Shapeshifting exsolved FeNi bimetallic nanostructures as catalytic switchers during the CO_2-mediated ethane conversion

Domain: chemistry
Published: 2026-04-13
Editorial outcome: minor_revision

Abstract
In the era of the energy transition, the development of sustainable, high-performance, and multifunctional catalysts that adapt to complex catalytic processes is essential. Here, we report shapeshifting bimetallic iron–nickel catalysts developed via an exsolution strategy for carbon dioxide–mediated ethane conversion. By controlling the reduction temperature of a perovskite host, either alloyed iron–nickel nanoparticles or oxide–alloy core–shell nanoparticles are selectively formed. Oxidative regeneration of the perovskite enables reversible interconversion between these distinct nanostructures within the same parent material. As a result, the catalyst exhibits switchable selectivity between ethane dry reforming and carbon dioxide–assisted oxidative dehydrogenation while maintaining high stability. Repeated redox cycling confirms that the structural transformation and catalytic performance are largely reversible. These results demonstrate that exsolution provides a robust platform for designing regenerable catalysts with deliberately tunable and switchable catalytic states.

Introduction
The catalyst industry generated an estimated economic value of approximately USD 32 billion in 2024, with heterogeneous catalysts accounting for 71% of the market. The expanding oil and gas sector is expected to drive further catalyst demand in the coming years. Additionally, the growing focus on green/low carbon technologies and the increasing energy needs have made catalysts crucial in refining processes such as reforming, (de-)hydrogenation, and cracking.

As the world moves towards reducing CO2 emissions, the energy transition not only involves new technologies but also a substantial increase in the demand for specific materials. This regards particularly critical minerals like cobalt and noble metals, fundamental in heterogeneous catalysis, which need to be substituted with more abundant elements such as iron. For this reason, the energy transition is deeply intertwined with a material transition. In the field of heterogeneous catalysis this transformation includes increasing investments from industries in catalyst recycling and substantial innovation in the development of novel catalytic converters with high performance.

In recent years, metal exsolution from doped metal oxide matrices stood out as a highly promising approach for the design of innovative and sustainable catalyst materials1 with improved performance2, lifetime3, and recyclability4,5. Understanding the underlying mechanistic processes such as dopant diffusion and reduction as well as nanoparticle nucleation and growth represents the first prerogative for the development of exsolved materials for the future catalyst market.

Among the exsolved catalysts, the design of multimetallic nanoparticles attracts a lot of attention6,7. It is well known that by tuning the structure and composition of bimetallic nanoparticles the catalytic performance, and especially the selectivity, can be largely improved8,9. The development of iron-based multimetallic nanoparticles is currently dominating the scientific literature because this element is both the second most abundant metal on Earth, and offers high catalytic activity due to its rich redox chemistry. The rather electropositive character of Fe compared to the other metals forming the nanoalloy (e.g. Ni, Cu, Co) is also responsible for structural and compositional changes of the nanoparticles during catalytic operation, which in turn influence the performance of the catalyst. For example, Oh et al. discovered a rocking-chair behavior of Fe species in trimetallic Fe-Co-Ni exsolved nanoalloys during chemical looping reforming coupled with CO2 splitting. They found that Fe species move back and forth between the inside and the outside of the host oxide matrix, i.e. as Fe cations in the oxide lattice and as part of the metallic alloy, respectively6. The group around Chenghao Yang and Meilin Liu showed that iron nanoalloys exsolved at high temperature (T > 800 °C) form a core-shell M-Fe@FeOx structure (M = Ni, Cu) with the highly oxygen defective FeOx layer playing a fundamental role in the CO2 adsorption, dissociation and reduction during high-temperature CO2 electrolysis10,11. In a similar work, the formation of exsolved core-shell RuFe@FeOx nanoparticles was observed, which were shown to possess high electrocatalytic activity, with the FeOx phase being responsible for the adsorption and conversion of the CO212. The formation of such heterostructures appears to occur only at high temperatures, as for low-temperature exsolution (T < 700 °C) only nanoparticles with pure metallic surface are detected8,13. A common application for this variation between metallic alloy surface and M-Fe@FeOx heterostructure is for the reaction between ethane and CO214. This reaction has gained significant popularity in recent years, as a means to transform the underutilized ethane from shale gas and the waste CO2 captured from emission sources into value-added chemicals15. It mainly follows two different pathways, the CO2-assisted oxidative dehydrogenation of ethane (1 - ODH) and the dry reforming of ethane (2 - DER):

C2H6 + CO2 → C2H4 + CO + H2O (ODH) (1)

C2H6 + 2CO2 → 4CO + 3H2 (DER) (2)

Reaction (1) is undoubtedly more valuable, as it leads to the production of ethylene, a valuable petrochemical feedstock, with a reduced carbon footprint. Reaction (2) on the other hand can also be utilized to produce synthesis gas (H2 and CO mixture), which can be used in subsequent Fischer-Tropsch synthesis15.

For both of these reactions, bimetallic Fe-Ni catalysts have received remarkable research attention in recent years14,16–22 First, they avoid the use of precious metals (e.g., Pt, Pd), or toxic Cr, and they have also demonstrated an interesting ability to alter the reaction selectivity via the tuning of specific material characteristics (e.g., Fe:Ni molar ratio, metal loading, support nature and structure). Xie et. al.16 highlighted that this selectivity control in bimetallic catalysts can be influenced by the surface chemistry and various structural transformations (e.g., alloying or oxygen-induced segregation), with the metallic (alloy) surface favoring C-C bond scission and the dry reforming selectivity and the inverse M’Ox/M (in our case FeOx/Fe-Ni) interface favoring C-H bond scission and ethane dehydrogenation14. In our previous work, we showed that Fe-based bimetallic exsolved heterostructures can possess a metallic (alloy) or an oxidated surface, influencing the catalytic activity and selectivity during the CO2-assisted ethane conversion8. In general, although highly interesting, this selectivity control between ethane dehydrogenation and ethane reforming could thus far be obtained by using distinct catalyst materials.

Exploiting the unique properties of exsolved nanoparticles to be influenced by the exsolution treatment conditions, as well as to be reincorporated back into the parental oxide matrix upon oxidative treatment, we propose herein an innovative strategy to prepare single exsolved bimetallic catalysts with tunable and switchable catalytic performance. La0.4Sr0.4Ti0.6Fe0.35Ni0.05O3-δ (LSTFN2) with 20 at.% of A-site deficiency is chosen as the parental perovskite oxide matrix. The temperature-dependent exsolution behavior of FeNi nanoparticles is investigated by combining different complementary analysis techniques and a formation mechanism for the high-temperature formation of the FeOx shell layer is proposed. The shapeshifting from low-temperature (T = 400 °C) exsolved FeNi nanoparticles to high-temperature (T = 850 °C) exsolved FeOx@FeNi heterostructures mediated by the oxidative regeneration of the oxide matrix is carefully addressed, and we discover that it is a quasi-reversible process. The structural change is also accompanied by a corresponding switch in the catalytic performance/selectivity during the CO2-mediated ethane conversion.

Specifically, we show herein that the catalytic performance/ selectivity can be switched between CO2-assisted oxidative dehydrogenation of ethane and dry reforming of ethane by simply altering the exsolution treatment conditions on a single multifunctional perovskite material. The material exsolved at 400 oC shows approx. 78% selectivity for reforming, which is switched to approx. 75% selectivity for dehydrogenation when exsolved at 850 oC instead. In addition to this, the La0.41Sr0.39Ti0.68Fe0.27Ni0.05O3-δ shapeshifted/regenerated catalysts (following re-oxidation and re-exsolution) are also tested, and the selectivity switch in this case was also achieved to a great extent. Similar results were replicated via in situ regeneration (oxidation/reduction) treatments during a multi-cyclic operation. This research therefore shows that by tuning the exsolution conditions and exploiting the regeneration of the oxide parental matrix, the exsolution of bimetallic structures can be tailored for the design of ideal nanomaterials with switching functional properties. These findings, obtained by a careful assessment of the chemical and structural changes of the materials, open new prospects for the use of exsolution as an innovative design strategy for advancing material transitions in energy applications and the development of smart materials.

Results
Parental material

The LSTFN2 material shows a main phase with the 𝑃𝑚3̅𝑚 cubic space group, typical of SrTiO3 (PDF Nr. 01-079-0175), as already observed. Moreover, a minor spinel phase ascribed to NiFe2O4 (PDF Nr. 00-034-0641) can be noticed (Fig 1a). Its formation can be related to a partial phase reconstruction, as a consequence of the high A-site deficiency during the high-temperature treatment. The crystallite size and the lattice parameter of the main perovskite phase are calculated to be 45 nm and 3.910 Å, respectively.

LSTFN2 is characterized by a fair specific surface area (SSA) of 15 m2/g determined by nitrogen physisorption (Table 1, and Supplementary Fig. 1a). The formation of a quite porous morphology is also verified by transmission electron microscopy (TEM, Fig. 1b) analysis, which evidences the presence of a nanostructured material with intraparticle porosity. Fig. 1c shows an atomically resolved TEM image of LSTFN2, presenting cubic perovskite with a d-spacing of 2.877 Å in the (110) plane, which matches well with the one obtained by XRD (d = 2.758 Å). All metal elements are homogeneously occupying the bright cation sites without any segregated parts, which implies the successful synthesis of the scaffold without any significant amount of secondary phase formation. In addition, energy dispersive X-ray spectroscopy (EDX) from TEM measurement was performed to investigate the elemental distribution. All the cations are homogeneously distributed within the oxide structure (Supplementary Fig. 1b,c) and the calculated atomic percentages lead to an experimental composition very close to the nominal one, thus showing that, although present, the spinel side phase is marginal to the perovskite one.

More precise information on the oxidation state and local structure of the metals, and particularly on the Ni and Fe species, was obtained by X-ray Absorption Near-edge Structure (XANES) spectroscopy. The XANES spectra of Fe and Ni in LSTFN2, along with the reference spectra of SrFeO3, LaFeO3, LaNiO3, and NiFe2O4, are displayed in Fig. 1d,e. The Ni K-edge spectrum shows a good match with the one for NiFe2O4 indicating that Ni species are also allocated in the spinel phase, thus corroborating the XRD findings. Regarding the Fe K-edge spectrum, Fe species in LSTFN2 resemble a combination of LaFeO3 and NiFe2O4, as can be noticed by the pronounced white line at 7130 eV and the neighboring shoulders at 7135 eV and 7142 eV. In contrast to what was observed on LSTFN2 annealed at low temperatures (T = 600 °C) the presence of SrFeO3 domains in the material, and so of Fe(IV) species seems unlikely, due to the marked mismatch with the corresponding reference spectrum. This finding indicates that upon high-temperature treatment (T = 900 °C) SrFeO3 domains evolve into a more stable configuration.

Better insight into the Fe speciation was provided by Mössbauer spectroscopy. According to Fig. 1f, the Mössbauer spectrum of the pristine material consists of an intense paramagnetic absorption, centered around ≈0.36 mm/s, together with a broad sextet, attributable to the presence of magnetically coupled species. From the fitting of the spectrum the two doublets are ascribed to bulk (Δ = 0.44 mm/s) and surface (Δ = 0.82 mm/s) ferric site of the perovskite LSTFN2 lattice. The hyperfine parameters of the two other sextets can be attributed to the octahedral (δ: 0.38 mm/s and H: 50.6T) and tetrahedral (δ: 0.28 mm/s and H: 47.1T) sites of a partially inverse spinel lattice, as NiFe2O4 (Table S1). The broad linewidth of both sites (0.23 and 0.32 mm/s respectively) suggests a certain disorder around the ferric sites, as a consequence of different local environments.

Exsolution process

The parental oxide LSTFN2 underwent a reduction treatment to promote the exsolution of FeNi nanoparticles with negligible loss of SSA (Table 1). Treatments at different temperatures (T = 400 – 850 °C) were carried out with the intent to control the final composition of the exsolved phase.

From the XRD pattern of the material reduced at T = 400 °C, no metallic phases are visible. However, the darker color of the powder after reduction (Supplementary Fig. 2a) and, more significantly, the hydrogen consumption observed in the mass spectrogram acquired during the exsolution process (Supplementary Fig. 2b), proved that the reduction process took place even at such a low temperature. From Fig. 2a it is evident how the perovskite matrix retained the cubic 𝑃𝑚3̅𝑚 structure even after reduction at 850 0C. The NiFe2O4 spinel phase disappears after the reduction treatment at 650 0C. Its vanishing is most likely linked to the appearance at this temperature of two metallic phases. The reflection at 2θ = 44.8° is attributed to an α-phase, either Fe or Fe-Ni, (lattice parameter a = 2.86 Å) whereas the more prominent reflection centered at 2θ = 43.77° (see magnification in Fig. 2a) is ascribed to a bimetallic FeNi γ-phase (PDF-Ref. Nr.: 00-047-1405, space group 𝐹𝑚3̅𝑚 ). By increasing the exsolution temperature (T = 850 °C), the Bragg peak of the γ-phase increases in intensity, indicating a crystal growth up to 42 nm. The α-phase contribution in the R850 sample is almost absent, suggesting that at high temperature the alloy phase evolves to the 𝐹𝑚3̅𝑚 allotrope, which is the most thermodynamically stable phase. Interestingly, it can be noticed that the position of the (110) reflection of the perovskite parental structure shifts to lower 2θ values compared to the pristine material, thus indicating a lattice expansion, with the lattice parameter increasing from 3.910 Å to 3.923 Å (Supplementary Fig. 2c) indicative of oxygen vacancy formation during the exsolution process. Although the exsolved materials underwent significant structural modifications, their SSA remained comparable to the pristine sample (Table 1).

Further information regarding the reduction of the metallic species in the exsolved materials after the exsolution process at various temperatures is provided by XANES spectroscopy (Fig. 2b,c). Concerning the Fe spectra of R400, a slight increment of the pre-edge feature as well as a decrease of the white line intensity are observed, indicating the beginning of the reduction process. For R650 and R850 a significant change of these features is visible. The absorption edge shifts towards lower energies indicating the presence of Fe2+ and Fe0. Also, the shape of the white line along with other spectral features gradually resembles the shape of the metallic Fe0 spectrum. Interestingly, by increasing the reduction temperature up to 650 °C the white line peak (at E = 7128.6 eV) gets sharper. Using the reference spectra as a comparison (see Supplementary Fig. 3a), this effect is likely ascribed to the consumption of the NiFe2O4 side phase, in agreement with the XRD data. Beyond 650 °C also the perovskite component LaFeO3 gets massively converted both to a FeO and Fe0 phase. In the case of the Ni XANES spectrum of R400, a decrease in the white line intensity and a corresponding increase in the pre-edge feature is visible, indicating the presence of metallic Ni in the material. The spectra of the samples reduced at 650 °C and 850 °C are very similar and resemble a metallic nickel structure. This indicates two things: the first is that a great extent of Ni in the parental material has been reduced to the metallic state, and the second is that a significant amount of the Ni ions were contained in the NiFe2O4 phase.

