Ni redispersion from SiO_2 to molybdenum carbide creates dual interfaces to boost tandem CO_2 hydrogenation

Domain: chemistry
Published: 2025-12-23
Editorial outcome: major_revision

Abstract
Interface engineering is crucial in the design of supported metal catalysts, as it significantly influences the catalytic process, particularly in terms of selectivity. Herein, we discover the redispersion of Ni nanoparticles from SiO2 to molybdenum carbide (Mo2C) being induced by the strong interaction between metal and Mo2C. Parameters affect such migration are thoroughly investigated from carbon source, proximity between Ni and Mo2C to activation atmosphere and temperature. The established dual interface on Mo2C-Ni/SiO2 catalyst exhibits excellent catalytic performance for CO2 hydrogenation, readily shifting the selectivity from 91% CO on Ni/Mo2C to near 100% CH4 on Mo2C-Ni/SiO2. Density functional theory calculations further verify the interfacial synergy between Ni/Mo2C and Ni/SiO2 sites with low barrier for CO2 activation and a subsequent successive hydrogenation of CO*. These findings highlight the important role of strong metal-support interaction (SMSI) induced metal redispersion for the rational fabrication of dual interfaces, leading to a highly active catalyst for target products.

Introduction
Supported metal catalysts are widely used in many industrial processes for the sustainable production of fuels and chemicals1. Typically, the interaction between metal and support directly determines the structure and properties of the resulting interfaces, thereby exerting a substantial influence on catalytic processes, with selectivity particularly being affected2–4. Therefore, much attention has been given to the precise tuning of the metal-support interface to attain desired products.

Distinct from the classical strong metal-support interaction (SMSI) effect, which typically characterized by reducible oxide encapsulation of metal nanoparticles, recent advances have expanded the scope of SMSI behaviors. Among these, metal redispersion represents a prominent SMSI-induced phenomenon under activation or reaction conditions5,6. Note that the SMSI as the driving force, is able to fragment large metal cluster into high density assemblies by various approaches, such as oxidative fragmentation7,8 and atomic trapping9,10. As a result, the interfacial contact between metal and support undergoes change, influencing the activity and selectivity of synthesized catalysts11. For example, a pioneering work performed by Jones et al.9 has revealed the restructuring of Pt on CeO2 surface during oxidative activation, and emphasized the importance of Pt-CeO2 interaction to incur the migration and redispersion of Pt via gas-solid route. Eventually, the movable Pt atoms could be effectively trapped by CeO2 support to suppress sintering, resulting in an improved activity in CO oxidation as well as prolonged durability. In another study, Paredis et al.12 observed the NO-induced redispersion of Pd over ZrO2 at the low temperature range (≤120°C) of NO reduction process, leading to a shifted selectivity toward N2O. These studies indicate that both the supporting material and redox environment play a pivotal role in the evolution of metal structure, thus influencing the performance of the reaction.

Transition-metal carbides (TMCs), molybdenum carbides (MoxC) in particular, have emerged as promising substrates for stabilizing metal nanoparticles (NPs), typically forming two characteristic configurations: epitaxial clusters with few atomic layer thickness13–15 or isolated single atoms16–21. Distinct from conventional metal oxides, the TMCs exhibit stronger interfacial chemical bonding with loaded metals under high-temperature reductive conditions22–27, a unique attribute that drives structural reorganization through SMSI. Notably, this SMSI-driven redispersion phenomenon enables metal migration between different substrates. For example, our previous study demonstrated the redispersion of Pt NPs from carbon nanotubes (CNTs) to α-MoC1-x substrate under reductive treatment28. Subsequent work revealed a significant decrease in Ni particle size along with the altered electronic properties of relocated Ni species on the MoC-Ni/Al2O3 catalyst, achieving 38% activity enhancement in dry reforming of methane29,30. Similarly, Zhou et al. demonstrated Cu migration from SiO2 to Mo2CTx, forming atomically dispersed Cu-Mo2CTx interfaces that boost methanol synthesis rates31. This analogous behavior also extends to nitride systems, in which the loaded Ni NPs undergo structural evolution into undercoordinated layer-like structure on γ-Mo2N substrate32. Despite these advances, three critical knowledge gaps remain: (i) the atomic mechanisms governing the SMSI-driven metal redispersion between two distinct substrates are elusive; (ii) current systems face intrinsic limitations in reconciling high metal loading with atomic-level dispersion; (iii) the catalytic implications of dual interfacial systems are underexplored. To address these challenges, further investigation is required. Therefore, as motivated by this intriguing behavior, there is a call for studies on dual interfacial effect to gain precise control over the underlying mechanism of metal migration across supports as well as the influence of major factors, ultimately enabling the tailored catalytic systems to obtain target products in cascade reactions.

Herein, we report how to optimize the selectivity/activity in CO2 hydrogenation by leveraging the SMSI effects to engineer the degree of metal dispersion as well as the amounts of metal-oxide/carbide interfaces. The Mo2C-Ni/SiO2 catalysts have been fabricated and taken as model systems for catalyzing methanation in CO2 hydrogenation. Effects of various factors (carbon source, mixing method, activation temperature and atmosphere) that influenced the redispersion of Ni NPs from oxide to carbide surface are investigated in attempt to understand the driving forces behind the migration as well as discriminate the key factors for such redispersion. The process of Ni redispersion from SiO2 to Mo2C substrate was confirmed through direct visualization of structural evolution by high-resolution transmission electron microscopy (HRTEM) and electronic state characterization by X-ray photoelectron spectroscopy (XPS). This combined evidence demonstrates the redispersion of Ni NPs from oxide to carbide, leading to the generation of new Ni/Mo2C interfaces. The synergy between the dual interface of Ni-Mo2C and Ni-SiO2 results in a doubled increase of CO2 conversion and significantly shifts the product selectivity, from 46% CO over Ni/SiO2 and 91% CO over Ni/Mo2C to 97% CH4 over the Mo2C-10Ni/SiO2 catalyst. The CH4 formation rate on the optimized Mo2C-10Ni/SiO2 catalyst (127 μmol gcat−1 h−1) is about 4.2 and 18.1 times higher than that of the 10Ni/SiO2 (30 μmol gcat−1 h−1) and Ni/Mo2C (7 μmol gcat−1 h−1) catalysts, respectively. After detailed characterizations and density functional theory (DFT) calculations, we discover that the observed changes in activity and selectivity originate from the tandem catalysis occurring at the established dual interfaces of Ni-Mo2C and Ni-SiO2, in which the activation of CO2 initially occurs on the Ni/Mo2C sites, resulting in the formation of CO* and subsequently, these CO* intermediates were successively hydrogenated on Ni/SiO2 sites to produce CH4. Findings from this study greatly broaden the applicability of the SMSI effects and provide insights into a promising approach to enhance catalysis by constructing dual interfaces.

Results
Evidence and driving force for Ni migration from SiO2 to Mo2C
To evidence and elucidate the intrinsic driving force for Ni redispersion, a systematic study was performed by examining the influence of various factors (carbon source, mixing method, activation temperature, and atmosphere) involved in the preparation of Mo2C-Ni/SiO2 catalysts. Firstly, the activated carbon (C) and Mo2C were individually chosen and mixed mechanically with the 10Ni/SiO2 in a mass ratio of 1–3 before undergoing the reduction treatment with a gas mixture of 15% CH4/H2 at 590°C. The transmission electron microscopy (TEM) analyses were employed to determine the cluster size of Ni. It was found that a small portion of Ni aggregated unevenly on SiO2 over the Ni/SiO2 reference, with an average particle size of 19.5±0.4 nm (Figs. 1a and S1). In contrast, the Ni-Mo2C/SiO2 catalyst exhibited well-distributed Ni-enriched dark dots on SiO2, characterized by a decreased particle size of 13.8±0.2 nm (Figs. 1b and S2). While the estimated Ni particle size is about 18.1±0.2 nm on the C-Ni/SiO2 catalyst (Fig. S3), indicating a negligible impact on Ni distribution compared to the Ni/SiO2 reference. Therefore, we can deduce that carbon (C) does not possess similar ability as Mo2C does, an indication of weak interaction between Ni and C. Figure 1c shows the Rietveld-refined powder X-ray diffraction (PXRD) profiles of the prepared Ni-based catalysts. Notably, the Mo2C-Ni/SiO2 catalyst exhibited a broad diffraction peak with reduced intensity on Ni (111) reflection plane compared to the Ni/SiO2 reference. The crystallite size of Ni decreased from 21.6 to 17.3 nm by calculating the reflection of Ni (111) plane (Fig. S4). Meanwhile, the estimated crystallite size of Ni obtained from CO pulse measurement showed a decrease upon mixing with Mo2C (Table S1). The X-ray photoelectron spectroscopy (XPS) spectra of Mo 3d 5/2 (binding energy, B.E.=227.7 eV) and Ni 2p 3/2 (B.E.=855.1 eV) clearly evidenced the formation of Mo-C-Ni motifs (Fig. 1d–f)29,33. The binding energy (B.E.) of Mo 3d 5/2 being characteristic of Mo2C negatively shifted from 228.2 to 227.7 eV over the Mo2C-Ni/SiO2 catalyst, and correspondingly the B.E. of Ni 2p 3/2 being ascribed to metallic Ni0 showed a positive shift from 852.7 to 853.0 eV. The newly emerged peak at 855.1 eV in the Ni 2p 3/2 spectra, except for Ni0 and Ni2+ (856.3 eV, NiO) was assigned to Ni-Cx motif as confirmed in our previous studies29,30. Notably, the Ni2+ content in the Mo2C-Ni/SiO2 catalyst (22%) exhibited a marked decrease compared to that in the pristine Ni/SiO2 catalyst (47%). This reduction can be rationalized by the interfacial synergy between Mo2C and Ni as induced by the migration of Ni from SiO2 to Mo2C, which diminishes the anchoring effect of SiO2 support on Ni species. Consequently, the weakened metal-support interaction promotes the reduction of Ni2+ during catalyst activation process. This phenomenon aligns with our prior observation on the Mo2C-Ni/Al2O3 system29. Meanwhile, the low-valence Moδ+ (0<δ<2) species at B.E. of 227.7 eV were detected on the Mo2C-Ni/SiO2 catalyst, an indication of weakened Mo-C bonds, as a result of C being linked with Ni and the creation of Ni-Cx motifs. The assignment of 227.7 eV peak to Moδ+ aligns with our established methodology in an analogous system29. Such valence change of Ni and Mo in the synthesized composite catalyst indicates the charge transfers from Ni to Mo2C. The quantitative peak-deconvoluted data revealed that about 36% of Ni remains at electron-deficient states (Niσ+) after CH4/H2 activation on Mo2C-Ni/SiO2 catalyst (Table S2). The relative amount of Moδ+ (0 < δ<2) increases to 44% after obtaining electrons. Thereafter, the relative amounts of Niσ+ and Moδ+ (0 < σ<2, 0 < δ<2) have been defined as descriptors to express the amounts of generated Ni-Mo2C interfacial sites. Different from Mo2C-Ni/SiO2, the C-Ni/SiO2 catalyst showed the formation of nickel carbides after CH4/H2 activation with the B.E.s of Ni 2p at 854.4 eV and C 1s of 280.9 eV due to the strong Ni-C bonding (Fig. 1f).

The effects of mechanical strength of different mixing methods on the preparation of Mo2C-Ni/SiO2 catalysts were examined. Noticeably, the crystallite size of Ni obtained by ball milling (BM) and motor milling (MM) prepared Mo2C-Ni/SiO2 catalysts exhibits reduced particle size compared to their granular stacking (GS) counterparts across the (111) plane (BM: 17.3 nm; MM: 18.7 nm; GS: 20.6 nm), underscoring the critical role of mechanical strength on Ni dispersion (Fig. S5). Importantly, the TEM-derived particle size shows a reasonable agreement with the XRD-derived crystallite dimensions (Fig. S6, Table S3), which validates the reliability of our multi-scale characterization approach. The difference of Ni particle size between BM and MM-prepared samples may arise from the varied distance between Ni/SiO2 and Mo2C. In order to rule out the possible physical structure change caused by mixing process, a control experiment was conducted by ball-milling 10Ni/SiO2 catalyst. It is worth noting that the crystallite size of Ni remained on the BM-treated 10Ni/SiO2 catalyst compared to the as-synthesized one (Fig. S7). Also, the XPS results showed that the relative contents of formed Ni-C species and the ratio of Niσ+/Ni0 (0 < σ<2) and Moδ+/Mo2+ (0 < δ<2) of BM-prepared Mo2C-Ni/SiO2 are higher than that of the MM-prepared Mo2C-Ni/SiO2. Such findings imply that the enhanced mechanical strength promotes the proximity between Ni and Mo2C sites, thus facilitating the migration of Ni and leading to an increased formation of Ni-Mo2C interfacial sites. A linear correlation of Moδ+/Mo2+ or Niσ+/Ni0 with Ni crystallite size was established as shown in Fig. S8. Thus, we can infer that the proximity between Ni and Mo2C is able to be adjusted from micro- to nano-scale based on the mechanical strength provided by different mixing methods, which in turn influences the dispersion of Ni NPs.

Next, the effects of gas atmosphere and reduction temperature as key factors were investigated. Both the TEM measurement and XRD profiles of Mo2C-Ni/SiO2 catalysts showed the decrease of Ni particle size under H2 or CH4/H2 atmosphere, which demonstrates the redispersion of Ni under reducing gases (Figs. S9 and S10, Table S4). Meanwhile, the quasi in-situ XPS spectra showed a comparable distribution of valence states for the Mo2C-Ni/SiO2 catalyst treated with H2 and CH4/H2, which is significantly distinct from the N2-treated one (Figs. 1f and S11). Also, the TEM analyses revealed a reduction in Ni particle size from 19.5±0.4 nm for the pristine Ni/SiO2 catalyst to 14.7±0.2 nm following mixing with Mo2C and CH4/H2 treatment at 500°C. Elevating the activation temperature to 590°C resulted in a further decrease to approximately 13.8±0.2 nm (Fig. S12). However, the crystallite size of Ni significantly increased to 19.9±0.3 nm when reduced at 650°C (Fig. S13, Table S5). This result suggests the effectiveness of Mo2C on keeping Ni NPs from growing at an appropriate temperature range. However, the severe coalescence of Ni NPs on SiO2 carrier was not able to be compensated by Ni redispersion above 590°C. The XPS spectra (Fig. 1g, Table S2) revealed a temperature-dependent evolution of metal species. As the activation temperature increased from 500 to 590°C, the Moδ+/Mo2+ ratio progressively increased from 1.59 to 1.67, reaching a plateau above 590°C. Concurrently, the Niσ+/Ni0 ratio showed a parallel enhancement from 0.81 to 0.85 within the same temperature window, indicative of Mo2C-mediated interfacial interactions facilitating Ni redispersion. However, a decline in the Niσ+/Ni0 ratio was observed between 590 and 650°C, because the thermodynamic driving force for Ni redispersion is overtaken by Ni0 agglomeration on SiO2 support. This inversion suggests that while elevated temperatures initially promote the formation of Ni-Mo2C interfacial sites through the enhanced metal migration kinetics, beyond 590°C the dominant mechanism shifts to Ni agglomeration on SiO2 surface, where the cohesive energy of metallic Ni clusters overcomes the dispersion forces generated by the Mo2C matrix34. Furthermore, the diffuse reflectance infrared Fourier-transform spectra (DRIFTS) were employed by using CO as a probe molecule to provide additional evidence on the electronic states of Ni species. The emerged Niσ+ adsorption features in 2120~2170 cm−1 displayed a distinct blue shift under identical thermal treatment conditions (Figs. S14 and S15)35. Overall, the above analysis suggests that the metallic Ni0 species become activated on the inert SiO2 surface when the activation temperature is beyond its Hüttig temperature (THüttig = 518 K). Also, part of the added Mo2C was slightly reduced because of the electron transfer from the relocated Ni species that reside on the surface of Mo2C36–38.

As illustrated in Fig. 2a, the Mo2C-Ni/SiO2 catalyst was prepared using a two-step synthesis method. Three distinct areas surrounding a Mo2C patch were randomly chosen and labeled as Regions I to III in Fig. 2b. Moreover, the high-magnification high-angle annular dark-field (HAADF-STEM) images with the simultaneous energy-dispersive X-ray spectroscopy (EDX) analyses, clearly revealed the spatial distribution of Ni and Mo species (Figs. 2c–e and S16–S18). Noted that the elemental mappings showed a pronounced distribution of Ni within Si- or Mo-enriched regions, as exemplified in Region (I). Specifically, Ni and Mo signals were well correlated in the bright region above the boundary line in Fig. 2c, indicating that Ni species were highly dispersed at high density on Mo2C surface. This observation is consistent with the EDX line-scanning results, in which the Ni signal increased in tandem with the Mo signal (Fig. 2f). In contrast, Ni species exhibited a more disordered distribution as small patches on the Si-enriched regions below the bright area. Fig. 2d, e further substantiated the distinct distribution of Ni on Mo2C and SiO2. Overall, this observation provides a compelling evidence of Ni redispersion from SiO2 substrate onto the Mo2C surface during the synthesis of Mo2C-Ni/SiO2 catalyst. To further verify the presence of Ni on Mo2C, an acid treatment (3 vol% HF) was employed to selectively dissolve the Ni/SiO2 component from the Mo2C-10Ni/SiO2 catalyst, thus confirming the formation of Ni-Mo2C interfacial sites (Fig. S19). Additionally, EDX line-scanning analysis across the Mo2C-Ni/SiO2 interface boundary tracked the progressive evolution of Ni distribution with increasing treatment temperature. The resulting line profiles corroborated the XPS data, demonstrating a rise in the Ni/Mo ratio from 0.11 at 500°C to 0.21 at 590°C, followed by stabilizing at temperature exceeding 590°C (Figs. S20–S23).

Electronic interaction upon metal redispersion
The X-ray adsorption fine structure (XAFS) studies were performed to elucidate the electronic states of Ni species. All samples were properly treated in a glove box without exposure to air. Herein, the Mo2C-1Ni/SiO2 composite catalysts and 1Ni/SiO2 reference with 1 wt% of Ni were evaluated, as it is more conductive to obtain precise structural and chemical information from XAFS analysis. The Ni/SiO2 reference exhibits both characteristic metallic Ni0 and oxidized Ni2+, with electronic configurations aligning with the XPS results (Fig. S24). Also, the comparative analysis reveals that the low-temperature activated Mo2C-Ni/SiO2 catalyst (denoted as Mo2C-1Ni/SiO2-LT, LT=400°C) maintains electronic signatures nearly identical to that of the Ni/SiO2 reference, which confirmed the absence of interfacial electronic coupling without adequate thermal activation. The Ni K-edge (8333 eV) X-ray absorption near-edge structure (XANES) spectra (Fig. 3a) of high-temperature activated Mo2C-1Ni/SiO2 catalyst (denoted as Mo2C-1Ni/SiO2-HT thereafter, HT=590°C) showed a positive shift of Ni K absorption edge compared to the low-temperature treated Mo2C-1Ni/SiO2 catalyst. Also, the intensity of “white-line” (8350.5 eV for Ni K edge) increased with increased activation temperature. Both phenomena indicate the enhanced charge transfer resulting from the formed Ni/Mo2C interface, which is similar to the reported Co/γ-Mo2N and Pt1/FeOx catalysts39,40. Since most of the Mo ions still remain as carbide in Mo2C-1Ni/SiO2 catalysts, there is no obvious change on the Mo XANES (20000 eV) spectra (Fig. 3b). From the above analysis, we can deduce that the strong interaction between Ni and Mo2C is able to induce the electronic perturbation of Ni species, leading to the formation of charge-redistributed Ni-Mo2C interfaces, eventually the re-dispersed Ni could stay in cationic state. Similar phenomenon is also observed on the redispersion process of Pt or Rh NPs on CeO2 substrate under oxidative atmosphere9,41.

