Optical imaging of the intrinsic adsorption kinetics in single zeolite nanoparticles

Domain: biology
Published: 2026-03-11
Editorial outcome: major_revision

Abstract
The confinement effect is increasingly recognized as a critical factor influencing guest–framework interactions in molecular sieves, yet its impact on adsorption kinetics remains largely unexplored. Conventional ensemble measurements on milligram-scale particle assemblies yield apparent adsorption kinetics that conflate dynamic molecular interactions with macroscopic mass transport. Here, we present an optical imaging approach that quantitatively monitors interaction-dominated adsorption by reducing the sample size to the single-nanoparticle level (sub-picogram scale). The results enable the determination of intrinsic rate constants and activation energy barriers for elementary adsorption and desorption steps. A confinement-induced reversal of adsorption kinetics, relative to proton affinities, is observed among homologous light olefins on the same ZSM-5 nanoparticle. This finding reveals that confinement—rather than interaction strength—primarily governs adsorption kinetics at the single-nanoparticle level and provides a general platform for probing and rationally designing molecular sieves for diverse applications.

Introduction
Solid porous materials, such as zeolites and molecular sieves, have been widely used in industrial applications since the 1950s, particularly in gas separation and heterogeneous catalysis, due to their well-defined as well as tunable pore structures.1-3 Beyond simple consideration of size and shape selectivity, the confinement effect of nanopores—where molecules are trapped in a constrained environment—has been increasingly recognized as an essential factor influencing their performance, including reaction pathways and adsorption selectivity.4-6 To achieve a fundamental understanding of the confinement effect in solid porous materials and to further tailor their behavior in real applications, it is indispensable to characterize molecule-framework interactions experimentally.

Adsorption serves as a key process for studying the confinement effect in molecular sieves, as it represents the first step and a fundamental interaction between confined molecules and the framework.7-9 Spectroscopic techniques, such as vibrational and absorption spectroscopy, have been widely used to probe the electronic and structural states of target molecules before and after adsorption on nanoporous materials.10-13 Increased molecular orbital energies compared to their bulk counterparts are observed, providing experimental evidence that supports theoretical predictions, as a result of the restricted mobility and limited structural flexibility of molecules encapsulated in confined nanopores.14 More recently, state-of-the-art fluorescence microscopy and transmission electron microscopy enabled the direct visualization of single molecules within the framework, offering insights into their spatial distribution and coordination environment at the nanoscale.15-18 While these results have significantly enhanced our understanding of the confinement effect on adsorption within solid porous materials, they primarily represent static “end-point” characterizations, leaving the influence on the dynamic adsorption kinetics of guest molecules elusive.

More broadly, this knowledge gap stems from the inherent complexity of adsorption kinetics within molecular-scale nanoporous materials, where multiscale processes are commonly at play—including macroscopic transport limitations and site-specific adsorption at the nanoscale.5 This issue, coupled with the conventional dynamic adsorption characterizations typically conducted on bulk-phase samples at the milligram scale, such as adsorption-desorption breakthrough curve analysis, temperature-programmed desorption, and intelligent gravimetric analysis, leads to the intrinsic adsorption kinetics becoming more entangled with macroscale mass transfer in the observed apparent results.19-21 Fortunately, as suggested by diffusion theory and the zero-length column technique, reducing the sample size offers a promising strategy to minimize mass transfer contributions on experimentally obtained apparent adsorption kinetics.22,23 The diffusion kinetics of molecules within a single microcrystal have been achieved by Interference microscopy (IFM) and infrared microscopy (IRM), but IFM is limited to observe the nanoporous materials with well-defined morphologies and large crystal sizes (>20 μm),and synthesis of such large crystals is time-consuming and requires complex experimental conditions.22,24,25 To achieve an accurate characterization and quantitative determination of the intrinsic dynamic adsorption kinetics for studying the confinement effect in molecular sieves, it is therefore highly desirable—yet remains technically challenging and largely unexplored—to further reduce the sample size to a single nanoparticle level (at the picogram level), which represents the fundamental unit of solid porous materials in practical applications.

In the present work, we employed an atmosphere and temperature controllable dark-field microscopy (DFM) to optically image the dynamic adsorption process on single solid porous nanoparticles in situ and in real time, by tracking changes in their scattering intensity as a result of refractive index variations induced by mass density change. A reversible increase and decrease in the scattering intensity of individual Zeolite Socony Mobil-5 (ZSM-5) nanoparticles were clearly observed during the adsorption and desorption of olefins, respectively. Quantitative analysis first confirmed the negligible contribution of mass transfer to the observed adsorption dynamics and subsequently revealed a pseudo-first-order reversible adsorption mechanism. Built on these findings, the intrinsic rate constants for the elementary adsorption and desorption steps were extracted. In addition to providing kinetic insights, the determination of intrinsic rate constants also enabled the calculation of adsorption thermodynamics, with equilibrium constants derived from the ratio of rate constants. In contrast to the adsorption kinetics, the determined equilibrium constants showed good agreement with theoretically calculated protonation energies of the three olefins, validating the reliability of the developed methodology. A reversal trend, compared to their proton affinities, was uncovered in the adsorption rate of light olefins (C2H4, C3H6, n-C4H8) on the very same ZSM-5 nanoparticles. This was further supported by a corresponding reversal in their activation energy barrier heights and a systemical comparsion of adsorption kinetics on zeolites with different pore sizes. These findings provide comprehensive insights for understanding and optimizing their performance in catalytic and separation applications, and highlight the necessity of assessing the confinement effect on adsorption kinetics within solid porous materials.

Results
Optical imaging of the dynamic adsorption and desorption process of C3H6 on single ZSM-5 nanoparticles. ZSM-5 was selected as a model solid porous material due to its important role in various industrial catalytic reactions, such as fluidized catalytic cracking and methanol-to-olefins.26 Among these applications, C3H6 is one of the most common reactants or products and was thus chosen as the adsorbate in this study.27 Before the kinetic measurements, the ZSM-5 nanoparticles were comprehensively characterized in terms of their structural features and acidity (Supplementary Fig. 1). Transmission electron microscopy images and X-ray diffraction patterns confirmed that the ZSM-5 nanoparticles exhibited a typical coffin-like morphology with a well-defined MFI framework. The Si/Al ratio was determined to be 52.1 by an inductively coupled plasma optical emission spectrum (Supplementary Table 1). The surface area was determined to be 352 m2/g from the N2 adsorption isotherm using the Brunauer-Emmett-Teller equation. To evaluate the acidity of the used ZSM-5 nanoparticles, ammonia temperature-programmed desorption (NH3-TPD) analysis was performed, revealing two distinct desorption peaks at approximately 199 °C and 433 °C. These results are in good agreement with the literature,28,29 suggesting the structural integrity and good performance of the ZSM-5 nanoparticles.

To optically image the dynamic adsorption and desorption process of C3H6 molecules on a single ZSM-5 nanoparticle, the DFM was built by integrating a home-designed micro-gas-flow system and a micro-area-heating module into a commercial Ti-2E setup (Supplementary Fig.2), based on our recently developed technique for measuring the NH3-TPD spectra of single zeolite nanoparticles.30 Briefly, individual ZSM-5 nanoparticles were deposited on a home-fabricated substrate, which serves to both support the ZSM-5 nanoparticles for imaging and regulate their temperature via Joule heating. The substrate was then sealed by a micro-chamber, allowing for precise control of the gas atmosphere around ZSM-5 nanoparticles via a multi-channel valve to trigger the adsorption and desorption cycles. Miniaturizing the gas flow and temperature control modules helps to improve their compatibility with the microscope and to stabilize optical imaging performance against thermal and atmospheric fluctuations. During the in-and-out movement of C3H6 molecules from single ZSM-5 nanoparticles, the adsorption of C3H6 on a single ZSM-5 nanoparticle was monitored in real time and in situ by the refractive-index sensitive DFM, by taking advantage of the inherent refractive index change of the particle accompanied by the change in the amount of C3H6 molecules adsorbed on their surfaces. The dynamic process was recorded using a CCD camera. Representative DFM images of ZSM-5 nanoparticles are shown in Fig. 1a and Supplementary Fig. 3, where each bright dot represents an individual ZSM-5 nanoparticle with high contrast to the dark background.

In a typical measurement, the ZSM-5 nanoparticles were pre-heated at 400 °C for five minutes under a pure N2 flow to remove any potential pre-adsorbed species and to activate their surface for the following adsorption. The temperature was then lowered and kept at 105 °C throughout the measurement. At a certain moment (t = 0 s), C3H6 vapor was introduced into the chamber with a gas flow rate of 3 mL/min. This rate was chosen to balance the effects of gas flow on mass transfer, thermal equilibrium, and stability of the imaging system (Supplementary Fig. 4). During the entire experiment, the camera continuously recorded DFM images at a rate of 1 frame per second. A gradual increase in the optical intensity of the ZSM-5 nanoparticles was immediately observed after switching the gas from N2 to C3H6 vapor (Fig. 1b), indicating the successful uptake of C3H6 onto the particle, driven by the interaction between the electron-rich π-bonding orbital of C3H6 molecules and the vacant orbital of the proton in the ZSM-5 framework. Further in-situ spectroscopic measurements confirmed this interaction occurs on Brønsted acid sites (Supplementary Fig. 5). The increased optical intensity was resulted from the increased mass density and corresponding refractive index of the particle during adsorption, thus reflecting the amount of the adsorbed C3H6 molecules. This observation is consistent with earlier findings, where guest molecule adsorption induces changes in the refractive index of nanoporous materials, resulting in shifts in their optical interference fringes.22,25 This point was further supported by the results as follows. i) The optical intensity of ZSM-5 nanoparticles gradually decreased to the original value after switching the gas back to N2. Alternative mechanisms such as thermal decomposition, carbon/pollutant deposition, or surface contamination were excluded, as they would result in irreversible changes. ii) No change in optical intensity was observed in control experiments when acidic CO2 or neutral O2 was used to replace electron-rich C3H6 (Supplementary Fig. 6), or when non-acidic Si nanoparticles replaced the ZSM-5 nanoparticles (Supplementary Fig. 7). iii) Quantitatively, the observed ~4% change in optical intensity is in excellent agreement with the 1 mmol/g adsorption capacity commonly reported in the literature.31,32 Note that the change in optical intensity was normalized to the initial intensity of ZSM-5 nanoparticles (ΔI/I0), enabling a more effective comparison between measurements. Detailed data analysis was provided in the Supplementary Information (Supplementary Fig. 8).

Quantitative assessment of the intrinsic adsorption and desorption kinetics using the pseudo-first-order reversible chemical adsorption model. To further elucidate the adsorption kinetics at a single nanoparticle level, the adsorption-desorption cycles were performed at varying adsorbate concentrations. As shown in Fig. 2a, the amount of adsorbed C3H6 molecules on the same individual ZSM-5 particle increases with the partial pressure of C3H6. Further quantitative analysis suggested that the time course of the adsorbed C3H6 molecules followed single-exponential growth kinetics across all partial pressures (Fig. 2a and Supplementary Fig. 9). Plotting the growth rate constants (kobs,a) as a function of the partial pressure of C3H6 revealed a linear dependence (Fig. 2b), indicative of a pseudo-first-order adsorption mechanism herein.33 By contrast, no adsorbate concentration dependence was observed in the apparent desorption rate constant (kobs,d) (Fig. 2c), although it still followed exponential kinetics. This discrepancy was further confirmed by the statistical result of 79 particles (Supplementary Fig. 10), excluding diffusion as a primary contributor to the observed optical response, since the adsorbate concentration should similarly affect both adsorption and desorption under diffusion-limited conditions. We clarify that a continuous flow of N2 was pumped throughout the desorption process to ensure the effective removal of desorbed C3H6 from the atmosphere surrounding the ZSM-5 particle.

To further validate our hypothesis, we examined the dependence of adsorption rate constants on particle size, as distinct correlations would arise in diffusion-dominated and interaction-controlled kinetics. Taking advantage of the high throughput of the developed technique, the adsorption behaviors of tens of ZSM-5 particles with varying sizes were assessed in a single experiment. In line with the prediction, no significant size dependence was found in either kobs,a or kobs,d (Supplementary Fig. 10). Interestingly, under the very same measurement condition, a negative correlation gradually emerged when the acidity of particles was reduced by increasing the Si/Al ratio in their structure (maintaining the same MFI framework), particularly in non-Al silicalite-1 particles (Supplementary Fig. 11 and Supplementary Fig. 12). These findings suggest that the strong acidity of ZSM-5 nanoparticles leads to C3H6-acid site interactions that dominate the adsorption kinetics, thereby providing an effective model for studying intrinsic adsorption and desorption kinetics under confinement.