To get better insights into the state of iron species during the exsolution process, Mössbauer spectroscopy was performed (Table 1, Fig. 2d-f, and Supplementary Table 1). The spectrum of R400 is dominated by a broad, intense, and asymmetric absorption centered around 0.28 mm/s, along with a magnetically coupled component of smaller intensity. From the four components (one singlet, one doublet, and two sextets) of the fitting, the doublet can be ascribed to distorted ferric sites in the LSTFN2 lattice, the singlet to a 15% of metallic iron (or an iron-nickel alloy) in a superparamagnetic regime (Supplementary Table. 1), confirming that even at temperatures as low as 400 °C a significant reduction of iron to the metal state takes place. The two sextets are compatible with octahedral (6CN) and tetrahedral (4CN) iron sites in the partially inverted spinel structure. This result perfectly agrees with the XRD and XANES measurements, as these ferric sites can be attributed to NiFe2O4, which is still present after the reduction at 400°C and does not vary much from the pristine state. By increasing the reduction temperature to 650 °C the metallic phase (identified by a singlet and a sextet) increased to 35% of the total amount of iron. In addition, a further contribution assigned to Fe2+ species in tetrahedral coordination is observed, thus indicating the presence of iron oxides by 5% formed during the course of the reduction process. At the last reduction stage at 850 °C the amount of metallic iron or iron alloy increased to 43% and that of Fe2+ species to 29%. The ferrous sites constitute of two different species tentatively ascribed to Fe2+ in wustite (FeO) with different defective sites.

HR-TEM investigations of the exsolved materials show that NiFe segregations are present over the parent scaffold with 20 nm diameter for R400 (Fig. 3a), confirming the Mössbauer analyses, the MS results and the reduction-related color change. It should be noted that Fe is not readily reduced at low temperatures, however, we achieve Fe exsolution likely due to the hydrogen spillover effect and nucleation role mediated by Ni. As the reduction temperature increased up to 850 °C, the exsolved NiFe alloy segregation got larger, around 150 nm in diameter with higher crystallinity (Fig. 3b). The significant difference between the nanoparticle size compared to the XRD results from the fact that EDX mapping reveals the elemental segregation, whereas XRD the average size of the crystalline domains of the alloy. To understand the microscopic structure of the exsolved NiFe species, high-resolution analysis was further conducted (Fig. 3c,d). As can be seen in the images, exsolved nanoparticles in R400 (Fig. 3d) have low crystallinity and are covered with thin amorphous shell (~ 1 nm). EDXS-line scan analysis reveals that the outmost layer is iron oxide (FeOx), and the metallic core is composed of FeNi3. Such a core-shell structure could probably be formed by direct air exposure following the exsolution process, thus indicating the formation of an amorphous oxide passivation layer. Concerning the R850 system the particle has a similar core-shell structure but the outmost layer is crystalline (Fig. 3d). EDXS-line scan analysis indicates that the crystalline outmost layer (overlayer) is again iron oxide and it is separated from the core FeNi3 alloy by a thin Ni layer. This is a general trend observed also in the other particles. In Fig. 3e, atomic resolution TEM image and electron energy loss spectroscopy (EELS) reveal that the overlayer comprises a spinel iron oxide structure (magnetite, space group: Fd-3m) presenting clear crystallographic periodicity. The spectra present a low tail height compared to the core, implying the oxidized feature. Those results are well-coincided with the prior Mossbauer and XAS analysis and likely to conclude that such a phase can readily form upon the exsolution process. The distinct difference of this iron oxide shell in R850 to the one in R400, might be related to its different origin depending on the exsolution temperature. This difference would also confirm the findings of Mössbauer spectroscopy, which indicated the formation of highly defective iron oxide phase to be increasingly formed by 650 °C. To get better insights into the formation of the exsolved core-shell structure we performed in situ TEM experiments under high-vacuum conditions to avoid the disturbing effect of the air exposure (Fig. 4a). At T = 400 °C NiFe metal nanoparticles were observed without the presence of amorphous oxide layer. Interestingly, as the temperature increased, the pseudo-crystalline overlayer started to arise on the top of the NiFe alloy with clear contrast and it eventually covered the core alloy at T = 900 °C. EDX results of the in situ TEM analyses show that the shell layer is composed of iron and oxygen only (Supplementary Fig. 4). Considering the high vacuum conditions of the measurement, it is more likely that the oxygen species are coming from the support material without the participation of gaseous species. It is not easy to provide a clear explanation for the formation of iron oxide shell due to the high activity of the material at high temperature. One possible reason could be due to the well-known strong metal support interaction (SMSI) of iron oxide. SMSI refers to a phenomenon in which the support material (typically a reducible oxide) strongly interacts with metal nanoparticles, often leading to the encapsulation of the metal surface by a thin oxide overlayer under reductive or high-temperature conditions23,24. In this system, iron exsolution occurs at low temperatures within the subsurface region (~ 10 nm) in which low-coordinated iron species bound by alpha oxygen are located (see Supplementary Fig. 5). As the temperature increases, SMSI is sequentially triggered on the exsolved particle, leading to the migration and reconstruction of bulk iron oxide species onto the particle surface. These migrating species, coordinated by more stable beta oxygen, form a passivating oxide layer over the metallic FeNi3 core.

The selective formation of a FeOx layer from the La0.4Sr0.4Ti0.6Fe0.35Ni0.05O3-δ solid solution can be rationalized by considering the Tammann temperatures for the binary oxides forming the perovskite structure - i.e., the temperature at which ions in the bulk of a solid become thermally mobile and can diffuse more readily, approximately half of the material’s absolute melting temperature. Neglecting NiO due to its low content, FeO and Fe3O4 have Tammann temperatures of roughly 560 °C and 600 °C, respectively, whereas TiO₂, SrO, and La₂O3 exhibit much higher values, exceeding 800 °C. These estimates are in excellent agreement with our experimental observations. Based on extensive ex situ characterization—including XANES, Mössbauer spectroscopy, XRD, and TEM of reduced samples at different temperatures—supplemented by in situ TEM, it is observed that the formation of the iron oxide shell is temperature-activated, initiating at approximately 600 °C. In situ TEM and Mössbauer spectroscopy further reveal that the shell’s thickness and atomic ordering increase with temperature up to 850 °C. Mössbauer data indicate that its atomic composition resembles that of wüstite, whereas TEM imaging reveals magnetite domains. As both phases coexist in the Fe-O phase diagram25, it is reasonable to assume that the shell generally consists of a defective FeOx layer with Fe(II/III) in a cubic crystal habit.

Shapeshifting exsolution

So far, we have shown that exsolved nanoparticles with two different structures/compositions can be obtained by applying a low or a high reduction temperature. Now we want to demonstrate that it is possible to switch between these two nanoparticle conformations within the same material by mediating through an oxidative step at 850 °C, in which the pristine perovskite structure is regenerated and the metal nanoparticles are dissolved in the matrix (Fig. 4c). In this fashion, shapeshifting nanoparticles using the same parental oxide structure are obtained. The regeneration of the perovskite structure performed at T = 850 °C under oxidative conditions via the redissolution of the exsolved nanoparticles, represents a fundamental step for the shapeshifting exsolution process and requires therefore particular attention.

In general, we can conclude that, because the oxidation temperature is equal to the reduction temperature for R850-O, a full reincorporation of the exsolved ions into the perovskite matrix can hardly be achieved. This can clearly be observed in the most intense XRD reflection of the spinel side phase and a residual signal of the bimetallic nanoparticles (Fig. 5a, and Supplementary Fig. 6). The extent of the reincorporation in the parental oxide matrix is also dependent on the type of the ion. From the complete superimposition of the Ni XANES spectra in Fig. 5b it is clear that Ni completely regains the chemical environment of the pristine LSTFN2 system. However, this is not the case for Fe, since it has a much larger concentration and thus it exsolves much more than nickel. Although the shape of the XANES curves at the Fe K-edge of the re-oxidized materials is the same as that of the pristine material (Fig. 5b), their intensity is significantly lower. This phenomenon can be ascribed both to the presence of metallic iron residuals, as shown in the XRD pattern of R850-O, and to a loss of symmetry in the geometric arrangement of the Fe cations as a consequence of the likely formation of disordered iron oxide species upon the reoxidation treatment. This latter hypothesis is confirmed during the Mössbauer analyses (Fig. 5d, Supplementary Fig. 7, Table 1, and Supplementary Table 1). Both R400-O and R850-O materials, in addition to the doublet signals belonging to the perovskite phase, present a sextet ascribed to ferric site in a highly defective environment and assigned to the cation deficient spinel maghemite, γ-Fe2O3, which would also explain the intensity increase of the spinel reflection in the XRD of R850-O. Hence, the reoxidation of the exsolved materials leads only to partial reincorporation of the exsolved ions into the parental oxide matrix. This is particularly true for the iron species that, due to their much lower mobility in contrast to nickel, form additional defective iron oxide phases.

The effectiveness of the shapeshifting exsolution process, i.e. the reduction of the reoxidized materials to the respective opposite original exsolution temperature (Fig. 5a) was first addressed by XRD. The pattern for R400-O-R850 is identical as the one for R850, with a pronounced signal of metallic exsolved particles ascribed to the FeNi3 phase. However, when comparing R850-O-R400 with R400 after the shapeshifting process the signal of the metallic FeNi nanoparticles is still clearly visible and is explained by the incomplete dissolution of the metallic phase in R850-O (Supplementary Fig. 6). However, this difference does not seem to affect the porosity as both shapeshifted materials possess the same SSA (Table 1). Looking at the re-reduction process of the single ions by XANES spectroscopy (Fig. 5b,c), it can be clearly seen that in both switched materials the white line and the pre-edge features of the Ni K-edge spectra strongly increased compared to the R400 and R850 systems. This indicates that Ni species underwent a stronger reduction after the shapeshifting process. However, in case of the Fe K-edge spectra, no significant difference is noticed before and after shifting. The higher metallic content (intensity increase of the pre-edge feature) observed in R850-O-R400 is a consequence of the incomplete dissolution of the metallic phase in R850-O, as showed by the XRD. This finding was further corroborated by Mössbauer spectroscopy (Fig. 5d, Supplementary Fig. 7, Table 1, and Supplementary Table 1). In the case of R850-O-R400 material, the re-exsolution at 400°C seems to promote the formation of a consistent amount of magnetically ordered phases. The presence of a narrow absorption, centered at ≈ 0.4 mm/s, is typical of ferric sites in the LSTFN2 configuration. A broad magnetic pattern with two sextet indicates the formation of a consistent amount of magnetically ordered phases close to those obtained in the R400-O material, that are related to a partially inverse spinel. In addition to that, a small amount of metallic Fe phase is observed from the fitting. Concerning the material reduced at higher temperature, i.e. R400-O-R850, the spectrum components are exactly the same as those found in R850 (Table 1), indicating the presence of an iron metallic phase (40%) along with a highly defective iron oxide (25%). The optimal congruence between the materials exsolved and switched at high temperature, was further confirmed by TEM-EDX (Fig. 5e,f). Regarding the reduction at 850 °C, micrographs of the R400-O-R850 material indicate the formation of large alloy nanoparticles surrounded by a thick crystalline FeOx shell (as in R850). Regarding the R850-O-R400 material, the nanoparticle microstructure and the elemental distribution were also found to be similar as in R400, indicating the presence of a FeNi3 core surrounded by a thin oxide shell (Supplementary Fig. 8). However, the particle size in R850-O-R400 is far larger than in R400, probably as a consequence of metallic residuals from R850-O, which might act as sites for further particle growth during the re-exsolution process.

Clear evidence of the material transformation on a single system was provided by in situ XRD experiments. We performed two sets of measurements reproducing the R850-O-R400 and the R400-O-R850 redox cycles on LSTFN2 (Supplementary Fig. 9, and 10). Experimental details are reported in the supporting information. The XRD data reveal significant structural changes during reduction at 850 °C under H2. The emergence of a new peak at Q = 3.0 Å-1, coupled with a pronounced intensity increase at Q = 3.5 and 4.9 Å-1, is attributed to the formation of the FeNi3 alloy nanoparticles. The concurrent decay of the peak at approx. 2.5 Å-1 confirms the depletion of the NiFe2O4 phase. Notably, exsolution was triggered consistently upon exposure to 850 °C in H2, independent of the sample's thermal and redox history. The reversibility of this process was confirmed by the redissolution of the nanoparticles upon removal of either the reducing atmosphere or the high temperature. As shown in Fig. 5a, the particle regeneration (shapeshifting) is almost complete for R400-O-R850 and only partial for R850-O-R400. As a consequence of the prolonged high temperature oxidation followed by the re-reduction process, a slight decrease of the surface area is observed for the shapeshifted materials (Table 1).

Catalytic experiments on exsolved materials

The exsolved perovskites at 400 and 850 °C (R400, R850) were subsequently evaluated regarding their catalytic activity and selectivity for the reaction between C2H6 and CO2. The reactant conversions for C2H6 and CO2, as well as the product selectivities for C2H4 (dehydrogenation) and CO (reforming) are presented in Fig. 6. Table 2 presents the overall reaction metrics at the end of the experiments. It is noted, that a small amount of CH4 is also produced via ethane cracking2,26,27, but its yield and selectivity values are quite small (below 1.5 %). During the first phase of temperature ramping from 400 up to 700 °C (first 3 h), the reactant conversions (C2H6 and CO2) increase steadily and then stabilize upon reaching the final temperature of 700 oC. During the second phase of time-on-stream (i.e., between the 3rd and 11th h), the rather limited change in the reactant conversion and product selectivity values is a testament to the great catalytic stability of the exsolved perovskite materials8,28–30.

The differences in the reactant conversion values between R400 and R850 are evident in Fig. 6a, b. In general, R400 can reach much higher reactant conversions compared to R850, although for CO2 conversion in particular the difference is much greater. Most importantly however, great differences are observed regarding the selectivity towards C2H4 and CO (Fig. 6c), or regarding the reaction pathways of ethane oxidative dehydrogenation (ODH) and dry ethane reforming (DER). For R400, the reforming pathway dominates, as the CO selectivity is stabilized at approx. 78% at 700 oC (Supplementary Table 2). In contrast, for R850, the dehydrogenation pathway is the dominant one, with the C2H4 selectivity stabilizing at approx. 75% at 700 oC. Therefore, it is shown that the different exsolution treatments over the same perovskite oxide material (LSTFN2) can effectively tune the reaction selectivity towards either the dehydrogenation or the reforming pathway.

The reason for this great discrepancy in product selectivity during the reaction between C2H6 and CO2 can be traced back to the physicochemical properties of these two materials, such as the oxidation state of the Fe and Ni active metals, the material nanostructure, and the exposed catalytically active surface sites. For R400, the exsolved metal nanoparticles were shown to have a composition of FeNi3 (Fig. 3c,d). The thin amorphous FeOx shell observed during HRTEM (Fig. 3e), attributed to air exposure, is most likely easily removed under the reducing reaction conditions9. As a result, it is expected that the surface-exposed FeNi3 metallic sites anchored on the redox-active and defect-rich LSTFN2 perovskite support render this material more active towards C-C bond scission and the ethane reforming pathway2,8,31,32. A possible reaction mechanism (Fig. 7) is that C2H6(g) molecules are activated on the FeNi3 metallic sites to various adsorbed intermediate species, incl. C2Hx(ads), C2HOx(ads) and CHx(ads) (the latter likely following C-C bond scission), while CO2 is activated on the support or the metal-support interface (e.g., on the surface oxygen vacancies) to generate CO(g) and adsorbed oxygen species8,27,32. The strong electrophilic oxygen species supplied by the redox-active support can then further oxidize the adsorbed carbonaceous intermediates over the metallic sites to CO, thus favoring the reforming selectivity, all the while mitigating the amount of deposited coke and promoting the catalytic stability8,17,19,31.

