Supplementary Figs. 28 and 29). The experimental results confirm that TYUT-18 can effectively remove low concentration C2H6 impurities, demonstrating excellent separation performance. In addition, five consecutive breakthrough cycles were performed for both gas mixtures (Figs. 6c and 6d and Supplementary Figs. 30-33) and the results demonstrated that TYUT-18 retained excellent cyclic stability at both 298 K and 313 K.

Based on the excellent separation performance of TYUT-18 for C2H6/C2H4 gas mixtures, we further conducted the quantitative analysis of the product yield and purity using breakthrough curves to intuitively evaluate the C2H4 separation effect of TYUT-18. At 298 K, TYUT-18 enabled the recovery of C2H4 from a C2H6/C2H4 (v/v = 10/90) mixture, affording a highly pure product (99.99%) with a yield reaching 50.4 L kg-1 (Supplementary Figs. 34-36). This performance markedly surpassed that of several representative C2H6-selective adsorbents, including TYUT-12 (24.5 L kg-1)19, Zn(ad)(int) (36.2 L kg-1)55, MUF-15 (20.3 L kg-1)22, JNU-2 (27.5 L kg-1)56, ZJU-120a (10.8 L kg-1)57, and ZIF-7 (7.2 L kg-1)28. Although its performance is slightly lower than that of Fe2(O2)(dobdc) (72.3 L kg-1) and TYUT-17 (77.4 L kg-1), it fully demonstrated the application potential of TYUT-18 in C2H6/C2H4 separation (Supplementary Table 7). In order to further verify the feasibility of deep purification, a ternary C2H2/C2H4/C2H6 (1/98/1, v/v/v) gas mixture was designed to mimic a complex industrial feedstock with a total flow rate of 2 mL min-1 and employed to evaluate the capacity for producing ultra-high purity C2H4 (>99.995%). Supplementary Fig. 37 illustrates that C2H4 was the first component to elute from the packed column at 21 min with its purity rapidly increasing to 99.999% by 24 min. The C2H6 and C2H2 were subsequently eluted and detected at about 29 min and 30 min, respectively. Gas chromatography-mass spectrometry analysis (detection limits: 0.001% for C2H6 and 0.1 ppm for C2H2) confirmed that the concentrations of C2H6 and C2H2 in the ultra-pure C2H4 product were below 0.005% and 0.1 ppm, respectively. Ultimately, TYUT-18 enabled the separation of ultra-high purity C2H4 (>99.995%) with a yield of up to 15.7 L kg-1. In three breakthrough cycle tests of C2H2/C2H4/C2H6 (1/98/1, v/v/v), the separation performance remained stable, indicating that there is no irreversible retention of C2H2 in the pores of TYUT-18 (Supplementary Fig. 37b). Moreover, regeneration experiments of C2H2 showed that C2H2 can be completely and reversibly desorbed from TYUT-18 (Supplementary Fig. 38). In summary, these results fully demonstrate the excellent cycling stability and regeneration performance of TYUT-18, providing a reliable and efficient strategy for the deep purification of C2H4, and showing promising prospects for industrial applications.

In actual industrial separation processes, a certain amount of moisture is inevitably encountered, typically originating from high-temperature processes such as steam cracking and ethane dehydrogenation. The presence of water can lead to competitive adsorption between the gas and water, thereby reducing the hydrothermal stability of the adsorbent and weakening its separation performance. To evaluate the reliability of TYUT-18 in humid environments, we first conducted room temperature water vapor adsorption tests. The results showed that under a relative humidity of 40%, TYUT-18 absorbed only 0.008 g g-1 of water, exhibiting excellent hydrophobic properties. The water contact angle test further confirmed its excellent hydrophobicity (Supplementary Fig. 39a). This is mainly attributed to the fact that TYUT-18 is composed of dense aromatic rings, forming a highly hydrophobic microenvironment. Simultaneously, the absence of open metal sites or strongly polar functional groups in the framework results in weak interactions between the adsorbent and water molecules, thus ensuring the TYUT-18 exhibits excellent resistance to water competitive adsorption under humid conditions. Furthermore, the positions and intensities of the characteristic peaks in the PXRD pattern after water absorption (Supplementary Fig. 39b) did not change, indicating that the crystal structure of the material remains stable under humid conditions. Based on this, we further conducted dynamic breakthrough experiments at 298 K and 1 bar using C2H4/C2H6 mixtures (v/v = 50/50) with different relative humidities (RH = 40% and 70%) (Supplementary Figs. 39c and 38d). Notably, even under high humidity (70% RH) conditions, the breakthrough time of TYUT-18 remained almost identical to that under dry conditions, demonstrating its excellent stability in high-humidity environments and showcasing highly competitive industrial application prospects and environmental adaptability.

Stability study

Adsorbents must exhibit both excellent structural stability and efficient regenerability for practical application. Therefore, a systematic investigation was carried out from three perspectives in order to comprehensively assess the application viability of TYUT-18: Long-term structural stability, solvent resistance, and acid-base tolerance. After five consecutive adsorption–desorption cycles, the PXRD pattern of TYUT-18 remained unchanged when compared to the original sample and no loss in its C2H6 adsorption capacity was observed (Supplementary Fig. 40). Furthermore, after storage in air for six months, the PXRD pattern of TYUT-18 remained identical to that of the fresh sample. In addition, its crystalline structure was preserved even after multiple adsorption and breakthrough experiments (Fig. 6e and Supplementary Fig. 41). In the chemical stability test, the intensity of the characteristic diffraction peaks observed in the PXRD spectrum did not change after TYUT-18 was soaked in solvents of different polarities such as dichloromethane, methanol and ethanol for 7 d or soaked in acidic and alkaline solutions with pH in the range of 1–13 for 48 h, which indicated that it could maintain high crystallinity in polar/non-polar solvents over a wide pH range. At the same time, its C2H6 adsorption performance was almost unaffected and the adsorption capacity remained stable even after being soaked in acidic (pH = 1) or alkaline (pH = 13) solutions (Fig. 6e and Supplementary Figs. 42–45). A photograph of TYUT-18 single crystals obtained using microscopy revealed that the TYUT-18 crystals retained their intact particle structure after solvent exchange, activation, adsorption testing, and soaking in solutions at pH = 3 and 13, exhibiting a smooth surface without cracks (Fig. 6f). In summary, TYUT-18 exhibited excellent structural stability and regenerability. It not only withstood harsh chemical environments, but also demonstrated strong reusability, laying a robust foundation for its application in industrial scale continuous separation processes.

Methods
Synthesis of TYUT-18

A mixture Zn(NO3)2·6H2O (29.7 mg, 0.1 mmol), 1,3-di(4 carboxyphenyl)benzene (33 mg, 0.1 mmol ) and 1,4-di(pyridin-4-yl)benzene (23.2 mg, 0.1 mmol) were dissolved in 8 mL DMF of 20 ml vial. After placed the vial in 373 K oven for 2 days, colourless plate type single crystals obtained. The contents were cooled to room temperature, filtered, and washed with fresh DMF for couple of times.

Single-crystal X-ray diffraction

The SCXRD data of TYUT-18 (α) and TYUT-18 (β) were collected on the Bruker D8 VENTURE TXS PHOTON II diffractometer. For in situ SCXRD measurements, the TYUT-18 sample was first purged with N2 at 423 K for 12 hours to completely remove solvent molecules from the pores. Then, the target feed gas was introduced to the set pressure and equilibrated for 6 h. The specific conditions are as follows: for TYUT-18(β)•0.25C2H6 and TYUT-18(α)•3C2H6, the C2H6 gas was pressurized to 0.13 bar and 1 bar respectively using the Micromeritics ASAP 2020 analyzer; for TYUT-18(α)•1C2H6 and TYUT-18(α)•0.25C2H4, the C2H6 and C2H4 gases were first pressurized to 1 bar, and then desorbed to 0.4 bar and 0.6 bar respectively. The SCXRD data of TYUT-18(β)•0.25C2H6, TYUT-18(α)•1C2H6 and TYUT-18(α)•0.25C2H4 were collected on the Bruker D8 VENTURE TXS PHOTON II diffractometer.
The SCXRD data of TYUT-18(α)•3C2H6 was collected Single crystal X-ray diffraction data were collected at the Shanghai Synchrotron Light Source Line BL10U2 station and station equipped with a Dectris Eiger 16M, S/N E-32-0111 surface detector respectively. The structure was solved by direct methods using the SHELXTL software package and further refined with different Fourier syntheses. All non-hydrogen atoms on the framework were refined anisotropically; all hydrogen atoms were generated geometrically and refined in the riding mode. All the phenyl rings were treated with rigid constraints.

In situ PXRD measurements

A customized gas partial pressure control system was developed (Supplementary Fig. 52). To precisely regulate gas composition, two mass flow controllers (MFCs) with different flow ranges (100 sccm and 5 sccm for low partial pressures below 5%) were connected to either the C2H6 or C2H4 gas cylinders. An additional pair of MFCs was linked to a nitrogen (N2) cylinder, serving as the purge gas for sample activation. The gas mixture was then introduced into an in situ PXRD chamber (Bruker D8 Advance, Cu Kα radiation, λ = 1.5418 Å). Diffraction patterns were collected over the 2θ range of 4–40° with a total acquisition time of 5 min at room temperature about 298 K. All stainless-steel valves and fittings were sourced from Shanghai X-tec Fluid Technology Co., Ltd., and the MFCs were supplied by Alicat Scientific (a Halma company).

PXRD refinement

The refined package is TOPAS V5.0, which describes the background using 24th-order Chebyshev polynomials and the peak shapes using pseudo-Voigt peak shapes. Preferred orientation is described using the spherical cofunction of order 4. The refinement was performed sequentially on the scale factor, atomic coordinates, isotropic displacement parameters, site occupancies, and preferred orientation. Guest molecules were introduced into the host framework model as rigid bodies, and their possible positions were determined through a simulated annealing algorithm.

Density functional theory calculations

The structures of TYUT-18 as well as their complexes with C2 molecules were optimized at GFN2-xTB level by using a tight-binding quantum chemical xTB method performed with the ASE software suite. The energy difference of the TYUT-18 framework from closed phase to open phase was calculated by DFT method. To gain deeper insights into the energy change in the adsorption process, we evaluated the energy landscape in the C2H6 and C2H4 adsorption processes on TYUT-18. The adsorption position of the guest molecules were estimated using classical Monte-Carlo simulations, then optimized using DFT calculations with the dispersion-corrected Perdew-Burke-Ernzerhof functional (PBE-D3), and the interaction energy of the gas (Eint) at each adsorption step was then calculated.

Adsorption

Adsorption isotherms for C2H6 and C2H4 at 298 K and 313 K were measured using a Micromeritics ASAP 2020 analyzer. Prior to measurement, the sample was activated under high vacuum at 423 K for 10 hours until no further mass loss was detected. High-purity C2H6 and C2H4 gases (both 99.995%) were employed for the adsorption studies.

Breakthrough Experiments

The breakthrough experiments are performed on a homemade set-up involving two gas columns; one is linked to a stainless-steel column loaded with activated TYUT-18, while the other served as a blank control to stabilize the gas flow (Supplementary Fig. 53). Both columns had an inner diameter of 6 mm. The temperature of the adsorption bed is maintained at 298 K or 313 K using a thermostat. The outlet and inlet flow rates and pressures of the C2H6/C2H4 mixtures are regulated by a mass flow meter and a pressure gauge, respectively. Gas from the outlet of the adsorption column is monitored by gas chromatography (Agilent 490) equipped with a thermal conductivity detector (TCD). Before the experiment, the adsorption column is heated at 423 K whilst purging with Ar, and then, the inlet gas is switched to the mixture to be tested at a total gas flow of 2 or 8 mL min-1. For the cycling experiments, the sample is regenerated by in situ purging with Ar at a flow rate of 50 mL min-1 at 298 K for 1 h. The sample mass of TYUT-18 was 0.6 g.