Moreover, the Ni K-edge extended X-ray absorption fine structure (EXAFS) was employed to study the local chemical environment of Ni species. The fitting results (Figs. 3c and S25, Table S6) revealed the presence of Ni-C, Ni-Mo, and Ni-Ni coordination on the Mo2C-1Ni/SiO2-HT catalyst. The mean bond length of Ni-C is about 2.07 Å, while the bond length of Ni-Mo is around 2.91 Å. According to a previous study20, we can deduce that the Mo atoms are located beneath the subsurface layer of C. Notably, the average coordination number of Ni-Ni (CNNi-Ni) decreased from 4.3 to 1.9 as the reduction temperature increased over the prepared Mo2C-1Ni/SiO2 catalyst. This result again confirmed the redispersion of Ni on Mo2C, which can occur at HT, and the anchored Ni atoms bond to Mo2C surface via C as bridges. In addition, Mo K-edge (20000 eV) spectra were analyzed (Figs. 3d and S26, Table S7). Obviously, the CNMo-C-Mo decreased with increased reduction temperature from 9.5 to 8.7, perhaps due to the formation of Ni-C-Mo bonds, thus reducing the intensity of the second-shell scattering of Mo2C. This result is in accordance with the Ni K-edge spectra. The EXAFS fittings were further validated by a wavelet transformation (WT) of the EXAFS spectra. The WT contour maps of the Mo2C-1Ni/SiO2-LT and Mo2C-1Ni/SiO2-HT catalysts are distinct, as shown in Fig. 3e, f, respectively. The component in the R range near 1.6 Å is attributed to the coordination between Ni and C/O, whereas the R at 2.1 Å is contributed by the Ni-Ni coordination based on the similar k-space intensity distribution. Interestingly, the R range appeared at ca. 2.6 Å belongs to the Ni-Mo bond, indicating the significant role of activation temperature on the extent of Ni NPs redispersion.

In addition, the ab-initio thermodynamic calculations proved that the Ni NPs prefer to be atomically dispersed over the Mo2C (101) plane with a relatively large formation energy of −5.41 eV (Fig. S27a). The population analysis verified the charge transfer between Ni and Mo2C (Ni: +0.18|e|) and confirmed the energetically favorable connection between Ni and Mo2C via Ni-C-Mo bonds. (Fig. S27b–d), Figs. S28–S30, Tables S8–S10).

Catalytic performance in CO2 hydrogenation
The catalytic performance of Mo2C-10Ni/SiO2 catalyst and several references was evaluated in CO2 hydrogenation due to the structure-sensitive nature of this reaction42–45. As shown in Fig. 4a, b, the 10Ni/SiO2 catalyst exhibited a CO2 conversion of 20.9% with CH4 selectivity of 54% at 350°C with a WHSV of 30,000 mL g−1 h−1. In addition, both the Mo2C and Ni/Mo2C references showed an enhanced CO2 conversion due to their unique atomic arrangement and platinum-like behaviors, endowing an effectiveness for CO2 adsorption and activation. Note that the Mo2C-based catalysts presented an ultra high CO selectivity up to 91%, which is consistent with Zhang et al.17 observation. However, the limited surface areas of β-Mo2C could impede the maximum Ni loading. How to resolve the intrinsic trade-off of metal loading and dispersion becomes an issue in catalyst design. To address this, we designed a Mo2C-Ni/SiO2 composite catalyst with Ni loading of 10% by taking advantage of the redispersion of Ni from SiO2 to Mo2C via the SMSI between Mo2C and Ni. Impressively, the CO2 conversion of the dual interfacial Mo2C-10Ni/SiO2 catalyst is the highest, more than two times that of the 10Ni/SiO2 catalyst. Moreover, the selectivity shifts from CO over Mo2C (~92%) and 10Ni/SiO2 (~45%) towards CH4 (~97%) over the Mo2C-10Ni/SiO2 catalyst at the same CO2 conversion level (Fig. S31a). In contrast to Mo2C, there is no improvement on the activity while adding C as additive (Fig. S32). Therefore, we propose that the enhanced CH4 yield may result from the synergistic interplay between Ni-Mo2C and Ni-SiO2 interfaces that single interfacial system cannot be obtained. To further confirm this, we prepared another reference sample by physically mixing 10Ni/SiO2 with 1Ni/Mo2C without thermal pretreatment in CH4/H2 (denoted as 10Ni/SiO2 + 1Ni/Mo2C). It was found that the two interfaces that involved in the 10Ni/SiO2 + 1Ni/Mo2C reference (CO2 conv.=45.1%; CH4 selec.=95.5%) work synergistically in CO2 hydrogenation, resulting in a comparable performance to that of the Mo2C-10Ni/SiO2 catalyst (CO2 conv.=48.6%; CH4 selec.=97.1%). Therefore, we can conclude that Ni redispersion induced by the SMSI between Mo2C and Ni results in the formation of Ni-Mo2C interfaces, establishing highly-dispersed catalysts at high metal loading with dual interfacial sites for CO2 hydrogenation, which breaks the limitation of conventional preparation method.

Followed by this, the effects of the integration manner were investigated (Figs. 4c, d and S31b). It was found that both the CO2 conversion and CH4 selectivity increase in the order of double layer (DL-conv. 25.5%; CH4: 65.4%) < granule stacking (GS-conv. 27.7%; CH4: 72.2%) < motor milling (MM-conv. 38.2%; CH4: 89.4%) < ball milling (BM-conv. 48.6%; CH4: 97.1%), which is consistent with the increase in Ni-Mo2C interfacial sites. As a result, a higher degree of redispersion resulting from distinct mixing methods was able to generate more Ni-Mo2C interface, thus enhancing the formation of CH4. Aside from the mixing method, other factors were investigated as well, including the mass ratio of Ni/SiO2 to Mo2C, activation temperature, and atmosphere (see details in Figs. S33 and 34). Therefore, we can reasonably deduce that the relative ratio between Ni-Mo2C and Ni-SiO2 and the activation process significantly impact the activity and selectivity of CO2 hydrogenation by the SMSI-induced Ni redispersion. As depicted in Fig. S34, the obtained molar ratio of Ni/Mo was about 0.5, indicating that the redispersion degree of Ni was closely related to the amount of Mo2C. Also, the CO2 conversion exhibited a gradual increase as the activation temperature increased up to 590°C and slightly dropped thereafter (Fig. S34). Only a good match between CO2 activation and COx hydrogenation is able to enhance the CH4 formation rate.

To ensure the measurements were maintained in a kinetic-relevant regime, the CO2 conversion was limited to 15% with a relatively high space velocity of 80,000 mL g−1 h−1 at various temperatures. The calculated approach to equilibrium (η) is about 0.16, which aligns with the recommended threshold (η<0.2) for kinetic control and suggests that the experimental condition applied is far from equilibrium46. All rate measurements were thermodynamically corrected, which confirmed the kinetic control throughout the experimental range (Fig. S35, Tables S11–S14). As displayed in Fig. 4e and Table S15, the calculated turnover frequency (TOF; normalized by the number of CO chemisorption sites) of CH4 formation of the Mo2C-10Ni/SiO2 catalyst (7.1E-04 s−1) is about 7.8 x’s higher than that of the 10Ni/SiO2 catalyst (9.0E-05 s−1), indicating the improved intrinsic activity of Ni sites due to their altered electronic properties. Taking the observed Ni redispersion from SiO2 to Mo2C and the established electron transfer into account, we propose that the increased TOF originates from synergistic effects combining better Ni exposure and optimized electronic structure. Moreover, the apparent activation energy (Ea) of Mo2C-10Ni/SiO2 and 10Ni/SiO2 catalyst for CO2 hydrogenation was determined to be 67.7±1.1 and 85.2±0.7 kJ mol−1, respectively (Table S12). The obtained Ea over 10Ni/SiO2 catalyst is in good agreement with the literature reported value47–49. Importantly, the activation energy (Ea) of CH4 formation exhibited a substantial reduction from 93.8±0.6 kJ mol−1 over Ni/SiO2 to 67.6±1.1 kJ mol−1 for the Mo2C-Ni/SiO2 catalyst, demonstrating that Mo2C incorporation effectively lowers the energy barrier for methane generation (Fig. 4f, Table S16). In contrast, the Ea decreased for CO formation was less pronounced, shifting from 79.8±0.7 to 72.4±3.2 kJ mol−1 upon Mo2C addition (Fig. S36). This differential effect highlights the preferential enhancement of CH4 pathway kinetics by Mo2C-containing sites. The variation in the activation barrier of 10Ni/SiO2 and Mo2C-Ni/SiO2 catalyst implies the facile activation of CO2 on Mo2C-Ni/SiO2, which may result from the Ni redispersion-induced electronic and geometric structure change on active Ni sites.

Reaction mechanism exploration
As shown in Fig. 5a–h, we performed a two-step temperature-programmed surface reaction (TPSR) to explore the reaction mechanism of CO2 hydrogenation over the Ni/SiO2, Mo2C-Ni/SiO2, and Mo2C catalysts. Initially, a 2% CO2/He mixture (50 mL min−1) was introduced at 300°C after activation. Noted that a small amount of CO(g) was immediately produced on the Ni/SiO2 catalyst (Fig. 5a). While no gaseous CO was detected over the Mo2C-Ni/SiO2 catalyst (Fig. 5d), either because of the strong interaction of CO* to the active sites or an alternative CO2 activation route. To verify the potential intermediates, we performed a temperature-programmed desorption (TPD) under He flow after CO2 dissociation (Fig. 5c, f). Notably, the attached intermediates gradually desorbed as gaseous CO with increased temperature on both catalysts. For Ni/SiO2 catalyst, a broad CO desorption peak was detected, which starts at around 400°C; while only one CO desorption peak appeared with the onset temperature of 500°C on the Mo2C-Ni/SiO2 catalyst, which implies that the interaction between CO* and Mo2C-Ni/SiO2 surface is stronger than that of the Ni/SiO2 catalyst. Also, the amount of desorbed CO on Mo2C-Ni/SiO2 is about two times that of the Ni/SiO2 catalyst, indicating that more CO* species are preserved on the former catalyst. In sharp contrast, the Mo2C alone exhibited a spontaneous CO2 dissociation, forming CO(g) as a major product, indicating the weak interaction between CO and the O* occupied Mo carbides surface (Fig. 5g). This result is similar to that of the Ni/Mo2C reference (Fig. S37). Followed by this, the system was switched to 5% H2/He (50 mL min−1) at the same temperature after purged with N2 (50 mL min−1, 30 min) (Fig. 5b, e). Note that the amount of generated CH4 in the 2nd step of hydrogenation over Ni/SiO2 was less than that of Mo2C-Ni/SiO2, which is consistent with the TPD results as well as our experimental data. It suggests that the produced CH4 mainly originates from the hydrogenation of adsorbed CO. Similar to the Mo2C-Ni/SiO2 catalyst, the physically mixed 10Ni/SiO2 + 1Ni/Mo2C reference also exhibits a considerable formation of CH4 as a result of the two-step tandem process on the involved dual interface (Fig. S38).

Meanwhile, the in-situ DRIFT experiments were carried out to probe surface intermediates by co-feeding CO2 and H2 mixture (1:4) over the Mo2C-Ni/SiO2 catalyst (Fig. S39). It was found that more CO* intermediates are detected at low temperature, as indicated by the bands located at 2141, 2075, 2030, and 2010 cm−1, which are attributed to the adsorbed CO* on the Niσ+, Ni0, and Mo2C sites over the Mo2C-Ni/SiO2 catalyst, respectively. The emergence of CO* indicates the strong CO2 dissociation ability of the Mo2C-Ni/SiO2 catalyst, even at a relatively low temperature. This result is in agreement with the two-step MS experiment. Also, the intensity of CH4 signal at 3016 cm−1 increases with increased reaction temperature, most likely due to the successive hydrogenation of CO*.

To get more insights on the catalytic function of involved active sites, the Ni1/SiO2, Ni/Mo2C(101), and Mo2C(101) models were built and used as references, representing Ni/SiO2, Ni/Mo2C, and Mo2C catalysts, respectively. The energy barrier of these three catalyst models for CO2 and H2 dissociation (Ediss,CO2 & Ediss,H2) was calculated and compared, as displayed in Fig. 5i. The Ediss,CO2 of Ni/Mo2C(101) (0.46 eV) is lower than those of Ni1/SiO2 (1.83 eV) and Mo2C(101) (0.63 eV), indicating that the Ni/Mo2C catalyst is favorable for CO2 activation. The value of Ediss,H2 follows the trend of Mo2C (0.31 eV) > Ni/Mo2C (0.17 eV) > Ni1/SiO2 (0.15 eV), indicating the outstanding performance of Ni1/SiO2 in H2 activation. We then investigated the important successive step by calculating CO adsorption energy (Eads,CO) over those three models (Fig. 5j). The results show that the Ni/SiO2 model binds CO much stronger (−2.30 eV) than Ni/Mo2C (−1.95 eV) and Mo2C(101) (−1.58 eV), which is consistent with the CO-TPD measurement. Apart from this, Fig. S40 displays the CO desorption behavior on Ni/SiO2, Mo2C, and Mo2C-Ni/SiO2 surface. Clearly, a new CO-desorption peak (ca. 242°C) appeared on the Mo2C-Ni/SiO2 catalyst, indicating the formation of new active sites, which might originate from the Ni-Mo2C domains. Similar result was also observed by Ma et al.50 on a tandem Pt-Mo2C/C catalyst. Therefore, we can deduce that the electronic interfacial sites provided by Ni-Mo2C interface showed the potential of stabilizing undercoordinated Niδ+ species for the selective cleavage of C=O bond, while the structural interfacial sites of Ni-SiO2 maintained the high-density metallic ensembles for efficient H2 dissociation. The presence of Mo2C modulated the interaction between metal and support by preventing the over stabilization of intermediates on Ni/SiO2 sites. This bifunctional synergy, in which the Mo₂C dictates electronic states and SiO₂ control nanostructure, resolves the persistent activity-selectivity-lifetime trade-off.

Extensive DFT-based calculations were performed to highlight the synergy between Ni/SiO2 and Ni/Mo2C dual interfaces in CO2 hydrogenation (Fig. 5k). Ni atoms are stabilized by two-fold coordinated C atoms on Mo2C(101) plane as shown on the insert of Fig. 3f. These partially charged and undercoordinated Ni atoms are more efficient than surface Mo as reaction sites for CO2 and H2 activation. The initial barrier for CO2 dissociation (CO2*+4H*→CO*+O*+4H*) on Ni/Mo2C interface is about 0.63 eV, which is comparable to that over bare Mo2C(101) surface (Fig. S41). Also, this step is 0.69 eV exothermic, forming stable Ni-carbonyl in-situ. Moreover, we notice that the hydrogenation of adsorbed O* can be regarded as the most sluggish step on the Ni/Mo2C (101) and Mo2C (101) surface with energy barrier of 1.18 and 1.49 eV (TS3 and TS5, Fig. 5k), respectively, but is vital to keep the reaction proceed. Originating from the Ni/Mo2C interface, the previously formed Ni-carbonyl sites could convert the adsorbed CO and H at an energy barrier of 0.46 and 0.17 eV (TS6 and TS4, Fig. 5k), respectively, which are significantly lower than those over Mo2C(101) plane and Ni/SiO2 interface. Furthermore, CO generated by CO2 dissociation will be shifted to a surface Mo atom that is not available for CO adsorption/desorption on Mo2C(101), where CO desorbs easily at a barrier of 0.85 eV (step 16-17) at reaction conditions. Compared to Mo2C(101), this value decreased about 1.0 eV. In contrast, we found that the rate determine step of CO hydrogenation over Ni1/SiO2 model is CO2 dissociation, which needs to overcome an energy barrier of 1.83 eV though the reaction is exothermic by 0.58 eV. These results indicate that CO2 can be activated easily on Ni/Mo2C interface to facilitate the breakage of C=O bonds as well as the CO desorption. Driven by the aforementioned strong CO adsorption ability, the released CO would migrate to Ni1/SiO2 interface for further hydrogenation, eventually forming CH4 as final product. Given the experimental and computational results, we can propose that the synthesized Mo2C-Ni/SiO2 catalyst constitutes a tandem catalytic system for CO2 hydrogenation as induced by the SMSI between Mo2C and Ni, in which the CO2 reduction could initially occur on the Ni/Mo2C interface while the subsequent hydrogenation of CO takes place on the Ni/SiO2 interface.

Methods
Catalyst synthesis
Preparation of Mo2C-Ni/SiO2 catalysts: The Ni-based catalysts (denoted as Ni/SiO2) were synthesized by incipient wetness impregnation (IWP) with Ni nominal loading in the range of 1–10 wt% on silica support. Molybdenum carbide (denoted as Mo2C) as the second component was synthesized by a temperature programmed reduction as follows: Firstly, the ammonium heptamolybdate ((NH4)6Mo7O24·4H2O) was heated to 500°C in a muffle furnace and held for 4 h to prepare MoO3 precursor. After that, the obtained MoO3 was heated from room temperature (RT) to 300°C in 20 vol% CH4/H2 mixture with a ramping rate of 5°C/min, then increased from 300 to 700°C at a ramping rate of 1°C/min and held for 2 h at 700°C. The resulting material was quickly quenched to room temperature and passivated by 1% O2/Ar mixture (20 mL/min) for 4 h. The investigated materials were further prepared by mixing Ni/SiO2 with Mo2C with a mass ratio of 5:1–1:3. Finally, the prepared mixture is subjected to a 15% CH4/H2 treatment at designated temperature (400–650°C) for 2 h. The resulting samples were denoted as Mo2C-Ni/SiO2.

Preparation of Ni/Mo2C reference catalysts: Ni/Mo2C catalysts were prepared by co-precipitation and carburization for comparison. Prior to air exposure, the Ni/Mo2C catalyst was typically passivated in 1% O2/N2 flow for 2 h.

Catalyst characterization and CO2 hydrogenation evaluation
X-ray diffraction (XRD): Powder X-ray diffraction (XRD) data were collected using a Rigaku SmartLab 9kW diffractometer with Cu Kα radiation (λ=1.5406 Å) with a step size of 0.02° and counting time of 8 s per step in the range of 2θ=10-80°. The Diffraction patterns were compared to powder diffraction files from the Joint Committee on Powder Diffraction Standards (JCPDS) database. The crystallite size was estimated from the broadening peak of (111) plan for Ni by Scherrer equation. All the catalysts were passivated before measured.