On the other hand, for R850, the perovskite material is decorated with larger metallic FeNi3 nanoparticles that are encapsulated by a thick crystalline FeOx overlayer. This type of metal oxide/metal (M′Ox/M) inverse interface has been previously reported to favor C-H bond scission and the ethane dehydrogenation pathway (ODH) over the reforming one (DER)14,16,18,19,33. In particular, Guo et al19. and Yan et al.14,18 prepared various Fe-Ni bimetallic catalysts over different types of supports and concluded that the presence of a high amount of FeOx (as overlayers, or in the interfacial sites) can prevent the scission of C-C bonds, while selectively splitting the C-H bonds, which is attributed to the supply of weakly electrophilic oxygen species by FeOx19. In particular, weakly electrophilic oxygen species can arise in some metal oxides (incl. FeO or Fe3O4), serving as Lewis acid sites and Lewis acid-base pairs, favoring ethane dehydrogenation to ethylene34. Furthermore, the presence of an FeOx overlayer on top of a metallic core has been identified as more active compared to bulk FeO or just FeO adjacent to the support14,16. In our case, the thick, crystalline FeOx overlayer over the metallic FeNi3 particles, which is likely formed by SMSI during exsolution, is much harder to reduce under the catalytic reaction conditions. Also, it is expected to supply these weakly electrophilic oxygen species required for the selective C-H activation (initially to C2H5(ads) and then to C2H4(ads) and C2H4(g)), all the while blocking the access of the gaseous reactants to the reduced metallic sites (metal core) that are selective for C-C bond scission14,16,19 (as also indicated by CO chemisorption). The CO2 activation could take place either on the surface of the redox-active LSTFN2 support, the metal-support interface, or also on the FeOx overlayer, and replenish the consumed active oxygen species15,18,19,22 (Fig. 7).

Additional CO chemisorption experiments were conducted to evaluate the accessibility of the FeNi3 metallic core sites to gaseous species. As depicted in Supplementary Table 1, R400 can adsorb much more CO than R850. It should be noted, that R850 may hold more exsolved nanoparticles on the surface, however, it is less to interact with CO molecules, which suggests that the thick crystalline iron oxide overlayer in R850 covers the surface FeNi3 metal core and thus stirs the reaction towards the dehydrogenation pathway.

In order to establish a comparison of the catalytic performance of R400 and R850 with other relevant materials reported in the literature, we prepared a comparison table, which can be found in the Supporting Information (Supplementary Table 3). In short, R850 compares quite favorably for the dehydrogenation reaction (ODH) even when compared to works using similar reaction temperatures (650 – 700 oC). R400 does provide a decent dry reforming reactivity, but it can be outcompeted by other reported catalysts operating at a similarly high temperature, providing that they also show high stability with minimal coke deposition. In any case however, the ability to switch the catalytic selectivity over the same multifunctional material by simply altering the exsolution treatment temperature is a unique feature of the current work.

The materials following re-oxidation and shapeshifting exsolution, i.e. R850-O-R400 and R400-O-R850 were also tested (Fig. 8, and Supplementary Table 1). To some extent, the catalytic performance is different from the R400 and R850 materials. Such a result is somehow expected, due to the different surface characteristics of the host matrix and the re-exsolved nanoparticles, i.e., their incomplete dissolution during reoxidation, thus leading to the generation of different surface-active sites following the shapeshifting process. However, it can be observed that R400-O-R850 has a rather more similar catalytic performance to R850, with only slightly lower reactant conversion and C2H4 selectivity values, since a similar thick FeOx overlayer and the inverse M′Ox/M interface are also present in this material (Fig. 5e)14,16,19. In contrast, R850-O-R400 presents significantly lower reactant conversions than R400 and lower selectivity values towards ethane reforming. This can be ascribed to the significant surface reconstruction of the material during the prior re-oxidation treatment at 850 °C (R850-O), due to the presence of residual spinel oxide and bimetallic FeNi side phases, as previously confirmed by XRD, XANES, and Mössbauer spectroscopy (Fig.5). As already mentioned, during re-reduction for R850-O-R400, these residual phases can act as sites for further particle growth, leading to significantly larger FeNi3 metal nanoparticles when compared to R400, thus restricting the population of reforming active sites (for C-C bond scission). As a result, the shapeshifting treatment (re-oxidation and re-reduction) of the LSTFN2 material can be considered viable for switching the catalytic performance from DER to ODH, but it needs to be further optimized when the ODH to DER switch is required, due to the incomplete perovskite matrix regeneration during reoxidation in the latter case. As such, the switchability of catalytic performance upon shapeshifting largely depends on the ability of the reoxidation treatment to regenerate the parental oxide structure.

To provide a comparison with a commercial reference catalyst, monometallic Ni/Al2O3 with 1 wt% Ni loading was also tested (Supplementary Fig. 11). It is shown that this commercial material is more active towards the dry ethane reforming pathway (as is expected for Ni-based catalysts)2,27. Despite the prior pretreatment step at 850oC under pure H2 flow, it still displayed a continuous increase for the C2H6 and CO2 conversion values long after reaching the final reaction temperature of 700 oC. This hints to a continuous and slow material activation over time under the reactant stream and demonstrates the rather unstable nature of the commercial reference catalyst when compared to our perovskite-based multifunctional material.

The reactant conversion and product formation rates were also calculated at the end of the stability experiments and presented in Supplementary Table 4. Regarding ethane dehydrogenation (ODH), a comparison with the literature can be made by utilizing the work of Qiang et al.35where it can be concluded that R850, with a STY for C2H4 at 692 μmol g-1 min-1 has a quite high C2H4 production rate compared to the other literature works, that is only slightly smaller to the higher value obtained in their own work at 700 oC (798 μmol g-1 min-1).

Additional experiments utilizing a 10 oC temperature step during the temperature ramping (560 – 660 oC) were carried out for the calculation of the activation energy values, and in order to compare catalyst behavior at similar (C2H6) conversion levels. The Arrhenius plots along with small insets for the reactant conversion/ product formation rates can be found in Supplementary Fig. 12, whereas the activation energy values for C2H6 and CO2 conversion, as well as for CO and C2H4 production are listed in Supplementary Table 5. These activation energy values are in agreement with those reported in other literature works8,19,21,32,36–39 In all of the materials, the CO2 activation energy values are lower than those for C2H6 activation, which can be ascribed to the concurrent side-reaction of reverse water-gas shift (RWGS)32,38. The activation energy values for CO production generally follows the trend of CO2 and C2H6 conversion, whereas for C2H4 production, the values are quite higher, even for the ODH-selective materials. By comparing the different materials, R400 has the lowest activation energy values, due to its significantly pronounced low-temperature catalytic activity. On the contrary, the activation energy values are the highest for R850, whereas the regenerated samples (R850-O-R400 and R400-O-R850) show intermediate values.

A comparison is also made between the different materials at similar C2H6 conversion levels (7-8% C2H6 conversion values, temperature range 630-660 oC, Supplementary Fig. 13). As shown in Supplementary Fig. 13, the CO2 conversion varies greatly between the materials, as do the ethane-basis selectivity values for CO (DER) and C2H4 (OSDH). In particular, R400 shows the highest DER selectivity and R850 the highest ODH selectivity, with the regenerated samples falling in between (particularly R850-O-R400). This verifies that the observed activity and selectivity differences stem from the intrinsic catalytic activity (kinetics)14.

Subsequently, in order to evaluate whether the aforementioned catalytic performance/ selectivity switch (and thus the corresponding material structural transformations) can occur in situ, a new cyclic catalytic experiment was designed which consisted of 3 catalytic cycles with intermediate in situ oxidation and reduction treatment steps. In each catalytic cycle, the same procedure of temperature ramping (400 to 700 oC) and time-on-stream (700 oC constant) was performed as in Fig. 6 (with just a reduced time-on-stream duration of 4 h). In situ oxidation was always performed at 850 oC, whereas in situ reduction was performed alternately at 850 and 400 oC in order to mimic the corresponding ex-situ treatments of the regenerated materials that were previously tested. The results are presented in Fig. 8.

From Fig. 8, it is clear that the first catalytic cycle (Cycle 1) for the R400 material proceeds similarly to the experiment in Fig. 6 (relatively high C2H6 and CO2 conversions that remain relatively stable at 700 oC). The R400 material is quite selective towards dry ethane reforming (DER), with approx. 78% CO selectivity. Following in situ oxidation and reduction at 850 oC, a dramatic shift in the catalytic performance during Cycle 2 is observed. On the one hand, lower C2H6 and CO2 conversion values are reached at 700 oC, but on the other hand, the reaction selectivity is completely switched in favor of oxidative ethane dehydrogenation (ODH), with C2H4 selectivity of approx. 74%. This catalytic behavior is quite similar to R400-O-R850 with the corresponding ex-situ oxidation/reduction treatments, but without undergoing prior catalytic operation, and even to the freshly exsolved R850 material (Fig. 8).

Afterwards, during Cycle 3, and following in situ oxidation at 850 oC and in situ reduction at 400 oC, an attempt is made to revert the catalytic activity and selectivity back to the initial one of R400 (Cycle 1). However, the C2H6 and CO2 conversion values are stabilized at lower levels than during Cycle 1 (though higher than during Cycle 2), and the selectivity is rather intermediate between DER and ODH (though slightly favoring DER), at approx. 56% CO selectivity vs 42% C2H4 selectivity (a small amount of CH4 is also produced in all cycles). This means that the catalytic performance and selectivity switch from ODH to DER is only partial. This is also reflected however in the previous catalytic performance results (Fig. 6) for R850-O-R400, since, as explained before, the initial active state of R400 cannot be completely regenerated. Therefore, although an efficient selectivity switch from DER to ODH following in situ regeneration over the same material was achieved, future research work needs to be directed on the complete structural regeneration of the initial perovskite structure, in order to achieve complete catalytic performance and selectivity switch during multi-cyclic operation.

Spent material characterization after the reaction (post-catalysis) was also carried out. It is shown that the spent perovskites display no signs of coke deposition, in contrast to spent Ni/Al2O3, where coke deposition is evident via the appearance of intense D and G bands in the Raman spectra (Supplementary Fig. 14), attributed to the turbostratic carbon40–44. TEM images of the spent perovskites also show the lack of carbon growth over these materials (Supplementary Fig. 15-18), whereas for Ni/Al2O3, the formation of typical carbon baffles is observed (Supplementary Fig. 19). XRD was also performed for the spent catalysts (Supplementary Fig. 20), although in this case, the presence of high amounts of quartz sand in the catalyst bed gave rise to intense quartz (SiO2) diffractions. The perovskite reflections can however be observed, alongside the presence of crystalline FeNi3 alloy phase (2theta = 43.7°) in the exsolved and regenerated perovskite materials. We further investigate the crystallinity of the outermost layer for the redox-treated (regenerated) spent samples (R400-O-R850 and R850-O-R400). As can be seen in the TEM images of Supplementary Fig. 21, the active species vary depending on the final reduction treatment. For R400-O-R850, the outermost layer presents crystallinity with a relatively well-resolved O K edge spectrum in EELS, while the R850-O-R400 shows an amorphous FeOx layer similar to what we’ve observed in reduced samples, and these are well coincident with our prior in situ XRD results. We would like to note that they are maintained during catalysis when compared to the corresponding fresh/ exsolved samples, as in the cases of R400 and R850, owing to the high structural stability of all perovskite-derived materials used in this study.

In the present work we showed how the shape and composition of FeNi bimetallic nanoparticles can be tailored by the exsolution approach as a function of temperature. Reduction treatments at temperature as low as 400 °C formed small bimetallic FeNi3 nanoparticles whereas treatments at higher temperature (T = 850 °C) produced core-shell system of FeOx@FeNi3. The iron oxide shell formation was explained to be originated via SMSI combined with reverse oxygen spillover from the perovskite oxide matrix. We demonstrated that we can shapeshift these nanoparticle conformations within the same host to a great extent by regenerating the perovskite oxide under oxidative conditions and re-reducing it at the opposite temperature.

The application of such exsolved nanostructures in the CO2-mediated ethane conversion indicated that the FeNi3 and FeOx@FeNi3 nanostructures, obtained via different exsolution treatments (at 400 oC and 850 oC respectively) over the same multifunctional perovskite parent material, were highly selective for the ethane dry reforming and the oxidative dehydrogenation pathway, respectively. We additionally showed that the regeneration/ shapeshifting process results in a switching of the catalytic performance/ selectivity (also in situ) to a great extent.

In this way, we demonstrate that the very same material can be used both for ethane dry reforming and ethane oxidative dehydrogenation using CO2, by simply changing the exsolution (reduction) conditions, and that even switching of catalytic performance/ selectivity can be achieved following in situ oxidation/ reduction, at least partially. However, to reach full switching of the catalytic performance during multi-cyclic operation, further work needs to be done to improve the oxidative nanoparticle dissolution and the complete regeneration of the initial perovskite host. In the era of the energy transition, these results pave the way towards the development of innovative multifunctional sustainable catalysts, which adapt to complex catalytic processes.

Methods
Chemicals

Titanium (IV) isopropoxide (97%, Alfa Aesar), strontium nitrate (99%, Acros Organics), iron (III) nitrate nonahydrate (98%, Alfa Aesar), lanthanum (III) nitrate hexahydrate (99.9%, Alfa Aesar), nickel (II) nitrate hexahydrate (97%, Sigma-Aldrich) anhydrous citric acid (99.6%, Acros Organics), glycerol (99%, Alfa Aesar) were used as received without further purification.

Material synthesis

For the purpose of this study, the system of interest is a A-site deficient, B-site doped strontium titanate based perovskite oxide, with stoichiometric formula La0.4Sr0.40Ti0.6Fe0.35Ni0.05O3±δ (hereafter abbreviated as LSTFN2), which has been designed with 20% A-site deficiency for promoting the migration of B-site Fe and Ni metal ions and therefore favor the exsolution process. The mesoporous perovskite powders have been synthesized via a template-free modified Pechini method36. In such a synthesis procedure, glycerol has been selected as polyol; this choice being related to its better chelating and crosslinking properties, when compared with conventionally used ethylene glycol37,38. In this synthesis, titanium (IV) isopropoxide (Ti(OCH(CH3)2)4) was initially combined with 11.9 ml of glycerol and stirred at room temperature for 30 min. Then, 40.7 mmol of citric acid were added, and the solution was heated to 60°C using an oil bath. After 45 min of stirring to dissolve the citric acid, stoichiometric amounts of Sr(NO3)2, La(NO3)3∙6H2O, Fe(NO3)3∙9H2O, and Ni(NO3)2∙6H2O were sequentially added at 30 min intervals. Before adding Sr(NO3)2, the salt was dissolved in the maximum amount of deionized H2O and stirred for 30 min. The molar ratio of glycerol to citric acid to the total metal cations was set at 30:4:1. Once all the metal precursors were added, the solution was further stirred for 2 h to ensure thorough mixing. Subsequently, the temperature was raised to 130 °C, and the solution was maintained at this temperature for another 2 h under continuous stirring. The combination of polyol (glycerol) and polycarboxylic acid (citric acid) resulted in the formation of a polyester gel through a polycondensation reaction. The polymer gel was then subjected to calcination at 400 °C for 2 h, followed by heating at 900 °C for another 2 h, using a temperature increase rate of 2 °C min-1. The prepared as-synthesized perovskite is named LSTFN2, with “2” representing the 20% A-site deficiency of the material.