Given the adsorption process is reversible and essentially governed by the competition between elementary adsorption and desorption and adsorption steps, the obtained kobs,a was accordingly derived as the sum of rate constants for the two elementary steps: kobs,a = ka⨯PC3H6 + kd, where ka (kPa-1·s-1), kd (s-1) and P (kPa) represent the elementary adsorption rate constant, desorption rate constant and partial pressure of C3H6, respectively. More details about the derivation can be found in the supplementary information. The intrinsic ka and kd were quantitatively determined as 4.1⨯10-4 kPa-1·s-1 and 6.6⨯10-3 s-1, for the first time, from the transient kinetic measurements of adsorption processes at a single ZSM-5 nanoparticle level. Note also that the kd value deduced from the y-intercept (6.6⨯10-3 s-1, Fig. 2b) closely matches that obtained from direct measurements (kobs,d, 4.4⨯10-3 s-1, Fig. 2c). This consistency suggests the reliability of both the measurement and the analysis.

In addition to providing insights into the adsorption kinetics and mechanisms, the developed methodology also enables the assessment of adsorption thermodynamics. This is because the equilibrium association constant (KA), a key parameter proportional to adsorption affinity, could be calculated as the ratio of the elementary adsorption and desorption rate constants, i.e., KA = ka/kd.34,35 A consistent slope between ka and kd was observed across tens of particles exhibiting very different adsorption kinetics, following a Gaussian distribution with an average KA value of 2.38⨯10-2 kPa-1 and a standard deviation of 5.10⨯10-3 kPa-1 (Supplementary Fig. 13). It is worth noting that no equilibrium is required to determine adsorption thermodynamics from transient kinetics experiments, which represents a strength of this approach, particularly in cases where equilibrium cannot be reached or is difficult to achieve.

Exploration of the confinement effects on olefin adsorption kinetics via single particle intrinsic kinetic analysis. Based on the developed methodology, we further studied the confinement effect on the adsorption kinetics by comparing the adsorption behaviors of three homologous light olefins (C2H4, C3H6, n-C4H8) on the very same single ZSM-5 nanoparticle (Fig. 3a and Fig. 3b). One significant difference is that the change in optical intensity linearly increased with their molecular weights, and the ratio closely mirrored the relative molecular weights of the three molecules, suggesting that all three light olefin molecules can effectively access the active sites on the surface of ZSM-5 nanoparticles. This is sensible as their kinetic diameters are all smaller than the pore size of ZSM-5 nanoparticles.36,37 Secondly, the experimentally determined KA values of the three adsorbates (Fig. 3c)—obtained from the statistical linear dependence between their elementary adsorption and desorption rate constants across 103 ZSM-5 particles—exhibited a positive correlation with the theoretically calculated gas-phase protonation energies (Fig. 3d),38-41 further validating the reliability of the developed technique. It is noteworthy that no size dependence was observed in the adsorption rate constants of any of the three olefins, suggesting that the comparison herein is effectively based on intrinsic adsorption and desorption kinetics (Supplementary Fig. 14). Thirdly, a trend was observed when comparing the intrinsic adsorption kinetics of the three olefins with their equilibrium association constants: both the adsorption and desorption rate constants decrease as proton affinity increases (Fig. 3d and Supplementary Fig. 15). This behavior represented a reversal of the trend in the gas phase, where molecules with higher proton affinities tend to bind more rapidly to the same acid sites.42 These findings highlighted the confinement effect, rather than interaction strength, as the primary factor governing the adsorption kinetics of olefins in single zeolite nanoparticles.

The observation of confinement-induced reversal of the adsorption kinetics (CIRAK) was further validated from two complementary perspectives. First, the activation energy barriers for the elementary adsorption and desorption steps of these three olefins on ZSM-5 nanoparticles were estimated and compared, since these barriers serve as another key characteristic for understanding the adsorption kinetics under confinement. Fig. 4a demonstrates that both the adsorption and desorption rates of C3H6 increase with temperature, and a linear temperature dependence was further observed. The activation energy barriers for adsorption (Fig. 4b, Ea) and desorption (Fig. 4c, Ed) were subsequently determined from their slopes according to the Arrhenius equation. The results for C2H4 and n-C4H8 are shown in Supplementary Fig. 16 and Supplementary Fig. 17, respectively. Note that the nearly constant adsorption amounts observed at all temperatures are possibly due to the relatively narrow experimental temperature range (Supplementary Fig. 18). The reproducibility of the extracted kinetic parameters was also confirmed by the identical results obtained from repeatable measurements (Supplementary Fig. 19).

By counting the Ea and Ed values for tens of particles in the field of view, the statistical results clearly demonstrate that both barrier heights for elementary adsorption (Fig. 4d) and desorption (Fig. 4e) of light olefins increased with the proton affinity of the adsorbates. The activation energy distributions reflects the inter-particle heterogeneity within the same batch of ZSM-5 particles. Specifically, n-C4H8, which has the highest affinity with acid sites, also has the highest barrier height to overcome for adsorption, thus with the slowest adsorption rates as shown in Fig. 3. Accordingly, we speculate that the observed reversal in adsorption kinetics induced by the confinement effect originates from the spatial constraints within the zeolite framework, which limit the structural flexibility of olefin molecules. As a result, the adsorption process requires passing through a transition state with a higher activation energy compared to that in free space. This effect is more pronounced for larger molecules, leading to the inverse trend in adsorption kinetics relative to their proton affinities.

On the other hand, we systematically investigated the adsorption behaviors of the three olefin molecules on zeolites with a range of pore sizes, including those both smaller and larger than that of ZSM-5 (Supplementary Table 2). The results indicated that the reversal between adsorption kinetics (ka) and thermodynamics (KA) became progressively weaker with increasing pore size, directly evidencing the critical role of pore size in the observed CIRAK. Specifically, identical measurements were performed on SSZ-13—a representative small-pore CHA-type zeolite with a three-dimensional pore system featuring 8-membered-ring (8MR) windows, whose pore size is smaller than that of 10MR windows in ZSM-5 (Supplementary Fig. 20 and Supplementary Table 2). Single nanoparticle kinetic measurements showed that ka maintained a negative correlation with the proton affinity of the three olefins in SSZ-13 (Fig. 5a). In contrast, CIRAK was absent for HY zeolite, which possesses a 12MR pore system with a larger aperture. In this case, both ka and Ka exhibited positive correlations with proton affinity (Fig. 5b). Moreover, analogous CIRAK behavior was observed in the adsorption of light alcohols on ZSM-5 (Supplementary Fig. 21). These results not only validate our hypothesis but also highlight the broad applicability of CIRAK in the adsorption of diverse adsorbates on zeolites with distinct framework structures.

Methods
Materials. The ZSM-5 (Si/Al= 50 and 400), silicalite-1, SSZ-13 (Si/Al = 40) and HY (Si/Al = 50) zeolite particles used in this work were purchased from the Catalyst Plant of Nankai University (Tianjin, China). All gases used in this work, including N2, C2H4, C3H6 and n-C4H8, have a purity of above 99.99% and were purchased from Nanjing Tianze Gas Co., Ltd. The Si nanoparticles were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

Materials characterization. The crystallographic structure of the used ZSM-5 powder was characterized by X-ray diffraction (Shimadzu XRD-600) with monochromatic Cu Kα1 radiation. The morphology of the ZSM-5 catalysts was investigated via a field-emission scanning electron microscope (SEM, Phenon) with a secondary electron detector and a transmission electron microscope (TEM, JEOL-F200) with accelerating voltages of 200 kV. The temperature-programmed desorption spectrum was characterized on a multipurpose dynamic adsorption instrument with a thermal conductivity detector (TP-5076, Tianjin Xianquan Industry and Trade Development Co., Ltd), where the sample mass was 50 mg and NH3 was used as the probe molecule. The samples were pretreated at 600 °C in a helium gas for 1h, then 20vol% NH3 in helium was introduced at 100 °C for 30min. After adsorption, the samples were purged with helium to remove the physically adsorbed ammonia. The desorption of NH3 was conducted from 100 °C to 600 °C in the helium flow at a heating rate of 10 °C/min. The Brunauer-Emmett-Teller surface area was measured by N2 adsorption-desorption methods with a Micromeritics gas adsorption analyzer (ASAP 2460). The bulk Si/Al ratios were determined using an inductively coupled plasma-optical emission spectrometer (ICP-OES, Agilent 720ES). The in situ infrared spectrum was recorded by an infrared fourier transform spectroscopy (Bruker, INVENIO S).

Sample preparation. 50 mg ZSM-5 powder was dispersed into 5 mL deionized water (18.2 MΩ·cm, Thermo Fisher) and sonicated for 5 minutes to prevent nanoparticle aggregation. A 20 μL suspension was then dropped onto a coverslip, where ZSM-5 nanoparticles adhered to the substrate via electrostatic interaction. The solution was removed after the substrate achieved a suitable surface coverage (~100 particles/100 ⨯ 100 μm2). The sample was dried in a vacuum oven for 12 hours to remove the water adsorbed on the surface of ZSM-5 particles. Before the optical measurement, the sample was sealed with a coverslip using a 1.5 mm-thick polytetrafluoroethylene spacer to form a microchamber, which was compatible with the working distance of the dark-field condenser. Also, pre-fabricated channels on both sides of the spacer enabled connection to a gas switching system for controlling the microchamber atmosph

Detailed experimental set-up of optical measurements. The experimental set-up consists of three main components.

Gas switching system: This module was used to control the atmosphere of the micro-chamber surrounding the ZSM-5 nanoparticles. A syringe pump (LongerPump, LSP02-1B) was used to control the gas flow rate, and a six-port valve (Cheminert, C25Z-3186D) was introduced to switch different gases smoothly.

Optical imaging system: This module was used to monitor the change of the optical refractive index (mass) of single ZSM-5 nanoparticles during adsorption and desorption processes. The DFM was built on an inverted commercial optical microscopy (Ti-2E, Nikon) with a dark-field condenser (N.A. = 0.80 - 0.95) and a 20X objective (N.A. = 0.45). A white LED was used as the illumination source, and a CCD camera (Pike F-032B, Allied Vi-sion Technologies) was used to record the optical images during the entire process with a frame per second of 1.

Temperature control system: This system was designed to control the temperature of the ZSM-5 nanoparticles. A substrate covered with a 50 nm-thicked gold layer served as a resistor to heat the particles sitting on its surface via Joule heating effect. The pattern of the gold film was designed to limit the effective heating area to 500 ⨯ 500 μm2 to reduce the influence of heating on the stability of the optical imaging system. The voltage applied on the resistor was diiven by a voltage source (CS120, Corrtest) .