Quasi in-situ X-ray photoelectron spectroscopy (XPS): The information of surface structure of the as-prepared catalysts was collected by XPS of Axis Ultra Imaging Photoelectron Spectrometer (Kratos Analytical). The prepared Mo2C-Ni/SiO2 and their references were activated in a continuous flow fixed-bed quartz reactor and treated under the target feed gas. Treated catalysts were made into small tablets (6.0 mm diameter) and placed on the sample holder without exposure to air in a glove box. The sample was then introduced into the ultra-high vacuum chamber for XPS measurements without air exposure. 284.6 eV was used as an internal binding energy standard of C 1s to correct for surface charging shift. XPSPEAK 41 was used for spectra deconvolution by a nonlinear least-squares method with a combination of Lorentzian (20%) and Gaussian (80%) peak shapes.

Electron microscopy characterization: The high-resolution transmission electron microscope (HR-TEM) images of the prepared catalysts were recorded on a (JEOL) JEM 2200FS electron microscope with an accelerating voltage of 200 kV. Samples were prepared by dispersing in ethanol and sonicated for 300 s. A drop of the suspension was placed on a 230-mesh copper grid coated with Formvar-carbon film and then dried in a vacuum chamber. The clusters/particles identified in the TEM images were measured and counted to yield a size distribution that was fitted to a Gaussian distribution (100–200 particles were counted for statistical analysis) to determine the average size of the cluster/particle. All image analysis was conducted with Digital Micrograph software.

CO-adsorbed diffuse reflectance infrared spectra (CO-DRIFTs) and in-situ DRIFT: DRIFT spectroscopy of CO adsorption was employed on a Thermo Nicolet iS50 spectrometer with a mercury cadmium telluride (MCT) detector cooled by liquid nitrogen to estimate the electronic state of Ni and Mo species. All catalysts were prepared by diluting with quartz sands at a mass ratio of 1:5 prior to DRIFTS measurements to minimize the intermolecular dipole interaction of adsorbed CO. All the tests were performed in Harrick Praying Mantis high temperature reaction chamber with ZnSe windows. A thermocouple mount that allowed direct measurement of sample surface temperature. Each recorded spectrum was averaged over 32 scans in the region of 4000-650 cm−1 with a nominal 32 cm−1 resolution. Prior to CO adsorption, the precursor was pre-treated by 15% CH4/H2 at 590°C for 2 h, unless otherwise indicated. After that, the flow was switched to N2 until the temperature decreased to 17°C at a flow rate of 40 ml (STC)/min to clean the catalyst surface and then a background spectrum was recorded. CO adsorption was conducted at 17°C by introducing CO into the system for above 20 min to ensure the complete saturation of CO gas molecules on catalyst surface. Finally, N2 was introduced to flush the physiosorbed CO. Several spectra were collected by 30 s interval until the spectra were stabilized.

X-ray absorption fine structure (XAFS): Ni L3 edge (8333 eV) and Mo K-edge (20000 eV) XAFS were measured at BL14W beamline of Shanghai Synchrotron Radiation Facility (SSRF) in transmission/fluorescence mode using Lytle detector to collect the data. Ni foil and NiO were used as standards for Ni K-edge spectra; Mo foil and Mo2C were used as standards for Mo K-edge spectra. All the samples were pre-activated in 10% H2/Ar at 350°C for 1 hour and sealed in a chamber under argon protection in a glove box.

Two-step temperature programmed surface reaction (TPSR): The 1st step is CO2 dissociation—The activated samples were exposed to 2% CO2/He (50 mL min−1) at a proper temperature for about 10 min. The effluent gases were measured online using a Mass Spectrometer (MKS-Cirrus 3, USA). After N2 puring (50 mL min−1), the samples were reduced in 5% H2/He (50 mL min−1) in the 2nd step hydrogenation. In the control experiment, the 2nd step hydrogenation was replaced by a temperature-programmed desorption (TPD) under H2 flow to observe the desorbed species.

CO temperature-programmed desorption (CO-TPD): Temperature programmed desorption of CO (CO-TPR) was carried out on Micromeritics AutoChem 2920. The sample (100 mg) was reduced at 400°C by 5% H2/Ar flow (30 mL min−1) for 1 h to remove passivation layer. After cooling down, the CO adsorption was performed at 40°C for 1 h. The sample was then flushed with N2 (30 mL min−1) until the baseline is stable. The desorption was conducted from 40 to 650°C with a ramping rate of 10°C/min. Desorbed species were monitored by mass spectrometer (MS).

CO Chemisorption: This technique was used to determine the number of active sites (#CO, μmol g−1) on a Quantachrome ChemBET Pulsar analyzer. Samples were purged with He at 100°C for 30 min to remove moisture, and then reduced by 5% H2/Ar flow at 350°C for 1 h to remove the passivation layer. Afterwards, the CO uptake was measured using pulsed chemisorption at 35°C by taking thermal conductivity detector (TCD) as detector. The turnover frequency (TOF), defined as the number of CO converted per surface site per second, was calculated based on the following equation:
TOF = FCO2,inlet * XCO2 / (#CO * M)
where the FCO2,inlet represented the inlet flow rate of CO2 (mol s−1), M represented the molecular weight of CO2 (g mol−1).
To determine Ni particle size (assuming cubic geometry), CO chemisorption measurements were performed on a Micrometritics AutoChem III 2930. Approximately 100 mg of the sample was loaded into a U-shaped quartz tube. The sample was prepared in situ under the same condition as the activity test. After the sample was cooled to 35°C and purged with He for 30 min. The sample was then exposed to ten pulses of 10% CO/He. The quantity of CO adsorbed was detected by TCD by assuming a stoichiometric ratio of one CO molecule per surface Ni atom.

CO2 hydrogenation was evaluated in a packed bed reactor, in which 100 mg catalyst powder mixed with 300 mg pre-calcinated SiO2 were loaded into a quartz tube with an inner diameter of 6 mm. The reactant was composed of 12% CO2/48% H2/15% Ar in N2 with a total flow rate of 50 mL (STP)/min. Ar was used as the internal standard. The activity test was conducted at 0.1 MPa in the temperature range of 548 to 623 K with a GHSV of 30,000 mL g−1 h−1. The products were analyzed online using an Agilent GC7890B equipped thermal conductivity (TCD) and flame ionization detector (FID), respectively. For the Mo2C-Ni/SiO2 samples, the standard pre-treatment was conducted at 590°C for 2 h in 15% CH4/H2 with a flow rate of 50 mL (STP)/min; whereas, H2 was only used for Ni/SiO2 as references. In the quantification, the conversion of CO2 is defined as:
XCO2 (%) = (ni,CO2 - nout,CO2) / ni,CO2 * 100%
The observed rate (robserved) is corrected using the Temkin-Pyzhev formalism as follows:
rcorrected = robserved / (1 - η)
The carbon balance is defined as:
BC (%) = (nout,CO2 + nout,CO + nout,CH4) / ni,CO2 * 100%
In all tests, the carbon balance of the system is above 94%.

Computational details
The spin-polarized first-principle calculations are performed with Vienna Ab Initio Simulation Package (VASP 5.4.4). Perdew-Burke-Ernzerhof (PBE) functional was used to solve the Kohn-Sham equations within periodic boundary conditions. The electron-nucleus interactions are described using PAW pseudopotentials. A 4×4×4 Monkhorst-Pack k-point grid was used for bulk β-Mo2C and Ni, and a 2×2×1 k-point grid was used for the layered SiO2 structure derived from a recently reported silicate. Γ-centered grids with equivalent k-point density were then used in calculations of clean and Ni-deposited surface structures on β-Mo2C and SiO2. A plane wave cutoff of 400 eV was used throughout this work. Second-order Methfessel-Paxton smearing with a width of 0.10 eV was used to handle the partial occupancies of the bands. The convergence criterion for energy is 1×10−5 eV and that for ionic relaxation is 0.01 eV/Å. With the above setup, the calculated lattice parameters a, b and c of bulk β-Mo2C are 6.06, 6.07 and 4.07 Å, respectively, while that for bulk face-center-cubic Ni was 3.51 Å. The layered SiO2 was found plausible in an orthorhombic lattice of 10.94×10.30 Å2. After test calculations, (101) surface slab with thickness of 4 Mo layer with mixed C and Mo termination was selected to mimic (101) surface of β-Mo2C, as the adsorption energy of a single Ni atom on (1×1) slabs in the configuration bridging 2 nearest neighboring surface C already converges within 0.03 eV. The stability of deposited Nin structures was investigated on a (2×2) supercell of (101) β-Mo2C and a (1×1) orthorhombic slab of SiO2. The freestanding Nin clusters were investigated in a 15.00×15.10×15.20 Å3 orthorhombic cell. The relative stabilities of Nin structures (ΔGf,Nin=Support) were determined with the normalized formation free energy, calculated as:
ΔGf,Nin=Support = G(Nin=Support) - n*ENi,atom - G(Support) / n
where G(Nin=Support), n, ENi,atom and G(Support) are the free energy of the Nin/support composite, the number of Ni atoms in the Nin/support composite, electronic energy of a single Ni atom and the free energy of the support, respectively. First-principles thermodynamics scheme was adapted to calculate free energy of Nin/support composites and the support at finite T. Free energy is approximated from Helmholtz free energy by ignoring pV term, and was calculated as:
G(T) = E_DFT + Evib - TSvib
Where Evib and Svib are vibrational energy and entropy, respectively. Svib was calculated with partition functions of structures in the temperature range of interest. For reference, the formation energies of these Nin structures (ΔEf,Nin=Support) were also calculated as
ΔEf,Nin=Support = E(Nin=Support) - n*ENi,atom - E(Support) / n
where E(Nin=Support), n, ENi,atom and E(Support) are the total energy of the Nin/support composite, the number of Ni atoms in the Nin/support composite, electronic energy of a single Ni atom and the total energy of the support, respectively. With the above setup and definition, the calculated ΔEf,BulkNi is −4.79 eV.