Data availability

The data generated in this study are provided in the Supplementary Information/Source Data file. The X-ray crystallographic coordinate for structures reported in this article have been deposited at the CCDC under deposition numbers CCDC 2407210 (TYUT-18 (α)), 2412958 (TYUT-18 (β)), 2449695 (TYUT-18(β)•0.25C2H6), 2449696 (TYUT-18(α)•1C2H6), 2473904 (TYUT-18(α)•3C2H6), 2449694 (TYUT-18(α)•0.25C2H4). These data can be obtained free of charge from the CCDC via https://www.ccdc.cam.ac.uk/data_request/cif. Source data are provided with this paper. All data are available in the main text or the supplementary information.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "In this work Zhang et al. report a metal–organic framework containing a two-fold pore system, in which sequential filling of pores is concomitant with a subtle reorganization of the pore structure. This framework exhibits apparent selectivity for ethane over ethylene, as initially indicated by the single component isothermal adsorption measurements. In situ XRD experiments reveal the relationships of adsorption with the sequential pore filling in the framework, namely subtle rotations leading to pore size/shape adaptation. Calculations identify the energetic relationships of adsorption and structural deformation, and its relationship to selectivity. Breakthrough measurements reveal high selectivity for ethane, with preferred adsorption leading to clean breakthrough of ethylene and production of high purity feedstock.\nOverall, this work reports a high-performance material with in-depth structural characterization of the adsorption pathway. However, there are several questions regarding analysis and reported data that must be addressed.\n- IAST as a theory applies to only rigid systems, therefore it is inappropriate to apply it to this system.\n- At multiple points in the manuscript the selectivity at 0.1 bar is discussed, and the flexibility is invoked. However, at 0.1 bar in the single component isotherms there is no change to the pore structure. This seems to be contradictory and therefore must be addressed.\n- There needs to be much more information provided regarding how the breakthrough measurements were performed. This work could not be reproduced with the provided information. Such as how the column was packed. Was the framework pelletized or mixed with a binder?\n- In this vein, the breakthrough data is exceptionally clean, which raises questions as to how it was performed. One key question is why upon the full breakthrough and saturation do the ratios of the two gases not match the inlet? In the previous work by this group this is seen as expected. What is different here? Providing the raw data would be beneficial.\n- In representative streams of ethane and ethylene, the ethane concentration is appreciably lower than 10%. Breakthrough measurements should be performed at 95:5 and 99:1 ethylene:ethane.\n- Fast kinetics are repeatedly invoked in the manuscript, however the data in the SI show that adsorption and desorption take about 10 minutes. Why would this be considered fast?\n- There does not appear to be any information provided on how the kinetics of adsorption and desorption were determined for the data provided in figures SFig 12 and 13.\n- Overall, there is an overselling of the “engineering” of the pores structure. The authors would be better off reported what was observed rather than trying to sell a concept.\n- To determine the heats of adsorption, there must be a least three temperatures, so that error bars can be determined. This is standard in the field and must be done.\n- The dual site Langmuir-Freundlich does not seem appropriate for fitting the adsorption data given that this material exhibits flexibility that changes the initial adsorption site upon the second adsorption event. That model is for rigid systems.", "reviewer_2": "In this manuscript, the authors report excellent C₂H₆/C₂H₄ selectivity and achieve ultra-high ethylene purity (99.995%) with an impressive separation productivity of 15.7 L kg⁻¹. They also systematically elucidate the dynamic filling behavior of ethane molecules within a flexible–robust framework system, using a comprehensive combination of single-crystal X-ray diffraction (SCXRD) and density functional theory (DFT) calculations. Overall, the study is carefully conducted, and the material is thoroughly characterized both experimentally and theoretically.\nHowever, the novelty of this work appears somewhat limited, as the findings do not provide fundamentally new insights or uncover any previously unknown mechanisms, and the separation performance does not represent a major breakthrough.\nFurthermore, the manuscript overlooks several benchmark C₂H₆-selective adsorbents, as listed below. In addition, I have identified several issues, which are outlined below.\n(1) Although the authors claim that “we clearly discovered the dynamic pore-filling behavior of C₂H₆ molecules in a flexible–robust MOF by combining SCXRD and DFT calculations for the first time…”, this statement is not accurate. Such sequential guest-filling behavior in flexible MOFs are not new and have been widely known and summarized in several review papers (for example, https://pubs.rsc.org/en/content/articlehtml/2021/fd/d1fd00037c). Moreover, the same filling mechanism for C2 gases in an isostructural material has already been reported and thoroughly analyzed using both in situ SCXRD and DFT calculations two years ago, as cited in reference 38 of the manuscript.\n(2) In the crystallographic data tables (Supplementary Tables 2–4), important parameters such as Rint, R1, wR2, and GOF should be included.\n(3) In Supplementary Figure 2, the pore size distribution is shown in the inset. The authors should clarify which method was used to calculate it.\n(4) More detailed information on the Rietveld refinement should be provided in the Supplementary Information. The authors should clearly indicate which software was used, how the initial structural model was constructed, and describe the refinement procedure in sufficient detail.\n(5) Additional details on the in situ SCXRD measurements are required. The authors should specify the instrumentation used, sample activation conditions, gas-loading method, gas pressure applied during measurements, and any other relevant experimental parameters.\n(6) Although the authors emphasize the industrial significance of C2 gas separation in the Introduction, the breakthrough experiments were performed at very low flow rate (2 mL/min), which does not reflect practical operating conditions. The authors must justify why such a small flow rate was chosen. Furthermore, the amount of adsorbent used in the breakthrough experiments is not specified and should be clearly reported, as it is essential for evaluating the reliability and relevance of the separation performance.\n(7) The manuscript overlooks several benchmark C₂H₆-selective adsorbents that have been reported, such as PCP-IPA [ref.1], TbMOF-76-NH₂ [ref.2], TJT-100 [ref.3], ZnF-PCP [ref.4], NKU-301 [ref.5], and FDMOF-2 [ref.6], etcs.\n[ref.1] P. Zhang, L. Yang, X. Liu, J. Wang, X. Suo, L. Chen, X. Cui, H.Xing, Nat. Commun. 2022, 13, 4928\n[ref.2] G. D. Wang, R. Krishna, Y. Z. Li, W. J. Shi, L. Hou, Y. Y. Wang,Z. Zhu, Angew. Chem. 2022, 134, e202213015\n[ref.3] H. G. Hao, Y. F. Zhao, D. M. Chen, J. M. Yu, K. Tan, S.Ma, Y. Chabal, Z. M. Zhang, J. M. Dou, Z. H. Xiao, G.Day, H.-C. Zhou, T.-B. Lu, Angew. Chem. 2018, 130, 16299–16303.\n[ref. 4] F. Chen, N. Prasetyo, S. Sakaki, K. Otake, S. Kitagawa, Angew. Chem. Int. Ed. 2025, 64, e202423371\n[ref.5] X. Lian, P. X. Liu, Y. C. Yuan, J. J. Pang, L. Li, S. S. Liu, B. Yue,Y. H. Zhang, L. Li, J. Xu, X.-H. Bu, Adv. Funct. Mater. 2024, 34,2312150\n[ref.6] S. Jiang, J. Li, M. Feng, R. Chen, L. Guo, Q. Xu, L. Chen, F. Shen,Z. Zhang, Y. Yang, Q. Ren, Z. Bao, J. Mater. Chem. A 2022, 10,24127–24136.\n(8) The authors claim that the reported material exhibits “fast adsorption kinetics.” However, they should compare the kinetics with those of previously reported materials. Without such a comparison, readers cannot be convinced that the adsorption is genuinely fast.", "reviewer_3": "The manuscript report a flexible–robust metal–organic framework TYUT-18, whose unique binary pore system combined with the flexible deformation of the framework produces significantly different gate-opening pressures for C2H6 and C2H4 at 298 K. More importantly, the paper elucidated the dynamic filling behavior of C2H6 molecules in the framework system, a process of preferentially occupying the large pore cavities then filling into the small ones was uncovered using a combination of extensive single-crystal X-ray diffraction studies and density functional theory calculations. The work addresses a significant problem in gas purification, and the strategy of developing a C2H6-selective adsorbent is well-justified due to its potential energy efficiency benefits over more traditional C2H4-selective materials. Therefore, I recommend publication after addressing the following minor points:\n(1) The authors mentioned a moderate Qst for C2H6. What is its level among C2H6-selective materials?\n(2) The kinetic diffusion characteristics of both gases are excellent. Which one is more outstanding? Does C2H6 with preferential gate-opening show better dynamic diffusion?\n(3) As the temperature decreases, the opening pressure of flexible materials will decrease. What are the adsorption curves of C2H6 and C2H4 at 273K?\n(4) How does this material regenerate in breakthrough experiments? The breakthrough desorption curve should be supplemented, because the regeneration is also a very important indicator in industry.\n(5) How is the water stability? It is suggested to supplement the relevant data after the water stability experiment, such as PXRD.", "reviewer_4": "The manuscript presents a study on the development of a flexible-robust metal-organic framework, TYUT-18, for the highly selective separation of ethane and ethylene. The authors demonstrate that its unique binary pore system, combined with framework flexibility, enables a distinct gate-opening pressure for ethane, achieving exceptional selectivity and the production of ultra-high-purity ethylene. The topic is of great significance, particularly for advancing energy-efficient alternatives to thermal distillation in the petrochemical industry. To further strengthen the manuscript, the following points should be addressed:\n1. A careful check and unification of units throughout the manuscript is recommended. For instance, “L/Kg” (line 23) and “L kg” (lines 357, 358) should be standardized to a consistent format, such as “L kg-1”, to adhere to scientific conventions\n2. In the description of the in-situ variable-pressure PXRD experiments (e.g., lines 180-200), gas “concentration” (e.g., 13%, 18%, 48%) is used to define the phase transition points. Since the thermodynamic driving force for structural transitions in flexible MOFs is the gas partial pressure, it is scientifically more precise to use this term. Revising “concentration” to “partial pressure” throughout the manuscript is strongly advised.\n3. The authors have masterfully delineated the structural evolution of TYUT-18. To provide a more complete energetic picture, a deeper integration of the thermodynamic data with these structural insights would be highly valuable. Specifically, correlating the Qst trends (Supplementary Fig. 11) with the precisely defined phase transition pressures for C2H6 and C2H4 would be very insightful. A discussion on how the Qst values evolve across the β-to-α phase transition for each gas would significantly enhance the understanding of the energy landscape governing the sequential pore-filling mechanism.\n4. The single-component data and IAST predictions convincingly show high selectivity. However, for practical separation, a critical question arises: does the C2H6-induced framework transition facilitate subsequent co-adsorption of C2H4 by lowering the diffusion or adsorption energy barrier for ethylene in the now-opened pores? It is crucial to elucidate this potential “cooperative adsorption” or “pore-opening effect”.\n5. The reported breakthrough experiments (e.g., with 50/50 and 10/90 C2H6/ C2H4) likely utilize the initial adsorption capacity of the large pores (Cavity A). To demonstrate the material’s full separation potential and explore its operational limits, it would be interesting to see a breakthrough experiment designed to actively trigger the gate-opening of the small pores (Cavity B).\n6. The successful demonstration of ternary mixture (C2H2/C2H4/C2H6) separation is a key strength. To fully support this claim and robustly assess the application potential, two additions are recommended:\nFirstly, providing the pure-component C2H2 adsorption isotherm is essential for a baseline understanding of its interaction with the framework and for comparison with C2H6 and C2H4.\nSecondly, and more critically, demonstrating the complete and reversible desorption of C2H2 under the reported regeneration conditions is necessary to rule out any risks of pore blockage, performance degradation, or product contamination in subsequent cycles.\n7. For any adsorbent targeting real-world olefin/paraffin separation, evaluating stability towards moisture is paramount, as industrial streams often contain trace water. A study on the interaction of TYUT-18 with water vapor is highly recommended. Key questions to address are whether H₂O molecules preferentially occupy the critical binary pore channels and, if so, whether this adsorption is fully reversible or leads to an irreversible degradation of the framework's structure and its unique flexible-robust separation mechanism."}, "author_response": "Response to the reviewer’s comments\nReviewer #1:\nIn this work Zhang et al. report a metal-organic framework containing a two-fold pore\nsystem, in which sequential filling of pores is concomitant with a subtle reorganization of\nthe pore structure. This framework exhibits apparent selectivity for ethane over ethylene,\nas initially indicated by the single component isothermal adsorption measurements. In situ\nXRD experiments reveal the relationships of adsorption with the sequential pore filling in\nthe framework, namely subtle rotations leading to pore size/shape adaptation. Calculations\nidentify the energetic relationships of adsorption and structural deformation, and its\nrelationship to selectivity. Breakthrough measurements reveal high selectivity for ethane,\nwith preferred adsorption leading to clean breakthrough of ethylene and production of high\npurity feedstock.\nOverall, this work reports a high-performance material with in-depth structural\ncharacterization of the adsorption pathway. However, there are several questions\nregarding analysis and reported data that must be addressed.\n(1) IAST as a theory applies to only rigid systems, therefore it is inappropriate to apply it to\nthis system.\nResponse: We thank the reviewers for their valuable suggestions.\nWe fully understand the limitations of IAST theory in terms of its applicability to flexible\nsystems. So, we have deleted the analysis and discussion related to IAST in the revised\nmanuscript.\n(2) At multiple points in the manuscript the selectivity at 0.1 bar is discussed, and the\nflexibility is invoked. However, at 0.1 bar in the single component isotherms there is no\nchange to the pore structure. This seems to be contradictory and therefore must be\naddressed.\nResponse: We thank the reviewers for their comments.\nWe have carefully reviewed the discussion regarding C H /C H selectivity and flexibility\n2 6 2 4\nof TYUT-18 at 0.1 bar in the manuscript. Indeed, as the reviewers pointed out, the\nadsorption isotherms of C H and C H of TYUT-18 within this pressure range do not show\n2 6 2 4\nsignificant changes in pore structure. Therefore, it may be misleading to associate the\nstructural flexibility of TYUT-18 with the C H /C H selectivity of 0.1 bar. In order to maintain\n2 6 2 4\nacademic rigor, we deleted the description in the manuscript about the relationship\nbetween C H /C H selectivity of TYUT-18 at 0.1 bar and its structural flexibility.\n2 6 2 4\n(3) There needs to be much more information provided regarding how the breakthrough\nmeasurements were performed. This work could not be reproduced with the provided\ninformation. Such as how the column was packed. Was the framework pelletized or mixed\nwith a binder?\nResponse: Thank the reviewers for their attention to the details and repeatability of the\nbreakthrough experiment.\n(a) Firstly, we have supplemented the specific operating conditions of the breakthrough\nexperiment in more detail, and the relevant contents are as follows:\n“The breakthrough experiments are performed on a homemade set-up involving two gas\ncolumns; one is linked to a stainless-steel column loaded with activated TYUT-18, while\nthe other served as a blank control to stabilize the gas flow (Supplementary Fig. 46). Both\ncolumns had an inner diameter of 6 mm. The temperature of the adsorption bed is\nmaintained at 298 K or 313 K using a thermostat. The outlet and inlet flow rates and\npressures of the C H /C H mixtures are regulated by a mass flow meter and a pressure\n2 6 2 4\ngauge, respectively. Gas from the outlet of the adsorption column is monitored by gas\nchromatography (Agilent 490) equipped with a thermal conductivity detector (TCD). Before\nthe experiment, the adsorption column is heated at 423 K whilst purging with Ar, and then,\nthe inlet gas is switched to the mixture to be tested at a total gas flow of 2 or 8 mL min-1.\nFor the cycling experiments, the sample is regenerated by in situ purging with Ar at a flow\nrate of 50 mL min-1 at 298 K for 1 h. The sample mass of TYUT-18 was 0.6 g.” Details of\nthe breakthrough experiment have been added in the revised manuscript.\n(b) Secondly, regarding the question of “How the column was packed. Was the framework\npelletized or mixed with a binder?”. The breakthrough experiment of TYUT-18 was carried\nout directly with powder samples. The reason is that the single crystal particle size of TYUT-\n18 is relatively large (about 40 μm), as shown in the microscope and SEM images in the\nsupplementary information (see Supplementary Figs. 1 and 5), and its particle size is\nenough to ensure uniform filling and moderate pressure drop. In addition, in order to avoid\nstructural collapse and performance loss that may be caused during granulation or tablet\npressing, we choose to use powder directly for breakthrough experiments.\n(4) In this vein, the breakthrough data is exceptionally clean, which raises questions as to\nhow it was performed. One key question is why upon the full breakthrough and saturation\ndo the ratios of the two gases not match the inlet? In the previous work by this group this\nis seen as expected. What is different here? Providing the raw data would be beneficial.