Characterization methods

Powder X-ray diffraction was carried out for the phase analysis of the synthesized materials. This has been performed with an X’Pert Pro diffractometer from PANalytical Corp., using a 1.5406 Å Ni-filtered Cu-Kα radiation, operating at 45 kV and 40 mA. The average crystallite sizes of the different materials were calculated from the full width at half maximum of the (101) reflection by using the Scherrer equation. The X-ray absorption spectra at the Ni K edge (8333 eV) and Fe K-edge (7112 eV) were acquired at the P64 beamline at the Deutsches Elektronen Synchrotron (DESY, Hamburg, Germany). A Si(111) double crystal monochromator was employed for the energy scans around the respective metal absorption edge. The XAFS spectra were collected in fluorescence geometry for both the Ni and Fe K-edges using gas ionization chambers to measure the photon intensities before and after the samples. The powders were diluted in cellulose, pressed into pellets, and then covered in Kapton® tape before placing them in the beam path. Normalization of the obtained XANES data was carried out by performing pre-edge and post-edge background subtraction in the XANESA software. The same software has also been employed for the plotting and the comparison of the normalized data. The nitrogen physisorption isotherms were obtained at −196 °C using a Quadrasorb SI-MP Quantachrome. Outgassing was performed with a Masterprep Degasser (Quantachrome Corp.) at 120 oC for 12 h. The specific surface area of pristine and exsolved materials was determined with the Brunauer-Emmett-Teller (BET) method39 at P/Po = 0.07-0.3. CO chemisorption was conducted through pulse mode with AutoChem II (Micrometrics). Prior to the experiment, 0.1 g of sample was reduced for 3 h at either 400 or 850 oC under 10 % H2 in Ar. After the sample was cooled to 50 oC, a 10% CO in He pulse was injected, and the amount of consumed CO was calculated. The composition of the bimetallic nanoparticles was investigated with a Corrected scanning High-Resolution Transmission Electron Microscope (Cs-TEM) measurements at KARA (KAIST Analysis center for Research Advancement). These included photographs of the samples through HR-TEM and the EDX (Energy-Dispersive X-Ray) microscopy. (FEI Tecnai Titan cube G2 60-300) The acceleration voltage was fixed at 300 keV. For the in situ experiment, powder samples are dispersed on the silicon nitride grid (Nanofactory, MEMS microheater), and further loaded in heating holder (FEI Nano-Ex). During the experiment, vacuum level was maintained under 9 x 10-8 mbar. Electron energy loss spectroscopy (EELS) were collected for R850 sample with a dispersion of 0.25 eV per channel for L edge of Fe (700 ~ 725 eV), Ni (850 ~ 880 eV) and K edge for O (532 eV). Room temperature Mössbauer spectroscopy was performed on a conventional constant acceleration spectrometer mounting a Rh matrix 57Co source, nominal strength 1850 MBq. The hyperfine parameters were obtained by means of standard least-squares minimization techniques. The Mössbauer parameter δ is quoted relative to α-Fe foil. In situ synchrotron XRD were performed at the P08 beamline at PETRA III, DESY, with a photon energy of 25 keV and a beam size of 100 μm x 400 μm. The LSTFN2 powder was filled in a quartz capillary with 2mm diameter, open at both ends. To prevent sample movement during gas flow, the powder was confined by quartz wool plugs on either side. One end of the capillary was connected to a gas-mixing system that regulated the type and flow rate of the gas, while the outlet was connected to a mass spectrometer to verify the gas flow and monitor the reaction products. The detailed procedure of the in situ experiments is reported in the supporting information. The exsolution of the materials consisted in a treatment at high temperature of the catalyst powders under reducing conditions. A U-shaped quartz tube was first filled with 0.1 g of powder, and a heating ramp of 10 oC min-1 was set while flushing Ar in the system, allowing for an inert atmosphere during the heating section. The temperature of the system was measured through a Pt-100 thermocouple mounted within the exsolution cell, for real time monitoring of the local temperature of the powder. Finally, once reaching the target temperature, the quartz tube was then subjected to a flowrate of 20 ml min-1 of 5% H2 in N2 for 3 h, providing the reducing conditions necessary for the nanoparticle formation. In a similar way, the re-oxidation treatments for the partial reincorporation of the Fe and Ni species in the parent perovskite structure were performed in the same experimental apparatus of the exsolution treatments. The quartz U-tube was filled with the exsolved (black) powder and subjected to a flowrate of 20 ml min-1 of air at 850 oC, which was flushed in the system for 5 h. The outlet composition of the exiting gas was monitored through a mass spectrometer. The exsolved materials were named “RT”, with T indicating the temperature of the treatment. The materials have been first exsolved at three reference temperatures: one lower (400°C, sample name “R400”), one intermediate (650°C, sample name “R650”) and one higher temperature (850°C, sample name “R850”). Each material was exsolved for 3 h by subjecting it to a flow of 20 ml min-1 of formation gas (5% H2 in N2). After the first exsolution treatment, the R400 and R850 materials were partially regenerated by re-oxidation at high temperature (850 °C) for 5 h under air. This has been carried out to induce the re-incorporation of the metallic species back into their lattice positions within the parent perovskite oxide. The samples thus obtained were referred to as “R850-O” and “R400-O”, for the materials initially exsolved at 850°C and 400 °C and then re-oxidized, respectively. Finally, the regenerated samples have been once again reduced at correspondent opposite temperature. That means, the “R400-O” was then re-exsolved (re-reduced) at 850°C (sample name: “R400-O-R850”), and the “R850-O” has then been re-exsolved at 400 °C (sample name: “R850-O-R400”). Raman spectra for the spent catalysts were recorded on a Bruker Senterra Raman microscope (λ = 532 nm, P = 20 mW). Measurements were acquired performing 16 scans with an integration time of 16s each, within the range 50-2740 cm-1.

Catalytic testing

Catalytic testing of the exsolved and regenerated perovskite materials (R400, R850, R850-O-R400 and R400-O-R850) was performed in a quartz glass tubular reactor (9 mm I.D.) at atmospheric pressure. Initially, 0.1 g of exsolved LSTFN2 perovskite oxide material were mixed with 0.5 g of quartz sand and loaded in the reactor. The total flow rate was set at 40 ml min-1 (10 ml min-1 C2H6, 10 ml min-1 CO2 and 20 ml min-1 Ar), with the C2H6:CO2 molar ratio being kept at 1:1. The initial reaction temperature was 400 oC, following a prior brief purge with Ar. The reaction procedure was carried out in two phases. During the first phase (activity testing), after passing the reaction mixture through the reactor at 400 oC, the reaction temperature was slowly increased with a rate of 100 oC per h (50 oC for every 30 min), up to 700 oC. During the second phase (time-on-stream), after the reactor temperature reached 700 oC (3 h), the temperature was kept constant at 700 oC for another 8 h. The testing of the 1% Ni/Al2O3 reference catalyst included a prior in situ reduction step under pure H2 flow at 850 oC for 1 h. A cyclic experiment (starting from R400) with intermediate in situ oxidation and reduction treatments was also carried out in the same reactor setup. The same catalyst weight, reactant flows, and temperature ramping procedure as above were used, but the time-on-stream duration was reduced to 4 h. Following each catalytic cycle, oxidation (Ox) was carried out in situ by increasing the temperature to 850 oC under Ar and then flowing 20% O2 in Ar for 5 h. In situ reduction was then carried out (following a brief Ar purge) by flowing 5% H2 in Ar for 3 h, either at 850 oC (before Cycle 2) or at 400 oC (before Cycle 3). Heating up and cooling down were always carried out under Ar flow. In order to calculate the activation energy values and compare the catalytic performance at similar (C2H6) conversion levels, additional temperature step experiments were conducted utilizing a temperature step of 10 oC in the 560 – 660 oC range, keeping the same catalyst weight and reactant flows as before. The gaseous reaction products were analyzed on-line via an Agilent-7890A gas chromatograph, as described in our previous work8. The ethane and carbon dioxide conversions, the hydrogen, carbon monoxide, ethylene, and methane yields, as well as the selectivities (ethane-basis) for ethylene (dehydrogenation), methane (cracking) and carbon monoxide (reforming), together with the H2/CO molar ratio were determined by using the following equations (Eqs. 1-10)8:

X_C2H6 = (F_C2H6,in - F_C2H6,out) / F_C2H6,in * 100 (1)

X_CO2 = (F_CO2,in - F_CO2,out) / F_CO2,in * 100 (2)

Y_H2 = F_H2,out / (3 * F_C2H6,in) * 100 (3)

Y_CO = F_CO,out / (2 * F_C2H6,in + F_CO2,in) * 100 (4)

Y_C2H4 = F_C2H4,out / F_C2H6,in * 100 (5)

Y_CH4 = F_CH4,out / (2 * F_C2H6,in) * 100 (6)

S_C2H4 = Y_C2H4 / X_C2H6 * 100 (7)

S_CH4 = Y_CH4 / X_C2H6 * 100 (8)

S_CO = 100 - S_CH4 - S_C2H4 (9)

H2/CO = F_H2,out / F_CO,out (10)