The pathways for CO2 hydrogenation over Mo2C(101) and Ni/SiO2 were investigated with spin-polarized first-principles-based calculations using Perdew-Burke-Ernzerhof (PBE) functional within the formalism of generalized gradient approximation (GGA) as implemented in the DMol3 package. DFT semi-core pseudopotentials (DSPP) and the double numerical plus polarization (DNP) basis sets were used to describe the core and valence electronic states. Test calculations on bulk and surface structures of Mo2C, Mo2C(101), Ni/Mo2C(101) and Ni1/SiO2, as well as energetics and structural of CO, CO2 and H2 adsorption over these model structures yield essentially the same results as those obtained with VASP.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Reviewer’s report\nNCOMMS-25-00094A-Z: Ni redispersion from SiO2 substrate to molybdenum carbide for dual interfaces generation to boost\ntandem CO2 hydrogenation\nAlong manuscript, the authors address the topic of redispersion of Ni nanoparticles from SiO2 to Mo2C after the mechanical\nmixture between a Ni/SiO2 catalyst with Mo2C. They characterize the samples with multiple bulk and surface sensitive\ntechniques, which allowed them in some cases to sustain their claims of redispersion, additionally commenting on the effect\nof integration method (i.e. GL, DS, MM, BM) and reduction temperature. The analysis of the structure of the catalysts is then\nrelated to kinetic measurements and a plausible reaction mechanism sustained by experimental observations and DFT\ncalculations is suggested. Although the results are sounding (e.g. an increase of 50% in product selectivity towards\nmethane) the work may lack the required novelty to be accepted for publication in Nature Communications, which needs to\nbe thoroughly highlighted. Moreover, multiple points need to be addressed over the manuscript, as stated hereafter, before\nbeing further considered for publication.\n1. From the perspective of a hypothetical reader who is not an expert on the effects of TMCs, the question of lack of novelty\nis immediately raised by comparing the state-of-the-art that the authors describe with one of the main conclusions from the\nwork. Within their introduction, they state that: “Compared to metal oxides, TMCs as carrier are able to form more stable\nchemical bonds with loaded metals, especially at high-temperature reductive conditions, thereby promoting a suitable\nsubstrate to redisperse metals and create new interfaces”, and then dedicate half of the manuscript to demonstrate exactly\nthis for Ni/SiO2 – Mo2C. In this sense, it seems that the novelty of this contribution lays in the solely application of this\nphenomena, previously reported in the literature, to the CO2 methanation, which may not be enough for the high standards\nof Nature Communications. The authors are invited to address this concern and reformulate the novelty of their work\ncompared to the state-of-the-art so that it is clear to the reader.\n2. In general, the authors sustain many of their conclusions in the first half of the manuscript with the Ni particle size\nmeasured from XRD and the Scherrer equation. Some examples are listed hereafter:\n- Page 5: “The average Ni crystallite size decreased from 21.6 to 17.3 nm by calculating the reflection of Ni (111) plane”.\n- Page 6: “Noticeably, the crystallite size of Ni obtained by ball milling (BM) and motor milling (MM) prepared Mo2C-Ni/SiO2\ncatalysts is remarkably smaller than that of the gradular stacking (GS) prepared one (BM: 17.3 nm; MM: 18.7 nm; GS: 20.5\nnm)”\n- Page : “The particle size reduction was further observed to be ca. 17.3 nm with an increase in activation temperature from\n500 to 590 ºC”.\nThe Scherrer equation based solely on one diffraction feature (i.e. a unique crystal plane) is highly imprecise and certainly\ndo not allow to make claims regarding the “average” particle size, nor to describe differences of ~3 nm as “remarkably”\nsmaller. In each of those cases, strong claims are made regarding the Ni particle size and based on them, conclusions are\ndrawn for the effect of mixing method and pretreatment temperature. This is out of proportions and needs to be corrected,\nespecially in this manuscript where more precise techniques like TEM and STEM-EDX are available for the quantitative\nanalysis of the particle size. Otherwise, a more elaborated approach, based for instance on a Rietveld analysis, is expected.\nFurthermore, in page 6 the authors claim that “Therefore, we can infer that the proximity between Ni and Mo2C is able to be\nadjusted from micro- to nano-scale based on the mechanical strength provided by different mixing methods, which in turn\ninfluences the dispersion of Ni NPs”, which is sustained by the gradual change in the oxidation states of both Ni and Mo. Is\nthere a correlation, ideally linear, between the oxidation state Ni or Mo and the Ni particle size which could sustain this\nsuggestion?\n3. The authors comment the trends from XPS with respect to the metallic Ni and the corresponding charge transfer.\nNevertheless, Figure 1 also shows a change in the contribution from Ni2+. To what is the decrease in Ni2+ ascribed? Could\nbe related to an easier reduction of Ni after its redispersion?\n4. The quantitative evidence from XPS is interpreted in terms of what the authors call “descriptors”. For instance, the authors\nclaim that “The XPS spectra (Figure 1g, Figure S2(c), Table S1) showed that the ratio of Moδ+/Mo2+ gradually increased\nfrom 1.59 to 1.67 as the temperature increased from 500 to 590ºC and almost remained after 590ºC”. Equivalently, what are\nthe trends from Ni? Figure 1f do not show differences consistent with the degree of redispersion as function of temperature\nthat the authors claim.\n5. As a general comment, up to the results from TEM, the conclusions from the effect of mixing and treatment temperature\nrelated to the Ni particle size are overestimated and poorly sustained.\n6. The results from CO-DRIFTS are poorly analyzed. Particularly, claims made by the authors are addressed hereafter:\n- In the methodology, the authors state that “All the spectra were obtained in transmission mode unless otherwise indicated”.\nHow can DRIFTS be measured in transmission mode?\n- Page 7: “One significant change is the red shift of CO on Moδ+ with increased activation temperature on Mo2C-Ni/SiO2\ncatalyst”. The low magnitude of the redshift mentioned by the authors is not evident and, if existent, could perfectly be\nascribed to differences in CO coverage and dipole effects in between measurements.\n- In the SI, Figure S5, the authors ascribe a significant change of the CO adsorption features to shifts of 2 cm-1. This is within\nthe margin of error of DRIFTS and could be related, among others, to the preparation of the sample for measurement in each\ncase.\n- Page 7: “Concomitantly, a new CO adsorption band at 2140 cm-1 appeared, which can be assigned to Niσ+ species”. The\nchange of the oxidation state of Ni and its relationship to redispersion is an idea that the authors themselves introduced\nbased on the XPS results, but the appearance of new vibration features from CO-DRIFTS over a sample treated at different\ntemperatures does not necessarily means redispersion. Furthermore, the authors claim in the manuscript that Ni would be in\nthe form of isolated sites over Mo2C. Under this hypothesis and considering that isolated sites are exempt of coverage\neffects, what would be the reason behind the blueshift observed for the Niσ+ feature as the reduction temperature\nincreases?\n- The authors are invited to further analyze the CO-DRIFTS results, for instance, by performing Gaussian deconvolution and\nretrieving the vibration features from Ni0 in the mixed samples. In contrast to XPS which slightly penetrates the surface of the\ncatalyst, CO-DRIFTS is a highly sensitive technique which only probes the exposed surface sites and, therefore, could yield\nmore reliable information for this this work.\n7. The measurement of the particle size from TEM could be the first quantitative and conclusive evidence regarding the\nparticle size change after the mixing with Mo2C. Nevertheless, the counts for statical significance are not presented and only\n2 images are depicted in the supplementary. This information is required. If the values are precise, then these results should\nbe presented before in the manuscript to sustain the claims regarding redispersion, rather than with the Scherrer equation.\n8. EDX mapping are also a compelling evidence of the formation of a Ni-Mo2C species. Nevertheless, the results are\npresented only for the BM-590ºC, and the effect of the temperature and mixing on the particle size and redispersion remains\nunaddressed with this technique. If this information is available, it should be added.\n9. Regarding Figure 2, the authors present a comparison between the different samples and state that Ni would be better\ndispersed over Mo2C than over SiO2. Nevertheless, it is intriguing that the number of points observed from the EDX\nmapping of Si is also low (Figure 2g). How different were the counts in each EDX experiment? To make conclusions of the\nNi dispersion in each phase, this is critical.\n10. Page 9: “From the above analysis, we can deduce that the electronic perturbation of Ni is mainly induced by the strong\ninteraction between Ni and Mo2C” How? Same experiments were not performed over a Ni/SiO2 reference?\n11. Figure 4: since the conversions at 350ºC drastically differ between the distinct catalysts, the selectivity is not directly\ncomparable under these conditions. Selectivity at the same conversion level should be provided as a compelling evidence\nof enhanced methane formation.\n12. Page 10: “As a result, close sites intimacy between Ni-Mo2C and Ni-SiO2 interface can be established, thus enhancing\nthe formation of CH4”. What happened with the argument of higher degree of redispersion among the distinct mixing\nmethods? Is this not playing a role here? Is it intimacy or redispersion from SiO2 to Mo2C?\n13. Page 11: “Also, the CO2 conversion exhibited a gradual increase as the activation temperature increased up to 590ºC\nand slightly dropped thereafter (Figure S18).” Considering the change in Ni particle size with treatment temperature and the\nstructure-sensitivity of the CO2 hydrogenation that they mention, do they expect any degree of structure-sensitivity related to\nthe particle size of Ni for the ranges analyzed in this work and the reported changes in dp? Is the increased conversion\nrelated to a change in the particle size or to the generation of a new active site?\n14. Page 11: “To ensure the measurements maintained in a kinetic-relevant regime, the CO2 conversion was limited to 15%\nwith a relatively high space velocity of 60,000 mL g-1 h-1 at various temperatures”. Under these conditions, the equilibrium\nconversion reported by the authors is around 60%, from where an approach to equilibrium close to 0.25 is obtained. Is this\ntruly kinetic regime? A correction of the rates by the approach to equilibrium is recommended. Please refer to\nhttps://doi.org/10.1021/acscatal.4c05805\n15. Page 11: “TOF; as normalized by the number of CO chemisorption sites” how was the CO chemisorption measured?\n16. Page 11: “strongly indicating the increased atomic utilization of Ni upon Mo2C addition” how do the authors get to this\nconclusion based on the TOF? This is only indicating that the rate normalized per “active site” is higher. Please elaborate.\n17. A suggestion: an analysis of the rates, TOF and Eapp separately for each reaction (i.e CH4 and CO formations) would\nyield more information, e.g. is there a product which formation is selectively inhibited? How is the new active site affecting each product?", "reviewer_2": "This manuscript discusses the effects of CO2 hydrogenation selectivity (CO or CH4 as the main product) resulting from the\nredispersion/re-speciation of Ni in Mo2C-SiO2 composite catalysts. The strong metal-support interaction (SMSI) is\nsuggested to drive the Ni migration from SiO2 to Mo2C, which is reflected in the hydrogenation selectivity. The manuscript is\nmostly reasonable, but the following criticism is pertinent:\n1) The discussion of the XPS results is extensive yet questionable. It is known that activated Mo2C-based catalysts react\nvigorously (oxidize) when exposed to ambient air. While the main text does not mention the sample handling before data\nacquisition, the SI description states that the sample preparation was conducted in a glove box; however, the sample holder\nwas then introduced into the XPS measurement with exposure to air. It is, therefore, unclear what the implications of this air\nexposure are. For instance, is the presence of the oxidized Mo4+ and Mo6+ states in Figure 1b due to the air exposure\nduring sample transfer from the glove box to the instrument? The handling (air exposure) should be stated clearly in the main\ntext, and its consequences should be discussed.\n2) The peak at 228.2 eV is ascribed to Mo2+ of Mo2C, which is justified. The peak at 227.7 eV is ascribed to Mo(delta +), i.e.,\nan oxidation state between 0 and 2+. However, Mo(0) in related catalytic systems has a BE at 227.5-227.7 eV, which is very\nclose to the fitted value of 227.7 eV. On what basis did the authors rule out the formation of Mo(0)? This is unclear, and if not\nexcluded rigorously, Mo(0) should be considered an alternative assignment for this peak.\n3) To induce the SMSI, the authors use a 15% CH4/H2. Why is the carbon source necessary, and what is the role of\nmethane’s carbon in the proposed SMSI mechanism? Would the redispersion and the associated switch in CO2\nhydrogenation selectivity not take place only when using the H2 pretreatment?\n4) The nature of Ni species formed in the interaction with Mo2C under the CH4/H2 pretreatment is unclear. Do the authors\nsuggest surface Ni carbide?\n5) The authors do not discuss the carbon balance of their experiments. Please provide this data.\n6) The authors write on page 12 that “the Mo2C alone exhibited a spontaneous CO2 dissociation, forming CO(g) as major\nproduct, indicating the weak interaction between CO and carbides”. Note that the spontaneous CO2 dissociation indicates\nstrong interaction of CO2 and pristine carbides. Instead, the authors wanted to say that Mo2C surface passivated with O*\nfrom the CO2 dissociation does not interact with CO strongly.\n7) There are several typos and small mistakes in the text; for instance, the traces are unlabelled in Fig. 1d; the caption to the\nsame Fig. has an unrelated chi+ symbol; the authors use the term “quasi in-situ XPS” for their method, but this is misleading\nand should be changed for to ex-situ XPS with air exposure; it is unclear what is meant by “graphically” confirming Ni\nredispersion with HRTEM; “Hütting” temperature should read “Hüttig”; “maraked” should be “marked”; “romve” should be\n“remove”, etc."}, "author_response": "A point-to-point response to the comments\nReviewer #1:\nAlong manuscript, the authors address the topic of redispersion of Ni nanoparticles from SiO to\n2 2 2\nsamples with multiple bulk and surface sensitive techniques, which allowed them in some cases to\nsustain their claims of redispersion, additionally commenting on the effect of integration method\n(i.e. GL, DS, MM, BM) and reduction temperature. The analysis of the structure of the catalysts is\nthen related to kinetic measurements and a plausible reaction mechanism sustained by experimental\nobservations and DFT calculations is suggested. Although the results are sounding (e.g. an increase\nof 50% in product selectivity towards methane) the work may lack the required novelty to be\naccepted for publication in Nature Communications, which needs to be thoroughly highlighted.\nMoreover, multiple points need to be addressed over the manuscript, as stated hereafter, before\nbeing further considered for publication.\nRESPONSE:\nWe sincerely thank Reviewer#1 for your insightful and constructive feedback. The reviewer has\nacknowledged several key strengths of our manuscript, which investigates the redispersion of Ni\nnanoparticles from SiO to Mo C following the mechanical mixing of Ni/SiO catalyst with Mo C.\n2 2 2 2\nWe comprehensively characterized the samples using multiple bulk- and surface-sensitive\ntechniques to substantiate the redispersion phenomenon, while also examined the effects of\nintegration method (GL, DS, MM, BM) and reduction conditions. Our structural analysis of the\ncatalysts correlates with kinetic measurements, leading to a plausible reaction mechanism supported\nby experimental observations and DFT calculations. The results are compelling, including a notable\n50% increase in methane selectivity.\nWe greatly appreciate the reviewer’s constructive criticisms regarding novelty and manuscript\nrefinement. The suggested points are invaluable for enhancing both the scientific impact and clarity\nof this study. We address each comment in detail below and are confident these revisions will\nsignificantly strengthen the paper’s overall quality and contribution to the field.\n2 / 41\nComment 1: From the perspective of a hypothetical reader who is not an expert on the effects of\nTMCs, the question of lack of novelty is immediately raised by comparing the state-of-the-art that\nthe authors describe with one of the main conclusions from the work. Within their introduction, they\nstate that: “Compared to metal oxides, TMCs as carrier are able to form more stable chemical\nbonds with loaded metals, especially at high-temperature reductive conditions, thereby promoting\na suitable substrate to redisperse metals and create new interfaces”, and then dedicate half of the\nmanuscript to demonstrate exactly this for Ni/SiO – Mo C. In this sense, it seems that the novelty\n2 2\nof this contribution lays in the solely application of this phenomena, previously reported in the\nliterature, to the CO methanation, which may not be enough for the high standards of Nature\ntheir work compared to the state-of-the-art so that it is clear to the reader.\nReply: We sincerely appreciate the reviewer’s insightful comments that prompted us to better\narticulate the fundamental advances of this work. We would like to emphasize the contribution and\nadvances of our present work from the following perspectives.\nPoint 1: Our present work is mainly focused on studying the redispersion of metal particles\nfrom one substrate to another, not their dispersion behaviors on one carrier. Indeed, Lin et al.[1]\nobserved the reversed sintering of Ni particles (2 wt%) on γ-Mo N under reductive treatment. Our\n2\nprevious works also uncovered the unique properties of α-MoC on Au[2] and Pt[3] dispersion with\nmaximum loading less than 5%, as raft-like structure or single atoms, respectively. All the listed\nstudies highlighted the significant role of Mo C on metal dispersion, akin to a spontaneous metal\n2\nself-dispersion process during catalyst synthesis due to the strong metal-support interaction (SMSI).\nIn our present study, we prepared a Ni/β-Mo C supported catalyst as reference and observed that\n2\nthe limited surface areas of β-Mo C impede the maximum Ni loading to <1.0 wt% due to the uneven\n2\nparticle size distribution. How to resolve the intrinsic trade-off of metal loading and dispersion\nbecomes the issue in catalyst design. To address this, we designed a Mo C-Ni/SiO composite\n2 2\ncatalyst with Ni loading of 10% by taking advantage of the redispersion of Ni from SiO to\n2 2\nMo C-Ni/SiO catalyst is about 7.8x’s higher than that of 10Ni/SiO , with near absolute CH\n2 2 2 4\n3 / 41\nselectivity. Therefore, we can demonstrate that the cross-support redispersion enables the\nunprecedented metal loading-activity synergies.\nPoint 2: Metal redispersion, a structural reorganization behavior driven by strong metal-\nsupport interaction (SMSI), serves as an effective tool to create multiple interfaces and\ngenerate more active sites on the pristine catalysts. While this approach has been recently\nreported on reducible metal oxides1, its application remains scarcely explored in metal carbide\nsystems. For example, earlier work conducted by our group uncovered the redispersion of Pt from\nCNT to α-MoC [4] as well as the redispersion of Ni from Al O to Mo C[5, 6]. Similarly, Zhou et\n1-x 2 3 x\nal.