\nResponse: Thank you very much for pointing out this problem.\n(a) Firstly, about the question of how breakthrough experiments are performed, the specific\nsteps are as follows:\nFirst, tests were conducted using a self-made breakthrough experimental setup. This\nsystem comprises two stainless steel columns, each with an inner diameter of 6 mm: one\nfilled with activated MOF sample (TYUT-18, sample mass approximately 0.6 g), and the\nother a blank control column used to stabilize the gas flow and eliminate systematic errors.\nThis dual-column design effectively reduced flow fluctuations and system noise, thereby\nsignificantly improving the stability and repeatability of experimental data. Before the\nexperiment, the adsorption columns were pretreated: heated at 423 K while purging with\nAr gas to thoroughly remove residual gases and adsorbed impurities from the sample,\nensuring that each experiment started from the same initial state, thus improving the\nrepeatability and reliability of the experimental results. Subsequently, the inlet gas was\nswitched to the C H /C H mixture, with the total gas flow rate controlled within the range\n2 6 2 4\nof 2 or 8 mL·min-1. The gas flow rate and pressure were precisely adjusted using a mass\nflow meter and a pressure gauge to maintain a constant component ratio and stable flow\nrate, thereby obtaining a high-precision breakthrough curve. Finally, a gas chromatograph\n(Agilent 490) equipped with a thermal conductivity detector (TCD) was used to\ncontinuously monitor the compositional changes of the gas exiting the adsorption column.\nThe TCD detector has good sensitivity and signal stability, enabling low-noise, continuous\nsignal output, thus obtaining a smooth and clean breakthrough curve.\n(b) In addition, we are very grateful to the reviewers for pointing out the question “the full\nbreakthrough and saturation do the ratios of the two gases not match the inlet”. We strongly\nagree with this opinion and would like to provide a clearer explanation here.\nC /C represents the ratio of the real-time gas concentration to the equilibrium\nA 0\nconcentration at the outlet. In the breakthrough experiment with a C H /C H volume ratio\n2 6 2 4\nof 50/50, initially (t ≈ 0), both C H and C H were adsorbed on TYUT-18, resulting in zero\n2 4 2 6\noutlet gas concentration, hence C /C = 0 of C H and C H . As time progressed, due to\nA 0 2 4 2 6\nthe stronger affinity of the adsorbent for C H , the adsorption capacity of C H was weaker,\n2 6 2 4\nthe C H molecules are the first to exit the adsorption column, causing the C /C of C H\n2 4 A 0 2 4\nto gradually increase. Moreover, since C H exhibits stronger adsorption interactions with\n2 6\nTYUT-18 than C H , competitive displacement occurred between the two gases, C H\n2 4 2 6\ncontinuously replaces the adsorbed C H in the column, resulting in a large amount of C H\n2 4 2 4\nbeing released and enriched at the outlet, where C /C exceeded 1 (up to approximately\nA 0\n2). Subsequently, as C H broke through, the C /C of C H gradually decreased, while the\n2 6 A 0 2 4\nC /C of C H slowly increased, eventually converging to 1 at adsorption equilibrium, with\nA 0 2 6\nthe outlet gas composition being the same as the inlet.\nBased on the above analysis, we re-examined the experimental data and found that there\nwere mistakes in the previous data processing. Therefore, we reprocessed all the data of\nbreakthrough experiment and presented the complete original experimental data in the\n\"Source Data\" file for reviewers to verify.\nThe figures related to the breakthrough experiment have been replaced in the revised\nmanuscriptand SI.\nModification:\nManuscript: Page 13, Figure 6.\nFigure 6 | Breakthrough experiments and stability. a, b, Breakthrough curves obtained for TYUT-18 with\nC H /C H mixtures (v/v = 50/50 and 10/90) at 298 K. c, d, Five breakthrough cycle curves obtained for\n2 6 2 4\nC H /C H mixtures (v/v = 50/50 and 10/90) at 298 K. e, PXRD patterns obtained for TYUT-18 under the above\n2 6 2 4\nconditions. F, Photograph of TYUT-18 crystals obtained using microscopy under the above conditions.\nModification:\nSupporting Information: Page 18 and 19, Supplementary Figs. 25–27.\nSupplementary Figure 25. Breakthrough curves of TYUT-18 for C H /C H mixtures (v/v\n2 6 2 4\n= 50/50 and 10/90) at 313 K.\nSupplementary Figure 26. Five breakthrough cycle curves for C H /C H mixtures (v/v =\n2 6 2 4\n50/50) at 313 K.\nSupplementary Figure 27. Five breakthrough cycle curves for C H /C H mixtures (v/v =\n2 6 2 4\n10/90) at 313 K.\n(5) In representative streams of ethane and ethylene, the ethane concentration is\nappreciably lower than 10%. Breakthrough measurements should be performed at 95:5\nand 99:1 ethylene: ethane.\nResponse: We greatly appreciate the comments of reviewers.\nWe fully agree that the concentration of C H in representative gas streams are typically\n2 6\nbelow 10%, therefore breakthrough experiments should be conducted under conditions\ncloser to real-world operating conditions (C H /C H , v/v = 5/95 or 1/99).\n2 6 2 4\nBased on the reviewers' comments, we supplemented the breakthrough experiment of\nmixed gas with C H /C H volume ratios of 5:95 and 1:99. The results show that the TYUT-\n2 6 2 4\n18 maintains excellent C H selectivity and separation performance under both ratios.\n2 6\nThe relevant experimental results and data have been added to the revised manuscript\nand SI.\nModification:\nManuscript: Page 11, Add corresponding descriptions.\n“To verify the separation capability of TYUT-18 for low-concentration C H impurities, we\n2 6\nconducted separation experiments using C H /C H mixtures with volume ratios of 5/95\n2 6 2 4\nand 1/99 (Supplementary Figs. 28 and 29). The experimental results confirm that TYUT-\n18 can effectively remove extremely low concentration C H impurities, demonstrating\n2 6\nexcellent separation performance.”\nModification:\nSupporting Information: Page 19 and 20, Supplementary Figs. 28 and 29.\nSupplementary Figure 28. Breakthrough curves of TYUT-18 for C H /C H mixtures (v/v\n2 6 2 4\n= 5/95) at 298 K and 313 K.\nSupplementary Figure 29. Breakthrough curves of TYUT-18 for C H /C H mixtures (v/v\n2 6 2 4\n= 1/99) at 298 K and 313 K.\n(6) Fast kinetics are repeatedly invoked in the manuscript, however the data in the SI show\nthat adsorption and desorption take about 10 minutes. Why would this be considered fast?\nResponse: We thank the reviewers for their valuable comments.\nRegarding the description of “rapid kinetics”, we would like to further clarify.\nFirst, under our experimental conditions, the gas pressurization rate was 100 mbar min-1,\nand it took approximately 10 minutes to go from the initial pressure to 1000 mbar. During\nthis process, the TYUT-18 reached adsorption equilibrium within 10 minutes for both C H\n2 6\nand C H simultaneously with the pressurization to the target pressure, indicating that its\n2 4\nadsorption rate was comparable to the pressurization rate, and no significant delay in mass\ntransfer or diffusion was observed. Therefore, within this experimental framework, we\nconsider the adsorption kinetics of the TYUT-18 was well.\nFurthermore, to further verify this, we conducted supplementary tests at a higher\npressurization rate (500 mbar min-1). The results showed that TYUT-18 rapidly reached\nequilibrium within 4 minutes (see Supplementary Fig. 15), indicating that this material has\nrelatively fast adsorption kinetics.\nWe have provided more detailed experimental descriptions in the revised SI.\nModification:\nSupporting Information: Page 12, Supplementary Fig. 15.\nSupplementary Figure 15. Kinetics of adsorption and desorption behaviors for (a) C H\n2 4\nand (b) C H on TYUT-18 at 298 K (C H or C H was introduced into the test chamber at\n2 6 2 6 2 4\na rate of 500 mbar·min-1).\n(7) There does not appear to be any information provided on how the kinetics of adsorption\nand desorption were determined for the data provided in figures S Fig 12 and 13.\nResponse: Thank you for your suggestion. We added relevant test conditions and\nperformance descriptions of kinetics of adsorption to the revised manuscript, and\nsupplemented the calculation of the diffusion time constant (Supplementary Fig. 14).\nModification:\nManuscript: Page 7, Add corresponding descriptions.\n“At 298 K, with a pressurization rate of 100 mbar min-1, both C H and C H reached\n2 6 2 4\nadsorption equilibrium in TYUT-18 within approximately 10 minutes. This adsorption\nequilibrium time is shorter than that of Cu(Qc) (13 minutes), MAF-7 (15 minutes), TYUT-\n2\n12 (18 minutes) and ZIF-7 (40 minutes) (Supplementary Figs. 16 and 17). And due to the\npreferential flexible response of TYUT-18 to C H , its diffusion time constant (1.77 × 10-2\n2 6\nmin-1) is greater than that of C H (1.27 × 10-2 min-1). Desorption experiments further\n2 4\nshowed that both C H and C H could be completely desorbed from TYUT-18 within 10\n2 6 2 4\nminutes.”\nModification:\nSupporting Information: Page 4 and 11-13, Supplementary Figs. 13-17.\n“Kinetic adsorption measurement\nThe kinetic adsorption isotherms of the sample were measured using an Intelligent\nGravimetric Analyzer (IGA 001, Hiden). This instrument employs a gravimetric method to\nprecisely quantify gas adsorption capacity on materials under various operating conditions.\nIn the adsorption experiment, approximately 100 mg of TYUT-18 was loaded into the\nsample cell and activated at 423 K under high vacuum until no further weight loss was\nobserved. Subsequently, after cooling the sample to 298 K or 313 K, C H or C H was\n2 6 2 4\nintroduced into the test chamber at a rate of 100 or 500 mbar·min-1. The software\nautomatically recorded the change in weight of the sample after gas adsorption.\nKinetic calculation\nDiffusion time constants (D’, D/r2) are calculated from a short-time solution of the diffusion\nequation assuming a step change in the gas-phase concentration, a clean bed initially, and\nmicroporous diffusion control:\n𝑞𝑡 6 𝐷\n= √ 2𝑡\nwhere q\nt\nrepresents the gas uptake at𝑞 t∞ime\n√\nt, 𝜋q\n∞\n𝑟represents the gas uptake at equilibrium,\nD represents the diffusivity, and r represents the radius of the equivalent spherical particle.\nThe slopes of q/q versus are obtained by fitting the plots in the low gas uptake range.”\nt ∞\n√𝑡\nSupplementary Figure 14. Diffusional time constant calculation details of C H and C H\n2 4 2 6\non TYUT-18 at 298 K.\n(8) Overall, there is an overselling of the “engineering” of the pores structure. The authors\nwould be better off reported what was observed rather than trying to sell a concept.\nResponse: We are very grateful to the reviewers for their review and constructive\nsuggestions.\nWe agree with them that academic papers should be better off reported what was observed\nrather than trying to sell a concept. In this study, we proposed the sequential adsorption\nbehavior of C H in TYUT-18 with the binary porous system. This conclusion was verified\n2 6\nby both single-crystal X-ray diffraction (SCXRD) and density functional theory (DFT)\ncalculations, clearly revealing the sequential filling mechanism of different pores during\nadsorption.\nAt the same time, we have adjusted and shortened the relevant descriptions in the revised\nmanuscript, weakening the promotional expression of the “engineering” concept and\nfocusing more on the experimentally observed structural features and adsorption behavior\nitself, so as to make the discussion more objective and rigorous.\n(9) To determine the heats of adsorption, there must be a least three temperatures, so that\nerror bars can be determined. This is standard in the field and must be done.\nResponse: Thank you for your valuable suggestion. Based on your suggestion, we\nrecalculated the isosteric heat of adsorption. The specific calculation steps are as follows:\nThe isosteric heat of adsorption for C H and C H were calculated by using the gas\n2 6 2 4\nadsorption data collected at 273, 298 and 313 K. The adsorption curves were first fitted\nwith the viral equation:\n𝑚 𝑛\n1 𝑖 𝑖\nln𝑃 =ln𝑞+ ∑𝑎𝑖𝑞 +∑𝑏𝑖𝑞\nWhere q is the amount of gas adsorbed a𝑇t t𝑖h=e0 pressu𝑖r=e0 P, a and b are Virial coefficients,\nm and n are the number of coefficients required to describe the isotherm adequately.\nTo calculate the Q values, the fitting parameters obtained from the equation were then\nst\nplugged into the following equation:\n𝑚\n𝑖\n𝑄𝑠𝑡 =−𝑅∑𝑎𝑖𝑞\nModification: 𝑖=0\nSupporting Information: Pages 9 and 10, Supplementary Figs. 10 and 11.\nSupplementary Figure 10. Virial fitting (lines) of the (a) C H and (a) C H adsorption\n2 6 2 4\nisotherms (points) of TYUT-18.\nSupplementary Figure 11. The isosteric heat of adsorption of C H and C H on TYUT-\n2 6 2 4\n18.\n(10) The dual site Langmuir-Freundlich does not seem appropriate for fitting the adsorption\ndata given that this material exhibits flexibility that changes the initial adsorption site upon\nthe second adsorption event. That model is for rigid systems.\nResponse: We appreciate the reviewers' professional comments.\nWe fully understand the concerns regarding the applicability of the dual site Langmuir-\nFreundlich model. We have removed the fitting results and related discussion based on\nthe dual site Langmuir-Freundlich model from the revised manuscript to ensure the\nobjectivity and reasonableness of the results.\nReviewer #2:\nIn this manuscript, the authors report excellent C H /C H selectivity and achieve ultra-high\n2 6 2 4\nethylene purity (99.995%) with an impressive separation productivity of 15.7 L kg1. They\nalso systematically elucidate the dynamic filling behavior of ethane molecules w- ithin a\nflexible–robust framework system, using a comprehensive combination of single-crystal X-\nray diffraction (SCXRD) and density functional theory (DFT) calculations. Overall, the study\nis carefully conducted, and the material is thoroughly characterized both experimentally\nand theoretically. However, the novelty of this work appears somewhat limited, as the\nfindings do not provide fundamentally new insights or uncover any previously unknown\nmechanisms, and the separation performance does not represent a major breakthrough.\nFurthermore, the manuscript overlooks several benchmark C H -selective adsorbents, as\n2 6\nlisted below. In addition, I have identified several issues, which are outlined below.\n(1) Although the authors claim that “we clearly discovered the dynamic pore-filling behavior\nof C H molecules in a flexible–robust MOF by combining SCXRD and DFT calculations\n2 6\nfor the first time…”, this statement is not accurate. Such sequential guest-filling behavior\nin flexible MOFs are not new and have been widely known and summarized in several\nreview papers (for example, https://pubs.rsc.org/en/content/articlehtml/2021\n/fd/d1fd00037c). Moreover, the same filling mechanism for C2 gases in an isostructural\nmaterial has already been reported and thoroughly analyzed using both in situ SCXRD and\nDFT calculations two years ago, as cited in reference 38 of the manuscript.\nResponse: Thank you very much for your suggestions.\nFirst, our use of “for the first time” in the manuscript was indeed inappropriate. We have\nremoved “for the first time” from the revised manuscript and revised the relevant sentence\nto: “We clearly discovered the dynamic pore-filling behavior of C H molecules in a flexible–\n2 6\nrobust MOF by combining SCXRD and DFT calculations.”\nSecond, we strongly agree with the work published by Kitagawa et al. in 2023, which was\nmentioned by the reviewers. Their study represents a groundbreaking contribution to\nunderstanding the structural responses and guest diffusion mechanisms in flexible–robust\nMOFs. In particular, they systematically revealed the framework transformation and\nsequential filling mechanism induced by C2 gases in flexible-robust MOFs through in situ\ngas-loaded SCXRD and DFT calculations at different temperatures. This work has\nsignificantly advanced the understanding of adsorption behavior in flexible–robust MOFs.\nBuilding on this, our research continues and expands upon the findings of Kitagawa et al.\nWe focused on the influence of pressure variations on the adsorption behavior of guest\nmolecules and the deformation of the framework structure in the TYUT-18. By combining\nin situ gas-loaded SCXRD analysis with DFT calculations under different pressure\nconditions, we further revealed the dynamic pore-filling behavior of C H molecules in\n2 6\nflexible–robust MOFs and its corresponding structural response.\nIn the revised manuscript, we have provided a clearer description of the work by Kitagawa\net al. and have added related discussion in the relevant sections to fully reflect the\nsignificance of their study and the extension represented by our research.\nModification:\nManuscript: Page 3, Add corresponding descriptions.\n“Subsequently, through in situ gas-loading SCXRD analysis and DFT calculations at\ndifferent temperatures, Kitagawa et al. systematically elucidated the sequential filling\nmechanism of C2 gas in flexible–robust MOFs and its correlation with framework flexibility,\ngreatly advancing the understanding of the sequential adsorption behavior of guest\nmolecules in flexible-robust MOFs38. Based on this, we further expanded our research\nperspective to pressure-mediated effects to reveal the sequential adsorption behavior of\nC H molecules in flexible–robust MOFs under different pressures and their corresponding\n2 6\nstructural responses.”\n(2) In the crystallographic data tables (Supplementary Tables 2–4), important parameters\nsuch as R , R , wR and GOF should be included.\nint 1 2\nResponse: Thank you for your valuable suggestion. We have included the key\ncrystallographic refinement parameters (R , R , wR , and GoF) in the Supplementary\nint 1 2\nTables 2–4 of the revised Supporting Information. These parameters have been added to\nensure completeness and to provide a clearer overview of the data quality.\nModification:\nSupporting Information: Page 30–32, Table S2–4.\n(3) In Supplementary Figure 2, the pore size distribution is shown in the inset. The authors\nshould clarify which method was used to calculate it.\nResponse: Thank you for reviewing and making valuable comments.\nThe pore size distribution shown in the illustration of Supplementary Fig. 2 is based on the\nN adsorption isotherm measured at 77 K and calculated by DFT model.\nSupporting Information: Page 5, Supplementary Fig. 2.\n“(the pore size distribution was calculated by DFT model)”\n(4) More detailed information on the Rietveld refinement should be provided in the\nSupplementary Information. The authors should clearly indicate which software was used,\nhow the initial structural model was constructed, and describe the refinement procedure in\nsufficient detail.