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The manuscript reports a label-free study using dark-field microscopy (DFM) single-particle imaging to quantify the intrinsic adsorption and desorption rate constants, as well as activation energies, of light olefins on ZSM-5, a type of molecular sieve. The integration of DFM under controlled atmosphere/temperature with microfluidic delivery enables in situ and real-time monitoring of single-particle adsorption–desorption events. Based on the observed unusual results, the authors introduce the concept of confinement-induced reversal of adsorption kinetics (CIRAK). The study is innovative, the experimental design is carefully thought out, and the data support the conclusion. Overall, the work makes a valuable contribution to the mechanistic understanding of adsorption in zeolites and could be broadly applied to other types of molecular sieve materials. The following specific questions/suggestions may further improve the manuscript’s quality.\n\nThe authors report that for three different olefins probed on the same particle, both ka and kd decrease with increasing molecular size, while the equilibrium constant KA continues to increase. This is the most interesting result of this study, and the hypothesis that pore confinement dominates the effective rates is reasonable, but without direct experimental data to support it. To prove the hypothesis that the observed reversal in adsorption kinetics is induced by the confinement effect originating from the spatial constraints within the zeolite framework, is it possible to perform the same experiment in a zeolite nanoparticle with a larger pore size? A less reversal effect should be expected in this case.\n\nSome aspects of the Arrhenius analysis are not entirely clear. The authors point out that with increasing affinity, both Ea and Ed increase. Under fixed partial pressure, exothermic adsorption should normally lead to lower equilibrium coverage at higher temperatures, so the plateau signal would be expected to vary with T.\n\nIn Figures 4a, S15a, and S16a, the maximum responses (Rmax) at different temperatures were pretty close. Is this because of the normalization or because the reaction equilibrium is not temperature-dependent (entropy-driven reaction)?\n\nWere the temperature series collected in a single continuous run or in multiple independent experiments? This information is important because, for C₂ olefins, high temperatures could lead to mild polymerization/coking or gradual site deactivation. Such effects may cause slow drifts in ka and kd, which would influence both the slopes (Ea, Ed) and intercepts (A) of the Arrhenius plots. A discussion of how such potential artifacts were controlled or excluded would strengthen the conclusions.", "reviewer_2": "The manuscript entitled “Optical imaging of the intrinsic adsorption kinetics in single zeolite nanoparticles” reports a novel dark-field microscopy–based approach that enables quantitative measurement of intrinsic adsorption kinetics at the level of single ZSM-5 nanoparticles. The authors extracted adsorption/desorption rate constants and activation barriers, and further revealed a confinement-induced reversal of adsorption kinetics. This work presents a highly innovative methodology with important implications for adsorption studies in porous materials. However, the mechanistic interpretation and supporting evidence require significant strengthening. I therefore recommend major revision, with additional validation and a more rigorous discussion, before the manuscript can be considered for publication in Nature Communications.\n\n1. The change in scattering intensity is fully attributed to refractive index variation upon adsorption. Additional validation (e.g., in situ IR/Raman spectroscopy or mass spectrometry) would help exclude contributions from surface contamination, thermal effects, or other artifacts.\n\n2. The pseudo-first-order reversible model may oversimplify the adsorption process. The possibility of multi-site adsorption, diffusion–reaction coupling, or site heterogeneity should be more thoroughly discussed, along with the limitations of the adopted model.\n\n3. The claim that confinement effects dominate adsorption kinetics is mainly supported by activation energy statistics and qualitative reasoning. The authors should consider providing additional support, such as molecular simulations (MD/DFT) or complementary spectroscopic evidence. Alternative explanations, such as acid site distribution or channel heterogeneity, should also be discussed.\n\n4. About the generality of the conclusions: The study is limited to ZSM-5 and three light olefins. The applicability of the findings to other adsorbates or zeolite frameworks remains unclear. The authors should either provide broader data or explicitly delimit the scope of their conclusions.", "reviewer_3": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts.", "reviewer_4": "The confinement effect has been well accepted in zeolite chemistry, as it can significantly influence the adsorption of adsorbates and overall catalytic performance in catalysis. In this work, Yi et al. correlate adsorption kinetics with the confinement effect in zeolites by employing optical imaging techniques to observe single ZSM-5 nanoparticles. By monitoring optical intensity changes, they assess the intrinsic adsorption and desorption kinetics. Overall, this is an interesting study; however, several major concerns should be addressed as follows:\n\n1. There is a critical lack of clarity and completeness regarding the characterization of the zeolite used in this work. The author states that three distinct materials were employed: ZSM-5 (with Si/Al ratios of 50 and 400) and silicalite-1. However, the authors state that only \"the ZSM-5 nanoparticles\" were characterized (Fig. S1), without specifying which Si/Al ratio this refers to. Besides, the acidity of those three samples should be evaluated, for example, the Bronsted acid site and Lewis acid site. Probably, the solid-sate NMR measurements can be conducted to provide more detailed information.\n\n2. The authors state that the NH3-TPD spectrum shows peaks \"at around 200°C and 400°C\". However, upon inspection of Fig. S1c, the second desorption peak appears to be located at a significantly different temperature (approximately 430°C). The text should be revised to accurately reflect the data presented in the figure. Besides, how much acid site in this zeolite? Is there any quantitative relationship between the acid site and the adsorbates adsorption?\n\n3. A significant discrepancy exists between Figure 1b and Supplementary Figure S5, which purportedly show the same phenomenon of the adsorption and desorption of C₃H₆ on ZSM-5. The magnitude of the optical intensity change (the y-axis value) is markedly different between the two figures. In Fig. 1b, the signal change appears to be approximately 0.05, while in Fig. S5 (yellow curve), it appears to be around 0.035.\n\n4. A critical clarification is required regarding the fundamental process under investigation. The manuscript consistently describes the interaction of C₃H₆ with Brønsted acid sites as a \"reaction\" (e.g., in the context of Fig. 1b). However, the experimental data presented (the reversible optical intensity change in Fig. 1b and the subsequent desorption in TPD profiles) unequivocally characterize a physical/chemical adsorption event, not a chemical reaction. Besides, what’s the effect of the Lewis acid site and the defect sites(in both the outside and inner surface) effect on the adsorption effect?\n\n5. The data in Supplementary Figure S11d appears to directly contradict the interpretation provided for the ZSM-5 system and instead points towards a diffusion-controlled process for silicalite-1. The authors show a clear negative correlation between the adsorption rate constant of C₃H₆ and the particle size in silicalite-1. This is a classic signature of a diffusion-limited process: in larger particles, molecules have to travel a longer average path to access the internal pore network, leading to a slower observed adsorption rate.\n\n6. L242-245: The claim that the increase in optical intensity with molecular weight suggests \"effective access\" to active sites is not logically sound. The optical signal is primarily a function of the adsorbed mass. A heavier molecule will naturally produce a larger signal per molecule, regardless of diffusion or accessibility limitations. The authors should either provide additional data to support the accessibility claim (e.g., adsorption capacities) or rephrase the conclusion to state that the data confirms adsorption occurs, with the signal intensity being mass-dependent.\n\n7. Regarding the analysis in Fig. 3c, the manuscript states that the equilibrium constants (KA) were determined from the \"statistical linear dependence\" between elementary adsorption and desorption rate constants. However, the actual KA values and the crucial statistical parameter (e.g., the coefficient of determination, R²) for this linear fit are not provided either in the figure, the caption, or the main text.\n\n8. In this work, the authors claim that it is the confinement effect but the interaction strength works as the main factor to control the adsorption kinetics of adsorbates. Personally, I don’t agree this statement, Confinement is not a standalone steric effect but a holistic one that includes how acid strength manifests in tight spaces. In other words, confinement effect is an overall effect, which contains the contribution of acid strength for adsorbates adsorption. Besides, only one type zeolite was adopted in this work, the different topology zeolite with different channel size should be involved for a systemic comparison.\n\nMinor error:\n1. In Supplementary Figure S4, the unit for milliliter is written as \"ml\". The correct SI symbol should be \"mL\"."}, "author_response": "***Responses to Reviewers’ Comments***\nReviewer #1 (Remarks to the Author):\nComments:\nThe manuscript reports a label-free study using dark-field microscopy (DFM) single-particle\nimaging to quantify the intrinsic adsorption and desorption rate constants, as well as activation\nenergies, of light olefins on ZSM-5, a type of molecular sieve. The integration of DFM under\ncontrolled atmosphere/temperature with microfluidic delivery enables in situ and real-time\nmonitoring of single-particle adsorption–desorption events. Based on the observed unusual results,\nthe authors introduce the concept of confinement-induced reversal of adsorption kinetics (CIRAK).\nThe study is innovative, the experimental design is carefully thought out, and the data support the\nconclusion. Overall, the work makes a valuable contribution to the mechanistic understanding of\nadsorption in zeolites and could be broadly applied to other types of molecular sieve materials.\nThe following specific questions/suggestions may further improve the manuscript’s quality.\nResponse: We appreciate this reviewer for acknowledging the novelty of our work and\nfor the valuable comments that helped us to improve the quality of the manuscript. Detailed\npoint-by-point responses are listed as follows.\nThe authors report that for three different olefins probed on the same particle, both ka and\nkd decrease with increasing molecular size, while the equilibrium constant KA continues to increase.\nThis is the most interesting result of this study, and the hypothesis that pore confinement\ndominates the effective rates is reasonable, but without direct experimental data to support it. To\nprove the hypothesis that the observed reversal in adsorption kinetics is induced by the\nconfinement effect originating from the spatial constraints within the zeolite framework, is it\npossible to perform the same experiment in a zeolite nanoparticle with a larger pore size? A less\nreversal effect should be expected in this case.\nResponse: We appreciate this reviewer for the valuable suggestions. Accordingly, we have\nconducted new experiments to systematically examine the adsorption behaviors of ethene\n(C H ), propene (C H ), and n-butene (n-C H ) on zeolites with a range of pore sizes, including\n2 4 3 6 4 8\nthose both smaller and larger than the zeolite investigated in the original manuscript (Table\nR1). An overview of the results is presented in Figure R1, which shows good agreement with\nthis reviewer’s comments that the reversal between adsorption kinetics (kₐ) and\nthermodynamics (K ) becomes progressively weaker as the pore size increases. A detailed\nA\ndiscussion is provided below.\nTable R1. The structural information of the samples used in adsorption-desorption experiments.\nTable R1. The structural information of the samples used in adsorption-desorption experiments.\nFigure R1. Confinement effect on the adsorption kinetics and thermodynamics of light olefins within\nmaterials with different pore sizes. Top row: Schematic representation of the structures of the investigated\nmaterials—SSZ-13 (8MR), ZSM-5 (10MR), HY (12MR), and HPW (non-porous solid acid)—arranged in order\nof increasing pore size. Bottom row: Adsorption results for CH , CH , and n-CH on each material, showing\n2 4 3 6 4 8\nthe relationships between the adsorption rate constant (kₐ) and equilibrium constant (K ) with proton affinity.\nA\nIt is clear that as the pore size increases, the confinement-induced reversal between kₐ and K progressively\nA\ndiminishes and ultimately disappears.\nWe first conducted experiments on SSZ-13, a representative small-pore CHA-type zeolite\nfeaturing a three-dimensional pore system with 8-membered-ring windows (8MR, 0.38 nm,\nFigure R2a), which are smaller than those of ZSM-5 (10 MR, 0.51×0.55 and 0.53×0.56 nm).\nSingle-nanoparticle kinetic measurements revealed that kₐ maintains a negative correlation\nwith the proton affinity of the three olefins, whereas K shows a positive correlation with\nA\nproton affinity (Figure R2g). Notably, the adsorption kinetic of n-C H was markedly\n4 8\nsuppressed, despite its highest K among the three adsorbates. These results further support\nA\nour hypothesis that confinement within the zeolite framework is the dominant factor\ngoverning the adsorption kinetics of the olefins.