[7] discovered the migration of Cu from SiO to Mo CT on silica-supported Cu/Mo CT (MXene)\n2 2 x 2 x\ncatalyst under H treatment at 500 oC, which further confirms the effectiveness of Cu redispersion\n2\nfor nano-structuring. Despite the limited number of reported studies, the scientific significance of\nthis phenomenon cannot be overstated, as it facilitates the formation of novel interfaces that are\ncrucial for catalytic applications. More importantly, the atomistic mechanisms governing metal\nredispersion remain unresolved. To address this, we conducted a systematic study on a model Mo C-\n2\nmodeling. To the best of our knowledge, this study provides the first atomic-level evidence of\nthe SMSI-driven forces to propel Ni particles migrate from oxide to carbide and eventually\nget redispersed on carbide surface. Furthermore, several influencing factors were thoroughly\ninvestigated to get a better control on the degree of metal dispersion. A correlation was\nestablished between interfacial sites and their performance in CO hydrogenation. Remarkably, this\n2\nstrategy enabled the creation of highly dispersed catalysts at high metal loading with dual interfacial\nsites, which breaks the limitation of conventional preparation method. This work not only deciphers\nthe fundamental SMSI dynamics in carbide systems, but also provides an innovative way of\ndesigning multifunctional catalysts.\nPoint 3: The third contribution of present work is utilizing Ni redispersion as a novel strategy\nto build dual interfacial system, achieving flexible tuning on products. This constructive\nstrategy enabled the synergistic interplay of distinctive active sites that single interfacial system\ncannot be obtained. In conventional Ni-based catalysts, the metal-support interface governs either\nthe charge transfer or ensemble control, but rarely both. However, the newly designed Mo C-\n2\n4 / 41\nNi/SiO composite catalyst breaks this constraint by establishing the dual interfaces of Ni-Mo C\n2 2\nand Ni-SiO . The electronic interfacial sites provided by Ni-Mo C interface showed the potential of\n2 2\nstabilizing undercoordinated Niδ+ species for selective C=O bond cleavage, while the structural\ninterfacial sites of Ni-SiO maintained the high-density metallic ensembles for efficient H\n2 2\ndissociation. The presence of Mo C modulated the interaction between metal and support by\n2\npreventing the over stabilization of intermediates on Ni/SiO sites. This bifunctional synergy, in\n2\nwhich the Mo C dictates electronic states and SiO controls nanostructure, resolves the\n2 2\npersistent activity-selectivity-lifetime trade-off. Both the experimental and computational results\nproved the effect of dual interfacial sits. The optimized Mo C-Ni/SiO composite catalyst could\n2 2\nachieves 97% CH selectivity at 320 oC, which outperforms state-of-the-art Ni catalyst (typically <\n4\n85% at equivalent conditions). Hence, metal redispersion has been proved to be an effective strategy\nto establish dual-interface systems for cascade reactions.\nPoint 4: Advanced techniques and theoretical analysis were employed to get more insights of\nmetal dispersion as well as the catalytic role of dual interfaces. Our previous work utilized Ni-\n(Mo C)/Al O catalysts for dry reforming of methane (DRM), which demonstrates reduced Ni\nx 2 3\nparticle size via TEM analysis[5, 6]. However, a comprehensive mechanistic understanding of\nelemental migration and re-dispersion was lacking. In contrast, several advanced in-situ\ncharacterization techniques were employed in our present study, including quasi in-situ XAS and\nquasi in-situ XPS, to unequivocally demonstrate the formation of the Ni/β-Mo C interface.\nthe reaction mechanism of dual interfaces in CO hydrogenation, thereby providing a detailed\n2\nunderstanding of the catalytic role of the newly generated Ni/Mo C interface. This enhanced\n2\nmethodology exhibits broader applicability, potentially extending to other elements (such as In, Ag,\nCu, etc.)\nOverall, the above-mentioned points enrich the current body of knowledge. Therefore, we deeply\nappreciate the reviewer’s input, which prompted us to reformulate our manuscript significantly. In\nthe revised manuscript, we clarified the knowledge gaps in this research field in the\n“Introduction” section and subsequently emphasized the contribution and advances of our\npresent work in the “Results and Discussion” part. We hope that these updates could better\n5 / 41\nshowcase the study’s originality and resolve your doubts about the study’s innovation.\nComment 2: In general, the authors sustain many of their conclusions in the first half of the\nmanuscript with the Ni particle size measured from XRD and the Scherrer equation. Some examples\nare listed hereafter:\n- Page 5: “The average Ni crystallite size decreased from 21.6 to 17.3 nm by calculating the\nreflection of Ni (111) plane”.\n- Page 6: “Noticeably, the crystallite size of Ni obtained by ball milling (BM) and motor milling\n(MM) prepared Mo C-Ni/SiO catalysts is remarkably smaller than that of the granular stacking\n2 2\n(GS) prepared one (BM: 17.3 nm; MM: 18.7 nm; GS: 20.5 nm)”\n- Page : “The particle size reduction was further observed to be ca. 17.3 nm with an increase in\nactivation temperature from 500 to 590 ºC”.\nComment 2-1: The Scherrer equation based solely on one diffraction feature (i.e. a unique crystal\nplane) is highly imprecise and certainly do not allow to make claims regarding the “average”\nparticle size, nor to describe differences of ~3 nm as “remarkably” smaller. In each of those cases,\nstrong claims are made regarding the Ni particle size and based on them, conclusions are drawn\nfor the effect of mixing method and pretreatment temperature. This is out of proportions and needs\nto be corrected, especially in this manuscript where more precise techniques like TEM and STEM-\nEDX are available for the quantitative analysis of the particle size. Otherwise, a more elaborated\napproach, based for instance on a Rietveld analysis, is expected.\nReply: We appreciate the insightful suggestions from the reviewer regrading crystallite size\ndetermination. In response to this comment, we conducted comprehensive Rietveld refinement\nanalyses on the powder X-ray diffraction (XRD) patterns of Ni/SiO reference and Mo C-Ni/SiO\n2 2 2\ncomposite catalysts to determine the crystallite size of Ni0 phases. Noted that, the refinement results\ndemonstrated excellent agreement between experimental data and calculated patterns with the\nweighted profile R-factor (R ) less than 10%, as evident in the (111) plane of Ni at 2θ=43~46o\nwp\n(Figures R1-R2, Table R1).\nTo corroborate these findings, TEM/STEM analysis was employed to determine the particle size of\nNi according to the suggestion from Reviewers. Also, the crystallite size of Ni was estimated by CO\n6 / 41\npulse analysis by assuming the stoichiometric ratio of Ni to CO equals to one. As summarized in\nTable R1, both the TEM derived particle size and the estimated crystallite size by CO pulse showed\na reasonable agreement with XRD-based crystallite dimension on three planes. Similarly, the same\nmethodology has been applied to investigate the influence of varying factors (such as mixing\nmethods, activation temperature, and activation atmosphere) on Ni crystallite size (Figures R3-R8,\nTables R2-R4). Overall, multi-technique validation strongly supports the accuracy of our structural\nanalysis. Therefore, we revised the relevant descriptions and updated the rietveld refined XRD\nprofiles in the revised manuscript (Fig. 1) and Supporting Information (Figs. S4, S5, S10, S13;\nTable S1, S3-S5).\nTable R1. The effect of different carbon sources on crystallite size of the as-prepared Ni-based\ncatalysts.\nCrystallite size (nm)a\nNo. Catalyst (111) Particle size (nm)b Crystallite size (nm)c\n2θ=43-46o\n2 wp\n2 wp\nMo C-Ni/SiO\n2 2\n3 17.3 (R =0.1%) 13.8±0.2 18.1\nwp\n(BM, 590 oC, CH /H )\n4 2\na. The crystallite size of Ni calculated by the Scherrer equation, which corresponds to the (111) plane.\nb. The estimated crystallite size of Ni obtained from TEM and STEM measurement by counting ≥100\nparticles.\nc. The estimated crystallite size of Ni obtained from CO pulse measurements by assuming Ni particle as\ncubic structure.\n7 / 41\nFigure R1. Rietveld refined XRD patterns for the as-prepared Ni-based catalysts and Ni/SiO\n2\nreference at 2θ=43-46o. (a) Ni/SiO ; (b) C-Ni/SiO ; (c) Mo C-Ni/SiO .\n2 2 2 2\nFigure R2. TEM images of the as-prepared Ni-based catalysts and Ni/SiO reference. (a-c) Ni/SiO ;\n2 2\n(d-f) C-Ni/SiO ; (g-i) Mo C-Ni/SiO .\n2 2 2\n8 / 41\nTable R2. The effect of mixing methods on crystallite size of Mo C-Ni/SiO composite catalysts.\n2 2\nCrystallite size (nm)a\nParticle size Crystallite\nNo. Catalyst (111)\n(nm)b size (nm)c\n2θ=43-46o\nMo C-Ni/SiO\n2 2\n1 20.6 (R =2.7%) 18.9±0.5 21.7\nwp\n(GS, 590 oC, CH /H )\n4 2\nMo C-Ni/SiO\n2 2\n2 18.7 (R =0.9%) 16.1±0.2 19.1\nwp\n(MM, 590 oC, CH /H )\n4 2\nMo C-Ni/SiO\n2 2\n3 17.3 (R =0.1%) 13.8±0.2 18.1\nwp\n(BM, 590 oC, CH /H )\n4 2\na. The crystallite size of Ni calculated by the Scherrer equation, which corresponds to the (111) plane.\nb. The estimated crystallite size of Ni obtained from TEM and STEM measurement by counting ≥100\nparticles.\nc. The estimated crystallite size of Ni obtained from CO pulse measurements by assuming Ni particle as\ncubic structure.\nFigure R3. Rietveld refined XRD patterns for the as-prepared Mo C-Ni/SiO composite catalysts\n2 2\nwith different mixing methods. (a) GS-granular stacking; (b) MM-Motor milling; (c) BM-Ball\nmilling.\n9 / 41\nFigure R4. TEM images of the as-prepared Mo C-Ni/SiO composite catalysts with different\n2 2\nmixing methods. (a-c) GS-granular stacking; (d-f) MM-Motor milling; (g-i) BM-Ball milling.\nTable R3. The effect of activation temperature on crystallite size of Mo C-Ni/SiO composite\n2 2\ncatalysts.\nCrystallite size (nm)a\nNo. Catalyst (111) Particle size (nm)b Crystallite size (nm)c\n2θ=43-46o\nMo C-Ni/SiO\n2 2\n1 17.6 (R =0.5%) 14.7±0.2 18.6\nwp\n(BM, 500 oC, CH /H )\n4 2\nMo C-Ni/SiO\n2 2\n2 17.3 (R =0.1%) 13.8±0.2 18.1\nwp\n(BM, 590 oC, CH /H )\n4 2\nMo C-Ni/SiO\n2 2\n3 20.1 (R =0.2%) 19.9±0.3 21.2\nwp\n(BM, 650 oC, CH /H )\n4 2\na. The crystallite size of Ni calculated by the Scherrer equation, which corresponds to the (111) plane.\nb. The estimated crystallite size of Ni obtained from TEM and STEM measurement by counting ≥100\nparticles.\nc. The estimated crystallite size of Ni obtained from CO pulse measurements by assuming Ni particle as\n10 / 41\ncubic structure.\nFigure R5. Rietveld refined XRD patterns for the as-prepared Mo C-Ni/SiO composite catalysts\n2 2\nwith different activation temperatures. (a) 500 oC; (b) 590 oC; (c) 650 oC.\nFigure R6. TEM images of as-prepared Mo C-Ni/SiO composite catalysts with different activation\n2 2\ntemperatures. (a-c) 500 oC; (d-f) 590 oC; (g-i) 650 oC.\n11 / 41\nTable R4. The effect of activation atmosphere on crystallite size of Mo C-Ni/SiO composite\n2 2\ncatalysts.\nCrystallite size (nm)a\nNo. Catalyst Particle size (nm)b Crystallite size (nm)c\n(111)\n2θ=43-46o\nMo C-Ni/SiO\n2 2\n1 17.5 (R =0.3%) 14.9±0.3 18.3\nwp\n(BM, 590 oC, H )\n2 2\n2 17.3 (R =0.1%) 13.8±0.2 18.1\nwp\n(BM, 590 oC, CH /H )\n4 2\na. The crystallite size of Ni calculated by the Scherrer equation, which corresponds to the (111) plane,.\nb. The estimated crystallite size of Ni obtained from TEM and STEM measurement by counting ≥100 particles.\nc. The estimated crystallite size of Ni obtained from CO pulse measurements by assuming Ni particle as cubic\nstructure.\nFigure R7. Rietveld refined XRD patterns for the as-prepared Mo C-Ni/SiO composite catalysts\n2 2\nunder different activation atmospheres. (a) H ; (b) CH /H .\n2 4 2\n12 / 41\nFigure R8. TEM images of the as-prepared Mo C-Ni/SiO composite catalysts with different\n2 2\nactivation atmospheres. (a-c) H ; (d-f) CH /H .\n2 4 2\nComment 2-2: Furthermore, in page 6 the authors claim that “Therefore, we can infer that the\nproximity between Ni and Mo C is able to be adjusted from micro- to nano-scale based on the\n2\nmechanical strength provided by different mixing methods, which in turn influences the dispersion\nof Ni NPs”, which is sustained by the gradual change in the oxidation states of both Ni and Mo. Is\nthere a correlation, ideally linear, between the oxidation state Ni or Mo and the Ni particle size\nwhich could sustain this suggestion?\nReply: We appreciate this valuable suggestion. To address this, we examined the correlation of\noxidation states of Ni and Mo (Niσ+/Ni0 and Moδ+/Mo2+) with Ni crystallite size, respectively. The\nanalysis revealed a good linear correlation of Moδ+/Mo2+ or Niσ+/Ni0 with Ni crystallite size (Figure\nR9), supporting the observed gradual change of Ni or Mo states with mechanical strength. These\nfindings have been included in the revised Supporting Information (Figure S8).\n13 / 41\nFigure R9. A correlation of the oxidation state of Mo or Ni with Ni particle size.\nTo sum up, major revisions are made as follows:\n- Page 5:“The average Ni crystallite size decreased from 21.6 to 17.3 nm by calculating the\nreflection of Ni (111) plane”. has been modified as “The transmission electron microscopy (TEM)\nanalyses were employed to determine the cluster size of Ni. It was found that a small portion\nof Ni aggregated unevenly on SiO over the Ni/SiO reference, with crystallite size of 19.5±0.4\n2 2\nnm (Figure 1a, Figure S1). In contrast, the Ni-Mo C/SiO catalyst exhibited well-distributed\n2 2\nNi-enriched dark dots on SiO , characterized by a decreased average particle size of 13.8±0.2\n2\nnm (Figure 1b, Figure S2). While the estimated Ni particle size is about 18.1±0.2 nm on the C-\nNi/SiO catalyst (Figure S3), indicating a negligible impact on Ni distribution over C-Ni/SiO\n2 2\ncatalyst. Therefore, we can deduce that C does not possess similar ability as Mo C does, an\n2\nindication of weak interaction between Ni and C. Figure 1c shows the Rietveld-refined powder\nX-ray diffraction (PXRD) profiles of the prepared catalysts …. The crystallite size of Ni\ndecreased from 21.6 to 17.3 nm by calculating the reflection of Ni (111) plane. Meanwhile, the\nestimated crystallite size of Ni obtained from CO pulse measurement showed a decrease as\nwell upon mixing with Mo C (Table S1).\n2\n- Page 6: “Noticeably, the crystallite size of Ni obtained by ball milling (BM) and motor milling\n(MM) prepared Mo C-Ni/SiO catalysts is remarkably smaller than that of the granular stacking\n2 2\n(GS) prepared one (BM: 17.3 nm; MM: 18.7 nm; GS: 20.5 nm)” has been modified as “Noticeably,\nthe crystallite size of Ni obtained by ball milling (BM) and motor milling (MM) prepared\n14 / 41\nMo C-Ni/SiO catalysts exhibits reduced particle size compared to their granular stacking (GS)\n2 2\ncounterparts across the (111) plane (BM: 17.3 nm; MM: 18.7 nm; GS: 20.6 nm), underscoring\nthe critical role of mechanical strength on Ni dispersion (Figure S5). Importantly, the TEM-\nderived particle size shows a reasonable agreement with the XRD-based crystallite dimensions\n(Figures S6, Table S3), which validates the reliability of our multi-scale characterization\napproach.”\n- Page 7: “The particle size reduction was further observed to be ca. 17.3 nm with an increase in\nactivation temperature from 500 to 590 ºC” has been modified as “The TEM analyses revealed a\nreduction in Ni particle size from 19.5±0.4 nm for the pristine Ni/SiO catalyst to 14.7±0.2 nm\n2\nfollowing mixing with Mo C and CH /H treatment at 500 oC. Elevating the activation\n2 4 2\ntemperature to 590 oC resulted in a further decrease to approximately 13.8±0.2 nm (Figure\nS12). However, the crystallite size of Ni significantly increased to 19.9±0.3 nm when reduced\nat 650 oC (Figure S13, Table S5).”\nComment 3: The authors comment the trends from XPS with respect to the metallic Ni and the\ncorresponding charge transfer. Nevertheless, Figure 1 also shows a change in the contribution from\nNi2+. To what is the decrease in Ni2+ ascribed? Could be related to an easier reduction of Ni after\nits redispersion?\nReply: We sincerely appreciate the reviewer’s insightful comments and apologize for the lack of\nclarity in our original statement. To address this point, we provide a detailed explanation for the\ndecrease of Ni2+ content in the Mo C-Ni/SiO catalyst. The XPS analysis reveals that the Ni2+ (likely\n2 2\nin Ni-O-Si structure) accounts for 47% in the pristine Ni/SiO catalyst, whereas this proportion\n2\ndecreases significantly to 22% in the reduced Mo C-Ni/SiO catalyst. This phenomenon aligns with\n2 2\nour prior observation on the Mo C-Ni/Al O system[8], where the introduction of Mo C similarly\n2 2 3 2\nsuppressed Ni2+ stabilization. We attribute this trend to the interfacial synergy between Mo C and\n2 2\nthe anchoring effect of the SiO support on Ni species. Consequently, fewer Ni atoms remain\n2\ncoordinated in the oxidized Ni-O-Si state, facilitating their reduction during catalyst activation to\nsome extent. This mechanism has been explicitly clarified in the revised manuscript to emphasize\n15 / 41\nthe role of Mo C in modulating metal-support interactions. We thank the reviewer for highlighting\n2\nthis critical discussion point.\nComment 4: The quantitative evidence from XPS is interpreted in terms of what the authors call\n“descriptors”. For instance, the authors claim that “The XPS spectra (Figure 1g, Figure S2(c),\nTable S1) showed that the ratio of Moδ+/Mo2+ gradually increased from 1.59 to 1.67 as the\ntemperature increased from 500 to 590ºC and almost remained after 590ºC”. Equivalently, what\nare the trends from Ni? Figure 1f do not show differences consistent with the degree of redispersion\nas function of temperature that the authors claim.\nReply: We thank the reviewer’s meticulous observation regarding the temperature-dependent trends\nof Ni and Mo species. Noted that, as the activation temperature increased from 500 to 590 oC, the\nNiσ+/ Ni0 ratio rised from 0.81 to 0.85, indicating an enhanced Ni redispersion driven by the\ninterfacial interactions with Mo C substrate. While, this ratio decreased when temperature is above\n2\n590 oC (e.g. at 650 oC), because the thermodynamic driving force for Ni redispersion is overtaken\nby Ni0 agglomeration on the SiO support. Therefore, there is a decline in Niσ+/ Ni0 ratio at 590~650\n2\noC. This result indicates that the 650 oC exceeds the optimal range for sustaining Ni migration and\nredispersion kinetics. Consequently, excessive thermal energy promotes Ni particle coalescence\nrather than interfacial redistribution, as evidenced by the reduced Niσ+/Ni⁰ ratio. Also, there is an\nobserved change on Ni particle size as evidenced by the Rietveld-refined XRD analysis, TEM,\nand\nCO pulse measurements (Figures R5-R6, Table R3). To make the statement clear, the above\ninterpretation has been updated into the “Results and Discussion” section of the revised manuscript\nto better align the Ni and Mo descriptor trends with the proposed mechanism. The modifications are\nas follows:\n“Manuscript Page 7: The XPS spectra (Figure 1g, Table S2) revealed a temperature-dependent\nevolution of metal species ratios. As the activation temperature increased from 500 to 590 oC, the\nMoδ+/Mo2+ ratio progressively increased from 1.59 to 1.67, reaching a plateau above 590 oC.\nConcurrently, the Niσ+/ Ni0 ratio showed a parallel enhancement from 0.81 to 0.85 within the same\ntemperature window, indicative of Mo C-mediated interfacial interactions facilitating Ni\n2\nredispersion. However, a decline in the Niσ+/Ni0 ratio was observed between 590 and 650 oC,\n16 / 41\nbecause the thermodynamic driving force for Ni redispersion is overtaken by Ni0 agglomeration on\nSiO support. This inversion suggests that while elevated temperatures initially promote the\n2\nformation of Ni-Mo C interfacial sites through enhanced metal migration kinetics, the dominant\n2\nmechanism shifts to Ni agglomeration on SiO surfaces beyond 590 oC, where the cohesive energy\n2\nof metallic Ni clusters overcomes the dispersion forces generated by the Mo C matrix.”\nmixing and treatment temperature related to the Ni particle size are overestimated and poorly\nsustained.\nReply: We sincerely appreciate the reviewer’s insightful critique regarding the statistical validity of\nNi particle size evolution. To rigorously address this concern, we have systematically implemented\na multi-modal characterization protocol to strengthen the quantitative correlation between thermal\ntreatment conditions and Ni particle dynamics by three independent analytic approaches:\nMethod I. XRD patterns as macro-average information\nWe performed Rietveld refinement of the X-ray diffraction (XRD) patterns to quantify the\ncrystallite size of Ni based on (111), (200) and (220) planes, with rigorous reporting of the “R-\nweighted pattern” (R ) (Figures R1, R3, R5, R7). It was found that these crystallographic\nwp\norientations yielded consistent results.\nMethod II. CO chemisorption\nThe CO uptake was measured using pulsed chemisorption at 35 oC. After that, the metal\ndispersion was calculated by assuming the adsorption stoichiometric ratio of CO/Ni of unity. Also,\nthe crystallite size was calculated based on CO uptake (Tables R1-R4).\nMethod III. Particle-size distribution utilizing TEM\nThe clusters/particles identified in the TEM images were measured and counted to yield a size\ndistribution that was fitted to a Gaussian distribution to determine the average size of the\ncluster/particle (Figures R2, R4, R6, R8). Tables R1-R4 have summarized the textural properties\nof all the as-synthesized Mo C-Ni/SiO catalysts.