Data availability

Data are available from the corresponding authors upon request.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Herein a reversible transformation between Fe₃Ni alloy nanoparticles and Fe₃Ni@FeOx core–shell structures was cleverly\ndesigned for the CO2-mediated ethane conversion. The results are interesting, and the characterization of the structure is\nadequate. This is of great significance for the promotion and application of smart catalysts based on perovskite structure.\nHowever, as the structural evolution of perovskite-based materials in reducing and oxidizing atmospheres has been\nreported, so the author should provide advanced insights in evolution of material\nstructure and the effect of exsolution process on catalytic performances. There are two key issues: (1) The reason for the formation of shells on the alloy surface\nhas not been explained clearly? The author only briefly discussed without providing sufficient experimental evidence; (2)\nThere is a difference in activity between the two catalysts, and no further experimental evidence has been provided, mainly\nrelying on the relationship between the structure and activity proposed in the reported literatures. Therefore, I recommend\nthat this paper should be resubmitted after revision. The other comments are as follows:\n1. The formation of a quite porous morphology is detected by transmission electron microscopy analysis. This is not enough,\nand the pore structure should be evaluated by nitrogen adsorption-desorption.\n2. The bar of TEM and EELS spectroscopy in Figure 3 is not clear. Please modify.\n3. The images of Figure 3C should be rotated to Intuitively display the thickness of thin amorphous shell.\n4. The description of Figure 3e is absent. Please add the information.\n5. In situ TEM experiments were performed under high-vacuum conditions to avoid the disturbing effect of the air exposure\n(Figure 4). In other word, H2 was absent, so that what’s the role of H2 atmosphere during the exsolution process?\n6. It was stated that EDXS results of the in situ TEM analyses show that the shell layer is composed of iron and oxygen only\n(Figure S4). Figure S4 should be corrected to Figure S3. Please check it. On the other hand, Accord to the EDXS results, the\nconclusion that iron and oxygen are enriched on the surface of particles is very inconclusive. Please provide more favorable\nEDXS evidence.\n7. Two Figure 4 are in present manuscript. The numbering of the image is incorrect.\n8. The author concluded that exsolved nanoparticles in R400 (Figure 3d) are covered with thin amorphous shell (~ 1 nm) of\niron oxide (FeOx). However, in Figure 4c, the shell was absent in the picture of the shapeshifting mechanism. Why?\n9. What’s the ideal product and reaction routine for CO2-mediated ethane conversion? The activity of the R400 and R850\ncatalysts should be compared with the literature results, to highlight the novelty of exsolution process for designing\nmultifunctional catalyst materials.", "reviewer_2": "The authors investigate dynamic redox behavior in layered double hydroxide (LDH)-derived NiFe catalysts for ethylene and\nCO₂ hydrogenation, focusing on the interplay between structural evolution and catalytic performance. Through a\ncombination of operando XAS, in situ STEM, and transient measurements, they propose that redox cycles during activation\nand reaction influence selectivity and conversion.\nThe topic aligns well with the scope of Nature Communications. However, the core claims remain unconvincing due to\noversimplification in the interpretation of catalytic performance. While the work touches on important themes in catalyst\nrestructuring and redox chemistry, the manuscript does not provide a comprehensive discussion of prior studies in LDH-\nderived systems or other dynamic metal-oxide catalysts in CO₂/ethylene hydrogenation. Several relevant works are\noverlooked, which limits the ability to understand the novelty and implications of the current findings. A stronger foundation\nin the literature would help frame the study’s contributions and gaps more clearly.\nThe reaction evaluation, which should form the basis for understanding structure–function relationships, is underdeveloped.\nThe authors primarily link catalytic behavior to exposure and conversion rather than through mechanistic insights. The\ntreatment of selectivity is superficial, lacking a detailed breakdown of product distribution or reaction pathways. Without a\nthorough kinetic or mechanistic discussion, the proposed correlation between structural states and catalytic performance\nlacks depth and robustness. Key reaction parameters such as activation energy, turnover frequency, and product-specific\nrates are absent, further limiting interpretability.\nThe dynamic nature of the reaction conditions, particularly the linear temperature ramp toward steady state, presents an\nopportunity for extracting mechanistic insights. The manuscript does not fully exploit this aspect. Comparing catalyst\nbehavior at equivalent conversion levels during the transient phase could reveal whether the observed performance\ndifferences stem from intrinsic activity or changes in redox state. Such analysis is absent, leaving ambiguity about whether\nthe differences between catalysts are kinetic, structural, or purely linked to the accessible number of sites.\nThe RX-O-RY sample, which appears to have undergone a reduction-oxidation-reduction treatment, is not described clearly.\nIt is implied that this sequence mimics potential in situ redox cycles during catalytic operation. However, the paper does not\nexplore whether these transformations can occur under actual reaction conditions, such as in the presence of ethylene or\nCO₂. The lack of post-reaction characterization or detailed in situ monitoring under working conditions makes it difficult to\nestablish whether the proposed redox cycling mechanism is relevant during catalysis. The stability and reversibility of the\ntransformations under reaction conditions are not adequately supported.\nFurthermore, the literature context is insufficiently developed. The title and abstract are very vague.", "reviewer_3": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature\nCommunications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career\nResearchers who co-review manuscripts."}, "author_response": "Ref: NCOMMS-25-47822\nTitle: Shapeshifting bimetallic nanoparticles with switching catalytic performance\nJournal: Nature Communications\nResponses to the Reviewer’s Comments\nAll authors are pleased to submit the revised version of our manuscript. We appreciate the\nreviewers for their careful consideration of our manuscript and favorable view of the\nsignificance of our findings. We endeavored carefully to address all of the constructive\ncomments and suggestions by the reviewers, all of which have been very useful to improve\nthe clarity of the manuscript.\nOur responses to the reviewers’ comments are given below. Also attached are the revised\nmanuscript and supplementary information, where revised parts are highlighted in red font.\nReviewer #1\nHerein a reversible transformation between Fe₃Ni alloy nanoparticles and Fe₃Ni@FeOx core–\nshell structures was cleverly designed for the CO -mediated ethane conversion. The results are\ninteresting, and the characterization of the structure is adequate. This is of great significance\nfor the promotion and application of smart catalysts based on perovskite structure. However,\nas the structural evolution of perovskite-based materials in reducing and oxidizing atmospheres\nhas been reported, so the author should provide advanced insights in evolution of material\nstructure and the effect of exsolution process on catalytic performances. There are two key\nissues: (1) The reason for the formation of shells on the alloy surface has not been explained\nclearly? The author only briefly discussed without providing sufficient experimental evidence;\n(2) There is a difference in activity between the two catalysts, and no further experimental\nevidence has been provided, mainly relying on the relationship between the structure and\nactivity proposed in the reported literatures. Therefore, I recommend that this paper should be\nresubmitted after revision. The other comments are as follows:\nWe appreciate reviewer #1 for acknowledging the academic significance and technical\nimpact of our research.\nThank you very much for bringing issue (1) to our attention. We acknowledge that presenting\ntwo different formation processes for the FeOₓ shell could be misleading to readers if not\nsupported by precise experimental evidence. A comprehensive understanding of the oxide\nshell formation would require multiple, complex in situ experiments (e.g., XPS, DRIFTS),\nwhich are beyond the scope of the present study. To simplify the discussion, we therefore\nfocus on the strong metal-support interaction (SMSI) mechanism, which is considerably\nbetter studied than the reverse oxygen spillover effect.\nIn this way, the selective formation of a FeO layer from the La Sr Ti Fe Ni O\nx 0.4 0.4 0.6 0.35 0.05 3-δ\nsolid solution can be rationalized by considering the Tammann temperatures for the binary\noxides forming the perovskite structure - i.e., the temperature at which ions in the bulk of a\nsolid become thermally mobile and can diffuse more readily, approximately half of the\nmaterial’s absolute melting temperature. Neglecting NiO due to its low content, FeO and\nFe O have Tammann temperatures of roughly 560 °C and 600 °C, respectively, whereas\n3 4\nTiO₂, SrO, and La₂O exhibit much higher values, exceeding 800 °C. These estimates are in\n3\nexcellent agreement with our experimental observations. Based on extensive ex situ\ncharacterization—including XANES, Mössbauer spectroscopy, XRD, and TEM of reduced\nsamples at different temperatures—supplemented by in situ TEM, it is observed that the\nformation of the iron oxide shell is temperature-activated, initiating at approximately\n600 °C. In situ TEM and Mössbauer spectroscopy further reveal that the shell’s thickness\nand atomic ordering increase with temperature up to 850 °C. Mössbauer data indicate that\nits atomic composition resembles that of wüstite, whereas TEM imaging reveals magnetite\ndomains. As both phases coexist in the Fe/O phase diagram [1], it is reasonable to assume\nthat the shell generally consists of a defective FeO layer with Fe(II/III) in a cubic crystal\nx\nhabit.\nThis new discussion has been added at page 8 of the manuscript.\nRegarding issue (2), we kindly note that we have proceeded to greatly expand the catalytic\nevaluation part and the corresponding discussion. New catalytic experiments have been\nperformed, additional key performance metrics (i.e., reaction rates, activation energy values\netc.) have been calculated, comparison of catalytic performance at similar C H conversion\n2 6\nlevels has been made, and also a multi-cyclic catalytic experiment incorporating in-situ\nregeneration (oxidation/ reduction) treatments has been performed. Moreover, additional\npost-reaction characterization on the spent materials has been carried out as follow: (1) the\ndiscussion on the potential reaction mechanism has been revised/ improved, based on the\nrelevant recent literature. Figure 7 has also been revised accordingly. (2) a relevant\ndiscussion has been included based on the new temperature step experiments with 10 ℃\ntemperature step (see also Supplementary Fig. 11, 12, and Supplementary Table 3 and 4).\nIn short, based on these new experiments, the activation energy values (for C H and CO\n2 6 2\nconversion, as well as for CO and C H production) were calculated and the results were\n2 4\ndiscussed. Moreover, a comparison of the intrinsic catalytic activity is made at similar C H\n2 6\nconversion levels for the four different materials. (3) a relevant discussion has been included\nbased on a new multi-cyclic catalytic experiment with intermediate in-situ regeneration\n(oxidation/ reduction) treatments (Figure 9). It is shown, that the regeneration treatments\n(previously done ex-situ) can also proceed in-situ during catalytic operation. In short,\nfollowing oxidation and reduction at 850 ℃, the catalytic performance and reaction\nselectivity can be almost entirely switched from reforming to dehydrogenation with great\nsuccess. During subsequent oxidation at 850 ℃ and reduction at 400 ℃, the catalytic\nperformance and selectivity switch was partial (similar performance also observed for\nR850-O-R400 in Figure 7). As such future work needs directed in the complete perovskite\nnanostructure regeneration and thus to full selectivity switching under multi-cyclic\noperation. For these changes, please refer to the aforementioned parts of the revised\nmanuscript and revised supplementary information.\nReferences\n[1]: Darken, L.S.; Gurry, R.W. “The system Iron-Oxygen:1.The Wüstite field and related\neuilibria J. Am. Chem. Soc. 1945, 67, 8, 1398–1412\nComment 1 of Reviewer 1: The formation of a quite porous morphology is detected by\ntransmission electron microscopy analysis. This is not enough, and the pore structure should\nbe evaluated by nitrogen adsorption-desorption.\nWe thank the reviewer for this valuable suggestion. In response, we further characterized\nthe materials by N₂ physisorption measurements. For all samples, the collected adsorption–\ndesorption isotherms correspond to Type II behavior, which is characteristic of\nmacroporous or non-porous materials (see Figure R1). As these isotherms do not exhibit a\nhysteresis loop, the mesopore size distribution cannot be reliably determined; therefore, the\nonly meaningful parameter that can be extracted is the specific surface area, calculated\nusing the BET model.\nFigure R1. Nitrogen physisorption isotherms of the pristine and exsolved materials\nAnalysis of the BET surface areas (see Table R1) shows that, after the first exsolution\ntreatment, only a non-significant decrease in specific surface area is observed. More\nimportantly, despite the different exsolution conditions and the substantial structural\nmodifications induced by exsolution, the overall porosity of the materials remains largely\nunaffected. A noticeable decrease in specific surface area is observed only for the\nshapeshifted materials, which can be attributed to the prolonged high-temperature oxidation\nfollowed by the re-reduction process.\nTable R1: BET specific surface area values of the pristine and exsolved materials\nSample BET specific surface area [m2g-1]\nLSTFN2 (pristine) 15\nR400 13\nR850 14\nR850OR400 10\nR400OR850 10\nWe added the discussion of the SSA at page 2 and 4 for the pristine, exsolved and at\nshapeshifted materials. The BET values have been added in Table 1 and the physisorp\ntion isotherms integrated in Supplementary Fig. 1\nComment 2 of Reviewer 1: The bar of TEM and EELS spectroscopy in Figure 3 is not clear.\nPlease modify. The images of Figure 3C should be rotated to intuitively display the thickness\nof thin amorphous shell. The description of Figure 3e is absent. Please add the information.\nWe thank for the reviewer’s comment. To clearly suggest the scale of each TEM images and\nthe thickness of shell layer, we revise the Figure 3 as below. We also added description for\nEELS data for R850 sample, as well. The revised version is presented in page 5 of\nmanuscript.\nFigure R2. HADDF-STEM image and respective iron (red) and nickel (yellow) EDX\nmapping result of the R400 (a), and R850 (b) materials; High-resolution images and EDX\nmapping result with line-scan signal (scan direction and shell thickness are denoted in the\nfigure) of R400 (c) and R850 (d) materials; (e) Atomic resolution STEM and EELS result of\nR850, indicating the different composition of the core and the shell portions in the exsolved\nnanoparticles.\nComment 3 of Reviewer 1: In situ TEM experiments were performed under high-vacuum\nconditions to avoid the disturbing effect of the air exposure (Figure 4). In other word, H2 was\nabsent, so that what’s the role of H2 atmosphere during the exsolution process?