\nFigure R2. (a) CHA topology of SSZ-13 zeolite. (b-d) The normalized optical intensity curves of the three\nolefin molecules on single SSZ-13 nanoparticles during an adsorption-desorption cycle. The gray line represents the\nresult obtained from each SSZ-13 nanoparticle. The color line represents the average signal of 37 SSZ-13\nnanoparticles in the field of view. (e-f) Statistical histograms of k and K values for three olefins measured\na A\non each SSZ-13 particle. (g) The experimentally determined k (left axis) and K values (right axis) of three\na A\nolefins from (e) as a function of their theoretically calculated protonation energies.\nWe then conducted experiments on HY nanoparticles, a representative FAU-type zeolite\ncontaining a three-dimensional pore structure of 12MR channels with a diameter of about\n0.74nm (Figure R3a), which are larger than those in ZSM-5. As expected, the results showed\nthat not only K but also kₐ increases with the proton affinity of the studied olefins, suggesting\nA\nthat the previously observed reversal in adsorption kinetics is significantly weakened in this\nlarger-pore environment (Figure R3g). This point is further confirmed by the result obtained\non phosphotungstic acid (HPW), a classic non-porous solid acid, where both k and K also\na A\nfollow a positive correlation with proton affinity—consistent with fundamental acid-base\ntheory that adsorption behavior is determined by intrinsic molecular interactions (Figure R4).\nFigure R3. (a) FAU topology of HY zeolite. (b-d) The normalized optical intensity curves of the three olefin\nmolecules on single HY nanoparticles during an adsorption-desorption cycle. The gray line represents the\nresult from a HY nanoparticle. The color line represents the average signal of 125 HY nanoparticles in the field\nof view. (e-f) Statistical histograms of k and K values of three olefins measured on each HY nanoparticle. (g)\na A\nThe experimentally determined k (left axis) and K values (right axis) of three olefins from (e) as a function\na A\nof their theoretically calculated protonation energies.\nFigure R4. (a) Chemical structure of HPW. (b-d) The normalized optical intensity curves of the three olefin\nmolecules on single HPW nanoparticles during an adsorption-desorption cycle. The gray line represents the\nresult from a HPW nanoparticle. The color line represents the average signal of 42 HPW nanoparticles. (e-f)\nStatistical histograms of k and K values of three olefins measured on each HPW nanoparticle. (g) The\na A\nexperimentally determined k (left axis) and K values (right axis) of three olefins from (e) as a function of\na A\ntheir theoretically calculated protonation energies.\nTaken together, the adsorption results from SSZ-13, ZSM-5, HY, and HPW establish a clear\nstructure–property relationship between pore confinement and adsorption kinetics. In the\nsmallest-pore SSZ-13 (8MR), kₐ shows a strong inverse correlation with proton affinity, whereas\nK increases with proton affinity, resulting in a pronounced reversal between adsorption\nA\nkinetics and thermodynamics driven by confinement. This reversal persists in ZSM-5 (10MR),\nconsistent with its moderately larger pores. In contrast, when moving to HY (12MR) or HPW (a\nnon-porous solid acid), both kₐ and K revert to being governed by intrinsic molecular\nA\ninteraction strength (proton affinity), and the reversal disappears. The systematic comparison\nnot only supports our hypothesis but also reveals the broad applicability of confinement-\ndependent adsorption behavior of olefins across diverse zeolite frameworks.\nRelevant results and discussion have been included in the revised manuscript (Page 10,\nFigure 5) and supplementary information (Table S2).\nSome aspects of the Arrhenius analysis are not entirely clear. The authors point out that with\nincreasing affinity, both Ea and Ed increase. Under fixed partial pressure, exothermic adsorption\nshould normally lead to lower equilibrium coverage at higher temperatures, so the plateau signal\nwould be expected to vary with T. In Figures 4a, S15a, and S16a, the maximum responses (Rmax)\nat different temperatures were pretty close. Is this because of the normalization or because the\nreaction equilibrium is not temperature-dependent (entropy-driven reaction)?\nResponse: We appreciate the reviewer’s insightful comment that helped us clarify the\ntemperature-dependent adsorption behavior of olefins on the same single zeolite\nnanoparticles and strengthen the rigor of our Arrhenius analysis. We agree that for an\nexothermic adsorption process, the equilibrium coverage generally decreases with increasing\ntemperature. The nearly constant adsorption amounts observed at different temperatures in\nFigures 4a, S15a, and S16a, however, are primarily due to the relatively narrow experimental\ntemperature range, in which the small changes in coverage are within the measurement error.\nTo verify this, we conducted additional C₂H₄ adsorption experiments on ZSM-5 over a\nbroader temperature range. These results clearly show that the equilibrium adsorption\namount decreased by approximately 25 % for a single nanoparticle when the temperature was\nincreased from 25 °C to 200 °C (Figures R5a and R5b), consistent with the statistical results\nfrom 156 particles (Figure R5c). In contrast, within the 25-105 °C range used in the original\nexperiments, the measured equilibrium adsorption amount remained nearly constant,\nindicating that the change in coverage is very small and below our measurement resolution.\nImportantly, although the equilibrium adsorption amount among measurements could\nnot be precisely resolved within this narrow temperature range, the measured kinetics remain\nrobust, as kₐ is determined from the temperature-dependent adsorption in each individual\nmeasurement. The temperatures selected (40 °C, 60 °C, 80 °C, 105 °C) were carefully chosen\nto optimize the accuracy of adsorption kinetic measurements. At high temperatures,\nadsorption proceeds too rapidly and can exceed the temporal resolution of our method.\nConversely, at low temperatures, adsorption becomes excessively slow, introducing\nmeasurement uncertainty. Moreover, as noted in the reviewer’s following comment, elevated\ntemperatures may also induce mild polymerization, coking, or gradual site deactivation,\npotentially affecting the reliability of the Arrhenius analysis. Therefore, the selected\ntemperature range provides sufficient variation to reliably extract Arrhenius parameters while\nminimizing artifacts in the kinetic measurements.\nRelevant results and discussion have been included in the revised manuscript (Page 9)\nand supplementary information (Page 19, Figure S18).\nFigure R5. (a) The normalized optical intensity curves of C H of single ZSM-5 nanoparticle from 25 °C to\n2 4\n200 °C during an adsorption-desorption cycle. (b) Plot of the equilibrium adsorption amount, extracted from\npanel (a), as a function of temperature. (c) The histograms of the equilibrium adsorption amount of 156 ZSM-\n5 particles under different temperatures.\nWere the temperature series collected in a single continuous run or in multiple independent\nexperiments? This information is important because, for C₂ olefins, high temperatures could lead\nto mild polymerization/coking or gradual site deactivation. Such effects may cause slow drifts in ka\nand kd, which would influence both the slopes (Ea, Ed) and intercepts (A) of the Arrhenius plots. A\ndiscussion of how such potential artifacts were controlled or excluded would strengthen the\nconclusions.\nResponse: We thank this reviewer for bringing this important point to our attention. In\nthis study, to minimize the influence of particle-to-particle variability and ensure that changes\nin k and k originate solely from temperature effects, the temperature-series measurements\na d\nwere carried out on the same ZSM-5 nanoparticles in a single experimental sequence. To\nfurther address potential concerns regarding mild polymerization, coking, or gradual site\ndeactivation at elevated temperatures, new experiments and complementary analyses were\ncarried out, as outlined below (Figure R6a). First, no appreciable changes were observed in the\nscattering intensity of the ZSM-5 nanoparticles before and after each measurement (Figure\nR6b), indicating that neither particle morphology nor optical properties were altered during\nthe temperature-series experiments.\nSecond, the adsorption behaviors of the three olefins at the highest temperatures used\nfor Arrhenius analysis were highly reproducible across repeated measurements. As shown in\nFigure R6f, both the extracted kinetic parameters and the equilibrium adsorption amounts\nwere nearly identical when the adsorption–desorption sequence was repeated on the same\nsingle ZSM-5 nanoparticle, suggesting that no measurable site deactivation or polymerization\noccurred during the temperature-series experiments. This is consistent with the fact that the\nmaximum temperature used for kinetic analysis (105 °C) is far below the temperatures\nreported in the literature (~250 °C), at which C₂ olefins begin to undergo significant coke\nformation on Brønsted acid sites.1-3\nFigure R6. (a) Experimental flowchart for adsorption measurements of three olefins. (b) The original optical\ncurves of a single ZSM-5 nanoparticle during the adsorption-desorption of three olefin molecules. (c-e)\nRepresentative single ZSM-5 particle adsorption-desorption kinetic curves for the cyclic adsorption process\nof three olefins. (f) The kinetic parameters extracted from (c-e). (g) The normalized optical intensity curves of\nthe three olefin molecules on single ZSM-5 nanoparticles during an adsorption-desorption cycle. The gray\nlines represent the result obtained from a ZSM-5 nanoparticle, and the color lines represent the average\nresponse of all ZSM-5 nanoparticles.\nThird, in situ IR spectroscopy on bulk ZSM-5 powder and confocal Raman measurements\non single ZSM-5 nanoparticles directly confirm olefin adsorption without additional vibrational\nfeatures associated with coking, or other side reactions. As shown in Figure R7, after 30 min\nof C H adsorption at 100 °C, the differential IR spectrum of bulk ZSM-5—obtained by\n3 6\nsubtracting the pre-adsorption spectrum from the post-adsorption spectrum—exhibits a\npronounced negative band at 3610 cm⁻¹, corresponding to the consumption of Brønsted acidic\nOH groups. Simultaneously, the occurrence of bands at 2955, 2930, and 2860 cm⁻¹\n(ν(CH₃)/ν(CH₂)) and 1470 cm⁻¹ (δ(CH)) indicates the formation of methyl/methylene species.4,5\nThese results demonstrate that C H interacts primarily with Brønsted acid sites, without\n3 6\nevidence of side reactions or contamination. Furthermore, we examined adsorption on a\nsingle ZSM-5 nanoparticle under identical conditions using confocal Raman microscopy. For\nthe particle shown in Figure R8a, two peaks at 1340 and 1590 cm⁻¹ emerge upon C H\n3 6\nadsorption, corresponding to C–O vibrational modes that confirm the formation of alkoxy-like\nspecies from chemisorption on Brønsted acid sites. This result further validates the adsorption\nprocess at the single-particle level. We note that the integrity and performance of the\nadsorption sites on ZSM-5 nanoparticles were also maintained through the experimental\ndesign. After each adsorption–desorption cycle, the sample was regenerated by heating to\n200 °C under a nitrogen atmosphere for 10 minutes, ensuring the complete removal of\nresidual adsorbates prior to the next measurement.\nFigure R7. (a-b)The original in-situ IR adsorbance spectra before and after adsorption of CH at 100 °C. (c-d)\n3 6\nThe differential IR spectrum of bulk ZSM-5—obtained by subtracting the pre-adsorption spectrum from the\npost-adsorption spectrum.\nFigure R8. (a) Bright field image of single ZSM-5 nanoparticle on the gold film. (b) Raman spectra of the gold\nfilm (background, black line), and the label ZSM-5 particle in (a) before adsorption of CH (blue line) as well\n3 6\nas after adsorption of CH (orange line).\n3 6\nOverall, these results confirm that the Arrhenius parameters obtained in this study are\nfree from artifacts arising from thermal degradation or site deactivation, supporting the\nreliability of our kinetic analysis.\nRelevant results and discussion have been included in the revised manuscript (Page 5 and\nPage 9) and supplementary information (Page 8 and Page 20, Figure S5 and S19) to strengthen\nthe conclusion.\n-------------------------------------------------\nReviewer #2 (Remarks to the Author):\nComments:\nThe manuscript entitled “Optical imaging of the intrinsic adsorption kinetics in single zeolite\nnanoparticles” reports a novel dark-field microscopy–based approach that enables quantitative\nmeasurement of intrinsic adsorption kinetics at the level of single ZSM-5 nanoparticles. The\nauthors extracted adsorption/desorption rate constants and activation barriers, and further\nrevealed a confinement-induced reversal of adsorption kinetics. This work presents a highly\ninnovative methodology with important implications for adsorption studies in porous materials.\nHowever, the mechanistic interpretation and supporting evidence require significant strengthening.\nI therefore recommend major revision, with additional validation and a more rigorous discussion,\nbefore the manuscript can be considered for publication in Nature Communications.\nResponse: We appreciate this reviewer’s recognition of the novelty and significance of\nour methodology. To address this reviewer’s concern, we have conducted additional\nexperiments and expanded our mechanistic discussion to provide stronger supporting\nevidence and clearer validation of our conclusions. Detailed point-by-point responses are\nprovided below.\n1. The change in scattering intensity is fully attributed to refractive index variation upon\nadsorption. Additional validation (e.g., in situ IR/Raman spectroscopy or mass spectrometry) would\nhelp exclude contributions from surface contamination, thermal effects, or other artifacts.