\nResponse: Thank you for your valuable comments.\nWe have added more detailed Rietveld refinement instructions of the revised manuscript,\nclarifying the software used, the initial structural model construction method, and the\nrefinement procedure. The supplementary content is as follows: The refined package is\nTOPAS V5.0, which describes the background using 24th-order Chebyshev polynomials\nand the peak shapes using pseudo-Voigt peak shapes. Preferred orientation is described\nusing the spherical cofunction of order 4. The refinement was performed sequentially on\nthe scale factor, atomic coordinates, isotropic displacement parameters, site occupancies,\nand preferred orientation. Guest molecules were introduced into the host framework model\nas rigid bodies, and their possible positions were determined through a simulated\nannealing algorithm.\nModification:\nManuscript: Page 14, the section of PXRD refinement.\n“The refined package is TOPAS V5.0, which describes the background using 24th-order\nChebyshev polynomials and the peak shapes using pseudo-Voigt peak shapes. Preferred\norientation is described using the spherical cofunction of order 4. The refinement was\nperformed sequentially on the scale factor, atomic coordinates, isotropic displacement\nparameters, site occupancies, and preferred orientation. Guest molecules were introduced\ninto the host framework model as rigid bodies, and their possible positions were\ndetermined through a simulated annealing algorithm.”\n(5) Additional details on the in situ SCXRD measurements are required. The authors should\nspecify the instrumentation used, sample activation conditions, gas-loading method, gas\npressure applied during measurements, and any other relevant experimental parameters.\nResponse: Thank you for your suggestion. We have added detailed information about in\nsitu SCXRD measurements to the revised manuscript.\nModification:\nManuscript: Page 14 and 15, the section of Single-crystal X-ray diffraction.\n“For in situ SCXRD measurements, the TYUT-18 sample was first purged with N at 423 K\n2\nfor 12 hours to completely remove solvent molecules from the pores. Then, the target feed\ngas was introduced to the set pressure and equilibrated for 6 h. The specific conditions are\nas follows: for TYUT-18(β)•0.25C H and TYUT-18(α)•3C H , the C H gas was\n2 6 2 6 2 6\npressurized to 0.13 bar and 1 bar respectively using the Micromeritics ASAP 2020 analyzer;\nfor TYUT-18(α)•1C H and TYUT-18(α)•0.25C H , the C H and C H gases were first\n2 6 2 4 2 6 2 4\npressurized to 1 bar, and then desorbed to 0.4 bar and 0.6 bar respectively. The SCXRD\ndata of TYUT-18(β)•0.25C H , TYUT-18(α)•1C H and TYUT-18(α)•0.25C H were\n2 6 2 6 2 4\ncollected on the Bruker D8 VENTURE TXS PHOTON II diffractometer. The SCXRD data\nof TYUT-18(α)•3C H was collected Single crystal X-ray diffraction data were collected at\n2 6\nthe Shanghai Synchrotron Light Source Line BL10U2 station and station equipped with a\nDectris Eiger 16M, S/N E-32-0111 surface detector respectively. The structure was solved\nby direct methods using the SHELXTL software package and further refined with different\nFourier syntheses. All non-hydrogen atoms on the framework were refined anisotropically;\nall hydrogen atoms were generated geometrically and refined in the riding mode. All the\nphenyl rings were treated with rigid constraints.”\n(6) Although the authors emphasize the industrial significance of C2 gas separation in the\nIntroduction, the breakthrough experiments were performed at very low flow rate (2\nmL/min), which does not reflect practical operating conditions. The authors must justify why\nsuch a small flow rate was chosen. Furthermore, the amount of adsorbent used in the\nbreakthrough experiments is not specified and should be clearly reported, as it is essential\nfor evaluating the reliability and relevance of the separation performance.\nResponse: Thank you very much for your suggestions.\nWe fully agree with your point. The differences between the breakthrough experiment flow\nrate and practical operating conditions, as well as the unclear adsorbent dosage you\npointed out, are essential for evaluating the reliability and relevance of the separation\nperformance. We have conducted in-depth explanations and supplementary experiments,\nand our specific response is as follows:\n(a) Reasons for choosing low flow rate (2 mL min-1).\nWe choose this flow rate mainly based on the following considerations:\nFirstly, numerous previously published articles have employed a gas flow rate of 2 mL min-\n1 in breakthrough experiments. Thus, we selected this flow rate to facilitate convenient and\ndirect comparisons with other materials (J. Am. Chem. Soc. 2018, 140, 12940–12946;\nAngew. Chem. Int. Ed.2023, 62, e202302564; Nat. Commun.2024, 15, 804; Angew. Chem.\nInt. Ed.2022, 61, e202208134).\nSecondly, during the breakthrough experiment, the activated TYUT-18 sample of about 0.6\ng was placed in a stainless-steel adsorption column with an inner diameter of 6 mm. The\ngas flow rate of 2 mL·min-1 ensures that TYUT-18 completes its structural transformation\nand reaches adsorption equilibrium within 60 minutes. These considerations led us to\nselect the gas flow rate of 2 mL min-1 for the breakthrough experiment.\nFinally, in this current stage of basic research, we chose a flow rate of 2 mL min-1 to\nprioritize obtaining reliable and accurate basic separation data under existing conditions\nand to verify the excellent separation performance of TYUT-18. For further industrial\napplications, we will focus our research on the scale-up preparation, molding process, and\nconstruction of related process equipment, which will be the main direction of our future\nwork.\n(b) Adsorbent Dosage and Supplementary Experiments.\nFirst, thank you very much for your reminder. In the breakthrough experiments (Figures 6\na-d) in the manuscript, the adsorbent loading was 0.6 g. We have added relevant\nexplanations to the experimental section of the revised manuscript.\nSecond, based on your suggestion, we investigated the separation potential of TYUT-18\nat higher flow rates. We synthesized additional material, increasing the adsorbent loading\nto 3.0 g, and conducted breakthrough experiments at a flow rate of 8 mL min-1. The results\nshowed that TYUT-18 still exhibited excellent separation performance at a relatively high\nflow rate of 8 mL min-1. Specifically, the breakthrough time for C H was 12 min g-1, and for\n2 4\nC H it was 16 min g-1, with a corresponding dynamic separation time of 4 min g-1. This\n2 6\nresult indicates that TYUT-18 possesses the potential for C H /C H separation under\n2 6 2 4\nhigher flow rate. The supplementary experiments and descriptions have been added to the\nrevised manuscript and SI.\nModification:\nSupporting Information: Page 20, Supplementary Fig. 30.\nSupplementary Figure 30. Breakthrough curves of TYUT-18 for C H /C H mixtures (v/v\n2 6 2 4\n= 50/50) at 298 K with the rate of 8 mL min-1.\n(7) The manuscript overlooks several benchmark C H -selective adsorbents that have\n2 6\nbeen reported, such as PCP-IPA [ref.1], TbMOF-76-NH [ref.2], TJT-100 [ref.3], ZnF-PCP\n2\n[ref.4], NKU-301 [ref.5], and FDMOF-2 [ref.6], etcs.\n[ref.1] P. Zhang, L. Yang, X. Liu, J. Wang, X. Suo, L. Chen, X. Cui, H. Xing, Nat. Commun.\n2022, 13, 4928\n[ref.2] G. D. Wang, R. Krishna, Y. Z. Li, W. J. Shi, L. Hou, Y. Y. Wang, Z. Zhu, Angew. Chem.\n2022, 134, e202213015\n[ref.3] H. G. Hao, Y. F. Zhao, D. M. Chen, J. M. Yu, K. Tan, S. Ma, Y. Chabal, Z. M. Zhang,\nJ. M. Dou, Z. H. Xiao, G. Day, H.-C. Zhou, T.-B. Lu, Angew. Chem. 2018, 130, 16299–\n16303.\n[ref. 4] F. Chen, N. Prasetyo, S. Sakaki, K. Otake, S. Kitagawa, Angew. Chem. Int. Ed.\n2025, 64, e202423371\n[ref.5] X. Lian, P. X. Liu, Y. C. Yuan, J. J. Pang, L. Li, S. S. Liu, B. Yue, Y. H. Zhang, L. Li,\nJ. Xu, X.-H. Bu, Adv. Funct. Mater. 2024, 34,2312150\n[ref.6] S. Jiang, J. Li, M. Feng, R. Chen, L. Guo, Q. Xu, L. Chen, F. Shen, Z. Zhang, Y.\nYang, Q. Ren, Z. Bao, J. Mater. Chem. A 2022, 10,24127–24136.\nResponse: Thank you for your suggestions.\nIn the manuscript, we compared the C H adsorption capacity and the C H /C H uptake\n2 6 2 6 2 4\nratio at 0.5 bar of flexible C H -selective MOFs. Since the comparison was limited to\n2 6\nflexible MOFs, this may have resulted in a lack of comprehensive understanding of the\noverall performance of C H -selective MOFs. To improve the representativeness and\n2 6\ncompleteness of the comparison, we further selected representative robust C H -selective\n2 6\nMOFs and compared their adsorption performance indicators with TYUT-18 in this work\nunder the same conditions. As shown in Supplementary Fig. 9, TYUT-18 exhibits a\nmoderately high C H adsorption capacity and C H /C H uptake ratio compared to most\n2 6 2 6 2 4\nreported robust C H -selective MOFs. Although its adsorption performance is not\n2 6\noutstanding, TYUT-18 still exhibits excellent separation performance, which may be closely\nrelated to its unique flexible mechanism. The relevant performance comparison picture and\ndescriptions have been added to the revised manuscript and SI.\nSupplementary Figure 9. (a) Comparison of C H uptake of TYUT-18 and robust C H -\n2 6 2 6\nselective MOFs at 298 K and 0.5 bar. (b) Comparison of the C H uptake and C H /C H\n2 6 2 6 2 4\nuptake ration of TYUT-18 and robust C H -selective MOFs at 298 K and 1bar.\n2 6\nModification:\nManuscript: Page 6, Add corresponding descriptions.\n“Furthermore, compared to most reported robust C H -selective MOFs, TYUT-18 exhibits\n2 6\na moderately high C H adsorption capacity (Supplementary Fig. 9).”\n2 6\n“When comparing with the robust C H -selective MOFs, although the uptake ratio of TYUT-\n2 6\n18 is not outstanding, TYUT-18 still exhibits excellent separation performance, which may\nbe closely related to its unique flexible mechanism (Supplementary Fig. 9).”\nSupporting Information: Page 9, Supplementary Fig. 9.\n(8) The authors claim that the reported material exhibits “fast adsorption kinetics.” However,\nthey should compare the kinetics with those of previously reported materials. Without such\na comparison, readers cannot be convinced that the adsorption is genuinely fast.\nResponse: We thank the reviewers for their valuable comments.\nRegarding the description of “rapid kinetics”, we would like to further clarify.\nFirst, under our experimental conditions, the gas pressurization rate was 100 mbar min-1,\nand it took approximately 10 minutes to go from the initial pressure to 1000 mbar. During\nthis process, the TYUT-18 reached adsorption equilibrium within 10 minutes for both C H\n2 6\nand C H simultaneously with the pressurization to the target pressure, indicating that its\n2 4\nadsorption rate was comparable to the pressurization rate, and no significant delay in mass\ntransfer or diffusion was observed. Therefore, within this experimental framework, we\nconsider the adsorption kinetics of the TYUT-18 is very well.\nSecondly, to further verify the excellent gas diffusion performance of TYUT-18, we\ncompared it with other with C H -selective materials. At 298 K, with a pressurization rate\n2 6\nof 100 mbar min-1, both C H and C H reached adsorption equilibrium in TYUT-18 within\n2 6 2 4\napproximately 10 minutes. This adsorption equilibrium time is significantly shorter than that\nof Cu(Qc) (13 minutes), MAF-7 (15 minutes), TYUT-12 (18 minutes) and ZIF-7 (40 minutes)\n2\n(Supplementary Figs. 16 and 17).\nFurthermore, to further verify this, we conducted supplementary tests at a higher\npressurization rate (500 mbar min-1). The results showed that TYUT-18 rapidly reached\nequilibrium within 5 minutes (see Supplementary Fig. 15), indicating that this material has\nrelatively fast adsorption kinetics.\nWe have provided more detailed experimental descriptions in the revised SI.\nModification:\nSupporting Information: Page 11-13, Supplementary Figs. 14-17.\nSupplementary Figure 14. Diffusional time constant calculation details of C H and C H\n2 4 2 6\non TYUT-18 at 298 K.\nSupplementary Figure 15. Kinetics of adsorption and desorption behaviors for (a) C H\n2 4\nand (b) C H on TYUT-18 at 298 K (C H or C H was introduced into the test chamber at\n2 6 2 6 2 4\na rate of 500 mbar·min-1).\nSupplementary Figure 16. As-synthesized and simulated PXRD patterns for TYUT-12,\nCu(Qc) , MAF-7 and ZIF-7.\n2 4\nC H on TYUT-18, TYUT-12, Cu(Qc) , MAF-7 and ZIF-7 at 298 K.\n2 6 2\nModification:\nManuscript: Page 7, Add corresponding descriptions.\n“At 298 K, with a pressurization rate of 100 mbar min-1, both C H and C H reached\n2 6 2 4\nadsorption equilibrium in TYUT-18 within approximately 10 minutes. This adsorption\nequilibrium time is significantly shorter than that of Cu(Qc) (13 minutes), MAF-7 (15\n2\nminutes), TYUT-12 (18 minutes) and ZIF-7 (40 minutes) (Supplementary Figs. 16 and 17).\nDue to the preferential flexible response of TYUT-18 to C H , its diffusion time constant\n2 6\n(1.77 × 10-2 min-1) is greater than that of C H (1.27 × 10-2 min-1). Desorption experiments\n2 4\nfurther showed that both C H and C H could be completely desorbed from TYUT-18\n2 6 2 4\nwithin 10 minutes.”\nReviewer #3:\nThe manuscript reports a flexible–robust metal–organic framework TYUT-18, whose\nunique binary pore system combined with the flexible deformation of the framework\nproduces significantly different gate-opening pressures for C H and C H at 298 K. More\n2 6 2 4\nimportantly, the paper elucidated the dynamic filling behavior of C H molecules in the\n2 6\nframework system, a process of preferentially occupying the large pore cavities then filling\ninto the small ones was uncovered using a combination of extensive single-crystal X-ray\ndiffraction studies and density functional theory calculations. The work addresses a\nsignificant problem in gas purification, and the strategy of developing a C H -selective\n2 6\nadsorbent is well-justified due to its potential energy efficiency benefits over more\ntraditional C H -selective materials. Therefore, I recommend publication after addressing\n2 4\nthe following minor points:\n(1) The authors mentioned a moderate Q for C H . What is its level among C H -selective\nst 2 6 2 6\nmaterials?\nResponse: Thank you for your suggestion. We have added relevant comparisons of\nadsorption heats in the revised SI. As can be seen from the Supplementary Fig. 11, the\nisosteric heat of adsorption of TYUT-18 for C H is 28.6 kJ·mol-1 at zero coverage, which\n2 6\nis at a moderate level among reported C H -selective MOFs. In summary, the moderate\n2 6\nisosteric heat of adsorption of TYUT-18 ensures strong interaction with C H molecules,\n2 6\nthus achieving a high adsorption capacity, while avoiding desorption difficulties caused by\nexcessively strong adsorption energy, demonstrating good adsorption reversibility and\nrapid adsorption-desorption kinetics. The related isosteric heat of adsorption contrast\ndiagram has been supplemented in the revised SI.\nModification:\nSupporting Information: Page 11, Supplementary Fig. 12.\nSupplementary Figure 12. Comparison of the isosteric heat of adsorption of C H on\n2 6\nTYUT-18 and C H -selective MOFs.\n2 6\n(2) The kinetic diffusion characteristics of both gases are excellent. Which one is more\noutstanding? Does C H with preferential gate-opening show better dynamic diffusion?\n2 6\nResponse: Thank you for your suggestion. Based on the kinetic adsorption data of C H\n2 4\nand C H on TYUT-18 at 298 K, we calculated their diffusion time constants to be 1.27 ×\n2 6\n10-2 min-1 and 1.77 × 10-2 min-1, respectively. The results indicate that the adsorption\nkinetics of C H in TYUT-18 are superior to those of C H . Under the same conditions,\n2 6 2 4\nC H reaches adsorption equilibrium more quickly, which is closely related to its preferential\n2 6\ngate-opening behavior triggered in TYUT-18 (Supplementary Figs. 13 and 14). C H\n2 6\nmolecules preferentially induce the framework to transition from the closed phase to open\nphase, thereby promoting the rapid diffusion and adsorption of C H molecules. Therefore,\n2 6\nalthough both gases exhibit good diffusion characteristics in TYUT-18, the diffusion kinetics\nof C H are superior.\n2 6\nModification:\nSupporting Information: Page 11 and 12, Supplementary Figs. 13 and 14.\nSupplementary Figure 13. Kinetics of adsorption and desorption behaviors for C H and\n2 4\nC H on TYUT-18 at 298 K and 313 K (C H or C H was introduced into the test chamber\n2 6 2 6 2 4\nat a rate of 100 mbar·min-1).\nSupplementary Figure 14. Diffusional time constant calculation details of C H and C H\n2 4 2 6\non TYUT-18 at 298 K.\n(3) As the temperature decreases, the opening pressure of flexible materials will decrease.\nWhat are the adsorption curves of C H and C H at 273K?\n2 6 2 4\nResponse: Thank you for your proposal. Based on your suggestion, we have added the\nadsorption isotherms of TYUT-18 for C H and C H at 273K, as shown in the\n2 6 2 4\nSupplementary Fig. 8. As the reviewer pointed out, the gate-opening pressure of TYUT-18\nfor C H and C H does indeed decrease with decreasing temperature. The revised SI\n2 6 2 4\nincludes relevant adsorption data.\nSupplementary Figure 8. C H and C H adsorption isotherms for TYUT-18 at 273 K and\n2 6 2 4\nModification:\nSupporting Information: Page 8, Supplementary Fig. 8.\n(4) How does this material regenerate in breakthrough experiments? The breakthrough\ndesorption curve should be supplemented, because the regeneration is also a very\nimportant indicator in industry.\nResponse: Thank you for your suggestion. Based on your suggestion, we have\nsupplemented the desorption curves of TYUT-18 for C H /C H (v/v = 50/50) mixture. High-\n2 6 2 4\npurity Ar was used as the purge gas at a flow rate of 50 mL min-1, and the temperature was\n2 4 2 6\ncompletely desorbed and efficiently regenerated within 8 min g-1. These results\ndemonstrate that the prepared material exhibits excellent regenerability and cycling\nstability under room temperature conditions, laying the foundation for its practical\nseparation applications. The relevant desorption data have been supplemented in the\nrevised manuscript and SI.\nSupplementary Figure 32. Desorption curves of C H and C H on TYUT-18 from\n2 4 2 6\nC H /C H (v/v = 50/50) mixtures by Ar purging with 50 mL min-1 at 298 K.\n2 6 2 4\nModification:\nManuscript: Page 11, Add corresponding descriptions.\n“Furthermore, their desorption curves (Supplementary Figs. 32) show that both C H and\n2 6\nC H can achieve complete desorption and regeneration within 8 min g-1 at 298 K.”\n2 4\nSupporting Information: Page 21, Supplementary Fig. 32.\n(5) How is the water stability? It is suggested to supplement the relevant data after the\nwater stability experiment, such as PXRD.