\nWe sincerely appreciate the reviewer’s valuable comment. Exsolution, a spontaneous phase\nseparation process in a multicomponent solid solution, based on the differences in reduction\ntendency of each ionic element. Once the oxygen chemical potential gradient is formed\nacross the solid-gas interface, it drives flux of point defect within the solid matrix to\nequilibrate the potential that accompanies oxygen vacancy and metal precipitate [2]. Such\nreaction can be expressed as below:\n𝑚 𝑚 𝑚\nM× + 𝑂× = 𝑉𝑚′ + 𝑉∙∙ +𝑀 + O\nM 2 𝑂 𝑀 2 O 𝑚𝑒𝑡𝑎𝑙,𝑠𝑢𝑟𝑓 4 2,(g)\nFrom a view of defect chemistry, exsolution involves the release of oxygen ions as a gas,\nleaving a positive oxygen vacancy and reduced metal cations in a form of metallic state.\nThese reduction processes occur when ∆G for a total reaction is negative, suggesting that\nhydrogen is not an essential factor to trigger exsolution. However, hydrogen can be the\nsimplest agent to create differences in oxygen chemical potential at relatively mild\nconditions. Table R2 summarizes ∆G for the reduction process of various binary metal\noxides. Once the hydrogen is introduced in the reduction process, it significantly lowers the\nvalue, thereby turns the equilibrium towards forward direction. Thus, hydrogen can shift the\noverall reaction forward, thereby accelerating the exsolution process. In our in-situ\nexperiment, the vacuum level reaches near 10-9 mbar, which is far lower than the typical\natmosphere (pO = 210 mbar). Also, there is a minute amount of hydrogen that inevitably\n2\ncomes from the metal parts of the TEM apparatus and the vacuum facility as well [3]. In\nsum, we would like to say that hydrogen stimulates the exsolution process, and our in situ\ncondition is far enough to trigger the initial growth behavior of exsolution as like reported\nin earlier literatures [4].\nTable R2. Comparison of ∆G for various binary metal oxide at 900 ℃ condition. ∆G\nred red\nrepresent Gibbs free energy changes for reduction process. We assume two reaction\nequation; 2MO = 2M + O , MO + H = M + H O for w/o H and w/ H , respectively.\n2(g) 2 2 (g), 2 2\nElement ∆G w/o H (kJ/mol) ∆G w/ H (kJ/mol)\nred 2 red 2\nNiO 267.2 -49.5\nCoO 289.1 -31.6\nMnO 596.9 115.3\nFeO 375.3 4.5\nPdO -17.5 -191.9\nReferences\n[2] S. Yanagisawa et al., J. Phys. Chem. C, 2013, 117 (3), 1278-1286.\n[3] N. Miyauchi et al., J. Vac. Sci. Technol., 2024, 42 (1), 013201.\n[4] D. Neagu et al., ACS Nano, 2019, 13 (11), 12996-13005.\nComment 4 of Reviewer 1: It was stated that EDXS results of the in situ TEM analyses show\nthat the shell layer is composed of iron and oxygen only (Figure S4). Figure S4 should be\ncorrected to Figure S3. Please check it. On the other hand, accord to the EDXS results, the\nconclusion that iron and oxygen are enriched on the surface of particles is very inconclusive.\nPlease provide more favorable EDXS evidence.\nWe thank the reviewer for the comment on the EDX data. We corrected the number of\nsupplementary figures. Regards to the EDX result during in situ TEM analysis, there are still\nundeveloped technical issues in acquiring X-ray signals at such high temperature (900 ℃).\nWe eliminate the drifts by using a piezoelectric stage and Velox software; however, incident\nelectrons and emitted X-ray scatters by intense infrared which increase the noise level. Even\nwith the integrated wide-angle detector in the Ultra-X EDX system (Thermo Fischer\nScientific), it is a challenge to eliminate the noise level during the high-temperature EDX\nanalysis. Thus, we conducted an extra EDX experiment and collected additional data on it\n(Figure R3). Also, we've measured the d-spacing of the shell layer (~ 1.7 Å), which implies\nthe shell is likely to be Fe O , not a metallic species. We henceforth revise the\n3 4\nSupplementary Fig. 4.\nFigure R3. In situ HADDF-EDX mapping of the LSTFN2 material at 900 ℃.\nComment 5 of Reviewer 1: Two Figure 4 are in present manuscript. The numbering of the\nimage is incorrect.\nWe thank for the reviewer’s kind attention to details. We hence revise the number of Figure\nin the manuscript.\nComment 6 of Reviewer 1: The author concluded that exsolved nanoparticles in R400 (Figure\n3d) are covered with thin amorphous shell (~ 1 nm) of iron oxide (FeOx). However, in Figure\n4c, the shell was absent in the picture of the shapeshifting mechanism. Why?\nWe appreciate the reviewer’s comment. Figure 4c still presents FeO outmost shell, which\nx\nis formed by the air exposure prior to the TEM analysis. However, the displayed images do\nnot clearly reveal the amorphous layer due to the contrast in the image. Thereafter, we’ve\nconducted overlay image mapping process and line profile including HADDF intensity to\nfigure out the presence of FeO shell for ROR400 sample (Figure R4). As can be seen in the\nx\nelement distribution along the line scan area, there are distinct FeO -domains (~ 1 nm of\nx\nthickness) which underpin the shell structure for ROR400. We’ve added it as Supplementary\nFig. 8 to prevent misleading the readers. Please refer to the figures as below:\nFigure R4. HADDF-STEM EDX analysis result for ROR400 and corresponding line profile\nof each element across the boundary area of the core-shell structure. The colored area\nrepresents the amorphous FeO shell domains, surrounding the alloy core.\nx\nComment 7 of Reviewer 1: What’s the ideal product and reaction routine for CO2-mediated\nethane conversion? The activity of the R400 and R850 catalysts should be compared with the\nliterature results, to highlight the novelty of exsolution process for designing multifunctional\ncatalyst materials.\nWe thank the Reviewer for his/her valuable comment. The reaction between ethane and CO\n2\ncan mainly lead to two different pathways, the CO -assisted oxidative dehydrogenation of\n2\nethane (1), and the dry reforming of ethane (2):\nC H + CO → C H + CO + H O (ODH) (1)\n2 6 2 2 4 2\nC H + 2CO → 4CO + 3H (DER) (2)\n2 6 2 2\nAmong them, the first reaction (1) – ODH, is undoubtedly more desired, since the produced\nC H is a more valuable product than H /CO (syngas). This reaction also proposes a\n2 4 2\npotential alternative to the current industrial production of ethylene (C H ) via steam\n2 4\ncracking. In the case of reaction (1), CO is used as a reactant (specifically as a soft oxidant),\n2\nand the reaction can also be operated at a lower temperature than steam cracking or the\nnon-oxidative dehydrogenation, which can significantly reduce the carbon footprint of\nethylene production, given the rapidly growing ethylene market [5].\nReaction (2) – DER, is less desired than ODH, but it can still be valuable, considering that\nunderutilized ethylene (e.g., from shale gas) reacts with captured CO in order to produce\n2\nvaluable synthesis gas (H and CO mixture), which can be used in subsequent Fischer-\nconditions (roughly 100 ℃ lower temperature) compared to the typical reaction of dry\nreforming of methane [6].\nReferences\n[5] A.N. Biswas, et al., Joule, 2022, 6(2), 269–273.\n[6] T. Zhang, et al., Engineering, 2022, 18, 173–185.\nUntil now, many different catalyst materials have been prepared in order to achieve high\ncatalytic activity, selectivity, and stability, but only for their respective targeted reaction (i.e.,\nCO -assisted dehydrogenation of ethane OR dry ethane reforming). Therefore, the novelty\n2\nof the current work does not specifically lie in overcoming these reaction metrics compared\nto other reported catalysts, but rather in demonstrating the potential to switch the reaction\nselectivity (between reactions (1) and (2)) by simply changing the exsolution treatment\nconditions on a single multifunctional perovskite catalyst material and also via potential\nregeneration treatments during multi-cyclic operation. As such, the different material\nstructures reported in this work are derived from a single perovskite material (with\nLa Sr Ti Fe Ni O formula) by just changing the exsolution conditions\n0.4 0.40 0.6 0.35 0.05 3±δ\n(specifically temperature), which subsequently leads to a different surface chemistry/\npresence of different surface-active sites, and thus different reaction selectivity. This is the\nfirst time that this has been reported for this particular reaction, as other works typically\nrely on changing the material composition in order to achieve variable reaction selectivity\n(e.g., via the variation of the Fe:Ni molar ratio). The fact that the catalytic performance/\nselectivity is (at least partially) switchable following re-oxidation and re-exsolution on the\nsame material composition is an added advantage to this approach, but further future work\nneeds to directed toward complete perovskite nanostructure regeneration and thus full\nselectivity switching under multi-cyclic operation.\nSubsequently, as per the Reviewer’s suggestion, we proceeded to provide a comparison Table\nin the supplementary information (Supplementary Table 2), where the catalytic performance\nof R400 and R850 (different exsolution treatment) is compared to other catalytic materials\nreported in the literature, for the respective reactions (CO -assisted oxidative ethane\n2\ndehydrogenation and dry ethane reforming). It is noted that the majority of the relevant\nliterature works perform this reaction at a lower temperature (600 ℃). Nevertheless, R850\ndoes compare quite favorably for the dehydrogenation reaction (ODH) even when compared\nto works using similar reaction temperature (650 – 700 ℃). R400 provides a decent dry\nreforming reactivity, but it can be outcompeted by other catalysts in the literature operating\nat a similarly high temperature, providing that they also show high stability with minimal\ncoke deposition. In any case, the ability to switch the catalytic selectivity on the same\nmaterial by simply altering the exsolution treatment is a unique advantage of the current\nwork, and this in turn highlights the novelty of the exsolution process for designing\nmultifunctional catalyst materials. The comparison Table is also presented below for\nconvenience:\nTable R3. Catalytic performance comparison between R400, R850, and other reported\ncatalysts in the literature for the respective reactions of CO -assisted oxidative\n2\ndehydrogenation of ethane (ODH) and dry ethane reforming (DER).\n1) CO -assited oxidative dehydrogenation of ethane (ODH)\nCatalyst Reaction conditions Ref.\nPerformance\nWHSV = 24000 ml\nR850\ng -1 h-1\nX 𝐶2𝐻6 = 22.1%\n(La Sr Ti Fe Ni O cat X = 30.2% This work\n0.4 0.40 0.6 0.35 0.05 3±δ C H :CO = 1:1 CO2\n2 6 2\nwith exsolution at 850 ℃) 𝑆 = 75.2%\nT = 700 ℃ (8 h) 𝐶2𝐻4\nNi Fe /CeO WHSV = 24000 ml X = 3.5% [7]\n1 3 2 𝐶2𝐻6\ng -1 h-1 X = 5.9%\ncat CO2\nC 2 H 6 :CO 2 = 1:1 𝑆 = 77.5%\n𝐶2𝐻4\nT = 600 ℃ (11-13 h)\nWHSV = 24000 ml\nX = 6.6%\ng -1 h-1\n𝐶2𝐻6\n1.0% PdFe (1:9)/ CeO cat X = 8.3% [8]\n2 6 2\n𝑆 = 85.8%\nT = 600 ℃ (11-12 h) 𝐶2𝐻4\nWHSV = 24000 ml\nX = 4.6%\nNiFe/CeO -C1 g -1 h-1\n𝐶2𝐻6\n2 cat X = 6.2% [9]\n(Ni:Fe = 1:4) C H :CO = 1:1 CO2\n2 6 2\n𝑆 = 83%\nT = 600 ℃ (12 h) 𝐶2𝐻4\nWHSV = 9000 ml\nX = 23.4%\nFe Ni /ZrO -M\ng cat -1 h-1 X 𝐶2𝐻6 = 23.4%\n1.5 0.5 2 C H :CO = 1:1 X = 28.0% [10]\n(ZrO monoclinic) 2 6 2 CO2\n𝐶2𝐻4\nmin)\nWHSV = 6000 ml\nX = 32.3%\ng -1 h-1\n𝐶2𝐻6\nTi Ce O cat X = 34.6% [11]\n0.5 0.5 2 C H :CO = 1:1 CO2\n2 6 2\n𝑆 = 54.2%\nT = 700 ℃ (8 h) 𝐶2𝐻4\nWHSV = 7500 ml\nX = 23%\nFe/NiO-MgO-ZrO g -1 h-1\n𝐶2𝐻6\n2 cat X = 25% [12]\n(5Fe/10NiMgZr, Fe-700 (5h)) C H :CO = 1:1 CO2\n2 6 2\n𝑆 = 90%\nT = 650 ℃ (6.5 h) 𝐶2𝐻4\nWHSV = 6000 ml\nX = 21%\nFe/MgAl O g -1 h-1\n𝐶2𝐻6\n2 4 cat X = 20% [13]\n(Fe/3Mg7Al) C H :CO = 1:1 CO2\n2 6 2\n𝑆 = 84%\nT = 650 ℃ (60 min) 𝐶2𝐻4\nWHSV = 9000 ml\nX = 20%\ng -1 h-1\n𝐶2𝐻6\nFe Ni /CeO cat X = 16% [14]\n1.5 0.5 2 C H :CO = 1:1 CO2\n2 6 2\n𝑆 = 65%\nT = 700 ℃ (2 h) 𝐶2𝐻4\nWHSV = 9000 ml\nX = 10.6%\nFe Ni /CeTi-C-2 g -1 h-1\n𝐶2𝐻6\n1.5 0.5 cat X = 16.3% [15]\n(2% Ti substitution) C H :CO = 1:1 CO2\n2 6 2\n𝑆 = 82.7%\nT = 650 ℃ (1 h) 𝐶2𝐻4\nWHSV = 9000 ml\nX = 25.1%\ng -1 h-1\n𝐶2𝐻6\nMgFeAlO cat X = 22.1% [16]\n2 6 2\n𝑆 = 92.8%\nT = 600 ℃ (8 h) 𝐶2𝐻4\n2) Dry ethane reforming (DER)\nCatalytic\nCatalyst Reaction conditions Ref.\nPerformance\nWHSV = 24000 ml\nR400 X = 32.6%\ng -1 h-1 𝐶2𝐻6\ncat\n(La Sr Ti Fe Ni O X = 67.6% This work\n0.4 0.40 0.6 0.35 0.05 3±δ C\n6\n:CO\n2\n= 1:1 CO2\nwith exsolution at 400 ℃) 𝑆 = 78.3%\nT = 700 ℃ (8 h) 𝐶𝑂\nNi Fe /CeO WHSV = 24000 ml X = 16.7% [7]\n3 1 2 𝐶2𝐻6\ng -1 h-1 X = 41.3%\ncat CO2\nC 2 H 6 :CO 2 = 1:1 𝑆 = 98.6%\n𝐶𝑂\nT = 600 ℃ (11-13 h)\nWHSV = 9000 ml\nX = 63.9%\ng -1 h-1 𝐶2𝐻6\ncat\nNi Ce O X = 88.1% [11]\n0.05 0.975 2 C\n6\n:CO\n2\n= 1:1 CO2\n𝑆 = 94.3%\nT = 700 ℃ (2 h) 𝐶𝑂\nWHSV = 24000 ml\ng -1 h-1 X = 21.4%\ncat 𝐶2𝐻6\nLaFe Ni O C H :CO = 1:1 X = 49.7% [17]\n0.9 0.1 3 2 6 2 CO2\nT = 600 ℃ (12-14 𝑆 = 97.5%\n𝐶𝑂\nh)\nWHSV = 24000 ml\nX = 22.8%\ng -1 h-1 𝐶2𝐻6\ncat\nPtNi/CeO (Pt:Ni = 1:3) X = 53.4% [18]\n6\n:CO\n2\n= 1:1 CO2\n𝑆 = 92.8%\nT = 600 ℃ (12 h) 𝐶𝑂\nWHSV = 60000 ml\nX = 96%\ng -1 h-1 𝐶2𝐻6\ncat\nNi/MgAl O X = 91% [19]\n2 4 C\n6\n:CO\n2\n= 1:2 CO2\n𝑆 = 93%\nT = 800 ℃ (18 h) 𝐶𝑂\nWHSV = 15000 ml\nX = 83%\ng -1 h-1 𝐶2𝐻6\ncat\nCaZr Ni O X = 82% [20]\n0.8 0.2 3-δ C\n6\n:CO\n2\n= 1:2 CO2\n𝑆 = 93%\nT = 700 ℃ (8 h) 𝐶𝑂\nWHSV = 24000 ml\nX = 11.7%\ng -1 h-1 𝐶2𝐻6\ncat\nFeNi/Ce-Al (Fe:Ni = 3:1) X = 33.1% [21]\n0.5 C\n6\n:CO\n2\n= 1:1 CO2\n𝑆 = 97.7%\nT = 600 ℃ (8 h) 𝐶𝑂\nWHSV = 60000 ml\nX = 31.5%\ng -1 h-1 𝐶2𝐻6\ncat\nNdFe Ni O X = 42.4% [22]\n0.7 0.3 3 C\n6\n:CO\n2\n= 1:2 CO2\n𝑆 = 97.8%\nT = 600 ℃ (8-10 h) 𝐶𝑂\nWHSV = 36000 ml\nX = 96%\ng -1 h-1 𝐶2𝐻6\ncat\nNi-2.4La@Si X = 86% [23]\nC\n6\n:CO\n2\n= 1:2 CO2\n𝑆 = 87%\nT = 700 ℃ (200 h) 𝐶𝑂\nWHSV = 24000 ml\nX = 70%\ng -1 h-1 𝐶2𝐻6\ncat\nNi-Si@Ce X = 71% [24]\nC\n6\n:CO\n2\n= 1:2 CO2\n𝑆 = 97%\nT = 650 ℃ (10 h) 𝐶𝑂\nReferences\n[7] B. Yan, et al., Proc. Natl. Acad. Sci., 2018, 115(12), 2902-2907.\n[8] Z. Xie, et al., Chem, 2020, 6(10), 2703–2716.\n[9] M. Guo, et al., ChemCatChem, 2021, 13(13), 3119-3131.\n[10] X. Li, et al., Fuel, 2022, 322, 124122.\n[11] L. Li, et al., Appl. Catal. A: Gen., 2022, 635, 118565.\n[12] M. Tasioula, et al., ACS Catal., 2023, 13(4), 2176–2189.\n[13] Y. Zheng, et al., ACS Catal., 2023, 14(7), 11153−11163.\n[14] X. Li, et al., Int. J. Hydrogen Energy., 2024, 79, 45–59.\n[15] X. Li, et al., Chem. Eng. J., 2024, 484, 149047.\n[16] Q. Du, et al., Carbon Capture Sci. Technol., 2025, 14, 100327.\n[17] B. Zhao, et al., J. Catal., 2018, 358, 168–178.\n[18] Z. Xie, et al., Appl. Catal. B: Environ., 2019, 245, 376–388.\n[19] K. H. Kim, et al., J. CO2 Util., 2021, 53, 101713.\n[20] A. I. Tsiotsias, et al., J. CO2 Util., 2022, 61, 102046.\n[21] T. Zhang, et al., Engineering., 2022, 18, 173–185.\n[22] Y. Wang, et al., Appl. Catal. B: Environ., 2023, 337, 123010.\n[23] C. Wang, et al., Chem. Eng. J., 2024, 491, 152091.\n[24] X. Chen, et al., Int. J. Hydrogen Energy., 2025, 103, 501–512.\nPlease note, that relevant changes have been made in the revised manuscript, and\nsupplementary information file with red font.\nReviewer #2\nThe authors investigate dynamic redox behavior in layered double hydroxide (LDH)-derived\nNiFe catalysts for ethylene and CO₂ hydrogenation, focusing on the interplay between\nstructural evolution and catalytic performance. Through a combination of operando XAS, in\nsitu STEM, and transient measurements, they propose that redox cycles during activation and\nreaction influence selectivity and conversion. The topic aligns well with the scope of Nature\nCommunications. However, the core claims remain unconvincing due to oversimplification in\nthe interpretation of catalytic performance. While the work touches on important themes in\ncatalyst restructuring and redox chemistry, the manuscript does not provide a comprehensive\ndiscussion of prior studies in LDH-derived systems or other dynamic metal-oxide catalysts in\nCO₂/ethylene hydrogenation. Several relevant works are overlooked, which limits the ability\nto understand the novelty and implications of the current findings. A stronger foundation in the\nliterature would help frame the study’s contributions and gaps more clearly.