\nResponse: We appreciate this reviewer for the insightful comment, which prompted us\nto systematically validate the origin of the scattering-intensity changes observed from ZSM-5\nnanoparticles during the adsorption-desorption cycles. To ensure that the optical response is\nsolely attributed to refractive-index variation induced by molecular adsorption, we have\nexpanded the discussion and conducted additional complementary spectroscopic\nexperiments. The supporting evidence is summarized below.\nFirst, in situ IR spectroscopy on bulk ZSM-5 powder and confocal Raman measurements\non single ZSM-5 nanoparticles both confirm olefin adsorption without additional vibrational\nfeatures associated with coking, or other side reactions. As shown in Figure R1, after 30 min\nof C H adsorption at 100 °C, the differential IR spectrum of bulk ZSM-5—obtained by\n3 6\nsubtracting the pre-adsorption spectrum from the post-adsorption spectrum—exhibits a\npronounced negative band at 3610 cm⁻¹, corresponding to the consumption of Brønsted acidic\nOH groups. Simultaneously, the occurrence of bands at 2955, 2930, and 2860 cm⁻¹\n(ν(CH₃)/ν(CH₂)) and 1470 cm⁻¹ (δ(CH)) indicates the formation of methyl/methylene species4,5.\nThese results demonstrate that C H interacts primarily with Brønsted acid sites, without\n3 6\nevidence of side reactions or contamination. We further examined adsorption on a single ZSM-\n5 nanoparticle under identical conditions using confocal Raman microscopy. For the particle\nshown in Figure R10a, two peaks at 1340 and 1590 cm⁻¹ emerge upon C H adsorption,\n3 6\ncorresponding to C–O vibrational modes that confirm the formation of alkoxy-like\nspecies from chemisorption on Brønsted acid sites. This result further validates the adsorption\nprocess at the single-particle level.\nFigure R9. (a-b)The original in-situ IR adsorbance spectra before and after adsorption of CH at 100 °C. (c-d)\n3 6\nThe differential IR spectrum of bulk ZSM-5—obtained by subtracting the pre-adsorption spectrum from the\npost-adsorption spectrum.\nFigure R10. (a) Bright field image of single ZSM-5 nanoparticle on the gold film. (b) Raman spectra of the gold\nfilm (background, black line), and the label ZSM-5 particle in (a) before adsorption of CH (blue line) as well\n3 6\nas after adsorption of CH (orange line).\n3 6\nSecond, the excellent recyclability of scattering intensity during repeated adsorption–\ndesorption cycles provides additional mechanistic support. The scattering intensity of single\nZSM-5 nanoparticles could be reversibly switched between two distinct values across\nexperiments (Figure R11). Alternative mechanisms such as thermal decomposition,\ncarbon/pollutant deposition, or surface contamination would result in irreversible changes,\ncontradicting the observed reversible behavior.\nFigure R11. (a)Experimental flowchart for adsorption measurements of three olefins. (b) The original optical\ncurves of a single ZSM-5 nanoparticle during the adsorption-desorption of three olefin molecules.\nThird, although the adsorption/desorption of olefins is accompanied by a reversible\nthermal effect, the temperature change should follow the trend of the adsorption/desorption\nrate. Taking the adsorption process as an example, the surface temperature is expected to rise\nas adsorption proceeds and then gradually return to its initial baseline once equilibrium is\nreached due to heat dissipation (Fig. R12a). This characteristic transient heating profile is\ninconsistent with the steady equilibrium signal observed in the optical curves (Fig. R12b).\nTherefore, thermal effects associated with adsorption heat cannot account for the observed\noptical response.\nFigure R12. (a)Schematic diagram of temperature changes during adsorption and desorption processes. (b)\nThe Normalized optical intensity curve of a single ZSM-5 nanoparticle during an adsorption-desorption cycle\nof C H.\n3 6\nCollectively, these complementary spectroscopic analyses, reversibility tests, and control\nexperiments provide comprehensive and conclusive evidence that the observed scattering-\nintensity change arises exclusively from refractive-index variation induced by molecular\nadsorption.\nRelevant results and discussion have been included in the revised manuscript (Page 5 and\nPage 9) and supplementary information (Page 8 and Page 20, Figure S5 and S19) to validate\nthe origin of the scattering-intensity changes observed from ZSM-5 nanoparticles during the\nadsorption–desorption cycles.\n2. The pseudo-first-order reversible model may oversimplify the adsorption process. The\npossibility of multi-site adsorption, diffusion–reaction coupling, or site heterogeneity should be\nmore thoroughly discussed, along with the limitations of the adopted model.\nResponse: We appreciate the reviewer’s concern regarding the simplicity of the pseudo-\nfirst-order reversible model in describing the real adsorption process. We agree that factors\nsuch as diffusion-reaction coupling, multi-site adsorption, and site heterogeneity may\ncontribute to the overall adsorption kinetics and therefore warrant careful consideration. In\nthis manuscript, we adopted the pseudo-first-order reversible model because it provides a\nphysically meaningful and mathematically tractable framework for interpreting the transient\nadsorption profiles under our experimental conditions.\nFirst, the interaction between the olefin molecules and the Brønsted acid sites in ZSM-5\nconstitutes the rate-determining step, while contributions from intracrystalline diffusion are\nnegligible. This conclusion is supported by the particle size-independent adsorption rate\nconstants (Figure S11), which rule out significant diffusion limitations.\nFigure R13. (a) Pseudo-first-order kinetic fitting for NH adsorption–desorption process. (b) Bi-exponential\n3\nkinetic fitting for NH adsorption–desorption process.\nBrønsted acid sites of the zeolite; as a result, a single dominant class of adsorption sites\ngoverns the observed kinetics. Under such conditions, a pseudo-first-order reversible model is\nboth appropriate and sufficient. We note that this situation differs for stronger bases such as\nNH₃, which can interact with both strong and weak acid sites. In those cases, a single first-\norder kinetic function would not adequately capture the system behavior, and a multi-site\nkinetic model—typically formulated as the sum of two first-order processes—would be\nrequired to describe the distinct adsorption pathways (Figure R13b).\nWe acknowledge that even within the category of “strong Brønsted acid sites”, subtle\nvariations in acid strength may exist, which could introduce minor broadening in the kinetic\nprofiles. However, such fine-scale heterogeneity cannot be resolved with the current temporal\nand spatial resolution of our single-particle measurement technique. Despite this limitation,\nthe pseudo-first-order reversible model successfully captures the dominant kinetic behavior\nand allows for reliable comparison of adsorption kinetics across different adsorbates and\nconfinement environments.\nIn the revised supplementary information, we have expanded the discussion to clarify\nboth the rationale for using this model and its inherent limitations (Page 12).\n3. The claim that confinement effects dominate adsorption kinetics is mainly supported by\nactivation energy statistics and qualitative reasoning. The authors should consider providing\nadditional support, such as molecular simulations (MD/DFT) or complementary spectroscopic\nevidence. Alternative explanations, such as acid site distribution or channel heterogeneity,\nshould also be discussed.\nResponse: We appreciate the reviewer’s valuable comments. We agree that molecular\nsimulations (MD/DFT) would provide complementary support for the mechanistic\ninterpretation; however, we do not have the capability to perform such simulations at this\nstage. Instead, we have accordingly carried out systematic adsorption experiments on zeolites\nwith different pore sizes and different acid site densities, and the result further supports our\nconclusion that confinement within the zeolite framework is the dominant factor governing\nthe reversal trend between adsorption kinetics and proton affinity of the olefins.\nOn the one hand, the observed reversal of adsorption kinetics is strongly dependent on\nthe pore size of zeolites, supporting the dominant role of confinement effects. We have\nconducted new experiments to systematically examine the adsorption behaviors of ethene\n(C₂H₄), propene (C₃H₆), and n-butene (n-C H ) on zeolites with a range of pore sizes, including\n4 8\nthose both smaller and larger than the zeolite investigated in the original manuscript (Table\nR2). An overview of the results is presented in Figure R14, where the reversal between\nadsorption kinetics (kₐ) and thermodynamics (K ) becomes progressively weaker as the pore\nA\nsize increases. A detailed discussion is provided below.\nTable R2. The structural information of samples used in adsorption-desorption experiments.\nFigure R14. Confinement effect on the adsorption kinetics and thermodynamics of light olefins within\nmaterials with different pore sizes. Top row: Schematic representations of the structures of the investigated\nmaterials—SSZ-13 (8MR), ZSM-5 (10MR), HY (12MR), and HPW (non-porous solid acid)—arranged in order\nof increasing pore size. Bottom row: Adsorption results for CH , CH , and n-CH on each material, showing\n2 4 3 6 4 8\nthe relationships between the adsorption rate constant (kₐ) and equilibrium constant (K ) with proton affinity.\nA\nIt is clear that as the pore size increases, the confinement-induced reversal between kₐ and K progressively\nA\ndiminishes and ultimately disappears.\nWe first conducted experiments on SSZ-13, a representative small-pore CHA-type zeolite\nfeaturing a three-dimensional pore system with 8-membered-ring windows (8MR, 0.38 nm,\nFigure R15a), which are smaller than those of ZSM-5 (10 MR, 0.51×0.55 and 0.53×0.56 nm).\nSingle-nanoparticle kinetic measurements revealed that k maintains a negative correlation\na\nwith the proton affinity of the three olefins, whereas K shows a positive correlation with\nA\nproton affinity (Figure R15g). Notably, the adsorption kinetic of n-C H was markedly\n4 8\nsuppressed, despite its highest K among the three adsorbates. These results support our\nA\nhypothesis that confinement within the zeolite framework is the dominant factor governing\nthe adsorption kinetics of the olefins.\nFigure R15. (a) CHA topology of SSZ-13 zeolite. (b-d) The normalized optical intensity curves of the three\nolefin molecules on single SSZ-13 nanoparticles during an adsorption-desorption cycle. The gray line\nrepresents the result on each SSZ-13 nanoparticle. The color line represents the average signal of 37 SSZ-13\nnanoparticles in the field of view. (e-f) Statistical histograms of k and K values of three olefins measured on\na A\neach SSZ-13 particle. (g) The experimentally determined k (left axis) and K values (right axis) of three olefins\na A\nfrom (e) as a function of their theoretically calculated protonation energies.\nWe then conducted experiments on HY nanoparticles, a representative FAU-type zeolite\ncontaining a three-dimensional pore structure of 12MR channels with a diameter of about\n0.74nm (Figure R16a), which are larger than those in ZSM-5. As expected, the results showed\nthat not only K but also kₐ increases with the proton affinity of the studied olefins, suggesting\nA\nthat the previously observed reversal in adsorption kinetics is significantly weakened in this\nlarger-pore environment (Figure R16g). This point is further confirmed by the result obtained\non phosphotungstic acid (HPW), a classic non-porous solid acid, where both ka and K also\nA\nfollow a positive correlation with proton affinity—consistent with fundamental acid-base\ntheory that adsorption behavior is governed by intrinsic molecular interactions (Figure R17).\nFigure R16. (a) FAU topology of HY zeolite. (b-d) The normalized optical intensity curves of the three olefin\nmolecules on single HY nanoparticles during an adsorption-desorption cycle. The gray line represents the\nresult from a HY nanoparticle. The color line represents the average signal of 125 HY nanoparticles in the field\nof view. (e-f) Statistical histograms of k and K values of three olefins measured on each HY nanoparticle. (g)\na A\nThe experimentally determined k (left axis) and K values (right axis) of three olefins from (e) as a function\na A\nof their theoretically calculated protonation energies.\nFigure R17. (a) Chemical structure of HPW. (b-d) The normalized optical intensity curves of the three olefin\nmolecules on single HPW nanoparticles during an adsorption-desorption cycle. The gray line represents the\nresult from a HPW nanoparticle. The color line represents the average signal of 42 HPW nanoparticles. (e-f)\nStatistical histograms of k and K values of three olefins measured on each HPW nanoparticle. (g) The\na A\nexperimentally determined k (left axis) and K values (right axis) of three olefins from (e) as a function of\na A\ntheir theoretically calculated protonation energies.\nOn the other hand, a consistent reversal dependence of adsorption kinetics on proton\naffinity was observed in zeolites with the same topological framework but different acid site\ndensities. To investigate the effect of acid site distribution on adsorption kinetics, we\nconducted experiments on ZSM-5 with varying Si/Al ratios (15, 100, and 400) to decouple the\neffects of pore confinement and acid site density. As shown in Figure R18, a larger K was\nA\nobserved for ZSM-5 with a lower Si/Al ratio, as a result of stronger interactions between C H\n3 6\nand the more abundant acid sites. Meanwhile, the negative correlation between k and proton\na\naffinity persisted across all Si/Al ratios, demonstrating that acid site density has a negligible\ninfluence on the observed reversal in adsorption kinetics.\nFigure R18. (a-c) The relationships between k and K with proton affinity for CH, CH andn-CH on ZSM-5\na A 2 4 3 6 4 8\nwith Si/Al ratios of 15, 100, and 400. (d-e) The summarized trends ofk andK as a function of the proton\na A\naffinity across varying Si/Al ratios.