\n2 2\nIn the meanwhile, a quantitative linear correlation was established between Moδ+/Mo2+ and Niσ+/Ni0\n17 / 41\nwith Ni crystallite size, respectively (Figure R9). The concurrent electronic state change of Ni2p\nand Mo3d was revealed and elucidated the charge transfer between Ni and Mo C. The binding\n2\nenergy (B.E.) of Ni2p shifted from 852.7 to 853.0 eV accompanied by the formation of Ni-C-Mo\n3/2\nbonds at 855.1 eV. At the same time, the B.E. of Mo3d shifted from 228.2 to 227.7 eV, which\n5/2\nconfirmed the charge transfer from Ni to Mo C. To sum up, these findings substantiate our proposed\n2\nmechanism where the strong metal-carbide interaction could modulate the surface free energy and\ncreate interfacial sites to suppress Ostwald ripening. The integrated analysis framework of XRD-\nTEM-XPS-chemisorption now provides statistically robust coherent evidence for temperature-\ndependent Ni size regulation. We have extensively revised the Results and Discussion section to\nexplicitly address these multi-technique correlations and their implications.\nComment 6. The results from CO-DRIFTS are poorly analyzed. Particularly, claims made by the\nauthors are addressed hereafter:\nComment 6-1: In the methodology, the authors state that “All the spectra were obtained in\ntransmission mode unless otherwise indicated”. How can DRIFTS be measured in transmission\nmode?\nReply: We sincerely appreciate the reviewer’s insightful comment. The statement regarding\nDRIFTS measurement modes contained an inaccuracy, as Diffuse Reflectance Infrared Fourier\nTransform Spectroscopy (DRIFTS) is fundamentally incompatible with transmission mode\nmeasurements by its operational principle. We have thoroughly revised the Methodology section in\nthe Supporting Information to remove this erroneous description and ensure technical precision in\nour experimental characterization. Again, we thank the reviewer for their meticulous attention to\nthis technical detail.\nComment 6-2: Page 7: “One significant change is the red shift of CO on Moδ+ with increased\nactivation temperature on Mo C-Ni/SiO catalyst”. The low magnitude of the redshift mentioned by\n2 2\nthe authors is not evident and, if existent, could perfectly be ascribed to differences in CO coverage\nand dipole effects in between measurements.\nReply: We appreciate the reviewer’s valuable insights regarding the interpretation of CO adsorption\nbehavior. Firstly, we fully concur with the reviewer’s observation that the CO coverage variation\n18 / 41\ncould induce the spectral shifts through dipole coupling effects. To mitigate such interference, all\ncatalysts were systematically diluted with quartz sand at a mass ratio of 1:5 prior to DRIFTS\nmeasurements. This standardized procedure could effectively reduce the CO molecular density on\nthe surface, thereby minimizing the intermolecular dipole interactions. We have explicitly\ndocumented the experimental detail in the revised Experimental Procedures of the revised\nSupporting Information. Secondly, there are two key observations support our electronic effect\ninterpretation over coverage-induced artifacts. (i) Neither peak broadening nor significant line shape\nmodifications were detected in either the Moδ+ (1950~2050 cm-1) or Niσ+ (2120~2170 cm-1)\nadsorption regions across the varied activation temperature. (ii) the observed concurrent redshift of\nMoδ+ and blueshift of Niσ+ with increased activation temperature presents a chemically meaningful\ncorrelation. This reciprocal shift pattern strongly suggests the electron redistribution, where the\nelevated temperature enhanced the electron transfer from Ni to Mo sites, which is consistent with\nour XPS valence analysis. A purely coverage-dependent mechanism could not produce such\nopposing directional shifts in neighboring adsorption sites. Finally, we acknowledge the reviewer’s\nvalid concern regarding the subtle red shift of Moδ+. The original text’s emphasis on this feature has\nbeen moderated in the revised manuscript, with parallel characterization data from XPS and XAS\nproviding complementary evidence for the electronic structure evolution. The modifications are as\nfollows:\n“Manuscript – Page 8: Furthermore, the diffuse reflectance infrared spectra (DRIFTS) was\nemployed by using CO as probe molecule to provide additional evidence on the electronic states of\nNi and Mo species. The systematic analyses revealed that CO stretching vibrations associated with\nMoδ+ sites exhibited a progressive redshift across the region of 1950~2050 cm-1 with increased\nactivation temperature. Concomitantly, the emerged Niσ+ adsorption features in 2120~2170 cm-1\ndisplayed a distinct blueshift under identical thermal treatment conditions. This anti-correlated\nspectral evolution strongly suggests temperature-dependent electron redistribution between adjacent\nNi and Mo centers, where the elevated activation temperatures promote electron donation from Ni\nto Mo species, which fully consistent with the XPS valence state and XAS analyses.\nSupporting Information-Experimental Procedures: DRIFT spectroscopy of CO adsorption was\nemployed on a Thermo Nicolet iS50 spectrometer with a mercury cadmium telluride (MCT)\n19 / 41\ndetector cooled by liquid nitrogen to estimate the electronic state of Ni and Mo species. All catalysts\nwere prepared by diluting with quartz sands at a mass ratio of 1/5 prior to DRIFTS measurements\nto minimize the intermolecular dipole interaction of adsorbed CO. All the tests were performed in\nHarrick Praying Mantis high temperature reaction chamber with ZnSe windows.”\nComment 6-3: In the SI, Figure S5, the authors ascribe a significant change of the CO adsorption\nfeatures to shifts of 2 cm-1. This is within the margin of error of DRIFTS and could be related,\namong others, to the preparation of the sample for measurement in each case.\nReply: We thank the reviewer for raising this critical methodological consideration. We fully\nacknowledge that the observed 2 cm-1 spectral shift in Figure S5 approaches the inherent resolution\nlimit of DRIFTS measurements. While we cannot entirely exclude the potential contributions from\nminor experimental variations, we have taken the following measures to ensure rigorous\ninterpretation. (i) The original emphasis on this marginal spectral shift has been substantially\nmoderated in the revised Supporting Information. (ii) Crucially, the electronic state evolution\nsuggested by the DRIFTS aligns conclusively with quantitative analysis from XPS and XANES.\nFor example, the XPS analysis revealed a 0.5 eV binding energy decrease from 228.2 to 227.7 eV\nfor Mo3d along with a concomitant increase of 852.7 to 853.0 eV for Ni2p. Also, the XANES\nspectra of Ni K-edge showed a positive shift with increased activation temperature, which confirmed\nthe electron redistribution from Ni to Mo C. In the main text and Supporting Information, we now\n2\nframe the DRIFTS results as supportive evidence rather than primary conclusions. Therefore, we\nbelieve these modifications could alleviate the reviewer’s concerns. Please see the modification\nbelow:\n“Supporting Information-Figure S5: Noted that the CO adsorption peak on the Mo C-Ni/SiO\n2 2\ncatalyst slightly shifted towards low wavenumber of 2033 and 2006 cm-1, as indicated in the green\nbox. Combined with XPS and XANES analyses, we deduce that one possible reason of the redshift\nof Moδ+ may cause by the electron transfer from Ni to Mo carbides.”\nComment 6-4: Page 7: “Concomitantly, a new CO adsorption band at 2140 cm-1 appeared, which\ncan be assigned to Niσ+ species”. The change of the oxidation state of Ni and its relationship to\nredispersion is an idea that the authors themselves introduced based on the XPS results, but the\n20 / 41\nappearance of new vibration features from CO-DRIFTS over a sample treated at different\ntemperatures does not necessarily means redispersion. Furthermore, the authors claim in the\nmanuscript that Ni would be in the form of isolated sites over Mo C. Under this hypothesis and\n2\nconsidering that isolated sites are exempt of coverage effects, what would be the reason behind the\nblueshift observed for the Niσ+ feature as the reduction temperature increases?\nReply: We thank the reviewer for these insightful comments. We fully agree that the emergence of\nthe Niδ+-CO vibrational feature at 2140 cm-1 primarily reflects the electronic state modifications\nrather than directly evidencing metal redispersion. In response to the reviewer’s concern, we have\nrevised the original statement on Page 7 to decouple the CO-DRIFT spectral assignment from Ni\nstructural redispersion claims. Also, we have built a correlation between Moδ+/Mo2+ and Niσ+/Ni0\nwith Ni crystallite size, respectively (Figure R9). Additionally, the observed ν(CO) blueshift for\nNiδ+ species originates from the electronic and coordination environment modifications rather than\ncoverage effects, consistent with the multi-technique characterization framework.\nComment 6-5: The authors are invited to further analyze the CO-DRIFTS results, for instance, by\nperforming Gaussian deconvolution and retrieving the vibration features from Ni0 in the mixed\nsamples. In contrast to XPS which slightly penetrates the surface of the catalyst, CO-DRIFTS is a\nhighly sensitive technique which only probes the exposed surface sites and, therefore, could yield\nmore reliable information for this this work.\nReply: We sincerely appreciate the reviewer’s insightful suggestion regarding the Gaussian\ndeconvolution analysis of CO-DRIFTS spectra. In agreement with the reviewer’s view about the\nsuperior surface sensitivity of CO-DRIFTS over XPS for probing exposed active sites, we\nperformed a detailed deconvolution of the spectra to resolve the vibrational contributions from\nmetallic Ni0 and oxidized Niσ+ in the Mo C-Ni/SiO catalysts. As shown in Figure R10 and Table\n2 2\nR5, the calculated Niσ+/Ni0 area ratios exhibit a clear trend of Mo C-Ni/SiO _590C (1.94) > Mo C-\n2 2 2\nNi/SiO _550C (1.87) > Mo C-Ni/SiO _500C (0.98). This sequence aligns well with the Niσ+/Ni0\n2 2 2\nratio derived from XPS analysis, thereby corroborating the complementary nature of these\ncharacterization techniques. While XPS provides bulk-sensitive chemical information, the CO-\nDRIFTS results specifically highlight the evolution of surface-exposed Ni species under different\nactivation temperatures. These findings have been systematically incorporated into the revised\n21 / 41\nmanuscript, further strengthening the discussion on structure-activity relationships.\nFigure R10. Peak deconvolution of CO-DRIFT spectra of Mo C-Ni/SiO composite catalysts.\n2 2\nTable R5. Peak deconvolution results of CO-DRIFT spectra of Mo C-Ni/SiO composite catalysts.\n2 2\nParameter Mo C-Ni/SiO _500C Mo C-Ni/SiO _550C Mo C-Ni/SiO _590C\n2 2 2 2 2 2\nIntegrated area of Niσ+ 0.0235 (9.24%) 0.0283 (13.01%) 0.0306 (13.93%)\nIntegrated area of Ni0 0.0239 (9.41%) 0.0151 (6.97%) 0.0158 (7.19%)\nNiσ+ /Ni0 0.98 1.87 1.94\nNote: The values in the parentheses represent the percentage of the area.\nComment 7: The measurement of the particle size from TEM could be the first quantitative and\nconclusive evidence regarding the particle size change after the mixing with Mo C. Nevertheless,\n2\nthe counts for statistical significance are not presented and only 2 images are depicted in the\nsupplementary. This information is required. If the values are precise, then these results should\nbe presented before in the manuscript to sustain the claims regarding redispersion, rather than with\nthe Scherrer equation.\n22 / 41\nReply: We appreciate the reviewer’s insightful comments. We fully agree with the reviewer that\ncomprehensive TEM characterization with adequate statistical sampling is crucial for quantitative\nconclusions. In response to this valuable suggestion, we have now supplemented the Supporting\nInformation with additional high-resolution TEM images covering multiple regions of both pristine\nNi/SiO and Mo C-Ni/SiO composite catalysts. These images demonstrated the morphological\n2 2 2\nevolution of Ni particles before and after Mo C incorporation. Furthermore, we conducted statistical\n2\nanalysis of over 100 individual particles from multiple TEM fields of view, with the corresponding\nsize distribution histograms and Gaussian fitting curves presented in Figures R2, R4, R6, and R8.\nThe quantitative results reveal a significant reduction in average Ni particle size from 19.5±0.4 nm\n(pristine Ni/SiO ) to 13.8±0.2 nm (Mo C-Ni/SiO ), strongly supporting the Mo C-induced\n2 2 2 2\nredispersion effect.\nFollowing the reviewer's recommendation, we have restructured the manuscript to prioritize these\nstatistically robust TEM findings, preceding the discussion of XRD-derived crystallite sizes via\nScherrer equation as well as the estimated crystallite size by CO uptake. This revision strengthens\nour mechanistic interpretation by establishing direct microscopic evidence for particle size reduction\nprior to complementary XRD and CO uptake analysis. The enhanced TEM characterization and\nstatistical validation better support our conclusion that Mo C effectively inhibits Ni particle\n2\naggregation through strong metal-support interactions. We believe these revisions have substantially\nimproved the technical rigor and persuasiveness of our work.\nComment 8: EDX mapping are also a compelling evidence of the formation of a Ni-Mo C species.\nmixing on the particle size and redispersion remains unaddressed with this technique. If this\ninformation is available, it should be added.\nReply: We thank the reviewer for this constructive suggestion. We agree that the systematic Energy\nDispersive X-ray Diffraction (EDX) mapping across different synthesis conditions provides deeper\ninsights into interfacial engineering of the Mo C-Ni/SiO composite systems. In response, we have\n2 2\nconducted comprehensive EDX elemental mapping for representative samples. The new results\nreveal a progressive temperature-dependent redistribution of Ni particle, in which the average\n23 / 41\nparticle size initially decreases from 14.7±0.2 (500 oC) to 13.8±0.2 nm (590 oC), indicating the\nredispersion of Ni, but increases significantly to 19.9±0.3 nm at 650 oC. Also, the EDX line-\nscanning profiles align with the XPS data, showing the Ni/Mo ratio rising from 0.11 (500 oC) to\n0.21 (590 oC), then stabilizing above 590 oC (Figures R11-R14). These finding have been integrated\ninto the first part of “Results and Discussion” section to explicitly address the relationship of\ntemperature and metal redispersion. We believe these additions strengthen the manuscript's\nconclusions about interfacial engineering.\nFigure R11. EDX line-scanning of Mo C-Ni/SiO catalysts with different activation temperatures.\n2 2\n(a) 500 oC; (b) 590 oC; (c) 650 oC.\n24 / 41\nFigure R12. HAADF-STEM images and the corresponding EDS elemental mappings of Mo, Ni, Si\nand C element over the Mo C-Ni/SiO -500C catalyst.\n2 2\nFigure R13. HAADF-STEM images and the corresponding EDS elemental mappings of Mo, Ni, Si\nand C element over the Mo C-Ni/SiO -590C catalyst.\n2 2\nFigure R14. HAADF-STEM images and the corresponding EDS elemental mappings of Mo, Ni, Si\nand C element over the Mo C-Ni/SiO -650C catalyst.\n2 2\nComment 9: Regarding Figure 2, the authors present a comparison between the different samples\nand state that Ni would be better dispersed over Mo C than over SiO . Nevertheless, it is intriguing\n2 2\n25 / 41\nthat the number of points observed from the EDX mapping of Si is also low (Figure 2g). How\ndifferent were the counts in each EDX experiment? To make conclusions of the Ni dispersion in each\nphase, this is critical.\nReply: We thank the reviewer for raising this important point regarding the interpretation of the\nEDX mapping data in Figure 2. We appreciate the opportunity to clarify our analysis. The reviewer\nnoted the lower apparent point density in the Si map (Figure 2g). We wish to emphasize that the\nrelative intensity (brightness/darkness) or point density within an EDX map is not a direct\nquantitative measurement of elemental abundance. EDX signal intensity can be significantly\ninfluenced by factors such as local sample thickness and topography. Our primary objective in\npresenting the EDX maps for the Ni/SiO sample was not to quantify the absolute dispersion of Si,\n2\nbut rather to demonstrate the morphological state of the Ni phase. Crucially, this interpretation is\nbased on correlative analysis with the corresponding HAADF-STEM images. First of all, the\nHAADF-STEM images clearly reveal the presence of distinct Ni nanoparticles on SiO support.\noriginates from these localized, particulate features. Furthermore, this observation of Ni existing\nprimarily as particles on SiO is robustly supported by additional STEM images provided in the\nevidence for the different states of Ni on Mo C versus SiO , specifically regarding Ni\n2 2\nmigration/sintering, we performed additional EDX line scans to offer complementary quantitative\ndata on Ni distribution and valid the conclusion that Ni is well-dispersed on Mo C (Figures R12-\n2\n14). We have revised the relevant section of the manuscript to more explicitly state the basis for our\nconclusion regarding Ni dispersion and to clarify the interpretation of the EDX mapping in\nconjunction with the STEM imaging.\nComment 10: Page 9: “From the above analysis, we can deduce that the electronic perturbation of\nNi is mainly induced by the strong interaction between Ni and Mo C” How? Same experiments were\n2\nnot performed over a Ni/SiO reference?\nelectronic perturbation mechanism, we conducted a control experiment by taking Ni/SiO as\n2\nreference. The Ni/SiO reference exhibits characteristic metallic Ni0 and oxidized Ni2+, with\n2\n26 / 41\nelectronic configurations aligning with the XAS results. Please see details in Figures R16. Some\nmodifications have been made in the revised manuscript. These revisions strengthen the causality\nbetween Mo C incorporation and Ni electronic modification while addressing the comparative\n2\nexperimental design concern. We thank the reviewer for prompting this methodological\nenhancement.\nFigure R16. Data analysis on XANES spectra. (a) A typical XAS spectrum consisting of XANES.\n(b) Methods of determination of oxidation state from the XANES spectra.\nComment 11: Figure 4: since the conversions at 350ºC drastically differ between the distinct\ncatalysts, the selectivity is not directly comparable under these conditions. Selectivity at the same\nconversion level should be provided as a compelling evidence of enhanced methane formation.\nReply: We thank the reviewer for pointing this out. We fully acknowledge that comparing selectivity\nat significantly different conversion levels may introduce thermodynamic biases. To address this\nconcern, we have conducted additional experiments by adjusting the space velocities to maintain\nCO conversion at the same level (as shown in Figure R17). It was found that the at the same\n2\nconversion level (24~28%), the Mo C-Ni/SiO catalyst exhibits a CH selectivity of 97.2%,\n2 2 4\nsignificantly surpassing that of Ni/SiO (55.9%) and Mo C (8.3%), confirming its intrinsic\n2 2\nselectivity advantage. These methodological refinements rigorously decouple intrinsic catalytic\nselectivity from conversion-dependent effects. We thank the reviewer for prompting this essential\nclarification, which strengthens the mechanistic interpretation of our findings.\n27 / 41\nFigure R17. The catalytic performance of Mo C-Ni/SiO and references in CO hydrogenation (a)\n2 2 2\nthe effects of different carbon source; (b) the effects of different mixing methods.\nComment 12: Page 10: “As a result, close sites intimacy between Ni-Mo C and Ni-SiO interface\n2 2\ncan be established, thus enhancing the formation of CH ”. What happened with the argument of\n4\nhigher degree of redispersion among the distinct mixing methods? Is this not playing a role here?\nIs it intimacy or redispersion from SiO to Mo C?\n2 2\nReply: We thank the reviewer for highlighting this critical point of ambiguity. We recognize that\nthe abrupt shift to discuss the “interface intimacy” without explicitly linking it to the redispersion\nmechanism, resulting in the logical discontinuity. To address this, we have restructured the analysis\nto clarify the relationship between mixing methods, interfacial site generation, and catalytic\nperformance. The revised text now states:\nManuscript Page11: “As a result, a higher degree of redispersion resulting from distinct mixing\nmethods was able to generate more Ni-Mo C interface, thus enhancing the formation of CH .”