\nResponse: Thanks to the reviewers for their suggestions on water stability test. According\nto your suggestion, we carried out the water stability experiment of TYUT-18, and added\nthe corresponding PXRD data and the microscope photographs of TYUT-18 after soaking\nin water in the revised SI. The results show that the diffraction peak position and intensity\nof TYUT-18 have not changed after being soaked in water for 48 hours, which shows that\nthe structure of TYUT-18 is still stable in water environment and has good water stability.\nAt the same time, the results of microscope observation show that the crystal morphology\nof the sample remains intact, which further verifies the stability of its structure.\nSupplementary Figure 42. PXRD pattern and microscope photographs of TYUT-18 after\nsoaking in water for 48 h.\nModification:\nSupporting Information: Page 26, Supplementary Fig. 42.\nReviewer #4:\nThe manuscript presents a study on the development of a flexible-robust metal-organic\nframework, TYUT-18, for the highly selective separation of ethane and ethylene. The\nauthors demonstrate that its unique binary pore system, combined with framework flexibility,\nenables a distinct gate-opening pressure for ethane, achieving exceptional selectivity and\nthe production of ultra-high-purity ethylene. The topic is of great significance, particularly\nfor advancing energy-efficient alternatives to thermal distillation in the petrochemical\nindustry. To further strengthen the manuscript, the following points should be addressed:\n(1) A careful check and unification of units throughout the manuscript is recommended. For\ninstance, “L/Kg” (line 23) and “L kg” (lines 357, 358) should be standardized to a consistent\nformat, such as “L kg-1”, to adhere to scientific conventions\nResponse: Thank you for your reminder. We have thoroughly checked and standardized\nthe units in the manuscript to ensure that the format is consistent with scientific writing\nstandards. For example, we have uniformly changed “L/Kg” and “L kg” in the manuscript\nto the standard form “L kg-1”. At the same time, we have also checked and standardized\nother units that may have been inconsistent to ensure the accuracy and standardization of\nthe overall expression of the manuscript.\n(2) In the description of the in-situ variable-pressure PXRD experiments (e.g., lines 180-\n200), gas “concentration” (e.g., 13%, 18%, 48%) is used to define the phase transition\npoints. Since the thermodynamic driving force for structural transitions in flexible MOFs is\nthe gas partial pressure, it is scientifically more precise to use this term. Revising\n“concentration” to “partial pressure” throughout the manuscript is strongly advised.\nResponse: Thank you for your suggestion. We have revised all descriptions involving\n“concentration” (such as 13%, 18%, 48%) in the manuscript to “partial pressure” to more\nscientifically and accurately describe the thermodynamic driving factors of phase\ntransitions and ensure consistency with the relationship of gas partial pressure.\nModification:\nManuscript: Page 6, revised corresponding descriptions and Fig. 3.\n(3) The authors have masterfully delineated the structural evolution of TYUT-18. To provide\na more complete energetic picture, a deeper integration of the thermodynamic data with\nthese structural insights would be highly valuable. Specifically, correlating the Q trends\nst\n(Supplementary Fig. 11) with the precisely defined phase transition pressures for C H and\n2 6\nC H would be very insightful. A discussion on how the Q values evolve across the β-to-\n2 4 st\nα phase transition for each gas would significantly enhance the understanding of the\nenergy landscape governing the sequential pore-filling mechanism.\nResponse: Thank you for your valuable suggestion. According to the suggestion of\nreviewer 1, we first recalculated the isosteric heat of adsorption with three temperatures.\nThen, according to your suggestion, we further discuss the changes in isosteric heat of\nadsorption at different adsorption stages.\nThe specific calculation steps are as follows: The isosteric heat of adsorption for C H and\n2 6\nC H were calculated by using the gas adsorption data collected at 273, 298 and 313 K.\n2 4\nThe adsorption curves were first fitted with the viral equation:\n𝑚 𝑛\n1 𝑖 𝑖\nln𝑃 =ln𝑞+ ∑𝑎𝑖𝑞 +∑𝑏𝑖𝑞\nWhere q is the amount of gas adsorbed a𝑇t t𝑖h=e0 pressu𝑖r=e0 P, a and b are Virial coefficients,\nm and n are the number of coefficients required to describe the isotherm adequately.\nTo calculate the Q values, the fitting parameters obtained from the equation were then\nst\nplugged into the following equation:\n𝑚\n𝑖\n𝑄𝑠𝑡 =−𝑅∑𝑎𝑖𝑞\n𝑖=0\nBased on calculations and experimental results, we further discuss the changes in isosteric\nheat of adsorption at different adsorption stages. First, it needs to be clarified that, as\npreviously reported by Li et al. (Nature, 2021, 595, 542–548), the isosteric heat of\nadsorption obtained based on adsorption isotherms and fitted using a virial model may not\nfully reflect the true thermodynamic behavior of flexible MOF materials during stepwise\nadsorption.\nTheoretically, the change in adsorption heat is closely related to the structural response of\nthe flexible framework. For flexible materials exhibiting phase transition behavior, the\ntransition of the framework from the β phase to the α phase requires a certain amount of\nstructural deformation energy. When the adsorption energy provided by the adsorbed\nmolecules is sufficient to induce a phase transition, some of the adsorption energy is used\nto overcome the energy barrier of structural deformation, thus leading to a decrease in the\napparent isosteric heat of adsorption in the phase transition region.\nFor the two gases C H and C H , we observed different evolution trends in their isosteric\n2 6 2 4\nheat of adsorption during the phase transition process.\nFor C H , its isosteric heat of adsorption exhibits an initial decrease followed by an increase:\n2 6\nDuring the β phase to α phase transition, DFT calculations indicate that the structural\ndeformation energy required to overcome is approximately 18.79 kJ·mol-1. Therefore,\nduring the phase transition, some adsorption energy needs to be used to offset the\nframework deformation energy, and this deformation process is relatively slow.\nConsequently, a gradual decrease in the apparent isosteric heat of adsorption is observed\nduring this stage; after the phase transition, the open phase exposes more adsorption\nspace, and the isosteric heat of adsorption increases accordingly.\nIn contrast, C H only induces framework opening under higher pressures, and its\n2 4\nadsorption isotherm shows a weaker flexible response, with the phase transition energy\nconsumption having a smaller impact on the apparent isosteric heat of adsorption.\nFurthermore, with increasing capping, C H gradually occupies the more affinity position,\n2 4\nthus the isosteric heat of adsorption continuously increases with capping amount.\nModification:\nSupporting Information: Pages 9 and 10, Supplementary Figs. 10 and 11.\nSupplementary Figure 10. Virial fitting (lines) of the (a) C H and (a) C H adsorption\n2 6 2 4\nisotherms (points) of TYUT-18.\nSupplementary Figure 11. The isosteric heat of adsorption of C H and C H on TYUT-\n2 6 2 4\n18.\n(4) The single-component data and IAST predictions convincingly show high selectivity.\nHowever, for practical separation, a critical question arises: does the C H -induced\n2 6\nframework transition facilitate subsequent co-adsorption of C H by lowering the diffusion\n2 4\nor adsorption energy barrier for ethylene in the now-opened pores? It is crucial to elucidate\nthis potential “cooperative adsorption” or “pore-opening effect”.\nResponse: Thank you for your suggestion. In many flexible framework materials, the\nframework transition induced by the initial guest molecule can often lower the diffusion or\nadsorption energy barrier for subsequent guest molecules to enter the open pores, thereby\npromoting their co-adsorption. Based on this general understanding, we attempted to test\nwhether the C H -induced framework transition in TYUT-18 could also lower the diffusion\n2 6\nor adsorption energy barrier for C H , thereby promoting its co-adsorption behavior.\n2 4\nTo verify this possibility, we calculated the dynamic adsorption capacities of C H and C H\n2 6 2 4\nin breakthrough experiments conducted with TYUT-18 in C H /C H (v/v = 50/50) mixed\n2 6 2 4\ngases. The results showed that under dynamic mixed gas conditions, the dynamic\nadsorption capacity of C H (62.5 cm3 g-1) was lower than its static adsorption capacity\n2 6\n(67.9 cm3 g-1), indicating that TYUT-18 exhibits stronger preferential recognition and rapid\nadsorption capacity for C H during the breakthrough process. In the competitive\n2 6\nadsorption process, C H preferentially occupies pore cavity more strongly, thereby\n2 6\ninhibiting the entry and adsorption of C H to some extent. Therefore, the dynamic\n2 4\nadsorption capacity of C H (29.2 cm3 g-1) is much lower than its static adsorption capacity\n2 4\n(60.0 cm3 g-1).\nThe above results indicate that, under the current operating conditions, the preferential\nadsorption effect of C H is dominant, and the breakthrough experiment did not\n2 6\ndemonstrate the synergistic promoting effect of C H -induced framework transition on C H\n2 6 2 4\nadsorption. The relevant calculation procedures have been supplemented and explained\nin the revised SI.\nModification:\nSupporting Information: Page 22, Supplementary Fig. 33.\nSupplementary Figure 33. The calculation for the captured amount of C H during the\n2 6\nC H /C H (v/v = 50/50) breakthrough process in TYUT-18.\n2 6 2 4\nThe dynamic uptake capacity of C H ( ) was calculated as:\n2 6\n𝑞𝐶2𝐻6\n𝑡1\n3 −1\nThe dyna𝑞m𝐶2𝐻ic6 u=pt𝑣ak×e𝑦 c𝐶a2𝐻p6a×cit∫y o(f 𝐶C0−H𝐶 (𝑖)𝑑𝑡 =) w𝑣a×s 𝑦c𝐶a2l𝐻c6u×lat(e𝑆d1 a+s𝑆: 2)≈62.5 𝑐𝑚 𝑔\n𝑡0 2 4\n𝑞𝐶2𝐻4\n𝑡1\n3 −1\nv represe𝑞n𝐶2 t𝐻s 4 th=e 𝑣flo×w𝑦 v𝐶2 e𝐻lo 4 c×ity∫ of( t𝐶h0e− ga𝐶s𝑖) m𝑑𝑡ix=tur𝑣e×, a𝑦n𝐶d 2 𝐻y 4 r×ep(r𝑆e1s−en𝑆t3s) t≈he2 m9.o2l a𝑐𝑚r fra𝑔ction of the\nt0\ncorresponding gas in the mixture.\n(5) The reported breakthrough experiments (e.g., with 50/50 and 10/90 C H /C H ) likely\n2 6 2 4\nutilize the initial adsorption capacity of the large pores (Cavity A). To demonstrate the\nmaterial’s full separation potential and explore its operational limits, it would be interesting\nto see a breakthrough experiment designed to actively trigger the gate-opening of the small\npores (Cavity B).\nResponse: Thank you very much for your detailed review and valuable suggestions on\nour work. At 1 bar, the partial pressure of C H in the mixed gas system is only 0.5 bar.\n2 6\nAccording to our gas-loaded in situ PXRD results, the C H -induced gate-opening pressure\n2 6\nis approximately 0.48 bar. Therefore, under this condition, the small pore cavity B may\nbegin to open partially, but are not yet fully activated, and the adsorption process is still\nmainly contributed by the large pore cavity A.\nTo further investigate the separation behavior of TYUT-18 under the fully open pore cavity\nB state, we conducted a C H /C H (v/v = 50/50) breakthrough experiment at 2 bar. At this\n2 6 2 4\npressure, the partial pressure of C H reaches 1 bar, significantly higher than its opening\n2 6\npressure, effectively driving a complete phase transition in the TYUT-18 framework.\nExperimental results showed that the breakthrough time for both gases was prolonged,\nwith C H breakthrough at 46 min g-1 and C H at 66 min g-1, resulting in a separation time\n2 4 2 6\nof 20 min g-1. This indicates that under higher pressures, the pores cavity B can fully open,\nproviding more adsorption space, thus leading to an increase in breakthrough and\nseparation times.\nModification:\nSupporting Information: Page 21, Supplementary Fig. 31.\nSupplementary Figure 31. Breakthrough curves of TYUT-18 for C H /C H mixtures (v/v\n2 6 2 4\n= 50/50) at 298 K and 2 bar.\n(6) The successful demonstration of ternary mixture (C H /C H /C H ) separation is a key\n2 2 2 4 2 6\nstrength. To fully support this claim and robustly assess the application potential, two\nadditions are recommended: Firstly, providing the pure-component C H adsorption\n2 2\nisotherm is essential for a baseline understanding of its interaction with the framework and\nfor comparison with C H and C H . Secondly, and more critically, demonstrating the\n2 6 2 4\ncomplete and reversible desorption of C H under the reported regeneration conditions is\n2 2\nnecessary to rule out any risks of pore blockage, performance degradation, or product\ncontamination in subsequent cycles.\nResponse: Thank you very much for your suggestions. Regarding the two questions\nraised, we have made the following additions and responses:\nRegarding the adsorption isotherm of the pure C H component:\n2 2\nWe fully agree with the reviewer's comments. We have added the adsorption isotherm of\nthe pure C H component of TYUT-18 at 298 K to the revised manuscript (see\n2 2\nSupplementary Fig. 37). The results show that the adsorption capacity of C H is higher\n2 2\nthan that of C H and C H , which further verifies that TYUT-18 has a strong adsorption\n2 6 2 4\naffinity for C H . This characteristic provides important evidence for achieving one-step\n2 2\nefficient purification of C H in a ternary system.\n2 4\nRegarding the completely reversible desorption and material regeneration performance of\nC H :\n2 2\nFollowing the reviewer's suggestion, we have added the desorption-regeneration curves\nof C H to the revised manuscript. For the C H regeneration experiment, we purged with\n2 2 2 2\nhigh-purity Ar at 298 K at a flow rate of 50 mL min-1. The experimental results clearly show\nthat C H can achieve complete and reversible desorption under these conditions, with no\n2 2\nobserved pore blockage or adsorption performance degradation.\nFurthermore, to further verify that TYUT-18 does not experience pore blockage due to C H\n2 2\nresidue, we conducted three breakthrough cycles on a C H /C H /C H (v/v/v = 1/98/1)\n2 2 2 4 2 6\nmixture. The separation performance remained stable in all three breakthrough cycles\nwithout any degradation, indicating that there is no C H residue in the TYUT-18 pores.\n2 2\nThese results fully demonstrate that TYUT-18 possesses excellent cycling stability and\nregenerability.\nModification:\nManuscript: Page 12, Add corresponding descriptions.\n“In three breakthrough cycle tests of C H /C H /C H (1/98/1, v/v/v), the separation\n2 2 2 4 2 6\nperformance remained stable, indicating that there is no irreversible retention of C H in\n2 2\nthe pores of TYUT-18 (Supplementary Fig. 36b). Moreover, regeneration experiments of\nC H showed that C H can be completely and reversibly desorbed from TYUT-18\n2 2 2 2\n(Supplementary Fig. 37). In summary, these results fully demonstrate the excellent cycling\nstability and regeneration performance of TYUT-18, providing a reliable and efficient\nstrategy for the deep purification of C H , and showing promising prospects for industrial\n2 4\napplications.”\nModification:\nSupporting Information: Page 23 and 24, Supplementary Figs. 36b and 37.\nSupplementary Figure 36. (b) Three breakthrough cycle curves of TYUT-18 on\nC H /C H /C H (v/v/v = 1/98/1) mixtures at 298 K and 1 bar (detection limit: C H : 0.001 %,\n2 2 2 4 2 6 2 6\nC H : 0.1 ppm).\n2 2\nSupplementary Figure 37. C H adsorption isotherms for TYUT-18 at 298 K and\n2 2\ndesorption curves of C H from C H /C H /C H (v/v/v = 1/98/1) by helium purging with 50\n2 2 2 2 2 4 2 6\nmL min-1at 298 K.\n(7) For any adsorbent targeting real-world olefin/paraffin separation, evaluating stability\ntowards moisture is paramount, as industrial streams often contain trace water. A study on\nthe interaction of TYUT-18 with water vapor is highly recommended. Key questions to\naddress are whether H O molecules preferentially occupy the critical binary pore channels\n2\nand, if so, whether this adsorption is fully reversible or leads to an irreversible degradation\nof the framework's structure and its unique flexible-robust separation mechanism.\nResponse: Thank you very much for your crucial suggestion. The industrial application\npotential of TYUT-18 indeed depends on its structural stability and separation performance\nretention in environments containing trace water. In response to this suggestion, we\nconducted and supplemented the following studies:\nRegarding water vapor adsorption behavior:\nWe have added water vapor adsorption isotherms for TYUT-18 to the revised SI (see\nSupplementary Fig. 38). The results show that TYUT-18 exhibits typical hydrophobicity,\nwith an adsorption capacity of 0.008 g of water at low relative humidity (< 40%).\nFurthermore, the measured water contact angle of TYUT-18 is 128.1°, further\ndemonstrating its excellent hydrophobicity.\nRegarding structural stability and reversibility:\nTo further confirm the effect of water on the framework structure, we performed PXRD tests\non samples that had adsorbed water vapor. The results show that the material framework\nremained intact, with no structural distortion.\nRegarding dynamic separation performance under humid conditions: To better reflect\nactual industrial conditions, we conducted a breakthrough experiment in a mixed gas\nenvironment containing trace amounts of moisture (see Supplementary Figs. 38c and 38d).\nThe results show that the separation performance of TYUT-18 remains stable under both\n75% and 40% relative humidity conditions, indicating that this material can maintain its\nexcellent separation performance even in slightly humid environments.\nModification:\nManuscript: Page 12, Add corresponding descriptions.\n“In actual industrial separation processes, a certain amount of moisture is inevitably\nencountered, typically originating from high-temperature processes such as steam\ncracking and ethane dehydrogenation. The presence of water can lead to competitive\nadsorption between the gas and water, thereby reducing the hydrothermal stability of the\nadsorbent and weakening its separation performance. To evaluate the reliability of TYUT-\n18 in humid environments, we first conducted room temperature water vapor adsorption\ntests. The results showed that under a relative humidity of 40%, TYUT-18 absorbed only\n0.008 g g-1 of water, exhibiting excellent hydrophobic properties. The water contact angle\ntest further confirmed its excellent hydrophobicity (Supplementary Fig. 38a). This is mainly\nattributed to the fact that TYUT-18 is composed of dense aromatic rings, forming a highly\nhydrophobic microenvironment. Simultaneously, the absence of open metal sites or\nstrongly polar functional groups in the framework results in extremely weak interactions\nbetween the adsorbent and water molecules, thus ensuring the TYUT-18 exhibits excellent\nresistance to water competitive adsorption under humid conditions. Furthermore, the\npositions and intensities of the characteristic peaks in the PXRD pattern after water\nabsorption (Supplementary Fig. 38b) did not change, indicating that the crystal structure of\nthe material remains stable under humid conditions. Based on this, we further conducted\ndynamic breakthrough experiments at 298 K and 1 bar using C H /C H mixtures (v/v =\n2 4 2 6\n50/50) with different relative humidities (RH = 40% and 70%) (Supplementary Figs. 38c\nand 38d). Notably, even under high humidity (70% RH) conditions, the breakthrough time\nof TYUT-18 remained almost identical to that under dry conditions, demonstrating its\nexcellent stability in high-humidity environments and showcasing highly competitive\nindustrial application prospects and environmental adaptability.