\nIn summary, our systematic experiments demonstrate that the observed reversal\nbetween adsorption kinetics and thermodynamics in zeolites is primarily governed by pore\nconfinement effects rather than variations in acid site density. This conclusion is supported by\nmeasurements across zeolites with different pore sizes (SSZ-13, ZSM-5, HY) and varying Si/Al\nratios. These findings confirm the robustness of our single-particle optical approach for\nprobing intrinsic adsorption kinetics and provide new mechanistic insights into the role of\nconfinement in zeolite catalysis.\nRelevant results and discussion have been included in the revised manuscript (Page 10,\nFigure 5) and supplementary information (Page 21 and Page 23, Figure S20 and Table S2) to\nvalidate the origin of the observed reversal between adsorption kinetics and thermodynamics\nin zeolites.\n4. About the generality of the conclusions: The study is limited to ZSM-5 and three light olefins.\nThe applicability of the findings to other adsorbates or zeolite frameworks remains unclear.\nThe authors should either provide broader data or explicitly delimit the scope of their conclusions.\nResponse: We appreciate this reviewer’s constructive suggestion to further assess the\ngenerality of our conclusions. To address this point, we have expanded our study to additional\nzeolite frameworks and adsorbates.\nFirst, we examined the adsorption kinetics of the three olefins in additional zeolite\nframework, SSZ-13 with a CHA topology (Figure R19). The confinement-induced reversal\nbetween adsorption kinetics and thermodynamics persists across these different pore\ntopologies, demonstrating that the phenomenon is not limited to ZSM-5. Moreover, based on\nthe discussion related to Question #3, we believe that pore size, rather than the specific zeolite\nframework, plays a direct and decisive role in governing the observed kinetic reversal.\nFigure R19. (a) CHA topology of SSZ-13 zeolite. (b) The normalized optical intensity curves of the three olefin\nmolecules on single SSZ-13 nanoparticle during an adsorption-desorption cycle at 130 °C. (c) The\nexperimentally determined k (left axis) and K values (right axis) of three olefin molecules as a function of\na A\ntheir theoretically calculated protonation energies.\nSecond, we investigated another important class of adsorbates—light alcohols (methanol,\nethanol, and n-propanol)—whose molecular sizes are comparable to those of the light olefins\nbut whose adsorption involves distinct hydrogen-bonding and acid–base interactions. Because\nthese alcohols are liquid at room temperature, their vapor-phase adsorption on ZSM-5 was\nmeasured via nitrogen bubbling. As shown in Figure R20, these alcohols also exhibit the same\nconfinement-dependent kinetic reversal, confirming that the observed behavior is not specific\nto olefins.\nFigure R20. (a)MFI topology of ZSM-5 zeolite. (b)The normalized optical intensity curves of the three alcohol\nmolecules on single ZSM-5 nanoparticle during an adsorption-desorption cycle at 100 °C. (c) The\nexperimentally determined k (left axis) and K values (right axis) of three alcohol molecules as a function of\na A\ntheir theoretically calculated protonation energies.\nCollectively, the additional experiments across different adsorbates and zeolite\nframeworks substantiate the broader applicability of our conclusions determined from the\ninitial study focused on the adsorption of light olefins on ZSM-5 nanoparticles.\nRelevant results and discussion have been included in the revised manuscript (Page 10,\nFigure 5) and supplementary information (Page 22, Figure S21) to demonstrate the broad\napplicability of the observed reversal between adsorption kinetics and thermodynamics in\nzeolites.\n--------------------------------------------------\nReviewer #3 (Remarks to the Author):\nComments:\nI co-reviewed this manuscript with one of the reviewers who provided the listed reports. This\nis part of the Nature Communications initiative to facilitate training in peer review and to provide\nappropriate recognition for Early Career Researchers who co-review manuscripts.\nResponse: We appreciate the opportunity to have our manuscript reviewed under the Nature\nCommunications co-review initiative and thank the reviewer for their careful evaluation and\nconstructive feedback.\n--------------------------------------------------\nReviewer #4 (Remarks to the Author):\nComments:\nThe confinement effect has been well accepted in zeolite chemistry, as it can significantly\ninfluence the adsorption of adsorbates and overall catalytic performance in catalysis. In this work,\nYi et al. correlate adsorption kinetics with the confinement effect in zeolites by employing optical\nimaging techniques to observe single ZSM-5 nanoparticles. By monitoring optical intensity changes,\nthey assess the intrinsic adsorption and desorption kinetics. Overall, this is an interesting study;\nhowever, several major concerns should be addressed as follows:\nResponse: We appreciate this reviewer’s valuable comments that help us to improve the\nquality of our manuscript. Detailed point-by-point responses are as follows.\n1. There is a critical lack of clarity and completeness regarding the characterization of the\nzeolite used in this work. The author states that three distinct materials were employed: ZSM-5\n(with Si/Al ratios of 50 and 400) and silicalite-1. However, the authors state that only \"the ZSM-5\nnanoparticles\" were characterized (Fig. S1), without specifying which Si/Al ratio this refers to.\nBesides, the acidity of those three samples should be evaluated, for example, the Bronsted acid\nsite and Lewis acid site. Probably, the solid-sate NMR measurements can be conducted to provide\nmore detailed information.\nResponse: We sincerely apologize for the insufficient clarity and completeness in the\ndescription of the zeolite materials used in this work. We thank the reviewer for pointing out\nthis issue that helps us to improve the rigor of the manuscript. Accordingly, we have\ncomprehensively characterized all materials used, including their Si/Al ratios, crystal structures,\nand Brønsted acid site densities. Detailed results are discussed as follows.\nFirst, the chemical composition of the ZSM-5 with different Si/Al ratios was determined\nby an inductively coupled plasma optical emission spectrum (ICP-OES). To avoid ambiguity, the\nZSM-5 samples with different Si/Al ratios were named accordingly (e.g., ZSM-5-15, ZSM-5-50,\nZSM-5-100, ZSM-5-400). As listed in Table R3, the ICP-OES results confirm that the measured\nSi/Al ratios are in good agreement with the values provided by the supplier.\nTable R3. Si/Al ratios of all materials used in this work, determined by ICP-OES.\nSecond, the crystal structures of all materials used in this work were characterized by X-\nray diffraction (XRD). The diffraction patterns of each material match well with the\ncharacteristic peaks reported in the literature for the corresponding MFI frameworks (Figure\nR21a),6 confirming that all samples possess the expected crystalline structure and phase purity.\nThird, the acidity of all materials used in this work was evaluated by NH -TPD. As shown\n3\nin Figure R21b, both the desorption temperature and the total amount of acid sites increase\nas the Si/Al ratio of ZSM-5 decreases. This trend is consistent with the expected increase in\nBrønsted acid site density and acid strength at lower Si/Al ratios, further confirming the\nreliability of the used materials and thus the corresponding conclusion.\nFigure R21. Characterization results of the ZSM-5 particles used in this work. (a, c) XRD patterns. (b, d) NH-\nRelevant results and discussion have been included in the revised\nsupplementary\ninformation (Figure S1, Figure S12, Figure S20 and Table S1). The Si/Al ratio of all ZSM-5 have\nbeen clarified in the revised manuscript and the supplementary information.\n2. The authors state that the NH3-TPD spectrum shows peaks \"at around 200°C and 400°C\".\nHowever, upon inspection of Fig. S1c, the second desorption peak appears to be located at a\nsignificantly different temperature (approximately 430°C). The text should be revised to accurately\nreflect the data presented in the figure. Besides, how much acid site in this zeolite?\nIs there any\nquantitative relationship between the acid site and the adsorbates adsorption?\nResponse: We appreciate this reviewer for pointing out this mistake. The temperatures\nof desorption peaks have been re-examined, and the maxima are located at 199 °C and 433 °C,\nrespectively (Figure R22). The corresponding values have been corrected in the revised\nmanuscript (Page 4) and supplementary information (Page 4, Figure S1).\nAdditionally, the acid site amounts were quantified from the peak areas of the NH -TPD\n3\nspectrum, where the amount of weak and strong acid sites in this ZSM-5 sample with Si/Al\nratio of 50 is determined to be 0.139 mmol/g and 0.093 mmol/g, respectively.\nFigure R22. NH -TPD of ZSM-5 with Si/Al of 50.\nZSM-5 nanoparticles, as reflected in the ΔI/I values during C H adsorption (Figure R23). To\n0 3 6\nfurther explore the relationship between acid site density and adsorbate adsorption, it would\nbe ideal to measure acid site amounts at the single nanoparticle level. While NH -TPD provides\n3\nreliable bulk measurements, it lacks the sensitivity and spatial resolution to resolve individual\nnanoparticles. Inspired by this technique, we employed the equilibrium adsorption amount of\nNH (ΔI/I ) as a proxy for the number of acid sites on single ZSM-5 nanoparticles. A positive\n3 0, NH3\ncorrelation between the ΔI/I (acid site amounts) and ΔI/I (adsorbates adsorption\n0, NH3 0, C3H6\namount) was found (Figure R23c), indicating that the adsorption capacity is strongly influenced\nby the local acid site density. By contrast, no dependence was found between C H adsorption\n3 6\nkinetics (k ) and acid site amounts (Figure R23d), consistent with our conclusion that the\na\nobserved confinement-induced kinetic reversal is governed primarily by pore structure rather\nthan the absolute number of acid sites.\nFigure R23. (a) The normalized optical intensity curves of 74 single ZSM-5 nanoparticles during an NH\n3\nadsorption-desorption cycle at 100 °C. (b) The normalized optical intensity curves of the same 74 single ZSM-\n5 nanoparticles during C H adsorption-desorption cycle at 130 °C. (c) The statistical dependence of ΔI/I\n3 6 0\nbetween NH and CH for the adsorption steps. (d) No significant correlation was observed between\n3 3 6\nadsorption kinetics and adsorption capacity.\n3. A significant discrepancy exists between Figure 1b and Supplementary Figure S5, which\npurportedly show the same phenomenon of the adsorption and desorption of C₃H₆ on ZSM-5. The\nmagnitude of the optical intensity change (the y-axis value) is markedly different between the two\nfigures. In Fig. 1b, the signal change appears to be approximately 0.05, while in Fig. S5 (yellow\ncurve), it appears to be around 0.035.\nResponse: We thank the reviewer for bringing this inconsistency to our attention and\napologize for the confusion caused by the discrepancy between Figure 1b and Figure S5. The\ndifference in the magnitude of the optical intensity change arose because Figure 1b originally\ndisplayed representative data from a different ZSM-5 nanoparticle than the one shown in\nFigure S5. The optical response naturally varies from particle to particle due to structural\nheterogeneity, including differences in acid site amounts, as discussed in Q#2.\nTo ensure clarity and consistency throughout the manuscript, we have revised Figure 1b\nto use the same nanoparticle as in Figures S5 and S7. This correction ensures that all figures\nconsistently represent the same adsorption–desorption behavior.\n4. A critical clarification is required regarding the fundamental process under investigation.\nThe manuscript consistently describes the interaction of C₃H₆ with Brønsted acid sites as a\n\"reaction\" (e.g., in the context of Fig. 1b). However, the experimental data presented (the\nreversible optical intensity change in Fig. 1b and the subsequent desorption in TPD profiles)\nunequivocally characterize a physical/chemical adsorption event, not a chemical reaction. Besides,\nwhat’s the effect of the Lewis acid site and the defect sites (in both the outside and inner surface)\neffect on the adsorption effect?\nResponse: We appreciate this reviewer’s valuable comment, which highlights the need\nfor precision in describing the fundamental process under investigation. We acknowledge that\nreferring to the interaction of C H with Brønsted acid sites as a “reaction” is misleading. The\n3 6\nexperimental data, including the reversible optical intensity changes in Fig. 1b and the\ndesorption behavior in TPD measurement, clearly indicate that the process is a reversible\nadsorption event rather than a chemical reaction. Accordingly, we have revised the manuscript\nto consistently describe these interactions as “chemical adsorption”.\nMoreover, to identify the chemical adsorption process, in situ IR spectroscopy and\nconfocal Raman microscopy were employed to characterize the bulk ZSM-5 powder and single\nZSM-5 nanoparticle before and after C H adsorption. As shown in Figure R24, after 30 min of\n3 6\nC H adsorption at 100 °C, the differential IR spectrum of bulk ZSM-5—obtained by subtracting\n3 6\nthe pre-adsorption spectrum from the post-adsorption spectrum—exhibits a pronounced\nnegative band at 3610 cm⁻¹, corresponding to the consumption of Brønsted acidic OH groups.\nSimultaneously, the occurrence of bands at 2955, 2930, and 2860 cm⁻¹ (ν(CH₃)/ν(CH₂)) and\n1470 cm⁻¹ (δ(CH)) indicates the formation of methyl/methylene species4,5. In addition, for the\nparticle shown in Figure R24, two Raman peaks at 1340 and 1590 cm⁻¹ emerge upon C H\n3 6\nadsorption, corresponding to C–O vibrational modes. These results provide direct evidence\nthat C H adsorption occurs mainly on Brønsted acid sites via chemical interaction.\n3 6\nFigure R24. (a-b)The original in-situ IR adsorbance spectra before and after adsorption of CH at 100 °C. (c-\n3 6\nd) The corresponding differential IR spectrum of bulk ZSM-5—obtained by subtracting the pre-adsorption\nspectrum from the post-adsorption spectrum.