\n2 4\nComment 13: Page 11: “Also, the CO conversion exhibited a gradual increase as the activation\n2\ntemperature increased up to 590ºC and slightly dropped thereafter (Figure S18).” Considering the\nchange in Ni particle size with treatment temperature and the structure-sensitivity of the CO\n2\nhydrogenation that they mention, do they expect any degree of structure-sensitivity related to the\nparticle size of Ni for the ranges analyzed in this work and the reported changes in dp? Is the\nincreased conversion related to a change in the particle size or to the generation of a new active\nsite?\nReply: The Rietveld refinement of XRD patterns revealed that the crystallite size of metallic Ni\n28 / 41\n(derived from the (111) plane) remained within a narrow range of 17.3~20.1 nm across the tested\nactivation temperatures. This finding is consistent with TEM measurements, which showed Ni\nparticle sizes in the range of 14~20 nm. Notably, prior studies[9] suggest that particle size effects on\nCO hydrogenation kinetics become negligible when Ni particle exceeds 5 nm, implying minimal\n2\ninherent structure-sensitivity within the specific size regime investigated here. The EDX\nquantification results (Figure R11) revealed a temperature-dependent migration of Ni onto the\nMo C support between 500~590 oC. This migration was accompanied by a proportional increase in\n2\nconfirmed by EDX elemental line scanning.\nThe initial enhancement in CO conversion (up to 590 oC) correlates strongly with the formation of\n2\nthese new Ni/Mo C interfacial active sites. This process is facilitated by thermally induced Ni\n2\nredistribution via SMSI effects. Conversely, the modest activity decline at 650 oC likely stems from\nNi particle agglomeration on the SiO support, reducing the accessible active surface area. Therefore,\n2\nthe observed catalytic trends are predominantly governed by two competing factors: (i) Dominant\nMechanism: Generation of Ni-Mo C interfacial sites through SMSI-driven Ni migration (activity\n2\nenhancer). (ii) Secondary Effect: High-temperature sintering of Ni on SiO (activity suppressor at\non activity, as confirmed by both our experimental data and literature benchmarks. Consequently,\nthis work highlights the interfacial engineering, rather than particle size modulation, as the primary\nstrategy for optimizing catalytic performance in this system.\nComment 14: Page 11: “To ensure the measurements maintained in a kinetic-relevant regime, the\nCO conversion was limited to 15% with a relatively high space velocity of 60,000 mL g-1 h-1 at\n2\nvarious temperatures”. Under these conditions, the equilibrium conversion reported by the authors\nis around 60%, from where an approach to equilibrium close to 0.25 is obtained. Is this truly kinetic\nregime? A correction of the rates by the approach to equilibrium is recommended. Please refer to\nhttps://doi.org/10.1021/acscatal.4c05805.\nReply: We appreciate the reviewer’s rigorous evaluation and valuable guidance on validating the\nkinetic regime. Upon re-examining our thermodynamic calculations, we identified an error in the\n29 / 41\noriginal equilibrium conversion estimation. Revised calculations based on the NIST-JANAF\nthermochemical table confirmed that the equilibrium conversion of CO is about 94.1% at 623 K,\n2\nsignificantly higher than our initial report. The equilibrium conversion is plotted as a function of\ntemperature, as shown in Figure R18. Under the experimental condition (WHSV of 80,000 mL g-1\nh-1, CO conversion<15%), the approach to equilibrium (η) is calculated as η= Xactual =\n0.15\n≈0.16 . This value aligns with the recommended threshold (η<0.2) for kinetic control, as\n0.941\noutlined in the reference study.[10] It reflects that the experimental condition applied is far from\nequilibrium, which remains in the kinetic regime. We have corrected the equilibrium conversion in\nour revised manuscript (please see Figure 4, Table S11-SS16). Moreover, the observed rate (r )\nobserved\nis corrected using the Temkin-Pyzhev formalism, which is r =r /(1-η). All rate\ncorrected observed\nmeasurements were thermodynamically corrected, which confirmed the kinetic control throughout\nthe experimental range. Overall, we would like to thank the reviewer for prompting this essential\nmethodological refinement and apologize for the initial thermodynamic miscalculation. The\nsupplemental documentation provides full transparency in our revised computational approach\n(Tables R6-R9).\nFigure R18. The calculated equilibrium conversion as a function of temperature.\nTable R6. The rate of CO formation corrected by the approach to equilibrium (η) over the 10Ni/SiO\n2\ncatalyst.\n30 / 41\nCO formation rate, Corrected CO formation\nTemperature, K 𝛈\nμmol g -1 h-1 rate, μmol g -1 h-1\ncat cat\n548.15 2.949 0.0048 2.964\n573.15 5.859 0.0140 5.942\n598.15 11.761 0.0447 12.311\n623.15 24.427 0.1645 29.237\nTable R7. The rate of CH formation corrected by the approach to equilibrium (η ) over the\n4\n10Ni/SiO catalyst.\n4 4\nTemperature, K 𝛈\nμmol g -1 h-1 rate, μmol g -1 h-1\ncat cat\n548.15 1.506 3.649E-13 1.506\n573.15 3.426 2.079E-11 3.426\n598.15 7.939 1.178E-09 7.939\n623.15 17.908 7.021E-08 17.908\nTable R8. The rate of CO formation corrected by the approach to equilibrium (η) over the Mo C-\n2\n10Ni/SiO catalyst.\nTemperature, K 𝛈\nμmol g -1 h-1 rate, μmol g -1 h-1\ncat cat\n548.15 0.461 0.0030 0.462\n573.15 0.932 0.0104 0.941\n598.15 2.507 0.0371 2.604\n623.15 2.732 0.0626 2.914\nTable R9. The rate of CH formation corrected by the approach to equilibrium (η) over the Mo C-\n4 2\n10Ni/SiO catalyst.\n4 4\nTemperature, K 𝛈\nμmol g -1 h-1 rate, μmol g -1 h-1\ncat cat\n548.15 15.991 6.163E-11 15.991\n573.15 36.329 5.123E-09 36.329\n598.15 58.587 1.480E-07 58.587\n623.15 98.338 5.335E-06 98.338\n31 / 41\nComment 15: Page 11: “TOF; as normalized by the number of CO chemisorption sites” how was\nthe CO chemisorption measured?\nReply: We thank the reviewer raising this question regarding the CO chemisorption measurement\nmethodology. We apologize for the inadvertent omission of these experimental details in the original\nmanuscript. The CO uptake was measured to determine the number of active sites as well as the\nmetal dispersion using Quantachrome ChemBET Pulsar analyzer. The detailed procedure is\nsummarized below: Firstly, the samples were purged with He flow at 100 oC for 30 min to remove\nthe adsorbed moisture, and subsequently reduced by 5%H /Ar flow at 350 oC for 1h to remove\n2\nsurface passivation layers; afterwards, the CO uptake was measured at 35 oC using a thermal\nconductivity detector (TCD); eventually, the turnover frequency (TOF, s-1), defined as the number\nof CO converted per active site per second, was calculated based on the following equation of\nCO2,inlet CO2 CO2, inlet 2\ns-1), M represents the molecular weight of CO (g mol-1). The experimental protocol has been added\n2\nto the Experimental Procedure of the Supporting Information. We thank the reviewer for\nhighlighting this essential methodological clarification.\nComment 16: Page 11: “strongly indicating the increased atomic utilization of Ni upon Mo C\n2\naddition” how do the authors get to this conclusion based on the TOF? This is only indicating that\nthe rate normalized per “active site” is higher. Please elaborate.\nReply: We thank the reviewer for pointing this out. Upon re-examining the original statement,\nwe acknowledge that interpreting increased TOF values as direct evidence for enhanced Ni atomic\nutilization constitutes an overextended conclusion, as TOF normalization inherently reflects activity\nper presumed active site rather than atomic efficiency. This conceptual misalignment has been\nrectified in the revised manuscript. The revised conclusion now states as follows:\n“Manuscript Page12: As displayed in Figure 4e and Table S15, the calculated turnover frequency\n(TOF; normalized by the number of CO chemisorption sites) of CH formation of the Mo C-\n4 2\n10Ni/SiO catalyst (7.1E-04 s-1) is about 7.8x’s higher than that of the 10Ni/SiO catalyst (9.0E-05\n2 2\ns-1), indicating the improved intrinsic activity of Ni sites due to their altered electronic properties.\nTaking the observed Ni redispersion from SiO to Mo C and the established electron transfer into\n2 2\n32 / 41\naccount, we propose that the increased TOF originates from synergistic effects combining better Ni\nexposure and optimized electronic structure.”\nComment 17: A suggestion: an analysis of the rates, TOF and E separately for each reaction (i.e\napp\nCH and CO formations) would yield more information, e.g. is there a product which formation is\n4\nselectively inhibited? How is the new active site affecting each product?\nReply: We sincerely appreciate the reviewer’s insightful suggestion. We fully agree that separate\nanalyses of turnover frequency (TOFs) and activation energy (Ea) for CH and CO formation\n4\npathway would provide critical mechanistic insights into product selectivity. The calculated results\nare summarized in Tables R10-11 and Figure R19. Notably, the Ea of CH formation exhibited a\n4\nsubstantial reduction from 93.8±0.6 kJ mol-1 over Ni/SiO to 67.6±1.1 kJ mol-1 for the Mo C-\n2 2\nNi/SiO catalyst, demonstrating that Mo C incorporation effectively lowers the energy barrier for\n2 2\nmethanegeneration. In contrast, the Ea decreased for CO formation was less pronounced, shifting\nfrom 86.0±1.3 to 74.8±3.2 kJ mol-1 upon Mo C addition. This differential effect highlights the\n2\npreferential enhancement of CH pathway kinetics by Mo C-containing sites. Consistent with the\n4 2\nEa trend, the TOF of CH formation increased dramatically from 9.03E-05 s-1 (Ni/SiO ) to 7.07E-\n4 2\n04 s-1 (Mo C-Ni/SiO ), representing more than x7.8 fold enhancement. These complementary\n2 2\nkinetic analyses conclusively demonstrate that the newly formed Mo C-Ni interfacial sites\n2\nselectively promote CH production through dual mechanisms: (i) significant activation energy\n4\nreduction for methane generation, and (ii) preferential acceleration of the methanation pathway over\ncompeting CO generation. The above results were added in the revised manuscript to enhance the\ninterfacial engineering by the formation of Ni/Mo C sites.\n2 2 2\nEa for CH formation, Ea for CO\nkJ mol-1 formation, kJ mol-1\n10Ni/SiO 85.2±0.7 93.8±0.6 86.0±1.3\n2 2\n33 / 41\nReaction conditions: 275-350 oC, 0.1 MPa, GHSV=80,000 ml g-1 h-1.\nTable R11. The calculated turnover frequency (TOF) of Ni/SiO and Mo C-Ni/SiO catalysts.\n2 2 2\nTOF of CH TOF of CO\nformation, s-1 formation, s-1\n10Ni/SiO 2.45E-04 9.03E-05 1.54E-04\n2 2\nReaction conditions: 300 oC, 0.1 MPa, GHSV=80,000 ml g-1 h-1.\nFigure R19. Apparent activation energy (E ) of 10Ni/SiO and Mo C-10Ni/SiO catalysts.\napp 2 2 2\nReviewer #2 (Remarks to the Author):\nThis manuscript discusses the effects of CO hydrogenation selectivity (CO or CH as the main\n2 4\nproduct) resulting from the redispersion/re-speciation of Ni in Mo C-SiO composite catalysts. The\n2 2\nstrong metal-support interaction (SMSI) is suggested to drive the Ni migration from SiO to Mo C,\n2 2\nwhich is reflected in the hydrogenation selectivity. The manuscript is mostly reasonable, but the\nfollowing criticism is pertinent:\nRESPONSE:\n34 / 41\nWe thank the reviewer for your valuable and constructive comments, and we appreciate so much\nfor giving us an opportunity to modify this paper. We have tried our best to eliminate any infelicities\nin the revision process, and we hoped that the revised manuscript could meet your approval.\nComment 1: The discussion of the XPS results is extensive yet questionable. It is known that\nactivated Mo C-based catalysts react vigorously (oxidize) when exposed to ambient air. While the\n2\nmain text does not mention the sample handling before data acquisition, the SI description states\nthat the sample preparation was conducted in a glove box; however, the sample holder was then\nintroduced into the XPS measurement with exposure to air. It is, therefore, unclear what the\nimplications of this air exposure are. For instance, is the presence of the oxidized Mo4+ and Mo6+\nstates in Figure 1b due to the air exposure during sample transfer from the glove box to the\ninstrument? The handling (air exposure) should be stated clearly in the main text, and its\nconsequences should be discussed.\nReply: We sincerely appreciate the reviewer’s insightful comments. We fully agree that the rigorous\ncontrol of ambient exposure is critical for accurate characterization, and we have taken the following\nsteps to address these concerns systematically: (i) XPS sample preparation was performed in an\nargon-filled glovebox. The sample transferred to the XPS load-lock chamber without air exposure.[4,\n6, 8, 11] The experimental protocol has been explicitly detailed in the revised manuscript. The observed\nMo4+ (B.E.=228.8 eV) in pure Mo C corresponds to its intrinsic oxycarbide phase (MoO C ) formed\n2 x y\nduring the passivation process. This surface reconstruction is thermodynamically stabilized and\nrequires a high-temperature reduction to fully eliminate residual oxygen.[12, 13] Similar to our\nprevious work of Ni-(ɑ-MoC)/Al O composite catalysts[6], we found the existence of high-valence\n2 3\nMo species on the Mo C-Ni/SiO catalysts in our present study, which may originate from the\n2 2\ninteraction between Mo C and SiO support. In order to prove our guess, we designed new\n2 2\nexperiments by running H -TPR (Figure R20). The H -TPR results showed that there is only one\n2 2\nH reduction peak appeared at 284 oC on pure Mo C catalyst, while the pure SiO remains inert\n2 2 2\nbelow 950 oC. Remarkably, the Mo C-SiO composite catalyst showed a shifted reduction peak\n2 2\ntowards high temperature (@295 oC), confirming the modified reducibility due to the interaction\nbetween SiO and MoO passivation layer of molybdenum carbide. These results collectively\n2 x\nconfirm that the observed oxidation states are intrinsic to the Mo C-SiO interface rather than\n2 2\n35 / 41\nexperimental artifacts. We deeply thank the reviewer for raising this critical point, which has\nstrengthened the rigor and clarity of our discussion.\nFigure R20. H -TPR of Mo C, SiO , and mixed Mo C-SiO catalysts.\n2 2 2 2 2\nComment 2: The peak at 228.2 eV is ascribed to Mo2+ of Mo2C, which is justified. The peak at\n227.7 eV is ascribed to Mo(delta +), i.e., an oxidation state between 0 and 2+. However, Mo(0) in\nrelated catalytic systems has a B.E. at 227.5-227.7 eV, which is very close to the fitted value of 227.7\neV. On what basis did the authors rule out the formation of Mo(0)? This is unclear, and if not\nexcluded rigorously, Mo(0) should be considered an alternative assignment for this peak.\nReply: We thank the reviewer for this critical assessment of the XPS peak assignments. The\ndistinction between Moδ+ (0<δ<2) and metallic Mo0 is indeed nuanced, and we address this\nambiguity from the following three aspects. (i) Absence of Metallic Mo Coordination: From the\nEXAFS analysis, we notice that the Mo-C (2.08 Å) and Mo-C-Mo (2.98 Å) bonds dominate the first\nand second coordination shell, respectively, which is consistent with the Mo C structure. Attempted\n2\nto fit Mo-Mo metallic bonds yielded statistically poor results. This conclusively demonstrates that\nMo species predominantly exist in carbide phase, with no detectable metallic Mo clusters. (ii)\nConsistency with Prior XPS Assignments: The assignment of 227.7 eV peak to Moδ+ aligns with\nour established methodology in an analogous system. In the Mo C-Ni/Al O catalyst, we observed\n2 2 3\na similar peak at 227.5 eV, which was attributed to the electron-deficient Mo species (Moδ+) arising\n36 / 41\nfrom the interfacial charge redistribution between Ni and Mo C.[8] (iii) Mechanistic Rationale for\nspecies. It is known that the Ni atoms migrate to the surface of Mo C during activation, which\n2\ninduces localized electron transfer from Ni to Mo C. This creates electron-deficient Mo sites, which\n2\nserve as active sites for reactant adsorption. The metallic Mo species, in contrast, would not align\nwith the charge redistribution implied by Ni/Mo C interactions or the catalytic behavior. To sum up,\n2\nwe can confidently assign the low-valance Mo species to metallic Mo0 based on the combination of\nEXAFS, XPS, and catalytic data analyses. We thank the reviewer for prompting this rigorous\nanalysis, which strengthens the validity of our spectral interpretations. The combined EXAFS,\nXPS,\nand mechanistic evidence robustly supports the assignment of the 227.7 eV feature to Moδ+ rather\nthan metallic Mo0.\nComment 3: To induce the SMSI, the authors use a 15% CH /H . Why is the carbon source\n4 2\nnecessary, and what is the role of methane’s carbon in the proposed SMSI mechanism? Would the\nredispersion and the associated switch in CO hydrogenation selectivity not take place only when\n2\nusing the H pretreatment?\n4\ninducing the strong metal-support interaction (SMSI) in the designed Mo C-Ni/SiO composite\n2 2\nsystem. Below, we address the necessity of CH as carbon source and its mechanistic role in the\n(i) Surface activation by CH /H mixture: The 15%CH /H gas mixture was selected to create a\n4 2 4 2\ncarbon-terminated surface on the Mo C-Ni/SiO composite catalyst, which is critical for SMSI\n2 2\nformation. In our previous work, we know that H alone could create Mo-rich surface on the Ni-(ɑ-\n2 3 4 2\nfrom our present system (CH /H treatment: Ni-C mol.% of 65.1%; H treatment: Ni-C mol.% of\n4 2 2\n56.2%), in which the C-rich surface is essential for stabilizing Ni species. Also, it was found that H\n2\nalone could strip surface carbon from Mo C during reduction, as demonstrated in our previous\n2\nstudies.[1-3] Methane acts as a carbon reservoir, dynamically replenishing surface carbon to maintain\nthe carbide structure.\n37 / 41\n(ii) Role of CH -derived carbon in SMSI effects: our experimental results showed that the CO\n4 2\nconversion is slightly higher on the CH /H treated Mo C-Ni/SiO catalyst than that of the H treated\n4 2 2 2 2\none (Figure S18). The XPS analyses also showed that the relative ratio of Niσ+/Ni0 and Moδ+/Mo2+\nwas higher on the former than that of the latter, indicating distinct degree of metal migration upon\ndifferent treatment gases, further varying the catalytic effects. Overall, these results suggest that\ncarbon-terminated Mo C surface drives the migration of Ni by forming Ni-C-Mo bonds. Moreover,\n2\nthe carbon termination could stabilize the electron-deficient Moδ+ species, thus enhancing the charge\ntransfer between Ni and Mo C.[1]\nredispersion and electronic modulation, which could enhance the CO hydrogenation activity. We\n2\nhave added a dedicated discussion to stress out the essential role of CH -derived carbon in SMSI.\n“Supporting Information-Catalytic Performance in CO Hydrogenation (Figure S35(d)):\n2\n“Also, it was noticed that the Mo C-Ni/SiO catalyst pretreated with CH /H exhibits a slightly\n2 2 4 2\nhigher CO conversion than its H -pretreated counterpart. This performance differences originates\n2 2\nfrom the distinct surface states induced by the pretreatment atmospheres. CH could replenish\n4\nsurface carbon through methane decomposition, maintaining the carbide structure and yielding a C-\nrich surface, which is more favorable for CO conversion. While H treatment alone promotes\n2 2\ncarbon depletion, resulting in a Mo-rich surface. Therefore, we can deduce that methane is\nindispensable for establishing the carbon-rich interface required for Ni redispersion and electronic\nmodulation.”\nComment 4: The nature of Ni species formed in the interaction with Mo C under the CH /H\n2 4 2\npretreatment is unclear. Do the authors suggest surface Ni carbide?\nReply: We sincerely appreciate the reviewer’s insightful inquiry regarding the nature of Ni species\nformed during CH /H treatment. Our comprehensive structural and electronic characterization\n4 2\nprovide critical evidence for the formation of distinct Ni-C interfacial sites rather than conventional\n38 / 41\nNi C phases, which we would like to clarify through the following perspective. (i) Structural\naround 2.07 Å and the Ni-Mo coordination shell is about 2.91 Å, which is consistent with our\nestablished model as shown on Figure S12(b) with Ni-C bond length of 1.86 Å and Ni-Mo bond\nlength of 3.1 Å. It suggests that Ni atoms preferentially occupy surface sites atop the Mo C substrate,\n2\nforming C-Ni interfacial motifs rather than penetrating into the carbide lattice. This structure\nconfiguration is consistent with previous reports of transition metal-carbon interfacial sites.\nFor\nexample, Lin et al.[1] observed similar Ni -C motifs on carbide supports. Diao et al.[8] reported\n1 x\nanalogous Ni-C interfacial sites. Zhang et al.[6] specifically identified Ni-C motifs at Ni-MoC\nx x\ninterfaces. (ii) Electronic State Characterization: Complementary XPS and EXAFS analyses\nreveal these interfacial Ni species exist in an electron-deficient state, distinct from both metallic Ni\nand stoichiometric Ni C phases. This electronic configuration likely arises from strong metal-\n3\nsupport interactions between Ni and Mo C substrate. Overall, this combination of structural and\n2\nelectronic evidence strongly supports the formation of unique Ni-C interfacial motifs rather than\nconventional Ni carbide phases. We have modified the manuscript text to clarify this distinction.