Surface hydroxyl-induced Pt^0 clusters on TiO_2 for synergistic water gas shift catalysis

Domain: neuroscience
Published: 2026-02-14
Editorial outcome: major_revision

Abstract
The regulation of active site electronic structure is a central strategy for optimizing supported metal catalysts, yet achieving precise and comprehensive control remains challenging due to the complex nature of metal-support interactions. This work presents a practical and reproducible approach to this challenge through the deliberate regulation of surface hydroxyls on TiO2 via a titanate-derived synthesis and controlled calcination, which correlates with improved water gas shift catalysis activity of Pt/TiO2 catalyst. The mechanistic interpretation by multiple characterizations suggest that a higher hydroxyl concentration is associated with the formation of more reduced Pt species, which enhanced CO activation. Subsequently, hydroxyl groups can be directly consumed by CO, which shows a correlation with the formation of oxygen vacancies. Catalysts with a higher density of oxygen vacancies exhibit stronger H2O dissociation capability. This work develops hydroxyl-content control as a viable strategy for catalyst optimization, supported by a mechanistic framework that rationalizes its impact on both metal electronic structure and oxide surface chemistry.

Introduction
The water gas shift (WGS) reaction is an important industrial process for hydrogen production and carbon monoxide elimination, where the efficient activation of reactant molecules on the active sites of the catalyst surface is the key determinant of catalytic performance1. Supported metal-oxide catalysts have garnered attention due to their high dispersion and stability of metals. On reducible oxide supports, active metal–oxygen vacancies synergy is one possible mechanistic motif for WGS reaction2,3. Pt/TiO2 stands as an exemplary catalytic system that has been extensively investigated in a variety of pivotal reactions, including the WGS reaction, CO oxidation, hydrogenation, and hydrocarbon reforming4–7. Currently, due to the electronic metal-support interaction (EMSI) between Pt and TiO2, electrons at the interface tend to transfer from Pt species to TiO2, resulting in the formation of Ptδ⁺-O-Ti3⁺ interfacial sites8–11. Although such interfacial sites possess unsaturated Ti3+ and oxygen vacancies that facilitate the H2O dissociation12–14, which frequently is the rate-determining step of the WGS reaction15,16, the oxidized Ptδ+ species exhibit limited ability for CO activation. This limitation hinders effective matching with the enhanced H2O dissociation capability, thus restricting the WGS reaction performance. Generally, the enrichment of electron density on Pt sites facilitates the adsorption of CO molecules2,17. Therefore, the targeted construction of metallic Pt sites to match the abundant defect structure on the TiO2 surface represents an effective strategy for further enhancing the WGS reaction, which has been almost overlooked.

Commonly, the electronic structure of metal species is intrinsically linked to their size. The aggregation of metallic Pt particles is often accompanied by the decrease in the dispersion, which, due to geometric effects, results in the loss of active sites18. Conversely, ultrasmall species (<1 nm) typically exhibit positively charged metal sites, which lead to weakened CO adsorption19. Therefore, precise regulation of the electronic structure of Pt sites while controlling the size of metal species is essential yet challenging. It has been reported that the structure of the active metals is closely related to the surface properties of oxide support, which can be modulated by introducing the functional groups on the support11,20. Surface hydroxyl groups have been well established for their roles in regulating catalyst structure, influencing the adsorption of reactant molecules, and participating in reactions21–23. Recent research has reached a consensus on the use of surface hydroxyl groups constructed on TiO2 as direct anchoring sites for active metals, which contributes to maintaining the size of the active metals24–27. Moreover, a perspective that surface hydroxyl groups on TiO2 facilitate hydrogen spillover from metal sites to the support surface has been clearly proposed28,29. During the H* transfer process, electrons are retained at the metal sites30,31. Consequently, it can be expected to the correlation between the construction of surface hydroxyl groups on TiO2 support and the enhancement of electron density at Pt sites. Furthermore, the hydroxyl groups, serving as the crucial intermediates in the WGS reaction7,32, are capable of directly reacting with CO adsorbed on Pt0 sites. This consumption is anticipated to generate the high density of defect sites throughout the catalytic process, thereby facilitating the activation and dissociation of more H2O molecules. However, the effectiveness of hydroxyl groups does not always exhibit the positive correlation with their abundance. This is attributed not only to the blocking of metal sites by excess hydroxyl groups, but also to the fact that there exists an optimal amount of hydroxyl groups for modulating the state of the active species33,34. Therefore, precise modulation of the hydroxyl content is essential for achieving optimal catalytic performance35,36.