\nFurthermore, to investigate the effects of Lewis acid sites and defect sites on adsorption,\nwe employed an in situ NaOH etching experiment at the single-nanoparticle level. This\ntreatment has two main effects: (1) partial extraction of framework silicon, generating defect\nsites, and (2) selective removal of extra-framework Al (EFAL) species, a major source of Lewis\nacid sites. The experimental protocol is illustrated in Figure R25a. The results before and after\nNaOH etching reveal heterogeneous responses among different nanoparticles, and\nrepresentative adsorption–desorption kinetics for three ZSM-5 nanoparticles are shown in\nFigures R25b-d. Some particles showed increased uptake and faster kinetics, others exhibited\nincreased uptake but slower kinetics, and a minority displayed decreased adsorption, which\nlikely originated from severe silicon removal. The complexity of these results hinders a clear\nassessment of the individual contributions of Lewis acid sites and defect sites, since their\neffects are entangled in the observed adsorption behaviors. As we were unable to selectively\nand independently modulate these structural features, a definitive conclusion regarding their\nseparate impacts on adsorption kinetics cannot be drawn at this stage.\nFigure R25. (a) The experimental workflow of in situ NaOH etching experiment. (b-c) Representative\nadsorption-desorption kinetic curves of single ZSM-5 nanoparticles before (blue) and after (orange) NaOH\netching.\nRelevant results have been included in the revised manuscript (Page 5) and\nsupplementary information (Page 8, Figure S5).\n5. The data in Supplementary Figure S11d appears to directly contradict the interpretation\nprovided for the ZSM-5 system and instead points towards a diffusion-controlled process for\nsilicalite-1. The authors show a clear negative correlation between the adsorption rate constant of\nC₃H₆ and the particle size in silicalite-1. This is a classic signature of a diffusion-limited process: in\nlarger particles, molecules have to travel a longer average path to access the internal pore network,\nleading to a slower observed adsorption rate.\nResponse: We apologize for the unclear description that may have confusion. We agree\nthat the adsorption of C H on Silicalite-1 is a diffusion-limited process, as evidenced by the\n3 6\nclear particle-size dependence of the adsorption rates—larger Silicalite-1 particles require\nlonger times to reach equilibrium. In contrast, adsorption on ZSM-5 does not exhibit\nnoticeable particle-size dependence, and both adsorption and desorption rates are\nsubstantially slower than those observed for Silicalite-1 of comparable size. This comparison\nsuggests that, in ZSM-5, the adsorption kinetics are dominated by the interactions between\nolefin molecules and the strong Brønsted acid sites rather than by intracrystalline diffusion,\nthereby providing a system in which the intrinsic interaction kinetics within zeolites can be\ndirectly studied---the focus of our manuscript.\nMoreover, the key conclusion we aim to convey is that the interaction kinetics between\nolefin molecules and Brønsted acid sites are strongly influenced by the confinement effect\nimposed by the microporous environment of ZSM-5. For instance, n-C H , being a stronger\n4 8\nbase than C H , should exhibit stronger and faster interactions with the same acid sites, as\n2 4\nconfirmed by control experiments on phosphotungstic acid (HPW, with further details\nprovided in the response to Q#8 below), a classic non-porous solid acid. However, this trend\nreverses in ZSM-5: the adsorption rate of C H becomes even faster than that of n-C H .\n2 4 4 8\nThis\nreversal highlights the decisive role of pore confinement in governing intrinsic interaction\nkinetics within zeolites.\nThe relevant discussion has been reorganized and clarified in the revised supplementary\ninformation to avoid potential confusion (Page 15, Figure S12).\n6. L242-245: The claim that the increase in optical intensity with molecular weight suggests\n\"effective access\" to active sites is not logically sound. The optical signal is primarily a function of\nthe adsorbed mass. A heavier molecule will naturally produce a larger signal per molecule, regardless of\ndiffusion or accessibility limitations. The authors should either provide additional data to support the\naccessibility claim (e.g., adsorption capacities) or rephrase the conclusion to state that the data\nconfirms adsorption occurs, with the signal intensity being mass-dependent.\nResponse: We thank the reviewer for this comment. We agree that heavier molecules\nadsorbed on the acid sites of ZSM-5 inherently produce larger optical signals due to the mass\ndependence of the scattering response. In our measurements, the ΔI/I₀ values of the three\nolefins on the same ZSM-5 nanoparticle not only increase with molecular weight but also\nexhibit a clear linear dependence (Figure R26). This linearity indicates that the number of\nadsorbed molecules (or equivalently, the number of accessed acid sites) is comparable for the\nthree olefins, and that the differences in signal magnitude arise primarily from their molar\nmasses rather than from variations in accessibility. Accordingly, we conclude that all three\nstudied olefins are able to access and interact with the Brønsted acid sites under the\nexperimental conditions.\nThe relevant description has been reorganized in the revised manuscript to avoid\npotential confusion (Page 7).\nFigure R26. (a) The optical adsorption-desorption curves of the three olefin molecules on a ZSM-5\nnanoparticle. (b) The linear dependence between the observed ΔI/I and the corresponding molar weight\n0\nof the three olefins.\n7. Regarding the analysis in Fig. 3c, the manuscript states that the equilibrium constants (KA)\nwere determined from the \"statistical linear dependence\" between elementary adsorption and\ndesorption rate constants. However, the actual KA values and the crucial statistical parameter (e.g.,\nthe coefficient of determination, R²) for this linear fit are not provided either in the figure, the\ncaption, or the main text.\nResponse: We apologize for the omission of crucial statistical parameters in the original\nmanuscript. The supplementary parameters, including the equilibrium constants (K ) and the\nA\ncoefficients of determination (R²) for the linear fits, have been added to the figure caption in\nthe revised manuscript (Figure 3).\nFigure R27. The statistical linear dependence between the rate constants for the elementary adsorption and\ndesorption steps of each olefin molecule, where yellow, orange, and purple dots represent the results of C H,\n2 4\nCH and n-CH, respectively. R2 = 0.84, R2 = 0.97, R2 = 0.95, K = 1.21 × 10-2 kPa-1, K =\n3 6 4 8 C2H4 C3H6 n-C4H8 A C2H4 A C3H6\n2.38 × 10-2 kPa-1, K = 1.61 × 10-1 kPa-1.\nAn-C4H8\n8. In this work, the authors claim that it is the confinement effect but the interaction strength\nworks as the main factor to control the adsorption kinetics of adsorbates. Personally, I don’t agree\nthis statement, Confinement is not a standalone steric effect but a holistic one that includes how\nacid strength manifests in tight spaces. In other words, confinement effect is an overall effect,\nwhich contains the contribution of acid strength for adsorbates adsorption. Besides, only one type\nzeolite was adopted in this work, the different topology zeolite with different channel size should\nbe involved for a systemic comparison.\nResponse: We thank the reviewer for this insightful comment. We fully agree that\nconfinement is not a standalone steric effect but a holistic phenomenon, where the spatial\nconstraints of the pore influence how the acid strength of Brønsted sites is expressed and\nexperienced by adsorbates. Under tight confinement, such as in the 10-membered ring\nchannels of ZSM-5, the pore geometry becomes the dominant factor controlling adsorption\nkinetics, overriding the trends predicted solely from intrinsic gas-phase proton affinity. In this\nsense, the confinement effect inherently includes the influence of acid–adsorbate interactions.\nTo further validate this conclusion, we have conducted new experiments to systematically\nexamine the adsorption behaviors of ethene (C H ), propene (C H ), and n-butene (n-C H ) on\n2 4 3 6 4 8\nzeolites with a range of pore sizes, including those both smaller and larger than the zeolite\ninvestigated in the original manuscript (Table R4). An overview of the results is presented in\nFigure R28, where the reversal between adsorption kinetics (kₐ) and thermodynamics (K )\nA\nbecomes progressively weaker as the pore size increases. A detailed discussion is provided\nbelow.\nTable R4. The structural information of the samples used in adsorption-desorption experiments.\nFigure R28. Confinement effect on the adsorption kinetics and thermodynamics of light olefins within\nmaterials with different pore sizes. Top row: Schematic representations of the structures of the investigated\nmaterials—SSZ-13 (8MR), ZSM-5 (10MR), HY (12MR), and HPW (non-porous solid acid)—arranged in order\nof increasing pore size. Bottom row: Adsorption results for C₂H₄, C₃H₆, and n-C₄H₈ on each material, showing\nthe relationships between the adsorption rate constant (kₐ) and equilibrium constant (K ) with proton affinity.\nA\nIt is clear that as the pore size increases, the confinement-induced reversal between kₐ and K progressively\nA\ndiminishes and ultimately disappears.\nWe first conducted experiments on SSZ-13, a representative small-pore CHA-type zeolite\nfeaturing a three-dimensional pore system with 8-membered-ring windows (8MR, 0.38 nm,\nFigure R29a), which are smaller than those of ZSM-5 (10 MR, 0.51×0.55 and 0.53×0.56 nm).\nSingle-nanoparticle kinetic measurements revealed that kₐ maintains a negative correlation\nwith the proton affinity of the three olefins, whereas K shows a positive correlation with\nA\nproton affinity (Figure R29g). Notably, the adsorption kinetic of n-C₄H₈ was markedly\nsuppressed, despite its highest K among the three adsorbates. These results support our\nA\nhypothesis that confinement within the zeolite framework is the dominant factor governing\nthe adsorption kinetics of the olefins.\nFigure R29. (a) CHA topology of SSZ-13 zeolite. (b-d) The normalized optical intensity curves of the three\nolefin molecules on single SSZ-13 nanoparticles during an adsorption-desorption cycle. The gray line\nrepresents the result on each SSZ-13 nanoparticle. The color line represents the average signal of all SSZ-13\nnanoparticles in the field of view. (e-f) Statistical histograms of k and K values of three olefins measured on\na A\neach SSZ-13 particle. (g) The experimentally determined k (left axis) and K values (right axis) of three olefins\na A\nfrom (e) as a function of their theoretically calculated protonation energies.\nWe then conducted experiments on HY nanoparticles, a representative FAU-type zeolite\ncontaining a three-dimensional pore structure of 12MR channels with a diameter of about\n0.74nm (Figure R30a), which are larger than those in ZSM-5. As expected, the results showed\nthat not only K but also kₐ increases with the proton affinity of the studied olefins, suggesting\nA\nthat the previously observed reversal in adsorption kinetics is significantly weakened in this\nlarger-pore environment (Figure R30g). This point is further confirmed by the result obtained\non phosphotungstic acid (HPW), a classic non-porous solid acid, where both k and K also\na A\nfollow a positive correlation with proton affinity—consistent with fundamental acid-base\ntheory that adsorption behavior is governed by intrinsic molecular interactions (Figure R31).\nFigure R30. (a) FAU topology of HY zeolite. (b-d) The normalized optical intensity curves of the three olefin\nmolecules on single HY nanoparticles during an adsorption-desorption cycle. The gray line represents the\nresult from a HY nanoparticle. The color line represents the average signal of 125 HY nanoparticles in the field\nof view. (e-f) Statistical histograms of k and K values of three olefins measured on each HY nanoparticle. (g)\na A\nThe experimentally determined k (left axis) and K values (right axis) of three olefins from (e) as a function\na A\nof their theoretically calculated protonation energies.\nFigure R31. (a) Chemical structure of HPW. (b-d) The normalized optical intensity curves of the three olefin\nmolecules on single HPW nanoparticles during an adsorption-desorption cycle. The gray line represents the\nresult from a HPW nanoparticle. The color line represents the average signal of 42 HPW nanoparticles. (e-f)\nStatistical histograms of k and K values of three olefins measured on each HPW nanoparticle. (g) The\na A\nexperimentally determined k (left axis) and K values (right axis) of three olefins from (e) as a function of\na A\ntheir theoretically calculated protonation energies.\nRelevant results and discussion have been included in the revised manuscript (Page 10,\nFigure 5) and supplementary information (Figure S20 and Table S2).\nMinor error:\n1. In Supplementary Figure S4, the unit for milliliter is written as \"ml\". The correct SI symbol\nshould be \"mL\".\nResponse: We thank the reviewer for pointing this error out. It has been corrected in the\nrevised Supplementary materials.\nReferences\n1. Zabihpour, A., Ahmadpour, J., Yaripour, F. Strategies to control reversible and irreversible\ndeactivation of ZSM-5 zeolite during the conversion of methanol to propylene (MTP): A review.\nChem. Eng. Sci.273, 118639 (2023).\n2. Wang, F., Luo, M., Xiao, W. D. Catalytic Performance and Coking Behavior of a Submicron HZSM-\n3. Tabernilla, Z., Ateka, A., Aguayo, A. T., Epelde, E. Unraveling the Role of HZSM-5 Zeolite Catalyst\nAcid Properties in Fuel Production and Coke Deactivation in Low-Pressure Ethylene\nOligomerization. Energy Fuels.39, 8639-8651 (2025).\n4. Spoto, G., Bordiga, S., Ricchiardi, G., Scarano, D., Zecchina, A., Borello, E. IR STUDY OF ETHENE\nAND PROPENE OLIGOMERIZATION ON H-ZSM-5 - HYDROGEN-BONDED PRECURSOR\nFORMATION, INITIATION AND PROPAGATION MECHANISMS AND STRUCTURE OF THE\nENTRAPPED OLIGOMERS. J. Chem. Soc.-Faraday Trans.90, 2827-2835 (1994).\n5. Yamazaki, H., Yokoi, T., Tatsumi, T., Kondo, J. N. Ethene oligomerization on H-ZSM-5 in relation\nto ethoxy species. Catalysis Science & Technology.4, 4193-4195 (2014).