\n”\nModification:\nSupporting Information: Page 24, Supplementary Fig. 38.\nSupplementary Figure 38. (a) Water vapor adsorption isotherm and water contact angle\nof TYUT-18. (b) PXRD of TYUT-18 after water vapor adsorption. (c, d) Breakthrough\ncurves of TYUT-18 for C H /C H (v/v = 50/50) mixture under varying relative humidity.\n2 4 2 6\nOur team is grateful for the opportunity to address the constructive feedback provided\nby the referees. As requested, we have revised the manuscript accordingly to fully\naddress your editorial and reviewers’ comments, and we have carefully reviewed and\nrevised the manuscript based on your comments, which are highlighted in yellow.\nResponse to the reviewer’s comments\nReviewer #1 (Remarks to the Author):\nThe authors have addressed all of my comments except for showing the error bars on\nthe supplementary Information figure 11 for the Q . This needs to be shown.\nst\nResponse: We thank the reviewer for suggestions. We have added error bars to the\nQ curve in Supplementary Fig. 11.\nst\nReviewer #2 (Remarks to the Author):\nIn this revision, the authors have carefully addressed the reviewers’ comments and\nimproved the overall clarity of the manuscript. However, the revised version also makes\nclear that sequential adsorption behavior in closely related MOFs has been reported\npreviously, which further limits the novelty of the present work. Moreover, comparison\nwith other robust C H -selective MOFs indicates that both the C H uptake and the\n2 6 2 6\nC H /C H selectivity of TYUT-18 are lower than those of previously reported materials.\n2 6 2 4\nAs a result, I feel that the current manuscript does not yet meet the high standard\nrequired for publication in Nature Communications at this point. The following points\nshould be carefully considered for clarification and further improvement.\nResponse: Our work reports a C H -selective metal–organic framework, TYUT-18,\n2 6\nwith the uncommon flexible–robust properties. From the perspective of understanding\nfor separation performance, we reveal that a binary pore system combined with flexible\ndeformation of the framework can effectively reduce the competitive adsorption of C2\nmixtures, thereby increasing the separation efficiency. And from the aspect of\nadsorption mechanism, the dynamic filling and desorbing behavior of C H molecules\n2 6\nin the flexible–robust framework was thoroughly elucidated through a combination of\nextensive single-crystal X-ray diffraction studies and density functional theory\ncalculations. The work addresses a significant problem in gas purification, and the\nstrategy of developing a C H -selective adsorbent is well-justified due to its potential\n2 6\nenergy efficiency benefits over more traditional C H -selective materials. The overall\n2 4\ninnovation of the article has also been unanimously recognized by the other three\nprofessional reviewers. Furthermore, in response to your valuable suggestions, we\nhave made further revisions and improvements to the manuscript to enhance its\nscientific rigor and expressive precision.\n(1) The authors should clearly state, in both the Abstract and the Introduction, what\nnew insight or specific advancement this work provides beyond prior reports. The\nmanuscript emphasizes sequential guest filling in TYUT-18; however, it remains\nunclear whether (and how) sequential pore filling is mechanistically linked to enhanced\nC H separation performance in general.\n2 6\nResponse: Thank you for suggestion.\nFirstly, we have emphasized the advantages of this binary pore flexible-robust TUYT-\n18 in reducing competitive adsorption, optimizing dynamic separation behavior, and\nimproving overall separation efficiency in the Abstract and Introduction sections to\nfurther highlight the design concept and innovation of this study.\nSupplementary Figure 25. Breakthrough curves obtained for (a)TYUT-18 and (b)\nTYUT-17 with C H /C H mixtures (v/v = 50/50) at 298 K with the gas flow of 2\n2 6 2 4\nml/min.Note: The data in Figure b comes from our previous work (Angew. Chem. Int.\nEd. 2025, 64, e202418853). And the breakthrough experiments of TYUT-18 and\nTYUT-17 were conducted by using the same equipment and adsorption column with\nthe similar sample loadings.\nAdditionally, the binary pore structure flexible-robust TYUT-18 constructed in this study\neffectively reduced the competitive adsorption behavior between C H and C H during\n2 6 2 4\ndynamic separation. Compared with the previously reported single pore flexible-robust\nTYUT-17 (Supplementary Fig. 25), TYUT-18 exhibits a shortened co-adsorption time\nin the C H /C H (50/50, v/v) breakthrough experiment, indicating that its binary porous\n2 6 2 4\nstructure can weaken the competitive adsorption of C H under dynamic conditions.\n2 4\nCorrespondingly, the overall separation cycle will shorten, thereby improving the\nseparation efficiency per unit time. These results demonstrate that the flexible-robust\ndesign of the binary porous structure can significantly improve the dynamic separation\nperformance in alkane/alkene systems.\nModification:\nManuscript: Page 1 and 2, Add corresponding descriptions.\n“effectively reducing competitive adsorption in the same pore and improving overall\nseparation efficiency”\n“Nevertheless, its single pore structure concentrates the flexible response and\nmolecular recognition function within the same pore, causing C H and C H molecules\n2 6 2 4\nto exhibit similar pore-opening behaviours during adsorption, resulting in competitive\nadsorption within the same pore.”\n(2) Related to the above, the authors emphasize the flexibility of TYUT-18, but the\nrelationship between structural flexibility and C H separation performance is not\n2 6\nclearly established. What specific positive effect do the authors expect framework\nflexibility to provide (e.g., affinity amplification, exclusion of C H , diffusion\n2 4\ndiscrimination, stabilization of specific adsorption sites), and what experimental\nevidence directly supports such an effect in this system? The authors should\nstrengthen this discussion and provide supporting evidence or analysis (e.g.,\nstructure–property correlation across phases, temperature/pressure-dependent\nstructural response linked to selectivity, adsorption energetics tied to structural change,\nin situ data demonstrating flexibility under mixture conditions, etc.).\nResponse: We thank the reviewer for this insightful comment regarding the role of\nframework flexibility in TYUT-18.\nIn TYUT-18, framework flexibility is not able to enhance the intrinsic adsorption affinity\nof a single gas molecule. However, its primary positive role is to enhance the diffusion\ndiscrimination and the gas-dependent pore-opening behavior under dynamic\nconditions. When combined with a binary pore structure, it can effectively weaking the\ncompetitive adsorption and shorten the co-adsorption time in the C H /C H separation.\n2 6 2 4\nIn addition, the advantage of synergistic effect of the flexible framework and the binary\npore structure is further manifested in the dynamic separation performance. For TYUT-\n18, the C H /C H uptake ratio obtained from breakthrough experiments (C H /C H ,\n2 6 2 4 2 6 2 4\nv/v, 50/50) is close to the static adsorption measurements. In contrast, for robust\nmaterials lacking strong adsorption sites (TYUT-12, Engineering, 2024, 41, 84–92;\nCu(Qc) , J. Am. Chem. Soc., 2018, 140, 12940−12946; MAF-7, J. Colloid Interface\n2 6 2 4\nthan their corresponding static values, reflecting the undesired competitive adsorption\nbehavior.\nIn conclusion, these results demonstrate that the synergistic effect of framework\nflexibility of TYUT-18 and its binary pore structure plays a crucial role in gas-dependent\npore-opening behavior under dynamic conditions, rather than merely strengthening\nstatic adsorption affinity. This unique feature effectively weakened the competitive\nadsorption during separation, shortens co-adsorption time, and ultimately improves\ndynamic separation efficiency. The corresponding discussion is supplemented to the\nbreakthrough experimental discussion part of the revised manuscript (Supplementary\nFig. 25).\nModification:\nManuscript: Page 11, Add corresponding descriptions.\n“Notably, compared to the previously reported single pore flexible-robust TYUT-17\n(Supplementary Fig. 25), TYUT-18 exhibits a significantly shorter co-adsorption time\nunder the same dynamic breakthrough conditions, indicating that the synergistic effect\nof its binary porous structure and flexibility effectively weakens the competitive\nadsorption behaviour of C H under dynamic conditions. This shortens the overall\n2 4\nseparation cycle, thereby improving its overall separation efficiency.”\n(3) More complete information on the Rietveld refinements must be provided. Although\nthe refinement workflow is described, essential experimental and refinement details\nare missing, which prevents assessment of reliability and reproducibility. At minimum,\nthe authors should report the measurement conditions, refinement\nconstraints/restraints, lattice-parameter treatment and instrumental corrections (zero\nshift/specimen displacement), and quantitative refinement indicators (phase-specific\nindicators such as R_Bragg or R_F). The refinement output file should also be provided\nas Supporting Information in the form of a CIF file containing these details.\nResponse: Thank you for the reviewers' suggestions. We have addressed each of\nthe questions you raised above.\nMeasurement conditions: A customized gas partial pressure control system was\ndeveloped (Supplementary Fig. 46). To precisely regulate gas composition, two mass\nflow controllers (MFCs) with different flow ranges (100 sccm and 5 sccm for low partial\npressures below 5%) were connected to either the C H or C H gas cylinders. An\n2 6 2 4\nadditional pair of MFCs was linked to a nitrogen (N ) cylinder, serving as the purge gas\n2\nfor sample activation. The gas mixture was then introduced into an in situ PXRD\nchamber (Bruker D8 Advance, Cu Kα radiation, λ = 1.5418 Å). Diffraction patterns were\ncollected over the 2θ range of 4–40° with a total acquisition time of 5 min at room\ntemperature about 298 K. All stainless-steel valves and fittings were sourced from\nShanghai X-tec Fluid Technology Co., Ltd., and the MFCs were supplied by Alicat\nScientific (a Halma company).\nRefinement constraints/restraints: In the process of structural optimization, specific\ngeometric parameters were constrained based on the single-crystal structures and\nintrinsic chemical characteristics of the system to ensure the structural stability and\nchemical plausibility. Specifically, Zn–O and Zn–N bond lengths were constrained,\nwhile the bond lengths, bond angles, and dihedral angles involving C and N atoms\nwithin the aromatic rings were restrained to preserve their planar configuration. In\naddition, C H and C H molecules were first optimized using DFT calculations and\n2 4 2 6\nsubsequently treated as rigid bodies during refinement and their internal degrees of\nfreedom were not further optimized.\nLattice-parameter treatment:The lattice parameters and space group derived from the\nsingle-crystal structural model were used as initial values. The lattice parameters were\nfirst refined by Pawley fitting, and the optimized values were subsequently adopted as\nfixed or starting parameters in the Rietveld refinement.\nInstrumental corrections: In the Rietveld refinement of the XRD data, a zero-shift\nparameter was introduced to correct the systematic instrumental error. The refined\nzero-shift value (~0.25° in 2θ) lies within the commonly accepted range (0–0.5°) and\ncan be attributed to minor sample displacement and instrumental geometry effects.\nIncorporation of this correction significantly improved the agreement between\nexperimental and calculated peak positions, thereby enhancing the reliability of the\nrefined lattice constants, atomic coordinates, and related structural parameters.\nQuantitative refinement indicators: The R_bragg values corresponding to TYUT-\n18(β)·1C H and TYUT-18(α)·2C H are 2.77% and 2.60% respectively, which are\n2 4 2 4\nwithin a reasonable range (the reasonable range is < 5%).\nWe have uploaded the refined CIF file as supporting information and named TYUT-\n18(β)·1C H and TYUT-18(α)·2C H as TYUT-18-C H -0.37bar.cif and TYUT-18-\n2 4 2 4 2 4\nC H -1bar.cif respectively.\n2 4\nRelevant contents have been added to the revised manuscript and Supporting\nInformation.\nModification:\nManuscript: Page 15, Add corresponding descriptions.\n“Diffraction patterns were collected over the 2θ range of 4–40° with a total acquisition\ntime of 5 min at room temperature about 298 K.”\nSupporting Information: Page 15 and 34, Add corresponding descriptions and\nparameters.\nSupplementary Table 5. Crystallographic data and structural refinement summary.\ncompound TYUT-18(β)•1C H TYUT-18(α)•2C H\n2 4 2 4\nsp. gr. C12/c1 C12/c1\na (Å) 22.3172 26.9125\nb (Å) 9.6834 8.3559\nc (Å) 28.2716 29.1355\nα (°) 90.0000 90.0000\nβ (°) 94.1405 91.8166\nγ (°) 90.0000 90.0000\nV (Å3) 6093.70 6548.65\nno. of reflection 295 315\n2-interval (°) 4-40 4-40\nR (%) 8.96 7.10\nwp\nR (%) 6.43 5.49\np\nR (%) 4.76 3.78\nexp\nGood of fitting 1.88 1.87\nR_Bragg (%) 2.77 2.60\nZero Shift 0.246720175 0.235164372\n(4) Supplementary Figure 18 shows reflections around 9 degree that are not explained\nby the expected Bragg positions of the proposed phase. The authors should explain\nthe origin of these peaks. Possibilities include a secondary phase/impurity, incomplete\nactivation, preferred orientation artifacts, or an unmodeled structural transformation;\nin any case, this needs to be addressed explicitly and, if possible, modeled or excluded\nwith justification.\nResponse: Thank you for your suggestion. Supplementary Fig. 18 shows the PXRD\npattern corresponding to the C H loading pressure of 0.37 bar. A diffraction peak\n2 4\nappears at 2θ≈9°, which represents an incomplete phase transition of TYUT-18 from\nthe β phase to the α phase under pressure-induced transformation, rather than a\nsecondary phase or impurity. As shown in Figure 1, no obvious diffraction peak\nappears at 2θ≈9° when the C H loading pressure is 0 bar; a weak diffraction peak\n2 4\nappears at this position when the loading pressure increases to 0.37 bar, and the\nintensity of this diffraction peak significantly increases with further pressure increases\nto 1 bar. Therefore, the small diffraction peak at 9° indicating the gas adsorption-\ninduced structural transformation were started at 0.37 bar in a few small size samples.\nAnd this behavior is common in flexible MOFs, as shows in some reported work\n(Science, 2013, 339, 193-196).\nThank you for your advice, and we added some corresponding descriptions in the\nrevised Supplementary Figure 18 for clarity.\nFigure. 1 In situ PXRD patterns obtained for TYUT-18 under varying C H gas pressures.\n2 4"}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have addressed all of my comments except for showing the error bars on the supplementary figure 11 for the Qst. This needs to be shown.", "reviewer_2": "In this revision, the authors have carefully addressed the reviewers’ comments and improved the overall clarity of the manuscript. However, the revised version also makes clear that sequential adsorption behavior in closely related MOFs has been reported previously, which further limits the novelty of the present work. Moreover, comparison with other robust C2H6-selective MOFs indicates that both the C2H6 uptake and the C2H6/C2H4 selectivity of TYUT-18 are lower than those of previously reported materials. As a result, I feel that the current manuscript does not yet meet the high standard required for publication in Nature Communications at this point. The following points should be carefully considered for clarification and further improvement.\n(1) The authors should clearly state, in both the Abstract and the Introduction, what new insight or specific advancement this work provides beyond prior reports. The manuscript emphasizes sequential guest filling in TYUT-18; however, it remains unclear whether (and how) sequential pore filling is mechanistically linked to enhanced C2H6 separation performance in general.\n(2) Related to the above, the authors emphasize the flexibility of TYUT-18, but the relationship between structural flexibility and C2H6 separation performance is not clearly established. What specific positive effect do the authors expect framework flexibility to provide (e.g., affinity amplification, exclusion of C2H4, diffusion discrimination, stabilization of specific adsorption sites), and what experimental evidence directly supports such an effect in this system? The authors should strengthen this discussion and provide supporting evidence or analysis (e.g., structure–property correlation across phases, temperature/pressure-dependent structural response linked to selectivity, adsorption energetics tied to structural change, in situ data demonstrating flexibility under mixture conditions, etc.).\n(3) More complete information on the Rietveld refinements must be provided. Although the refinement workflow is described, essential experimental and refinement details are missing, which prevents assessment of reliability and reproducibility. At minimum, the authors should report the measurement conditions, refinement constraints/restraints, lattice-parameter treatment and instrumental corrections (zero shift/specimen displacement), and quantitative refinement indicators (phase-specific indicators such as R_Bragg or R_F). The refinement output file should also be provided as Supporting Information in the form of a CIF file containing these details.