\nComment 5: The authors do not discuss the carbon balance of their experiments. Please provide\nthis data.\nReply: We appreciate the reviewer’s valuable suggestion regarding carbon balance analysis. In\nresponse, we have taken the following steps to address this matter comprehensively. Firstly, a\ndetailed section outlining the carbon balance methodology and results has been incorporated in the\nrevised Supporting Information. Secondly, the raw calculation process, including mass flow\nanalyses and carbon input/output quantification, is explicitly provided in the spreadsheet of\n\"Carbon_Balance_Calculations.xlsx\". It was found that the carbon balance ≥94%, which\ndemonstrates good consistency between feed inputs and quantified outputs.\nPlease see the modification below:\n“Supporting Information-Catalytic CO Hydrogenation:\n𝑛𝑜𝑢𝑡 +𝑛𝑜𝑢𝑡+𝑛𝑜𝑢𝑡\n𝐵 (%)=\n𝐶𝑂2 𝐶𝑂 𝐶𝐻4\n×100%\n𝐶 𝑛𝑖𝑛\n𝐶𝑂2\n39 / 41\nIn all tests, the carbon balance of the system is above 94%.”\nComment 6: The authors write on page 12 that “the Mo C alone exhibited a spontaneous CO\n2 2\ndissociation, forming CO(g) as major product, indicating the weak interaction between CO and\ncarbides”. Note that the spontaneous CO dissociation indicates strong interaction of CO2 and\n2\npristine carbides. Instead, the authors wanted to say that Mo C surface passivated with O* from the\n2\ninteraction with Mo C. The original wording indeed created ambiguity, and we fully agree with the\n2\ncritical clarification proposed. The relevant text has been rephased into the following sentence:\n“In sharp contrast, the Mo C alone exhibited a spontaneous CO dissociation, forming CO(g) as\n2 2\nmajor product, indicating the weak interaction between CO and the O* occupied Mo carbide\nsurface.”\nComment 7: There are several typos and small mistakes in the text; for instance, the traces are\nunlabelled in Fig. 1d; the caption to the same Fig. has an unrelated chi+ symbol; the authors use\nthe term “quasi in-situ XPS” for their method, but this is misleading and should be changed for to\nex-situ XPS with air exposure; it is unclear what is meant by “graphically” confirming Ni\nredispersion with HRTEM; “Hütting” temperature should read “Hüttig”; “maraked” should be\n“marked”; “romve” should be “remove”, etc.\nReply: We sincerely apologize for these editorial oversights and deeply appreciate the reviewer’ s\nmeticulous scrutiny, which has significantly enhanced the precision and professionalism of our\nmanuscript. All the raised issues here have been systematically addressed. Also, the final version\nhas been rigorously checked. Again, we extend our sincere gratitude for the opportunity to improve\nthe quality of this work.\nReferences:\n[1] L. Lin, Q. Yu, M. Peng, A. Li, S. Yao, S. Tian, X. Liu, A. Li, Z. Jiang, R. Gao, X. Han, Y.-w. Li,\nX.-d. Wen, W. Zhou, D. Ma, Atomically Dispersed Ni/α-MoC Catalyst for Hydrogen Production\nfrom Methanol/Water, Journal of the American Chemical Society, 143 (2021) 309-317.\n[2] S. Yao, X. Zhang, W. Zhou, R. Gao, W. Xu, Y. Ye, L. Lin, X. Wen, P. Liu, B. Chen, E. Crumlin,\n40 / 41\nJ. Guo, Z. Zuo, W. Li, J. Xie, L. Lu, C.J. Kiely, L. Gu, C. Shi, J.A. Rodriguez, D. Ma, Atomic-\nlayered Au clusters on α-MoC as catalysts for the low-temperature water-gas shift reaction,\nScience, 357 (2017) 389.\n[3] X. Zhang, M. Zhang, Y. Deng, M. Xu, L. Artiglia, W. Wen, R. Gao, B. Chen, S. Yao, X. Zhang,\nA stable low-temperature H -production catalyst by crowding Pt on α-MoC, Nature, 589 (2021)\n2\n396-401.\n[4] H. Cai, L. Wang, W. Liu, X. Zhang, B. Chen, P. Mao, J. Fang, R. Gao, C. Shi, Re-Dispersion of\nPlatinum From CNTs Substrate to α-MoC to Boost the Hydrogen Evolution Reaction, Small,\n1-x\n19 (2023) 2207146.\n[5] Y. Diao, X. Zhang, Y. Liu, B. Chen, G. Wu, C. Shi, Plasma-assisted dry reforming of methane\nover Mo C-Ni/Al O catalysts: Effects of β-Mo C promoter, Applied Catalysis B:\n2 2 3 2\nEnvironmental, 301 (2022) 120779\n[6] X. Zhang, Y. Xu, Y. Liu, L. Niu, Y. Diao, Z. Gao, B. Chen, J. Xie, M. Bi, M. Wang, D. Xiao,\nD. Ma, C. Shi, A novel Ni-MoC O interfacial catalyst for syngas production via the chemical\nx y\nlooping dry reforming of methane, Chem, 9 (2023) 102-116.\n[7] H. Zhou, Z. Chen, A.V. López, E.D. López, E. Lam, A. Tsoukalou, E. Willinger, D.A. Kuznetsov,\nD. Mance, A. Kierzkowska, Engineering the Cu/Mo CT (MXene) interface to drive CO\n2 x 2\nhydrogenation to methanol, Nature Catalysis, 4 (2021) 860-871\n[8] Y. Diao, X. Zhang, Y. Liu, B. Chen, G. Wu, C. Shi, Plasma-assisted dry reforming of methane\nover Mo C-Ni/Al O catalysts: Effects of β-Mo C promoter, Applied Catalysis B:\n2 2 3 2\nEnvironmental, 301 (2022) 120779.\n[9] J.F.M. Simons, T.J. de Heer, R.C.J. van de Poll, V. Muravev, N. Kosinov, E.J.M. Hensen,\nStructure Sensitivity of CO Hydrogenation on Ni Revisited, Journal of the American Chemical\n[10] T.C. Lin, E.E. Bickel Rogers, A. Bhan, Kinetic and Thermodynamic Considerations in\nThermocatalytic CO Hydrogenation, ACS Catalysis, 15 (2025) 780-788.\n2\n[11] X. Zhang, Y. Liu, M. Zhang, T. Yu, B. Chen, Y. Xu, M. Crocker, X. Zhu, Y. Zhu, R. Wang, D.\nXiao, M. Bi, D. Ma, C. Shi, Synergy between β-Mo C Nanorods and Non-thermal Plasma for\n2\n[12] Q. Bkour, O.G. Marin-Flores, M.G. Norton, S. Ha, A highly active and stable bimetallic Ni-\nMo C catalyst for a partial oxidation of jet fuel, Applied Catalysis B: Environmental, 245 (2019)\n2\n613-622.\n[13] X. Sun, J. Yu, S. Cao, A. Zimina, B.B. Sarma, J.-D. Grunwaldt, H. Xu, S. Li, Y. Liu, J. Sun, In\nSitu Investigations on Structural Evolutions during the Facile Synthesis of Cubic α-MoC\n1–x\nCatalysts, Journal of the American Chemical Society, 144 (2022) 22589-22598.\n41 / 41"}, {"round": 2, "reviewer_comments": {"reviewer_1": "I deeply thank the authors for the exhaustive revision of the manuscript. My concerns were addressed I consider that the\nmanuscript is now ready to be accepted. Some minor final suggestions are listed hereafter:\n- The concept of SMSI employed by the authors to describe the driving force behind the migration of Ni to MoC could be\nconfused within the catalysis community with the phenomena of encapsulation by a reducible oxide over metallic\nnanoparticles. If possible, a clarification regarding this matter should be added in the introduction.\n-Comment 6-2: Even if the authors argued against the dipole coupling, the redshift that they claim is still not observed in\nFigure S14. Furthermore, they developed a deconvolution of the spectra in Figure S14. Please correct the x-axis of these\nsubplots, which seem to be inverted. Rather than the redshift claimed, based on the deconvolution performed, is there a\nchange in the relative area of Mo versus Ni that could sustain the conclusion of the authors?\n-In general for DRIFTS-CO, I would definitively not make claims regarding the change in electronic structure of Mo. This\nsection could be removed without affecting the outcome of the work.", "reviewer_2": "The revision has been performed thoroughly.\nRemaining questions include:\n1) The authors use CO chemisorption to determine the number of surface Ni sites in Ni-Mo2C-SiO2. How is the contribution\nof surface Mo sites in Mo2C to the total measured CO amount taken into account to obtain Ni-specific surface sites?\n2) The authors refer to the CO-quantified surface sites as active sites. It would be more appropriate to refer to these sites as\nsurface sites rather than active sites, and use catalyst poisoning studies to determine the number of active sites (i.e., the\nassumption that all CO binding surface sites are catalytically active needs to be justified).\n3) The authors have added a discussion on the role of CH4 in CH4/H2 pretreatment in preventing the carbidic carbon loss of\nMo2C. Can the Mo-to-carbidic-C ratio from the XPS fittings validate this statement? (I.e., will the expected stoichiometric\nratio of 2 be obtained?)"}, "author_response": "A point-to-point response to the comments\nReviewer #1:\nI deeply thank the authors for the exhaustive revision of the manuscript. My concerns were\naddressed I consider that the manuscript is now ready to be accepted. Some minor final\nsuggestions are listed hereafter.\nRESPONSE:\nWe thank the reviewer for the overall positive views on our paper. We also appreciate that the\nreviewer pointed out some insightful comments of our present manuscript. Here, we have revised\nthe manuscript by incorporating all of Reviewer #1’s comments.\nComment 1: The concept of SMSI employed by the authors to describe the driving force behind\nthe migration of Ni to MoC could be confused within the catalysis community with the phenomena\nof encapsulation by a reducible oxide over metallic nanoparticles. If possible, a clarification\nregarding this matter should be added in the introduction.\nReply: We sincerely thank the reviewer for raising this insightful point. Indeed, the term “strong\nmetal-support interaction” (SMSI) is classically associated with the encapsulation of metal\nnanoparticles by reducible oxides (e.g. TiO , CeO ), as first described by Tauster et al.[1] in 1978.\n2 2\nThis canonical SMSI effect typically suppresses H /CO chemisorption capacity and induces the\n2\nformation of overlayer on active metal sites.[2, 3] However, recent advances have broadened the\nscope of SMSI phenomena, including elemental migration from metal to support. In this work, the\nobserved Ni migration towards Mo C represents an emerging subclass of SMSI-driven behavior,\n2\nwherein the interfacial energetics drive atomic redistribution rather than encapsulation. To\neliminate potential ambiguity, we have clarified this distinction in the “Introduction” section of the\nrevised manuscript. The modification is as follows:\n“Manuscript Page 3: Distinct from the classical strong metal-support interaction (SMSI) effect,\nwhich typically characterized by reducible oxide encapsulation of metal nanoparticles, recent\nadvances have expanded the scope of SMSI behaviors. Among these, metal redispersion\nrepresents a prominent SMSI-induced phenomenon under activation or reaction conditions.”\n2 / 7\nComment 2: Comment 6-2: Even if the authors argued against the dipole coupling, the redshift\nthat they claim is still not observed in Figure S14. Furthermore, they developed a deconvolution of\nthe spectra in Figure S14. Please correct the x-axis of these subplots, which seem to be inverted.\nRather than the redshift claimed, based on the deconvolution performed, is there a change in the\nrelative area of Mo versus Ni that could sustain the conclusion of the authors?\nReply: We sincerely appreciate the reviewer’s insightful comments and apologize for the error in\nthe original presentation of Figure S14. We acknowledge that the claimed redshift of the Moδ+\npeak is not statistically significant and falls within the margin of measurement uncertainty. Also,\nas the reviewer suggested, we have corrected the problem on Figure S14 (see Figure R1). The\ndeconvolution analysis revealed that the Mo/Ni peak area ratio increased with increased treatment\ntemperature from 500 to 550 oC, indicating the migration of metallic Ni0 species towards Mo C\n2\nsubstrate. Also, it was noted that the ratio of Mo/Ni slightly decreased at 590 oC, indicating that\nthermodynamic driving forces favoring Ni redispersion are overtaken by Ni0 agglomeration on the\nSiO support. Overall, the evolving Mo/Ni ratio provides direct evidence for\n2\ntemperature-dependent Ni migration dynamics, fully supporting our central conclusion.\n3 / 7\nFigure R1. DRIFT spectra of adsorbed CO on Mo C-Ni/SiO catalyst reduced as a function of\n2 2\ntemperature from 500 to 590 oC.\nTable R1. Peak deconvolution results of CO-DRIFTs spectra of Mo C-Ni/SiO composite\n2 2\ncatalysts.\nMo C-Ni/SiO Mo C-Ni/SiO Mo C-Ni/SiO\n2 2 2 2 2 2\nParameter\n_500C _550C _590C\nIntegrated area of Ni0 0.0092 0.0039 0.0058\nIntegrated area of Mo 0.13 0.12 0.11\nMo/Ni0 13.8 29.5 19.3\nComment 3: In general for DRIFTS-CO, I would definitively not make claims regarding the\nchange in electronic structure of Mo. This section could be removed without affecting the outcome\nof the work.\nReply: We sincerely appreciate the reviewer's expert guidance regarding the interpretation of\nCO-DRIFTS spectra. Upon careful reconsideration, we agree that claims about electronic structure\nmodifications of Mo based solely on CO adsorption profiles may overextend the experimental\nevidence. Accordingly, we removed the entire CO-DRIFTS analysis section (including related\ndiscussions in the main text and Supplementary Information) to maintain rigorous scientific\nstandards. The manuscript's key findings regarding Ni migration dynamics and SMSI effects are\nunaffected by this modification, which ultimately strengthens the work's focus on more direct\nevidence.\nReviewer #2 (Remarks to the Author):\nThe revision has been performed thoroughly.\nRESPONSE:\nWe sincerely thank the reviewer for the positive appraisal of revised manuscript and appreciate the\nopportunity to refine this manuscript. All remaining concerns have been thoroughly addressed in\nthis revision. We are confident that the current version fully addresses the requirement.\nRemaining questions include:\n4 / 7\nComment 1: The authors use CO chemisorption to determine the number of surface Ni sites in\nNi-Mo C-SiO . How is the contribution of surface Mo sites in Mo C to the total measured CO\n2 2 2\namount taken into account to obtain Ni-specific surface sites?\nReply: We sincerely thank the reviewer for this insightful question regarding CO chemisorption\nfor quantifying Ni surface sites. CO chemisorption is indeed a standard technique to determine\naccessible metal surface sites and dispersion. However, as the reviewer rightly points out, a key\nchallenge in the Ni-Mo C/SiO composite catalyst is deconvoluting the individual contributions of\n2 2\nMo C and Ni sites to the total measured CO uptake. This difficulty arises fundamentally because\n2\nthe catalyst is not a simple physical mixture. Elemental migration occurs during pretreatment,\ndistributing Ni atoms across both the Mo C and SiO support. Consequently, the CO adsorption\n2 2\nsignatures of surface Ni sites and Mo C sites are inherently intertwined and cannot be\n2\nexperimentally separated using this technique alone. Therefore, the CO chemisorption\nmeasurement provides the total number of accessible surface sites capable of adsorbing CO.[4-6]\nCrucially, to determine the number of intrinsic active sites relevant for catalysis (specifically the\nCO methanation reaction studied), we go beyond the raw CO uptake. The intrinsic active site\n2\ncount is derived by accounting for the competitive adsorption of reactants and products during the\nreaction. This analysis allows us to distinguish and exclude sites occupied by non-reactive species\nor spectator intermediates.[7]\nComment 2: The authors refer to the CO-quantified surface sites as active sites. It would be more\nappropriate to refer to these sites as surface sites rather than active sites, and use catalyst\npoisoning studies to determine the number of active sites (i.e., the assumption that all CO binding\nsurface sites are catalytically active needs to be justified).\nReply: We agree with the reviewer’s suggestion and appreciate the reviewer's distinction between\nsurface sites and active sites. While CO chemisorption quantifies accessible metal surface sites\nrather than directly confirming catalytic activity, this technique is well-established as a proxy for\nactive site enumeration in both Mo C and Ni-based catalyst systems.[4-6] In our study, we adopt\n2\nthis conventional approach based on extensive literature precedent. CO titration has been validated\nas a standard method for quantifying active sites in Ni-based catalysts. Similarly applied to Mo C\n2\nsystems where CO adsorption correlates with catalytic activity. A revision has been made in the\n5 / 7\nSupporting Information of revised manuscript.\n“Supporting Information – Structural characterization Page 10: The turnover frequency\n(TOF), defined as the number of CO converted per surface site per second, was calculated based\n2\non the following equation:”\nComment 3: The authors have added a discussion on the role of CH in CH /H pretreatment in\n4 4 2\npreventing the carbidic carbon loss of Mo C. Can the Mo-to-carbidic-C ratio from the XPS\n2\nfittings validate this statement? (I.e., will the expected stoichiometric ratio of 2 be obtained?)\nReply: We thank the reviewer for this insightful question. The role of methane (CH ) in the\n4 2\nreplenish the stripped carbidic carbon sites on Mo C. This approach directly extended our group’s\n2\nestablished methodology for activating molybdenum carbide catalysts.[8-10] In our previous work,\nwe systematically studied the Ni-(α-MoC)/Al O catalysts, demonstrating that CH /H\n2 3 4 2\npretreatment critically tunes the surface composition of molybdenum carbides, thereby governing\nthe activity/selectivity in methane dry reforming.[11] Critically, the CH /H treatment represents a\n4 2\nwell-established and widely adopted protocol for pretreating Mo C-based catalysts, as evidenced\n2\nby numerous studies.[6] This method allows a stoichiometric integrity by preventing carbidic\ncarbon loss. Noted that, our present XPS analysis validates this mechanism. The XPS results\nshowed that the Mo-C species on H -treated Mo C-Ni/SiO catalyst is lower than that of the\n2 2 2\nCH /H treated one (Table S2) This result confirms that CH is indispensable for maintaining\n4 2 4\nMo C surface by continuously replenishing reactive carbon. We have strengthened this discussion\n2\nin the revised Supporting Information.\n“Supporting Information Page 46-Figure S34: CH could replenish surface carbon through\n4\nmethane decomposition, maintaining the carbide structure and yielding a C-rich surface, which is\nmore favorable for CO conversion. The XPS results showed that the Mo-C species on H -treated\n2 2\nMo C-Ni/SiO catalyst is lower than that of the CH /H treated one (Table S2).”\n2 2 4 2\nReferences:\n[1] S. Tauster, S. Fung, R.L. Garten, Strong metal-support interactions. Group 8 noble metals\n6 / 7\nsupported on titanium dioxide, J. Am. Chem. Soc., 100 (1978) 170-175.\n[2] H. Tang, F. Liu, J. Wei, B. Qiao, K. Zhao, Y. Su, C. Jin, L. Li, J. Liu, J. Wang, Ultrastable\nhydroxyapatite/titanium‐dioxide‐supported gold nanocatalyst with strong metal–support\ninteraction for carbon monoxide oxidation, Angew. Chem. Int. Ed., 55 (2016) 10606-10611.\n[3] A. Chen, X. Yu, Y. Zhou, S. Miao, Y. Li, S. Kuld, J. Sehested, J. Liu, T. Aoki, S. Hong,\nStructure of the catalytically active copper–ceria interfacial perimeter, Nature Catal., 2 (2019)\n334-341.\n[4] V. Danghyan, S.C. Novoa, A. Mukasyan, E. Wolf, Pressure dilution, a new method to prepare a\nstable Ni/fumed silica catalyst for the dry reforming of methane, Appl. Catal. B: Environ.,\n234 (2018) 178-186.\n[5] P. Yan, J. Mensah, A. Adesina, E. Kennedy, M. Stockenhuber, Highly-dispersed Ni on BEA\ncatalyst prepared by ion-exchange-deposition-precipitation for improved\nhydrodeoxygenation activity, Appl. Catal. B: Environ., 267 (2020) 118690.\n[6] X. Du, K. Zhou, L. Zhou, X. Lei, H. Yang, D. Li, C. Hu, Efficient catalytic conversion of\njatropha oil to high grade biofuel on Ni-Mo C/MCM-41 catalysts with tuned surface\n2\nproperties, J. .Energy Chem., 61 (2021) 425-435.\n[7] R. Li, J. Shang, F. Wang, Q. Lu, H. Yan, Y. Tuo, Y. Liu, X. Feng, X. Chen, D. Chen,\nQuantification and optimization of platinum-molybdenum carbide interfacial sites to enhance\nlow-temperature water-gas shift reaction, Nature Commun., 16 (2025) 1098.\n[8] X. Zhang, M. Zhang, Y. Deng, M. Xu, L. Artiglia, W. Wen, R. Gao, B. Chen, S. Yao, X. Zhang,\nA stable low-temperature H -production catalyst by crowding Pt on α-MoC, Nature, 589\n2\n(2021) 396-401.\n[9] L. Lin, W. Zhou, R. Gao, S. Yao, X. Zhang, W. Xu, S. Zheng, Z. Jiang, Q. Yu, Y.-W. Li,\nLow-temperature hydrogen production from water and methanol using Pt/α-MoC catalysts,\nNature, 544 (2017) 80-83\n[10] S. Yao, X. Zhang, W. Zhou, R. Gao, W. Xu, Y. Ye, L. Lin, X. Wen, P. Liu, B. Chen, E.\nCrumlin, J. Guo, Z. Zuo, W. Li, J. Xie, L. Lu, C.J. Kiely, L. Gu, C. Shi, J.A. Rodriguez, D.\nMa, Atomic-layered Au clusters on α-MoC as catalysts for the low-temperature water-gas\nshift reaction, Science, 357 (2017) 389.\n[11] X. Zhang, Y. Xu, Y. Liu, L. Niu, Y. Diao, Z. Gao, B. Chen, J. Xie, M. Bi, M. Wang, D. Xiao,\nD. Ma, C. Shi, A novel Ni-MoC O interfacial catalyst for syngas production via the\nx y\nchemical looping dry reforming of methane, Chem, 9 (2023) 102-116.\n7 / 7"}, {"round": 3, "reviewer_comments": {"reviewer_1": "I consider that the manuscript is now ready for publication.", "reviewer_2": "The manuscript may be accepted in the current form."}, "author_response": ""}]

Decision letter