\n6. Zeng, B. J. et al. Directional Transport in Hierarchically Aligned ZSM-5 Zeolites with High\nCatalytic Activity. J. Am. Chem. Soc.146, 33423-33433 (2024)."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The revision has addressed all questions with new data and additional discussions. I think it is ready to be accepted.", "reviewer_2": "I appreciate the authors' thorough and detailed responses to my original comments. The authors have made substantial improvements to the manuscript. The additional experiments, particularly the systematic comparison across zeolites with different pore sizes (SSZ-13, ZSM-5, HY) and phosphotungstic acid, provide compelling evidence and significantly strengthen the manuscript. However, before final acceptance, I would like the authors to address the following remaining concerns:\n\n1. NaOH etching experiment design\nThe authors performed NaOH etching experiments to investigate the effects of Lewis acid sites and defect sites. However, I noticed that after alkaline treatment and water washing, the samples were directly dried and measured without ion-exchange and calcination steps. This means the measured samples are Na-form ZSM-5 rather than H-form ZSM-5, as the Brønsted acid sites have been occupied by Na⁺ cations. The correct procedure should include: NaOH etching → water washing → NH₄⁺ ion exchange → calcination → H-ZSM-5. The current experimental design confounds the effects of acid site loss with defect introduction, which likely explains the complex and inconclusive results. I suggest the authors provide control experiments with proper ion-exchange and calcination steps.\n\n2. Source of protonation energy data\nThe authors use \"theoretically calculated protonation energies\" as a key parameter to correlate adsorption kinetics and thermodynamics (Figure 3d, Figure 5c-d, etc.). However, the source and calculation method of these values are not specified. The authors should note that in confined zeolite environments, actual protonation/adsorption energies may significantly deviate from gas-phase values due to geometric constraints, van der Waals interactions, and local acid site environments. I recommend the authors clearly state the source and calculation method of the protonation energy data. If possible, provide DFT calculations of adsorption energies and transition state barriers within the confined zeolite channels, which would greatly strengthen the mechanistic interpretation.\n\n3. Discussion of crystal diversity and activation energy distribution\nThe histograms in Figure 4d-e show substantial broadening in the activation energy distributions across 50 ZSM-5 particles (e.g., Ea for C₃H₆ ranges from ~25 to ~70 kJ/mol). This particle-to-particle heterogeneity is consistent with the \"crystal diversity\" phenomenon reported by Saint Remi et al. (Nat. Mater. 15, 401-406, Ref. 22). I suggest the authors discuss the possible origins of this activation energy broadening and analyze how this inter-particle heterogeneity affects the reliability of the conclusions.\n\nOnce the above concerns are adequately addressed, I recommend acceptance of this manuscript for publication in Nature Communications.", "reviewer_3": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts.", "reviewer_4": "The authors have addressed my concerns, I am satisfied with the revisions and recommoned its publication in Nature Communications."}, "author_response": "***Responses to Reviewers’ Comments***\nReviewer #1 (Remarks to the Author):\nComments: The revision has addressed all questions with new data and additional discussions. I\nthink it is ready to be accepted.\nResponse: We sincerely thank the reviewer for their positive evaluation of our revisions and\nfor recommending the manuscript for publication in Nature Communications. We greatly\nappreciate the reviewer’s time, effort, and constructive feedback, which have helped improve\nthe quality and clarity of our manuscript.\n--------------------------------------------------\nReviewer #2 (Remarks to the Author):\nComments: I appreciate the authors' thorough and detailed responses to my original comments.\nThe authors have made substantial improvements to the manuscript. The additional experiments,\nparticularly the systematic comparison across zeolites with different pore sizes (SSZ-13, ZSM-5, HY)\nand phosphotungstic acid, provide compelling evidence and significantly strengthen the\nmanuscript. However, before final acceptance, I would like the authors to address the following\nremaining concerns:\nResponse: We appreciate this reviewer’s valuable comments, which have greatly helped us\nimprove the manuscript. We are glad to hear that our previous revision addressed most of the\nreviewer’s concerns. We will make every effort to clarify the remaining concerns in this\nrevision.\n1. NaOH etching experiment design. The authors performed NaOH etching experiments to\ninvestigate the effects of Lewis acid sites and defect sites. However, I noticed that after alkaline\ntreatment and water washing, the samples were directly dried and measured without ion-\nexchange and calcination steps. This means the measured samples are Na-form ZSM-5 rather than\nH-form ZSM-5, as the Brønsted acid sites have been occupied by Na⁺ cations. The correct procedure\nshould include: NaOH etching → water washing → NH₄⁺ ion exchange → calcination → H-ZSM-5. The\ncurrent experimental design confounds the effects of acid site loss with defect introduction, which\nlikely explains the complex and inconclusive results. I suggest the authors provide control\nexperiments with proper ion-exchange and calcination steps.\nResponse: We thank the reviewer for the constructive comments and for pointing out the\nimportance of ion-exchange and calcination in the NaOH etching experiments. Following the\nreviewer’s suggestion, we repeated the experiments using the corrected procedure, including\nNH₄⁺ ion exchange and subsequent calcination (Fig. R1a), to restore the H-form ZSM-5 after\nalkaline treatment.\nThe revised experiments show that, after NaOH etching followed by ion exchange and\ncalcination, the change in adsorption capacity decreases systematically for all investigated\nnanoparticles (Fig. R1b), which is consistent with partial framework silicon extraction and the\nassociated loss or restructuring of adsorption-active sites induced by alkaline treatment.\nDespite this uniform decrease in adsorption capacity, the adsorption-desorption kinetics\nremain highly heterogeneous across individual nanoparticles, with no clear or systematic trend\nemerging (Fig. R1c). These results indicate that, although the additional control experiments\nimprove experimental rigor, the effects of NaOH etching on adsorption behavior still remain\ncomplex, particularly with respect to adsorption-desorption kinetics, which is the key focus of\nthis work. This complexity is expected, as NaOH treatment simultaneously induces framework\ndesilication and acid-site modification, making it challenging to decouple their respective\ncontributions using this approach alone. Importantly, this coupling does not affect the main\nconclusions of the manuscript, which are based on consistently observed adsorption kinetic\ntrend across different olefin species at the single nanoparticle level and are independent of\nthe NaOH etching experiments.\nFigure R1. (a) The experimental workflow of in-situ NaOH etching experiment. (b) The histograms of ΔI/I of\n0\nkinetic curves of three representative ZSM-5 nanoparticles before (blue) and after (orange) NaOH etching.\n2. Source of protonation energy data. The authors use \"theoretically calculated protonation\nenergies\" as a key parameter to correlate adsorption kinetics and thermodynamics (Figure 3d,\nFigure 5c-d, etc.). However, the source and calculation method of these values are not specified.\nThe authors should note that in confined zeolite environments, actual protonation/adsorption\nenergies may significantly deviate from gas-phase values due to geometric constraints, van der\nWaals interactions, and local acid site environments. I recommend the authors clearly state the\nsource and calculation method of the protonation energy data. If possible, provide DFT calculations\nof adsorption energies and transition state barriers within the confined zeolite channels, which\nwould greatly strengthen the mechanistic interpretation.\nResponse: We appreciate the reviewer for raising this important point regarding the source\nand applicability of the protonation energy data. We agree that molecular simulations\n(MD/DFT) would provide more accurate protonation and adsorption energies for mechanistic\ninterpretation; however, we do not have the capability to perform such simulation at this stage.\nIn the revised manuscript, we have clearly stated that the protonation energies used in Figures\n3d and 5c-d are theoretically calculated gas-phase values obtained from the National Institute\nof Standards and Technology (NIST, https://webbook.nist.gov/chemistry/), with the\ncorresponding references explicitly added.\nAlthough absolute protonation energies depend to some extent on the computational method\nand geometric constraints, the relative protonation strength of the three olefins is invariant\nand well established (J. Chem. Theory Comput. 2014, 10, 3123-3128). Importantly, this\nordering is independently validated by experimental equilibrium association constants (K ),\nA\nwhich scale with adsorption affinity and exhibit the same trend across zeolites with distinct\npore sizes (SSZ-13, ZSM-5, and HY) and phosphotungstic acid, as demonstrated in our previous\nrevision and summarized in Fig. R2.\nFigure R2. Confinement effect on the adsorption kinetics and thermodynamics of light olefins within\nmaterials with different pore sizes. Top row: Schematic representation of the structures of the investigated\nmaterials—SSZ-13 (8MR), ZSM-5 (10MR), HY (12MR), and HPW (non-porous solid acid)—arranged in order\nof increasing pore size. Bottom row: Adsorption results for CH , CH , and n-CH on each material, showing\n2 4 3 6 4 8\nthe relationships between the adsorption rate constant (kₐ) and equilibrium constant (K ) with proton affinity.\nA\nIt is clear that as the pore size increases, the confinement-induced reversal between kₐ and K progressively\nA\ndiminishes and ultimately disappears.\nMoreover, the reverse trend observed between the equilibrium association constants (K ) and\nA\nadsorption rate constants (k ) of the three olefins on the very same nanoparticle provides\na\ndirect evidence supporting our conclusion. This further confirms that gas-phase protonation\nenergies serve as a reliable comparative descriptor of the intrinsic interaction strength\nbetween olefins and acid sites in these systems.\nRelevant references and discussion have been included in the revised manuscript (Page 8, 12\nand 13).\n3. Discussion of crystal diversity and activation energy distribution. The histograms in Figure 4d-e\nshow substantial broadening in the activation energy distributions across 50 ZSM-5 particles\n(e.g., Ea for C₃H₆ ranges from ~25 to ~70 kJ/mol). This particle-to-particle heterogeneity is consistent\nwith the \"crystal diversity\" phenomenon reported by Saint Remi et al. (Nat. Mater. 15, 401-406,\nRef. 22). I suggest the authors discuss the possible origins of this activation energy broadening and\nanalyze how this inter-particle heterogeneity affects the reliability of the conclusions. Once the\nabove concerns are adequately addressed, I recommend acceptance of this manuscript for\npublication in Nature Communications.\nResponse:We thank the reviewer for highlighting this point. The significant broadening of the\nactivation energy distributions reflects inter-particle heterogeneity within the same batch of\nZSM-5 particles, consistent with the \"crystal diversity\" phenomenon reported by Saint Remi et\nal. We would like to clarify that this heterogeneity does not compromise the reliability of our\nmain conclusion—that the adsorption rates of light olefins exhibit a reversed trend relative to\ntheir gas-phase proton affinities. This is because our single-particle measurements compare\nthe adsorption behaviors of the three light olefins within the same particle, and the reversed\ntrend is consistently observed across all individual particles, with a representative particle\nshown in Fig. 3b.\nImportantly, this heterogeneity also underscores the significance of our single-particle\nmeasurement strategy, as such trend may be masked in bulk measurements due to averaging\neffects. Regarding the possible origins of the observed heterogeneity, our preliminary analysis\nsuggests it may arise from differences in defect densities and subtle variations in pore\nstructure orientation among individual ZSM-5 crystals. While a comprehensive investigation\nof these factors is beyond the scope of the present work, we acknowledge the fundamental\nimportance of this phenomenon and note that a detailed study is currently underway. We look\nforward to the reviewer’s valuable comments on this topic in our future work.\n--------------------------------------------------\nReviewer #3 (Remarks to the Author):\nComments:\nI co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is\npart of the Nature Communications initiative to facilitate training in peer review and to provide\nappropriate recognition for Early Career Researchers who co-review manuscripts.\nResponse: We appreciate the opportunity to have our manuscript reviewed under the Nature\nCommunications co-review initiative and thank the reviewer for their careful evaluation and\nconstructive feedback.\n--------------------------------------------------\nReviewer #4 (Remarks to the Author):\nComments:\nThe authors have addressed my concerns, I am satisfied with the revisions and recommended its\npublication in Nature Communications.\nResponse: We sincerely thank the reviewer for their positive evaluation of our revisions and\nfor recommending the manuscript for publication in Nature Communications. We greatly\nappreciate the reviewer’s time, effort, and constructive feedback, which have helped improve\nthe quality and clarity of our manuscript."}]

Decision letter