\n(4) Supplementary Figure 18 shows reflections around 9 degree that are not explained by the expected Bragg positions of the proposed phase. The authors should explain the origin of these peaks. Possibilities include a secondary phase/impurity, incomplete activation, preferred orientation artifacts, or an unmodeled structural transformation; in any case, this needs to be addressed explicitly and, if possible, modeled or excluded with justification.", "reviewer_3": "The authors have addressed all the concerns raised by the reviewers, and I recommend accepting this work.", "reviewer_4": "This manuscript has been revised accordingly, and it is suitable for publication at present form."}, "author_response": "Response to the reviewer’s comments\nReviewer #1:\nIn this work Zhang et al. report a metal-organic framework containing a two-fold\npore system, in which sequential filling of pores is concomitant with a subtle reorganization of\nthe pore structure. This framework exhibits apparent selectivity for ethane over ethylene,\nas initially indicated by the single component isothermal adsorption measurements. In situ\nXRD experiments reveal the relationships of adsorption with the sequential pore filling in\nthe framework, namely subtle rotations leading to pore size/shape adaptation. Calculations\nidentify the energetic relationships of adsorption and structural deformation, and its\nrelationship to selectivity. Breakthrough measurements reveal high selectivity for ethane,\nwith preferred adsorption leading to clean breakthrough of ethylene and production of high\npurity feedstock.\nOverall, this work reports a high-performance material with in-depth structural\ncharacterization of the adsorption pathway. However, there are several questions\nregarding analysis and reported data that must be addressed.\n(1) IAST as a theory applies to only rigid systems, therefore it is inappropriate to apply it to\nthis system.\nResponse: We thank the reviewers for their valuable suggestions.\nWe fully understand the limitations of IAST theory in terms of its applicability to flexible\nsystems. So, we have deleted the analysis and discussion related to IAST in the revised\nmanuscript.\n(2) At multiple points in the manuscript the selectivity at 0.1 bar is discussed, and the\nflexibility is invoked. However, at 0.1 bar in the single component isotherms there is no\nchange to the pore structure. This seems to be contradictory and therefore must be\naddressed.\nResponse: We thank the reviewers for their comments.\nWe have carefully reviewed the discussion regarding C H /C H selectivity and flexibility\n2 6 2 4\nof TYUT-18 at 0.1 bar in the manuscript. Indeed, as the reviewers pointed out, the\nadsorption isotherms of C H and C H of TYUT-18 within this pressure range do not show\n2 6 2 4\nsignificant changes in pore structure. Therefore, it may be misleading to associate the\nstructural flexibility of TYUT-18 with the C H /C H selectivity of 0.1 bar. In order to maintain\n2 6 2 4\nacademic rigor, we deleted the description in the manuscript about the relationship\nbetween C H /C H selectivity of TYUT-18 at 0.1 bar and its structural flexibility.\n2 6 2 4\n(3) There needs to be much more information provided regarding how the breakthrough\nmeasurements were performed. This work could not be reproduced with the provided\ninformation. Such as how the column was packed. Was the framework pelletized or mixed\nwith a binder?\nResponse: Thank the reviewers for their attention to the details and repeatability of the\nbreakthrough experiment.\n(a) Firstly, we have supplemented the specific operating conditions of the breakthrough\nexperiment in more detail, and the relevant contents are as follows:\n“The breakthrough experiments are performed on a homemade set-up involving two gas\ncolumns; one is linked to a stainless-steel column loaded with activated TYUT-18, while\nthe other served as a blank control to stabilize the gas flow (Supplementary Fig. 46). Both\ncolumns had an inner diameter of 6 mm. The temperature of the adsorption bed is\nmaintained at 298 K or 313 K using a thermostat. The outlet and inlet flow rates and\npressures of the C H /C H mixtures are regulated by a mass flow meter and a pressure\n2 6 2 4\ngauge, respectively. Gas from the outlet of the adsorption column is monitored by gas\nchromatography (Agilent 490) equipped with a thermal conductivity detector (TCD). Before\nthe experiment, the adsorption column is heated at 423 K whilst purging with Ar, and then,\nthe inlet gas is switched to the mixture to be tested at a total gas flow of 2 or 8 mL min-1.\nFor the cycling experiments, the sample is regenerated by in situ purging with Ar at a flow\nrate of 50 mL min-1 at 298 K for 1 h. The sample mass of TYUT-18 was 0.6 g.” Details of\nthe breakthrough experiment have been added in the revised manuscript.\n(b) Secondly, regarding the question of “How the column was packed. Was the framework\npelletized or mixed with a binder?”. The breakthrough experiment of TYUT-18 was carried\nout directly with powder samples. The reason is that the single crystal particle size of TYUT-\n18 is relatively large (about 40 μm), as shown in the microscope and SEM images in the\nsupplementary information (see Supplementary Figs. 1 and 5), and its particle size is\nenough to ensure uniform filling and moderate pressure drop. In addition, in order to avoid\nstructural collapse and performance loss that may be caused during granulation or tablet\npressing, we choose to use powder directly for breakthrough experiments.\n(4) In this vein, the breakthrough data is exceptionally clean, which raises questions as to\nhow it was performed. One key question is why upon the full breakthrough and saturation\ndo the ratios of the two gases not match the inlet? In the previous work by this group this\nis seen as expected. What is different here? Providing the raw data would be beneficial.\nResponse: Thank you very much for pointing out this problem.\n(a) Firstly, about the question of how breakthrough experiments are performed, the specific\nsteps are as follows:\nFirst, tests were conducted using a self-made breakthrough experimental setup. This\nsystem comprises two stainless steel columns, each with an inner diameter of 6 mm: one\nfilled with activated MOF sample (TYUT-18, sample mass approximately 0.6 g), and the\nother a blank control column used to stabilize the gas flow and eliminate systematic errors.\nThis dual-column design effectively reduced flow fluctuations and system noise, thereby\nsignificantly improving the stability and repeatability of experimental data. Before the\nexperiment, the adsorption columns were pretreated: heated at 423 K while purging with\nAr gas to thoroughly remove residual gases and adsorbed impurities from the sample,\nensuring that each experiment started from the same initial state, thus improving the\nrepeatability and reliability of the experimental results. Subsequently, the inlet gas was\nswitched to the C H /C H mixture, with the total gas flow rate controlled within the range\n2 6 2 4\nof 2 or 8 mL·min-1. The gas flow rate and pressure were precisely adjusted using a mass\nflow meter and a pressure gauge to maintain a constant component ratio and stable flow\nrate, thereby obtaining a high-precision breakthrough curve. Finally, a gas chromatograph\n(Agilent 490) equipped with a thermal conductivity detector (TCD) was used to\ncontinuously monitor the compositional changes of the gas exiting the adsorption column.\nThe TCD detector has good sensitivity and signal stability, enabling low-noise, continuous\nsignal output, thus obtaining a smooth and clean breakthrough curve.\n(b) In addition, we are very grateful to the reviewers for pointing out the question “the full\nbreakthrough and saturation do the ratios of the two gases not match the inlet”. We strongly\nagree with this opinion and would like to provide a clearer explanation here.\nC /C represents the ratio of the real-time gas concentration to the equilibrium\nA 0\nconcentration at the outlet. In the breakthrough experiment with a C H /C H volume ratio\n2 6 2 4\nof 50/50, initially (t ≈ 0), both C H and C H were adsorbed on TYUT-18, resulting in zero\n2 4 2 6\noutlet gas concentration, hence C /C = 0 of C H and C H . As time progressed, due to\nA 0 2 4 2 6\nthe stronger affinity of the adsorbent for C H , the adsorption capacity of C H was weaker,\n2 6 2 4\nthe C H molecules are the first to exit the adsorption column, causing the C /C of C H\n2 4 A 0 2 4\nto gradually increase. Moreover, since C H exhibits stronger adsorption interactions with\n2 6\nTYUT-18 than C H , competitive displacement occurred between the two gases, C H\n2 4 2 6\ncontinuously replaces the adsorbed C H in the column, resulting in a large amount of C H\n2 4 2 4\nbeing released and enriched at the outlet, where C /C exceeded 1 (up to approximately\nA 0\n2). Subsequently, as C H broke through, the C /C of C H gradually decreased, while the\n2 6 A 0 2 4\nC /C of C H slowly increased, eventually converging to 1 at adsorption equilibrium, with\nA 0 2 6\nthe outlet gas composition being the same as the inlet.\nBased on the above analysis, we re-examined the experimental data and found that there\nwere mistakes in the previous data processing. Therefore, we reprocessed all the data of\nbreakthrough experiment and presented the complete original experimental data in the\n\"Source Data\" file for reviewers to verify.\nThe figures related to the breakthrough experiment have been replaced in the revised\nmanuscriptand SI.\nModification:\nManuscript: Page 13, Figure 6.\nFigure 6 | Breakthrough experiments and stability. a, b, Breakthrough curves obtained for TYUT-18 with\nC H /C H mixtures (v/v = 50/50 and 10/90) at 298 K. c, d, Five breakthrough cycle curves obtained for\n2 6 2 4\nC H /C H mixtures (v/v = 50/50 and 10/90) at 298 K. e, PXRD patterns obtained for TYUT-18 under the above\n2 6 2 4\nconditions. F, Photograph of TYUT-18 crystals obtained using microscopy under the above conditions.\nModification:\nSupporting Information: Page 18 and 19, Supplementary Figs. 25–27.\nSupplementary Figure 25. Breakthrough curves of TYUT-18 for C H /C H mixtures (v/v\n2 6 2 4\n= 50/50 and 10/90) at 313 K.\nSupplementary Figure 26. Five breakthrough cycle curves for C H /C H mixtures (v/v =\n2 6 2 4\n50/50) at 313 K.\nSupplementary Figure 27. Five breakthrough cycle curves for C H /C H mixtures (v/v =\n2 6 2 4\n10/90) at 313 K.\n(5) In representative streams of ethane and ethylene, the ethane concentration is\nappreciably lower than 10%. Breakthrough measurements should be performed at 95:5\nand 99:1 ethylene: ethane.\nResponse: We greatly appreciate the comments of reviewers.\nWe fully agree that the concentration of C H in representative gas streams are typically\n2 6\nbelow 10%, therefore breakthrough experiments should be conducted under conditions\ncloser to real-world operating conditions (C H /C H , v/v = 5/95 or 1/99).\n2 6 2 4\nBased on the reviewers' comments, we supplemented the breakthrough experiment of\nmixed gas with C H /C H volume ratios of 5:95 and 1:99. The results show that the TYUT-\n2 6 2 4\n18 maintains excellent C H selectivity and separation performance under both ratios.\n2 6\nThe relevant experimental results and data have been added to the revised manuscript\nand SI.\nModification:\nManuscript: Page 11, Add corresponding descriptions.\n“To verify the separation capability of TYUT-18 for low-concentration C H impurities, we\n2 6\nconducted separation experiments using C H /C H mixtures with volume ratios of 5/95\n2 6 2 4\nand 1/99 (Supplementary Figs. 28 and 29). The experimental results confirm that TYUT-\n18 can effectively remove extremely low concentration C H impurities, demonstrating\n2 6\nexcellent separation performance.”\nModification:\nSupporting Information: Page 19 and 20, Supplementary Figs. 28 and 29.\nSupplementary Figure 28. Breakthrough curves of TYUT-18 for C H /C H mixtures (v/v\n2 6 2 4\n= 5/95) at 298 K and 313 K.\nSupplementary Figure 29. Breakthrough curves of TYUT-18 for C H /C H mixtures (v/v\n2 6 2 4\n= 1/99) at 298 K and 313 K.\n(6) Fast kinetics are repeatedly invoked in the manuscript, however the data in the SI show\nthat adsorption and desorption take about 10 minutes. Why would this be considered fast?\nResponse: We thank the reviewers for their valuable comments.\nRegarding the description of “rapid kinetics”, we would like to further clarify.\nFirst, under our experimental conditions, the gas pressurization rate was 100 mbar min-1,\nand it took approximately 10 minutes to go from the initial pressure to 1000 mbar. During\nthis process, the TYUT-18 reached adsorption equilibrium within 10 minutes for both C H\n2 6\nand C H simultaneously with the pressurization to the target pressure, indicating that its\n2 4\nadsorption rate was comparable to the pressurization rate, and no significant delay in mass\ntransfer or diffusion was observed. Therefore, within this experimental framework, we\nconsider the adsorption kinetics of the TYUT-18 was well.\nFurthermore, to further verify this, we conducted supplementary tests at a higher\npressurization rate (500 mbar min-1). The results showed that TYUT-18 rapidly reached\nequilibrium within 4 minutes (see Supplementary Fig. 15), indicating that this material has\nrelatively fast adsorption kinetics.\nWe have provided more detailed experimental descriptions in the revised SI.\nModification:\nSupporting Information: Page 12, Supplementary Fig. 15.\nSupplementary Figure 15. Kinetics of adsorption and desorption behaviors for (a) C H\n2 4\nand (b) C H on TYUT-18 at 298 K (C H or C H was introduced into the test chamber at\n2 6 2 6 2 4\na rate of 500 mbar·min-1).\n(7) There does not appear to be any information provided on how the kinetics of adsorption\nand desorption were determined for the data provided in figures S Fig 12 and 13.\nResponse: Thank you for your suggestion. We added relevant test conditions and\nperformance descriptions of kinetics of adsorption to the revised manuscript, and\nsupplemented the calculation of the diffusion time constant (Supplementary Fig. 14).\nModification:\nManuscript: Page 7, Add corresponding descriptions.\n“At 298 K, with a pressurization rate of 100 mbar min-1, both C H and C H reached\n2 6 2 4\nadsorption equilibrium in TYUT-18 within approximately 10 minutes. This adsorption\nequilibrium time is shorter than that of Cu(Qc) (13 minutes), MAF-7 (15 minutes), TYUT-\n2\n12 (18 minutes) and ZIF-7 (40 minutes) (Supplementary Figs. 16 and 17). And due to the\npreferential flexible response of TYUT-18 to C H , its diffusion time constant (1.77 × 10-2\n2 6\nmin-1) is greater than that of C H (1.27 × 10-2 min-1). Desorption experiments further\n2 4\nshowed that both C H and C H could be completely desorbed from TYUT-18 within 10\n2 6 2 4\nminutes.”\nModification:\nSupporting Information: Page 4 and 11-13, Supplementary Figs. 13-17.\n“Kinetic adsorption measurement\nThe kinetic adsorption isotherms of the sample were measured using an Intelligent\nGravimetric Analyzer (IGA 001, Hiden). This instrument employs a gravimetric method to\nprecisely quantify gas adsorption capacity on materials under various operating conditions.\nIn the adsorption experiment, approximately 100 mg of TYUT-18 was loaded into the\nsample cell and activated at 423 K under high vacuum until no further weight loss was\nobserved. Subsequently, after cooling the sample to 298 K or 313 K, C H or C H was\n2 6 2 4\nintroduced into the test chamber at a rate of 100 or 500 mbar·min-1. The software\nautomatically recorded the change in weight of the sample after gas adsorption.\nKinetic calculation\nDiffusion time constants (D’, D/r2) are calculated from a short-time solution of the diffusion\nequation assuming a step change in the gas-phase concentration, a clean bed initially, and\nmicroporous diffusion control:\n𝑞𝑡 6 𝐷\n= √ 2𝑡\nwhere q\nt\nrepresents the gas uptake at𝑞 t∞ime\n√\nt, 𝜋q\n∞\n𝑟represents the gas uptake at equilibrium,\nD represents the diffusivity, and r represents the radius of the equivalent spherical particle.\nThe slopes of q/q versus are obtained by fitting the plots in the low gas uptake range.”\nt ∞\n√𝑡\nSupplementary Figure 14. Diffusional time constant calculation details of C H and C H\n2 4 2 6\non TYUT-18 at 298 K.\n(8) Overall, there is an overselling of the “engineering” of the pores structure. The authors\nwould be better off reported what was observed rather than trying to sell a concept.\nResponse: We are very grateful to the reviewers for their review and constructive\nsuggestions.\nWe agree with them that academic papers should be better off reported what was observed\nrather than trying to sell a concept. In this study, we proposed the sequential adsorption\nbehavior of C H in TYUT-18 with the binary porous system. This conclusion was verified\n2 6\nby both single-crystal X-ray diffraction (SCXRD) and density functional theory (DFT)\ncalculations, clearly revealing the sequential filling mechanism of different pores during\nadsorption.\nAt the same time, we have adjusted and shortened the relevant descriptions in the revised\nmanuscript, weakening the promotional expression of the “engineering” concept and\nfocusing more on the experimentally observed structural features and adsorption behavior\nitself, so as to make the discussion more objective and rigorous.\n(9) To determine the heats of adsorption, there must be a least three temperatures, so that\nerror bars can be determined. This is standard in the field and must be done.\nResponse: Thank you for your valuable suggestion. Based on your suggestion, we\nrecalculated the isosteric heat of adsorption. The specific calculation steps are as follows:\nThe isosteric heat of adsorption for C H and C H were calculated by using the gas\n2 6 2 4\nadsorption data collected at 273, 298 and 313 K. The adsorption curves were first fitted\nwith the viral equation:\n𝑚 𝑛\n1 𝑖 𝑖\nln𝑃 =ln𝑞+ ∑𝑎𝑖𝑞 +∑𝑏𝑖𝑞\nWhere q is the amount of gas adsorbed a𝑇t t𝑖h=e0 pressu𝑖r=e0 P, a and b are Virial coefficients,\nm and n are the number of coefficients required to describe the isotherm adequately.\nTo calculate the Q values, the fitting parameters obtained from the equation were then\nst\nplugged into the following equation:\n𝑚\n𝑖\n𝑄𝑠𝑡 =−𝑅∑𝑎𝑖𝑞\nModification: 𝑖=0\nSupporting Information: Pages 9 and 10, Supplementary Figs. 10 and 11.\nSupplementary Figure 10. Virial fitting (lines) of the (a) C H and (a) C H adsorption\n2 6 2 4\nisotherms (points) of TYUT-18.\nSupplementary Figure 11. The isosteric heat of adsorption of C H and C H on TYUT-\n2 6 2 4\n18.\n(10) The dual site Langmuir-Freundlich does not seem appropriate for fitting the adsorption\ndata given that this material exhibits flexibility that changes the initial adsorption site upon\nthe second adsorption event. That model is for rigid systems.\nResponse: We appreciate the reviewers' professional comments.