\nWe thank the Reviewer for his/her valuable comment. We kindly note, that the materials\nused in this work are perovskite-derived, not LDH-based materials. They consist of a\nperovskite backbone structure with supported exsolved bimetallic Fe-Ni nanostructures,\nthat differ based on the exsolution treatment conditions and the regeneration treatments.\nFurthermore, the catalytic testing that we performed utilized ethane and CO as co-\n2\nreactants. The two main reactions occurring are CO -assisted oxidative dehydrogenation of\n2\nethane (reaction (1)), and dry ethane reforming (reaction (2)), which are shown below:\nC H + CO → C H + CO + H O (ODH) (1)\n2 6 2 2 4 2\nC H + 2CO → 4CO + 3H (DER) (2)\n2 6 2 2\nIn any case, in agreement with the Reviewer’s suggestion, we proceeded to expand the\ndiscussion on relevant literature works, as a means to establish a stronger foundation with\nthe relevant literature and highlight the novelty and contributions of the current study (Table\nR1).\nTable R1. Catalytic performance comparison between R400, R850, and other reported\ncatalysts in the literature for the respective reactions of CO -assisted oxidative\n2\ndehydrogenation of ethane (ODH) and dry ethane reforming (DER).\n1) CO -assited oxidative dehydrogenation of ethane (ODH)\nCatalyst Reaction conditions Ref.\nPerformance\nWHSV = 24000 ml\nR850\ng -1 h-1\nX 𝐶2𝐻6 = 22.1%\n(La Sr Ti Fe Ni O cat X = 30.2% This work\n0.4 0.40 0.6 0.35 0.05 3±δ C H :CO = 1:1 CO2\n2 6 2\nwith exsolution at 850 ℃) 𝑆 = 75.2%\nT = 700 ℃ (8 h) 𝐶2𝐻4\nWHSV = 24000 ml\nX = 3.5%\ng -1 h-1\n𝐶2𝐻6\nNi Fe /CeO cat X = 5.9% [1]\n1 3 2 C H :CO = 1:1 CO2\n2 6 2\n𝑆 = 77.5%\nT = 600 ℃ (11-13 h) 𝐶2𝐻4\nWHSV = 24000 ml\nX = 6.6%\ng -1 h-1\n𝐶2𝐻6\n1.0% PdFe (1:9)/ CeO cat X = 8.3% [2]\n2 6 2\n𝑆 = 85.8%\nT = 600 ℃ (11-12 h) 𝐶2𝐻4\nWHSV = 24000 ml\nX = 4.6%\nNiFe/CeO -C1 g -1 h-1\n𝐶2𝐻6\n2 cat X = 6.2% [3]\n(Ni:Fe = 1:4) C H :CO = 1:1 CO2\n2 6 2\n𝑆 = 83%\nT = 600 ℃ (12 h) 𝐶2𝐻4\nWHSV = 9000 ml\nX = 23.4%\nFe Ni /ZrO -M\ng cat -1 h-1 X 𝐶2𝐻6 = 23.4%\n1.5 0.5 2 C H :CO = 1:1 X = 28.0% [4]\n(ZrO monoclinic) 2 6 2 CO2\n𝐶2𝐻4\nmin)\nWHSV = 6000 ml\nX = 32.3%\ng -1 h-1\n𝐶2𝐻6\nTi Ce O cat X = 34.6% [5]\n0.5 0.5 2 C H :CO = 1:1 CO2\n2 6 2\n𝑆 = 54.2%\nT = 700 ℃ (8 h) 𝐶2𝐻4\nWHSV = 7500 ml\nX = 23%\nFe/NiO-MgO-ZrO g -1 h-1\n𝐶2𝐻6\n2 cat X = 25% [6]\n(5Fe/10NiMgZr, Fe-700 (5h)) C H :CO = 1:1 CO2\n2 6 2\n𝑆 = 90%\nT = 650 ℃ (6.5 h) 𝐶2𝐻4\nWHSV = 6000 ml\nX = 21%\nFe/MgAl O g -1 h-1\n𝐶2𝐻6\n2 4 cat X = 20% [6]\n(Fe/3Mg7Al) C H :CO = 1:1 CO2\n2 6 2\n𝑆 = 84%\nT = 650 ℃ (60 min) 𝐶2𝐻4\nWHSV = 9000 ml\nX = 20%\ng -1 h-1\n𝐶2𝐻6\nFe Ni /CeO cat X = 16% [7]\n1.5 0.5 2 C H :CO = 1:1 CO2\n2 6 2\n𝑆 = 65%\nT = 700 ℃ (2 h) 𝐶2𝐻4\nFe Ni /CeTi-C-2\nWHSV = 9000 ml X 𝐶2𝐻6 = 10.6%\n1.5 0.5 g -1 h-1 X = 16.3% [8]\n(2% Ti substitution) cat CO2\nC 2 H 6 :CO 2 = 1:1 𝑆 𝐶2𝐻4 = 82.7%\nT = 650 ℃ (1 h)\nWHSV = 9000 ml\nX = 25.1%\ng -1 h-1\n𝐶2𝐻6\nMgFeAlO cat X = 22.1% [9]\n2 6 2\n𝑆 = 92.8%\nT = 600 ℃ (8 h) 𝐶2𝐻4\n2) Dry ethane reforming (DER)\nCatalytic\nCatalyst Reaction conditions Ref.\nPerformance\nWHSV = 24000 ml\nR400 X = 32.6%\ng -1 h-1 𝐶2𝐻6\ncat\n(La Sr Ti Fe Ni O X = 67.6% This work\n0.4 0.40 0.6 0.35 0.05 3±δ C\n6\n:CO\n2\n= 1:1 CO2\nwith exsolution at 400 ℃) 𝑆 = 78.3%\nT = 700 ℃ (8 h) 𝐶𝑂\nWHSV = 9000 ml\nX = 63.9%\ng -1 h-1 𝐶2𝐻6\ncat\nNi Ce O X = 88.1% [5]\n0.05 0.975 2 C\n6\n:CO\n2\n= 1:1 CO2\n𝑆 = 94.3%\nT = 700 ℃ (2 h) 𝐶𝑂\nWHSV = 24000 ml\nX = 16.7%\ng -1 h-1 𝐶2𝐻6\ncat\nNi Fe /CeO X = 41.3% [10]\n3 1 2 C\n6\n:CO\n2\n= 1:1 CO2\n𝑆 = 98.6%\nT = 600 ℃ (11-13 h) 𝐶𝑂\nWHSV = 24000 ml\ng -1 h-1 X = 21.4%\ncat 𝐶2𝐻6\nLaFe Ni O C H :CO = 1:1 X = 49.7% [11]\n0.9 0.1 3 2 6 2 CO2\nT = 600 ℃ (12-14 𝑆 = 97.5%\n𝐶𝑂\nh)\nWHSV = 24000 ml\nX = 22.8%\ng -1 h-1 𝐶2𝐻6\ncat\nPtNi/CeO (Pt:Ni = 1:3) X = 53.4% [12]\n6\n:CO\n2\n= 1:1 CO2\n𝑆 = 92.8%\nT = 600 ℃ (12 h) 𝐶𝑂\nWHSV = 60000 ml\nX = 96%\ng -1 h-1 𝐶2𝐻6\ncat\nNi/MgAl O X = 91% [13]\n2 4 C\n6\n:CO\n2\n= 1:2 CO2\n𝑆 = 93%\nT = 800 ℃ (18 h) 𝐶𝑂\nWHSV = 15000 ml\nX = 83%\ng -1 h-1 𝐶2𝐻6\ncat\nCaZr Ni O X = 82% [14]\n0.8 0.2 3-δ C\n6\n:CO\n2\n= 1:2 CO2\n𝑆 = 93%\nT = 700 ℃ (8 h) 𝐶𝑂\nWHSV = 24000 ml\nX = 11.7%\ng -1 h-1 𝐶2𝐻6\ncat\nFeNi/Ce-Al (Fe:Ni = 3:1) X = 33.1% [15]\n0.5 C\n6\n:CO\n2\n= 1:1 CO2\n𝑆 = 97.7%\nT = 600 ℃ (8 h) 𝐶𝑂\nWHSV = 60000 ml\nX = 31.5%\ng -1 h-1 𝐶2𝐻6\ncat\nNdFe Ni O X = 42.4% [16]\n0.7 0.3 3 C\n6\n:CO\n2\n= 1:2 CO2\n𝑆 = 97.8%\nT = 600 ℃ (8-10 h) 𝐶𝑂\nWHSV = 36000 ml\nX = 96%\nNi-2.4La@Si g -1 h-1 𝐶2𝐻6 [17]\ncat\nX = 86%\nC\n6\n:CO\n2\n= 1:2 CO2\nT = 700 ℃ (200 h) 𝑆 = 87%\n𝐶𝑂\nWHSV = 24000 ml\nX = 70%\ng -1 h-1 𝐶2𝐻6\ncat\nNi-Si@Ce X = 71% [18]\nC\n6\n:CO\n2\n= 1:2 CO2\n𝑆 = 97%\nT = 650 ℃ (10 h) 𝐶𝑂\nIn the introduction section, a relevant discussion on the two reactions occurring and the\nmost prominent relevant literature works has been provided. “A common application for this\nvariation … favoring C-H bond scission and ethane dehydrogenation.” (page 2-3). In the\ncatalytic experiments section, the discussion on relevant literature works has also been\nimproved, and a comparison Table has also been included in the Supplementary Table 2,\nwhere the catalytic performance of R400 and R850 catalysts (prepared from the same\nmaterial via different exsolution treatment) is compared to other catalytic materials reported\nin the literature, for the respective reactions (CO -assisted oxidative ethane\n2\ndehydrogenation and dry ethane reforming). As such, corresponded discussion part is added\nin the main text (page 12)\nPlease note, that relevant changes have been made in the revised manuscript, and\nsupplementary information file with red font.\nReferences:\n[1] B. Yan, et al., Proc. Natl. Acad. Sci., 2018, 115(12), 2902-2907.\n[2] Z. Xie, et al., Chem, 2020, 6(10), 2703–2716.\n[3] M. Guo, et al., ChemCatChem, 2021, 13(13), 3119-3131.\n[4] X. Li, et al., Fuel, 2022, 322, 124122.\n[5] L. Li, et al., Appl. Catal. A: Gen., 2022, 635, 118565.\n[6] M. Tasioula, et al., ACS Catal., 2023, 13(4), 2176–2189.\n[7] Y. Zheng, et al., ACS Catal., 2023, 14(7), 11153−11163.\n[8] X. Li, et al., Int. J. Hydrogen Energy., 2024, 79, 45–59.\n[9] X. Li, et al., Chem. Eng. J., 2024, 484, 149047.\n[10] Q. Du, et al., Carbon Capture Sci. Technol., 2025, 14, 100327.\n[11] B. Zhao, et al., J. Catal., 2018, 358, 168–178.\n[12] Z. Xie, et al., Appl. Catal. B: Environ., 2019, 245, 376–388.\n[13] K. H. Kim, et al., J. CO2 Util., 2021, 53, 101713.\n[14] A. I. Tsiotsias, et al., J. CO2 Util., 2022, 61, 102046.\n[15] T. Zhang, et al., Engineering., 2022, 18, 173–185.\n[16] Y. Wang, et al., Appl. Catal. B: Environ., 2023, 337, 123010.\n[17] C. Wang, et al., Chem. Eng. J., 2024, 491, 152091.\n[18] X. Chen, et al., Int. J. Hydrogen Energy., 2025, 103, 501–512.\nComment 1 of Reviewer 2: The reaction evaluation, which should form the basis for\nunderstanding structure–function relationships, is underdeveloped. The authors primarily link\ncatalytic behavior to exposure and conversion rather than through mechanistic insights. The\ntreatment of selectivity is superficial, lacking a detailed breakdown of product distribution or\nreaction pathways. Without a thorough kinetic or mechanistic discussion, the proposed\ncorrelation between structural states and catalytic performance lacks depth and robustness. Key\nreaction parameters such as activation energy, turnover frequency, and product-specific rates\nare absent, further limiting interpretability. The dynamic nature of the reaction conditions,\nparticularly the linear temperature ramp toward steady state, presents an opportunity for\nextracting mechanistic insights. The manuscript does not fully exploit this aspect. Comparing\ncatalyst behavior at equivalent conversion levels during the transient phase could reveal\nwhether the observed performance differences stem from intrinsic activity or changes in redox\nstate. Such analysis is absent, leaving ambiguity about whether the differences between\ncatalysts are kinetic, structural, or purely linked to the accessible number of sites.\nWe thank the Reviewer for his/her valuable comment. In agreement with the Reviewer’s\nsuggestions, we proceeded to make several significant changes, conducted additional\ncatalytic experiments, and greatly expanded the discussion regarding the catalytic\nevaluation section of our Manuscript. The relevant changes made are the following:\nFirst of all, we proceeded to calculate the reactant conversion rates and the product\nformation rates/ space time yields (STY) based on the values at the end of the catalytic tests\nin Figure 6. These have been included in a new Table presented in the Supporting\nInformation (Table R2). Regarding ethane dehydrogenation (ODH), a comparison with the\nliterature can be made by utilizing the work of Qiang et al. [19], where it can be concluded\nthat R850, with a STY for C H at 692 μmol g -1 min-1 has a quite high C H production\n2 4 cat 2 4\ncompared to the other literature works, that is only slightly smaller to the higher value\nobtained in their own work at 700 ℃ (798 μmol g -1 min-1).\ncat\nTable R2. Reactant conversion and product formation rates following 11 hours of reaction,\ni.e., 3 h of temperature ramping (400 to 700 ℃) and 8 h of time on stream (700 ℃ constant).\nReactant conversion rate (μmol Product formation rate/\ng -1 min-1) Space time yield (STY) (μmol g -1\ncat cat\nMaterial\nmin-1)\nC H CO C H CO H\n2 6 2 2 4 2\nR400 1357 2817 283 3650 2163\nR850 921 1260 692 1513 750\nR850-O- 995 1545 963\n463 1738\nR400\nR400-O- 870 1200 713\n579 1375\nR850\nRegarding the reaction mechanisms for ODH and DER, we kindly note that there are quite\nmany already published works in the literature that have studied the reaction mechanism\nand the reaction intermediates for similar materials (Fe-Ni based) in detail using several\ntechniques (incl. in-situ DRIFTS, pulse experiments, and DFT calculations). A quite\ninformative and representative reaction scheme has been presented in the work of Xie et al.\n[20]:\nFigure R1. Schematic illustration of potential reaction pathways for the reaction of CO\n2\nand C H [20].\n2 6\nIn short, CO is commonly reported to be activated to CO and reactive oxygen species (O*)\n2\non the support, the metal-support interface, or also on the FeO overlayer, and then O*\nx\nspecies are utilized for the ethane activation part. For ODH (or ODHE), ethane is activated\nto C H , then to C H (both indicated as C H in Figure 8), which eventually desorbs\n2 5(ads) 2 4(ads) 2 x\nto C H , i.e., the C-C bond is preserved, and only C-H bonds are cleaved. For DER (or\n2 4(g)\nDRE), potential adsorbed intermediate species include C H , C H O , and CH ,\n2 x(ads) 2 x (ads) x(ads)\nwhich, following various oxidation steps, are eventually oxidized to CO .\n(g)\nWe kindly note that we have provided a rather lengthy discussion in the Manuscript\nregarding the possible reaction mechanisms during ODH and DER based on prior literature\nworks, as well as a relevant Figure (Figure 8). We also note that we proceeded to perform\nsome important revisions in the relevant discussion part, and on Figure 9. The current\nmanuscript focuses heavily on the catalyst characterization part, the material structural\ntransformations occurring during different exsolution/ oxidation/ regeneration treatments,\nand how these can lead to selectivity switching between ODH and DER over a single\nmultifunctional perovskite material. Therefore, we kindly note, that an additional detailed\nmechanistic or kinetic investigation (via e.g., in-situ DRIFTS, DFT analysis, dedicated\nkinetic experiments etc.), such as those presented in many prior works (please refer to the\nreferences cited in the Manuscript during the relevant discussion) would deviate from the\nmain scope of the current work.\nHowever, in agreement with the Reviewer’s suggestion, we did proceed to conduct additional\nexperiments regarding the calculation of key reaction parameters, such as the activation\nenergy values, and to compare catalyst behavior at (almost) equivalent conversion levels.\nSince the obtained data points during the transient phase of the experiments in Figure 6 were\nnot enough to calculate these parameters we proceeded to conduct additional dedicated\nexperiments with more data points during the temperature ramp (10 ℃ step in the 560 –\n660 ℃ range), in order to be able to more accurately calculate the reaction rates at lower\nconversions, the activation energy values, and to better compare the catalytic activity and\nselectivity at almost equivalent C H conversions. The results are now presented as\n2 6\nSupplementary Fig. 11, 12, and Supplementary Table 3 and 4.\nFigure R2. displays the Arrhenius plots along with small insets for the reactant conversion/\nproduct-specific formation rates. Table R3 lists the activation energy values for C H and\n2 6\nCO conversion, as well as CO and C H production, obtained from the Arrhenius plots.\n2 2 4\nThese activation energy values are in agreement with those reported in other literature works\n[21-28]. In all of the materials, the CO activation energy values are lower than those for\n2 6\nshift (RWGS) [21,24]. The activation energy for CO production generally follows the trend\nof CO and C H conversion, whereas for C H production, the values are quite higher, even\n2 2 6 2 4\nfor the dehydrogenation-selective materials. By comparing the different materials, R400 has\nthe lowest activation energy values, due to its significantly pronounced low-temperature\ncatalytic activity (as also shown in Figure 7). On the contrary, the activation energy values\nare the highest for R850, whereas the regenerated samples (R850-O-R400 and R400-O-\nR850) show intermediate values. Please note, that we did not proceed to calculate the\nturnover frequency (TOF) values due to the following reasons: i) The catalyst structure is\nhighly complicated with different metallic and oxidic phases, meaning that there are also\nlikely different active sites for C H and CO activation, ii) there is a high degree of\n2 6 2\nuncertainty on the precise amount of Ni and Fe residing on the surface compared to the\namount in the bulk, and iii) probing the active sites with typical gas chemisorption (e.g., CO)\ndoes not take into account the sites in the FeO overlayer, which are active for\nx\ndehydrogenation (ODH).\nFigure R2. Arrhenius plots for the calculation of the apparent activation energies: Natural\nlogarithm of the consumption rates of C H (a) and CO (b), and the production rates of CO\n2 6 2\n(c) and C H (d) versus reciprocal temperature. The corresponding rates versus temperature\n2 4\nplots are presented as insets.\nTable R3. Activation energy values for C H and CO conversion, as well as CO and C H\n2 6 2 2 4\nproduction, calculated via the Arrhenius plots.\nMaterial E (C H ) E (CO ) E (CO) E (C H )\na 2 6 a 2 a a 2 4\nR400 104 84 88 143\nR850 151 138 110 158\nR850-O-R400 129 101 94 153\nR400-O-R850 144 119 97 152\nAdditionally, in agreement with the Reviewer’s suggestion, a comparison is made between\nthe different materials at almost equivalent C H conversion levels (7-8% C H conversion\n2 6 2 6\nvalues, Figure R3) based on these new catalytic experiments (necessary to achieve similar\nC H conversion values for all 4 materials at slightly different temperature). As shown in\n2 6\nFigure S10, the CO conversion varies greatly within the materials, as do the ethane-basis\n2\nselectivity values for CO (reforming, DER) and C H (dehydrogenation, ODH). In particular,\n2 4\nR400 still shows the highest DER selectivity and R850 the highest ODH selectivity, with the\nregenerated materials falling in between (particularly R850-O-R400, due to the incomplete\nregeneration of the initial perovskite structure during re-oxidation). This verifies that the\nobserved catalytic performance (activity and selectivity) differences over the 4 different\nmaterials obtained from the same parent perovskite, LSTFN, stem from the intrinsic catalytic\nactivity (kinetics) [29]. A similar comparison at comparable C H conversion levels,\n2 6\nshowing opposing selectivity values for CO (reforming) and C H (dehydrogenation) is also\n2 4\nreported in Ref. [29] from the Chen group. In their case, these opposing selectivity values\nare achieved via preparing two different materials with different Ni:Fe ratios over a CeO\n2\nsupport. As such, a relevant discussion on the reaction mechanism has been provided in the\nmain text (page 12-14)\nFigure R3. Comparison of C H and CO conversions (a), as well as C H and CO\n2 6 2 2 4\nselectivities (b) at similar C H conversion levels (7-8%).\n2 6\nPlease note, that relevant changes have been made in the revised manuscript, and\nsupplementary information file with red font.\nReferences:\n[19] W. Qiang, et al., Chinese J. Catal., 2025, 70, 272–284.\n[20] Z. Xie, et al., Matter, 2021, 4(2), 408–440.\n[21] Z. Xie, et al., Appl. Catal. B: Environ., 2019, 245, 376–388.\n[22] Y. Wang, et al., Appl. Catal. B: Environ., 2023, 337, 123010.\n[23] C. Wang, et al., Chem. Eng. J., 2024, 491, 152091.\n[24] X. Chen, et al., Int. J. Hydrogen Energy, 2025, 103, 501–512.\n[25] A. I. Tsiotsias, et al., ACS Nano, 2022, 16(6), 8904–8916.\n[26] F. Cancino-Trejo, et al., Chem. Eng. J. Adv., 2022, 12, 100404.\n[27] M. Guo, et al., ChemCatChem, 2021, 13(13), 3119–3131.\n[28] X. Li, et al., Int. J. Hydrogen Energy, 2024, 79, 45–59.\n[29] B. Yan, et al., Proc. Natl. Acad. Sci., 2018, 115(33), 8278–8283.\nComment 3 of Reviewer 2: The RX-O-RY sample, which appears to have undergone a\nreduction-oxidation-reduction treatment, is not described clearly. It is implied that this\nsequence mimics potential in situ redox cycles during catalytic operation. However, the paper\ndoes not explore whether these transformations can occur under actual reaction conditions,\nsuch as in the presence of ethylene or CO₂. The lack of post-reaction characterization or\ndetailed in situ monitoring under working conditions makes it difficult to establish whether the\nproposed redox cycling mechanism is relevant during catalysis. The stability and reversibility\nof the transformations under reaction conditions are not adequately supported.\nWe thank the Reviewer for his/her valuable comment. In agreement with the Reviewer’s\nsuggestion, we proceeded to perform in situ XRD characterization following oxidation and\nreduction (exsolution) treatments, additional catalytic experiments (temperature ramp +\ntime-on-stream) with in-situ intermediate oxidation and reduction (exsolution) treatments,\nAtomic resolution-TEM analysis as well as a deeper post-reaction characterization on the\nspent catalyst materials.\nTo ease the reviewer’s concerns on the actual surface transformation occurring on one single\nsystem we applied for beamtime at the synchrotron facility DESY, Hamburg and successfully\nperformed in situ XRD during reduction and oxidation cycles on the LSTFN2 material at the\nP08 beamline. We kindly ask to consider that due to safety restriction of the synchrotron\nfacility, it was not possible to carry out in situ catalysis experiments.\nWe performed two set of measurements mimicking the redox cycles of R400-O-R850 and\nR850-O-R400 on LSTFN2 (Figure R4). The exsolution and redissolution procedures of\nLSTFN2 powder sample were tracked following two protocols: 1) (Figure R5a) The sample\nwas heated to 850 °C under synthetic air (10 mL min-1) with a heating rate of 10 °C min-1.\nOnce the temperature was reached, the atmosphere was switched to 4% H in N . The gas\n2 2\nflow was initially 10 mL min-1 for ~20 minutes and then increased to 20 mL min-1 for a 3-\nhour reduction period. The gas was then switched back to synthetic air (20 mL min-1) for a\n5-hour of re-oxidation at 850 °C. Finally, the sample was cooled to 400 °C at 10 °C min-1 in\nair and subjected to a second reduction in 4% H₂ in N₂ (20 mL min-1) for 3 hours before\ncooling to room temperature. 2) (Figure R5b) The sample was heated to 400 °C in synthetic\nair (20 mL min-1) with 10 °C min-1. At 400 °C, the gas was switched to 4% H₂ in N₂ (20 mL\nmin-1) for a 3-hour reduction. The atmosphere was then switched back to air (20 mL min-1),\nand the temperature was raised to 850 °C for a 5-hour re-oxidation. Finally, while\nmaintaining 850 °C, the gas was switched to 4% H₂ in N₂ (20 mL min-1) for an additional 3-\nhour reduction.\nThe obtained results are in full agreement with the ex situ characterization shown in the\nmanuscript. The XRD data in Figures R5 reveal significant structural changes during\nreduction at 850 °C under H . The emergence of a new peak at Q = 3.0 Å⁻¹, coupled with a\n2\npronounced intensity increase at Q = 3.5 and 4.9 Å⁻¹, is attributed to the formation of\nFe Ni alloy nanoparticles. The concurrent decay of the peak at ~2.5 Å⁻¹ confirms the\n0.64 0.36\ndepletion of the NiFe O phase. Notably, exsolution was triggered consistently upon\n2 4\nexposure to 850 °C in H , independent of the sample's thermal and redox history. The\n2\nreversibility of this process was confirmed by the redissolution of the nanoparticles upon\nremoval of either the reducing atmosphere or the high temperature, indicating a reversible\ntransformation between a metallic Fe Ni alloy and a reincorporated oxide phase.\n0.64 0.36\nFigure R4. Picture of the high-temperature in situ cell (left) and gas profile of the mass\nspectrometer during the R400-O-R850 redox cycle (right). The purple curve indicates the\nconcentration of N , the light green indicates H and the dark green curve indicates the signal\n2 2\nof O\n2\n.\nFigure R5. In situ XRD patterns during the R850-O-R400 (a) and the R400-O-R850 (b)\nredox cycles of LSTN2 along with the respective XRD curves at each redox stage. The flow\nrate of air and H in N is shown in orange and blue, respectively. The temperature profile is\n2 2\nmarked in black.\nTo further evaluate whether the catalytic performance/ selectivity switch (and thus the\ncorresponding material structural transformations) can occur in-situ, i.e., in the catalytic\nevaluation setup, a new, cyclic, catalytic experiment was designed, which consisted of 3\ncatalytic cycles with intermediate in-situ oxidation and reduction treatment steps. As\ndescribed in the experimental section (page 17 of main text), we started with the R400\nmaterial (previously exsolved at 400 ℃) and performed the same procedure of temperature\nramping (400 to 700 ℃) and time-on-stream at 700 ℃, as in Figure R6 (albeit with a\nreduced time-on-stream duration of 4 h); this step being denoted as Cycle 1. Afterwards, in-\nsitu oxidation in the catalytic reactor setup was performed at 850 ℃ by flowing 20% O in\n2\nand reduction treatments performed ex-situ for R400-O-R850. The material was then\nevaluated again via the same catalytic procedure (Cycle 2), followed again by in-situ\noxidation (850 ℃) and reduction (400 ℃), in order to attempt a reversal to the catalytic\nperformance of R400, and another catalytic cycle followed (Cycle 3). The results are\npresented in Figure 9 in the Revised Manuscript.\nFigure R6. Trend over time for the (a) C H and CO conversions, as well as (b) C H and\n2 6 2 2 4\nCO selectivities during the catalytic testing for 3 cycles (temperature ramping from 400 to\n700 ℃ and time-on-stream at 700 ℃ constant) with intermediate in-situ oxidation and\nreduction steps at either 850 or 400 ℃.\nBased on Figure R6, it is clear that the first catalytic cycle (Cycle 1) for the R400 material\nproceeds similarly to the experiment in Figure 6, namely leading to relatively high C H and\n2 6\nCO conversions, which increase with temperature and remain relatively stable at 700 ℃\n2\nwith a small degree of deactivation. The R400 material is quite selective towards dry ethane\nreforming (DER), with approx. 78% CO selectivity. Following in-situ oxidation and\nreduction at 850 ℃, a dramatic shift in catalytic performance during Cycle 2 is observed.\nOn the one hand, lower C H and CO conversion values are reached at 700 ℃, which\n2 6 2\nhowever remain quite stable, but on the other hand, the reaction selectivity is completely\nswitched in favor of oxidative ethane dehydrogenation (ODH), with C H selectivity of\n2 4\napprox. 75%. This catalytic behavior is quite similar to R400-O-R850, with the\ncorresponding ex-situ oxidation/ reduction treatments, but without undergoing prior\ncatalytic operation, and even to the freshly exsolved R850 material (Figure 7 of main text).\nAfterwards, during Cycle 3, and following in-situ oxidation at 850 ℃ and in-situ reduction\nat 400 ℃, an attempt is made to revert the catalytic activity and selectivity back to the initial\none of R400 (Cycle 1). However, the C H and CO conversion values are stabilized at lower\n2 6 2\nlevels than during Cycle 1 (though higher than during Cycle 2), and the selectivity is rather\nintermediate between dry reforming and dehydrogenation (though slightly favouring dry\nreforming), at approx. 56% CO selectivity vs 42% C H selectivity (a small amount of CH\n2 4 4\nis also produced in all materials). This means that the catalytic performance and selectivity\nswitch from dehydrogenation to reforming is only partial. This is also reflected however on\nthe initial catalytic performance results on Figure 6 for R850-O-R400, as well as on the\nmaterial characterization results of R850-O-R400, where the initial state of R400 could not\nbe completely regenerated.\nTherefore, although opposite ethane reforming/dehydrogenation selectivities following\ndifferent exsolution treatments over the same perovskite starting material, and even efficient\nselectivity switch from reforming to dehydrogenation following in-situ treatments, were\nachieved, future research work needs to be directed on the complete structural regeneration\nof the initial perovskite structure, in order to achieve complete selectivity switching during\nmulti-cyclic operation.\nIn addition, we conducted HAADF-STEM, EDX, and EELS analysis on the post-catalysis\n(spent) samples R400, R850, R850-O-R400, and R400-O-R850 to study potential material\nnanostructure changes of the spent catalysts following the catalytic testing procedure\npresented in Figure R6 (temperature ramping and time-on-stream at 700 oC) We also wanted\nto observe whether the outmost FeO layer is maintained or altered during the catalytic\nx\noperation.\nFigure R7. HADDF-STEM images and corresponding EDX and EELS results on spent R850\n(post-catalysis).\nFigure R7 represents the exsolved nanoparticle (representative image) for spent R850 after\nthe catalytic reaction of temperature ramping and time-on-stream, which clearly shows the\nintact crystalline FeO overlayer (also present in the fresh/exsolved sample) even after the\nx\nprolonged reaction operation. The enrichment of iron species was observed in the line scan\narea (~ 2 nm), with less abundant Ni. The EELS result further reveals that the outermost\nlayer is composed of iron oxide (710.1 eV), with distinct differences in core metals. In the\ncase of the spent R400, the outermost FeO layer presents an amorphous-like state (Figure\nx\nR8), which is attributed to ex-situ air exposure during the handling process (similarly to\nfresh/ exsolved R400). In the O K edge, it reveals broader peak intensity compared to the\nR850, indicative of less hybridization between Fe and O, presumably resulting from native\noxide [30, 31]. Thus, it is likely to note that metallic FeNi nanoparticles are the major active\nspecies for R400, while FeNi nanoparticles encapsulated by FeO overlayer are the major\nx\nactive species for R850, and that the reaction conditions do not alter these initial active\nspecies any further.\nFigure R8. HADDF-STEM images and corresponding EDX and EELS results on spent R400\n(post-catalysis).\nWe further investigate the crystallinity of the outermost layer for the redox-treated\n(regenerated) spent samples (R400-O-R850 and R850-O-R400). As can be seen in the TEM\nimages of Figure R9, the active species vary depending on the final reduction treatment. For\nR400-O-R850, the outermost layer presents crystallinity with a relatively well-resolved O K\nedge spectrum in EELS, while the R850-O-R400 shows an amorphous FeO layer similar to\nx\nwhat we’ve observed in reduced samples, and these are well coincident with our prior in situ\nXRD results. We would like to note that they are maintained during catalysis when compared\nto the corresponding fresh/ exsolved samples, as in the cases of R400 and R850, owing to the\nhigh structural stability of all the perovskite-derived material used in this study.\nFigure R9. HADDF-STEM images and corresponding EDX and EELS results on spent (a)\nR400-O-R850, and (b) R850-O-R400 (post-catalysis).\nAs such, a relevant discussion on the reaction mechanism has been provided in the main text\n(page 9, 12-15, Figure 6, 9, 10, Supplementary Fig. 9, and 20)\nPlease note, that relevant changes have been made in the revised manuscript, and\nsupplementary information file with red font.\nReferences:\n[30] C. Wang, et al., J. Am. Chem. Soc., 2009, 131(25), 8824-8832.\n[31] C. H. Park, et al., Adv. Mater., 2024, 36(28), 2403392.\nComment 4 of Reviewer 2: Furthermore, the literature context is insufficiently developed. The\ntitle and abstract are very vague.\nWe thank the Reviewer for his/her valuable comment. In agreement with the Reviewer’s\nsuggestion, we have proceeded to expand and improve the literature context, as described in\nour previous answer to the first comment (Comment #1). Furthermore, as per the Reviewer’s\nsuggestion, we also proceeded to revise the title and the abstract. Please refer to the Revised\nversion as below:\nTitle: Shapeshifting exsolved FeNi bimetallic nanostructures as catalytic switchers during\nthe CO2-mediated ethane conversion\nAbstract: In the era of the energy transition, the development of sustainable, performing,\nand multifunctional catalysts that adapt to complex catalytic processes is essential. Herein\nwe present the development of shapeshifting bimetallic FeNi catalysts based on the\nexsolution approach for the CO -mediated ethane conversion. Fe Ni (3 nm) and\n2 3\nFeO @Fe Ni (40 nm) exsolved nanoparticles were obtained from a\nx 3\nLa Sr Ti Fe Ni O (LSTFN) parent perovskite when exposed to a reducing\n0.4 0.4 0.6 0.35 0.05 3-δ\natmosphere at 400 and 850 °C, respectively. The formation of the core-shell system was\nanalyzed by in situ TEM, Mössbauer and X-ray absorption spectroscopy and ascribed to the\nstrong metal-support interactions. Mediated by the oxidative regeneration of the perovskite\nhost, a shapeshift between the two different nanoparticle structures in the same perovskite\nparent material was realized to a great extent by a secondary reduction (exsolution)\ntreatment at the opposite temperature. Catalytic tests showed that the materials with\nsupported Fe Ni and FeOx@Fe Ni nanostructures (exsolved at 400 and 850 oC) were stable\n3 3\nand selective by approx. 80% towards the ethane dry reforming and the CO assisted ethane\n2\noxidative dehydrogenation pathway, respectively, i.e., achieving opposite catalytic selectivity\nvia simply treating the same parent material at different exsolution temperatures.\nFurthermore, upon regeneration treatment and nanoparticle shapeshifting, the catalytic\nselectivity was switched to a great extent. This trend was also observed during in situ\nregeneration (oxidation/ reduction) in a multi cyclic operation, thus showing that exsolution\noffers a novel and promising strategy for the design of modern, multifunctional catalyst\nmaterials with switching catalytic performance.\nReviewer #3\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\nprovide appropriate recognition for Early Career Researchers who co-review manuscripts."}, {"round": 2, "reviewer_comments": {"reviewer_1": "I have re-reviewed the manuscript and find that all the comments have been well-addressed. I have no further comments and\nthink it can be accepted as is.", "reviewer_2": "I am satisfied with the responses and changes made. I think additional refinement of the title is needed to be more precise:\nwhich specific bimetallic nanoparticles? otherwise the title is vague", "reviewer_3": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature\nCommunications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career\nResearchers who co-review manuscripts."}, "author_response": ""}]

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