\nWe fully understand the concerns regarding the applicability of the dual site Langmuir-\nFreundlich model. We have removed the fitting results and related discussion based on\nthe dual site Langmuir-Freundlich model from the revised manuscript to ensure the\nobjectivity and reasonableness of the results.\nReviewer #2:\nIn this manuscript, the authors report excellent C H /C H selectivity and achieve ultra-high\n2 6 2 4\nethylene purity (99.995%) with an impressive separation productivity of 15.7 L kg1. They\nalso systematically elucidate the dynamic filling behavior of ethane molecules w- ithin a\nflexible–robust framework system, using a comprehensive combination of single-crystal X-\nray diffraction (SCXRD) and density functional theory (DFT) calculations. Overall, the study\nis carefully conducted, and the material is thoroughly characterized both experimentally\nand theoretically. However, the novelty of this work appears somewhat limited, as the\nfindings do not provide fundamentally new insights or uncover any previously unknown\nmechanisms, and the separation performance does not represent a major breakthrough.\nFurthermore, the manuscript overlooks several benchmark C H -selective adsorbents, as\n2 6\nlisted below. In addition, I have identified several issues, which are outlined below.\n(1) Although the authors claim that “we clearly discovered the dynamic pore-filling behavior\nof C H molecules in a flexible–robust MOF by combining SCXRD and DFT calculations\n2 6\nfor the first time…”, this statement is not accurate. Such sequential guest-filling behavior\nin flexible MOFs are not new and have been widely known and summarized in several\nreview papers (for example, https://pubs.rsc.org/en/content/articlehtml/2021\n/fd/d1fd00037c). Moreover, the same filling mechanism for C2 gases in an isostructural\nmaterial has already been reported and thoroughly analyzed using both in situ SCXRD and\nDFT calculations two years ago, as cited in reference 38 of the manuscript.\nResponse: Thank you very much for your suggestions.\nFirst, our use of “for the first time” in the manuscript was indeed inappropriate. We have\nremoved “for the first time” from the revised manuscript and revised the relevant sentence\nto: “We clearly discovered the dynamic pore-filling behavior of C H molecules in a flexible–\n2 6\nrobust MOF by combining SCXRD and DFT calculations.”\nSecond, we strongly agree with the work published by Kitagawa et al. in 2023, which was\nmentioned by the reviewers. Their study represents a groundbreaking contribution to\nunderstanding the structural responses and guest diffusion mechanisms in flexible–robust\nMOFs. In particular, they systematically revealed the framework transformation and\nsequential filling mechanism induced by C2 gases in flexible-robust MOFs through in situ\ngas-loaded SCXRD and DFT calculations at different temperatures. This work has\nsignificantly advanced the understanding of adsorption behavior in flexible–robust MOFs.\nBuilding on this, our research continues and expands upon the findings of Kitagawa et al.\nWe focused on the influence of pressure variations on the adsorption behavior of guest\nmolecules and the deformation of the framework structure in the TYUT-18. By combining\nin situ gas-loaded SCXRD analysis with DFT calculations under different pressure\nconditions, we further revealed the dynamic pore-filling behavior of C H molecules in\n2 6\nflexible–robust MOFs and its corresponding structural response.\nIn the revised manuscript, we have provided a clearer description of the work by Kitagawa\net al. and have added related discussion in the relevant sections to fully reflect the\nsignificance of their study and the extension represented by our research.\nModification:\nManuscript: Page 3, Add corresponding descriptions.\n“Subsequently, through in situ gas-loading SCXRD analysis and DFT calculations at\ndifferent temperatures, Kitagawa et al. systematically elucidated the sequential filling\nmechanism of C2 gas in flexible–robust MOFs and its correlation with framework flexibility,\ngreatly advancing the understanding of the sequential adsorption behavior of guest\nmolecules in flexible-robust MOFs38. Based on this, we further expanded our research\nperspective to pressure-mediated effects to reveal the sequential adsorption behavior of\nC H molecules in flexible–robust MOFs under different pressures and their corresponding\n2 6\nstructural responses.”\n(2) In the crystallographic data tables (Supplementary Tables 2–4), important parameters\nsuch as R , R , wR and GOF should be included.\nint 1 2\nResponse: Thank you for your valuable suggestion. We have included the key\ncrystallographic refinement parameters (R , R , wR , and GoF) in the Supplementary\nint 1 2\nTables 2–4 of the revised Supporting Information. These parameters have been added to\nensure completeness and to provide a clearer overview of the data quality.\nModification:\nSupporting Information: Page 30–32, Table S2–4.\n(3) In Supplementary Figure 2, the pore size distribution is shown in the inset. The authors\nshould clarify which method was used to calculate it.\nResponse: Thank you for reviewing and making valuable comments.\nThe pore size distribution shown in the illustration of Supplementary Fig. 2 is based on the\nN adsorption isotherm measured at 77 K and calculated by DFT model.\nSupporting Information: Page 5, Supplementary Fig. 2.\n“(the pore size distribution was calculated by DFT model)”\n(4) More detailed information on the Rietveld refinement should be provided in the\nSupplementary Information. The authors should clearly indicate which software was used,\nhow the initial structural model was constructed, and describe the refinement procedure in\nsufficient detail.\nResponse: Thank you for your valuable comments.\nWe have added more detailed Rietveld refinement instructions of the revised manuscript,\nclarifying the software used, the initial structural model construction method, and the\nrefinement procedure. The supplementary content is as follows: The refined package is\nTOPAS V5.0, which describes the background using 24th-order Chebyshev polynomials\nand the peak shapes using pseudo-Voigt peak shapes. Preferred orientation is described\nusing the spherical cofunction of order 4. The refinement was performed sequentially on\nthe scale factor, atomic coordinates, isotropic displacement parameters, site occupancies,\nand preferred orientation. Guest molecules were introduced into the host framework model\nas rigid bodies, and their possible positions were determined through a simulated\nannealing algorithm.\nModification:\nManuscript: Page 14, the section of PXRD refinement.\n“The refined package is TOPAS V5.0, which describes the background using 24th-order\nChebyshev polynomials and the peak shapes using pseudo-Voigt peak shapes. Preferred\norientation is described using the spherical cofunction of order 4. The refinement was\nperformed sequentially on the scale factor, atomic coordinates, isotropic displacement\nparameters, site occupancies, and preferred orientation. Guest molecules were introduced\ninto the host framework model as rigid bodies, and their possible positions were\ndetermined through a simulated annealing algorithm.”\n(5) Additional details on the in situ SCXRD measurements are required. The authors should\nspecify the instrumentation used, sample activation conditions, gas-loading method, gas\npressure applied during measurements, and any other relevant experimental parameters.\nResponse: Thank you for your suggestion. We have added detailed information about in\nsitu SCXRD measurements to the revised manuscript.\nModification:\nManuscript: Page 14 and 15, the section of Single-crystal X-ray diffraction.\n“For in situ SCXRD measurements, the TYUT-18 sample was first purged with N at 423 K\n2\nfor 12 hours to completely remove solvent molecules from the pores. Then, the target feed\ngas was introduced to the set pressure and equilibrated for 6 h. The specific conditions are\nas follows: for TYUT-18(β)•0.25C H and TYUT-18(α)•3C H , the C H gas was\n2 6 2 6 2 6\npressurized to 0.13 bar and 1 bar respectively using the Micromeritics ASAP 2020 analyzer;\nfor TYUT-18(α)•1C H and TYUT-18(α)•0.25C H , the C H and C H gases were first\n2 6 2 4 2 6 2 4\npressurized to 1 bar, and then desorbed to 0.4 bar and 0.6 bar respectively. The SCXRD\ndata of TYUT-18(β)•0.25C H , TYUT-18(α)•1C H and TYUT-18(α)•0.25C H were\n2 6 2 6 2 4\ncollected on the Bruker D8 VENTURE TXS PHOTON II diffractometer. The SCXRD data\nof TYUT-18(α)•3C H was collected Single crystal X-ray diffraction data were collected at\n2 6\nthe Shanghai Synchrotron Light Source Line BL10U2 station and station equipped with a\nDectris Eiger 16M, S/N E-32-0111 surface detector respectively. The structure was solved\nby direct methods using the SHELXTL software package and further refined with different\nFourier syntheses. All non-hydrogen atoms on the framework were refined anisotropically;\nall hydrogen atoms were generated geometrically and refined in the riding mode. All the\nphenyl rings were treated with rigid constraints.”\n(6) Although the authors emphasize the industrial significance of C2 gas separation in the\nIntroduction, the breakthrough experiments were performed at very low flow rate (2\nmL/min), which does not reflect practical operating conditions. The authors must justify why\nsuch a small flow rate was chosen. Furthermore, the amount of adsorbent used in the\nbreakthrough experiments is not specified and should be clearly reported, as it is essential\nfor evaluating the reliability and relevance of the separation performance.\nResponse: Thank you very much for your suggestions.\nWe fully agree with your point. The differences between the breakthrough experiment flow\nrate and practical operating conditions, as well as the unclear adsorbent dosage you\npointed out, are essential for evaluating the reliability and relevance of the separation\nperformance. We have conducted in-depth explanations and supplementary experiments,\nand our specific response is as follows:\n(a) Reasons for choosing low flow rate (2 mL min-1).\nWe choose this flow rate mainly based on the following considerations:\nFirstly, numerous previously published articles have employed a gas flow rate of 2 mL min-\n1 in breakthrough experiments. Thus, we selected this flow rate to facilitate convenient and\ndirect comparisons with other materials (J. Am. Chem. Soc. 2018, 140, 12940–12946;\nAngew. Chem. Int. Ed.2023, 62, e202302564; Nat. Commun.2024, 15, 804; Angew. Chem.\nInt. Ed.2022, 61, e202208134).\nSecondly, during the breakthrough experiment, the activated TYUT-18 sample of about 0.6\ng was placed in a stainless-steel adsorption column with an inner diameter of 6 mm. The\ngas flow rate of 2 mL·min-1 ensures that TYUT-18 completes its structural transformation\nand reaches adsorption equilibrium within 60 minutes. These considerations led us to\nselect the gas flow rate of 2 mL min-1 for the breakthrough experiment.\nFinally, in this current stage of basic research, we chose a flow rate of 2 mL min-1 to\nprioritize obtaining reliable and accurate basic separation data under existing conditions\nand to verify the excellent separation performance of TYUT-18. For further industrial\napplications, we will focus our research on the scale-up preparation, molding process, and\nconstruction of related process equipment, which will be the main direction of our future\nwork.\n(b) Adsorbent Dosage and Supplementary Experiments.\nFirst, thank you very much for your reminder. In the breakthrough experiments (Figures 6\na-d) in the manuscript, the adsorbent loading was 0.6 g. We have added relevant\nexplanations to the experimental section of the revised manuscript.\nSecond, based on your suggestion, we investigated the separation potential of TYUT-18\nat higher flow rates. We synthesized additional material, increasing the adsorbent loading\nto 3.0 g, and conducted breakthrough experiments at a flow rate of 8 mL min-1. The results\nshowed that TYUT-18 still exhibited excellent separation performance at a relatively high\nflow rate of 8 mL min-1. Specifically, the breakthrough time for C H was 12 min g-1, and for\n2 4\nC H it was 16 min g-1, with a corresponding dynamic separation time of 4 min g-1. This\n2 6\nresult indicates that TYUT-18 possesses the potential for C H /C H separation under\n2 6 2 4\nhigher flow rate. The supplementary experiments and descriptions have been added to the\nrevised manuscript and SI.\nModification:\nSupporting Information: Page 20, Supplementary Fig. 30.\nSupplementary Figure 30. Breakthrough curves of TYUT-18 for C H /C H mixtures (v/v\n2 6 2 4\n= 50/50) at 298 K with the rate of 8 mL min-1.\n(7) The manuscript overlooks several benchmark C H -selective adsorbents that have\n2 6\nbeen reported, such as PCP-IPA [ref.1], TbMOF-76-NH [ref.2], TJT-100 [ref.3], ZnF-PCP\n2\n[ref.4], NKU-301 [ref.5], and FDMOF-2 [ref.6], etcs.\n[ref.1] P. Zhang, L. Yang, X. Liu, J. Wang, X. Suo, L. Chen, X. Cui, H. Xing, Nat. Commun.\n2022, 13, 4928\n[ref.2] G. D. Wang, R. Krishna, Y. Z. Li, W. J. Shi, L. Hou, Y. Y. Wang, Z. Zhu, Angew. Chem.\n2022, 134, e202213015\n[ref.3] H. G. Hao, Y. F. Zhao, D. M. Chen, J. M. Yu, K. Tan, S. Ma, Y. Chabal, Z. M. Zhang,\nJ. M. Dou, Z. H. Xiao, G. Day, H.-C. Zhou, T.-B. Lu, Angew. Chem. 2018, 130, 16299–\n16303.\n[ref. 4] F. Chen, N. Prasetyo, S. Sakaki, K. Otake, S. Kitagawa, Angew. Chem. Int. Ed.\n2025, 64, e202423371\n[ref.5] X. Lian, P. X. Liu, Y. C. Yuan, J. J. Pang, L. Li, S. S. Liu, B. Yue, Y. H. Zhang, L. Li,\nJ. Xu, X.-H. Bu, Adv. Funct. Mater. 2024, 34,2312150\n[ref.6] S. Jiang, J. Li, M. Feng, R. Chen, L. Guo, Q. Xu, L. Chen, F. Shen, Z. Zhang, Y.\nYang, Q. Ren, Z. Bao, J. Mater. Chem. A 2022, 10,24127–24136.\nResponse: Thank you for your suggestions.\nIn the manuscript, we compared the C H adsorption capacity and the C H /C H uptake\n2 6 2 6 2 4\nratio at 0.5 bar of flexible C H -selective MOFs. Since the comparison was limited to\n2 6\nflexible MOFs, this may have resulted in a lack of comprehensive understanding of the\noverall performance of C H -selective MOFs. To improve the representativeness and\n2 6\ncompleteness of the comparison, we further selected representative robust C H -selective\n2 6\nMOFs and compared their adsorption performance indicators with TYUT-18 in this work\nunder the same conditions. As shown in Supplementary Fig. 9, TYUT-18 exhibits a\nmoderately high C H adsorption capacity and C H /C H uptake ratio compared to most\n2 6 2 6 2 4\nreported robust C H -selective MOFs. Although its adsorption performance is not\n2 6\noutstanding, TYUT-18 still exhibits excellent separation performance, which may be closely\nrelated to its unique flexible mechanism. The relevant performance comparison picture and\ndescriptions have been added to the revised manuscript and SI.\nSupplementary Figure 9. (a) Comparison of C H uptake of TYUT-18 and robust C H -\n2 6 2 6\nselective MOFs at 298 K and 0.5 bar. (b) Comparison of the C H uptake and C H /C H\n2 6 2 6 2 4\nuptake ration of TYUT-18 and robust C H -selective MOFs at 298 K and 1bar.\n2 6\nModification:\nManuscript: Page 6, Add corresponding descriptions.\n“Furthermore, compared to most reported robust C H -selective MOFs, TYUT-18 exhibits\n2 6\na moderately high C H adsorption capacity (Supplementary Fig. 9).”\n2 6\n“When comparing with the robust C H -selective MOFs, although the uptake ratio of TYUT-\n2 6\n18 is not outstanding, TYUT-18 still exhibits excellent separation performance, which may\nbe closely related to its unique flexible mechanism (Supplementary Fig. 9).”\nSupporting Information: Page 9, Supplementary Fig. 9.\n(8) The authors claim that the reported material exhibits “fast adsorption kinetics.” However,\nthey should compare the kinetics with those of previously reported materials. Without such\na comparison, readers cannot be convinced that the adsorption is genuinely fast.\nResponse: We thank the reviewers for their valuable comments.\nRegarding the description of “rapid kinetics”, we would like to further clarify.\nFirst, under our experimental conditions, the gas pressurization rate was 100 mbar min-1,\nand it took approximately 10 minutes to go from the initial pressure to 1000 mbar. During\nthis process, the TYUT-18 reached adsorption equilibrium within 10 minutes for both C H\n2 6\nand C H simultaneously with the pressurization to the target pressure, indicating that its\n2 4\nadsorption rate was comparable to the pressurization rate, and no significant delay in mass\ntransfer or diffusion was observed. Therefore, within this experimental framework, we\nconsider the adsorption kinetics of the TYUT-18 is very well.\nSecondly, to further verify the excellent gas diffusion performance of TYUT-18, we\ncompared it with other with C H -selective materials. At 298 K, with a pressurization rate\n2 6\nof 100 mbar min-1, both C H and C H reached adsorption equilibrium in TYUT-18 within\n2 6 2 4\napproximately 10 minutes. This adsorption equilibrium time is significantly shorter than that\nof Cu(Qc) (13 minutes), MAF-7 (15 minutes), TYUT-12 (18 minutes) and ZIF-7 (40 minutes)\n2\n(Supplementary Figs. 16 and 17).\nFurthermore, to further verify this, we conducted supplementary tests at a higher\npressurization rate (500 mbar min-1). The results showed that TYUT-18 rapidly reached\nequilibrium within 5 minutes (see Supplementary Fig. 15), indicating that this material has\nrelatively fast adsorption kinetics.\nWe have provided more detailed experimental descriptions in the revised SI.\nModification:\nSupporting Information: Page 11-13, Supplementary Figs. 14-17.\nSupplementary Figure 14. Diffusional time constant calculation details of C H and C H\n2 4 2 6\non TYUT-18 at 298 K.\nSupplementary Figure 15. Kinetics of adsorption and desorption behaviors for (a) C H\n2 4\nand (b) C H on TYUT-18 at 298 K (C H or C H was introduced into the test chamber at\n2 6 2 6 2 4\na rate of 500 mbar·min-1).\nSupplementary Figure 16. As-synthesized and simulated PXRD patterns for TYUT-12,\nCu(Qc) , MAF-7 and ZIF-7.\n2 4\nC H on TYUT-18, TYUT-12, Cu(Qc) , MAF-7 and ZIF-7 at 298 K.\n2 6 2\nModification:\nManuscript: Page 7, Add corresponding descriptions.\n“At 298 K, with a pressurization rate of 100 mbar min-1, both C H and C H reached\n2 6 2 4\nadsorption equilibrium in TYUT-18 within approximately 10 minutes. This adsorption\nequilibrium time is significantly shorter than that of Cu(Qc) (13 minutes), MAF-7 (15\n2\nminutes), TYUT-12 (18 minutes) and ZIF-7 (40 minutes) (Supplementary Figs. 16 and 17).\nDue to the preferential flexible response of TYUT-18 to C H , its diffusion time constant\n2 6\n(1.77 × 10-2 min-1) is greater than that of C H (1.27 × 10-2 min-1). Desorption experiments\n2 4\nfurther showed that both C H and C H could be completely desorbed from TYUT-18\n2 6 2 4\nwithin 10 minutes.”"}]

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