In this work, we developed a practical and reproducible hydroxyl-regulation approach via controlled calcination of a titanate precursor to tailor the structure of Pt/TiO2 catalysts. This method enabled the formation of small Pt0 clusters (~2 nm) on the hydroxyl-tuned TiO2 surface, distinct from conventional common Ptδ+-O-Ti3+ interfacial structure. Multiple characterization indicated that the resulting Pt species was consistent with the more reductive electronic state, which enhanced CO adsorption and activation. Furthermore, hydroxyl groups were consumed under CO exposure, a process that correlated with the generation of oxygen vacancies. Catalysts with a higher density of oxygen vacancies exhibited stronger H2O dissociation capability. A reasonable mechanistic interpretation was that the synergistic combination of the strong CO adsorption on Pt0 and efficient H2O dissociation enabled the excellent reaction rate of 62.7 mol·gPt−1·h−1 and the turnover frequency (TOF) of 6.15 s−1 at 250 °C in WGS reaction, which were nearly 2–3 times greater than the Pt/TiO2 catalysts in the literature. This work thus offered a practical handle for tuning catalytic activity via hydroxyl regulation, alongside insights into how such tuning modulated the metal electronic and oxide surface structure.

Results
Regulation of hydroxyl content for the formation of target Pt/TiO2 catalysts
The scheme of regulating the hydroxyl content on the support to obtain the target Pt/TiO2 catalyst is shown in Fig. 1a. Commercial anatase (denoted as TiO2-A) was hydrothermally treated with the highly concentrated NaOH solution (10 mol/L), followed by washing with HCl solution. This process resulted in the phase transformation from anatase to H2Ti3O7, which was denoted as TiO2-T-UC (Supplementary Fig. S1). It was imperative to elucidate the surface structure of the modified TiO2 and the chemical state of the supported Pt species. Firstly, according to the O1s XPS spectra compared to that of TiO2-A, the peak of lattice oxygen in TiO2-T-UC shifted toward the higher binding energy, which originated from the distinct layered titanate structure of the H2Ti3O7 phase compared to the anatase phase (Fig. 1b)37. Moreover, the another peak at 531.4 eV was attributed to bridging hydroxyls and the weak peak appearing at 532.6 eV was considered to be adsorbed hydroxyl groups from the environment, which originated from the absence of any thermal treatment38. The results of ATR-IR and TGA experiments also confirmed the formation of abundant surface hydroxyls (Supplementary Fig. S2). However, the nanotubular morphology of TiO2-T-UC caused the supported Pt species to be completely embedded in the TiO2 support lattice during the WGS reaction (Supplementary Fig. S3). The observed hindrance of CO molecule adsorption and the suppression of activity also confirmed this encapsulation (Supplementary Fig. S4, S5 and Table S1). Therefore, further thermal treatment of TiO2-T-UC in the air atmosphere was conducted (Supplementary Fig. S6). As the calcination temperature increased, the nanotubular morphology of TiO2 progressively collapsed, leading to the exposure of previously encapsulated Pt species (Supplementary Fig. S7 and S8). Concurrently, the hydroxyl concentration decreased with rising calcination temperature, resulting in the increase in the size of the supported Pt species (Supplementary Fig. S9 and S10). By integrating the hydroxyl group content with the exposure and size of Pt species, the Pt-based catalyst supported on TiO2-T calcined at 500 °C (denoted as TiO2-T-500) exhibited the optimal catalytic activity (Fig. 1c). It was worth noting that O1s XPS spectra of TiO2-T-500 showed that adsorbed hydroxyl groups disappeared due to thermal treatment, but the residual bridging hydroxyls were still present (Fig. 1b). Moreover, the mass loss from hydroxyls desorption of TiO2-T-500 in the TGA experiments was 1.19%, while that of TiO2-A was only 0.20% (Fig. 1d), demonstrating that the TiO2-T-500 support possessed the higher abundance of surface hydroxyl groups compared to TiO2-A (Fig. 1e)35. The H−D exchange and ATR-IR experiment also indicated the hydroxyl groups on TiO2-T-500 were more abundant than those on TiO2-A (Supplementary Fig. S11). These results revealed that TiO2-T-500 support with optimal hydroxyls content was obtained through the two-step hydroxylation-thermal treatment process of TiO2-A.

As reported, the surface properties of the support are closely related to the state of the supported active metals. The aberration-corrected HAADF-STEM characterization revealed that in the fresh 0.3Pt/(TiO2-T-500) catalyst, Pt species primarily coexisted as single atoms and clusters, which was consistent with the state of Pt species in the fresh 0.3Pt/(TiO2-A) catalyst (Fig. 1f, g). After the WGS reaction, the aggregation of Pt species into clusters occurred in both catalysts (Fig. 1h−k and Supplementary Fig. S12 and S13). Statistical analysis of Pt species indicated that the average size in the spent 0.3Pt/(TiO2-T-500) catalyst was 1.6 nm, which was quite similar to the 1.7 nm observed in the spent 0.3Pt/(TiO2-A) catalyst (Supplementary Fig. S14). Moreover, CO chemisorption measurements revealed that the dispersions of the spent 0.3Pt/(TiO2-T-500) and 0.3Pt/(TiO2-A) catalysts were 55.2% and 48.1%, respectively (Supplementary Table S1). The non-identical dispersions were derived from CO uptake based on a 1:1 CO:Pt stoichiometry, which might be influenced by various factors, such as support-dependent spillover, dynamic readsorption, or differences in CO binding strength. Nevertheless, they served as a supplementary indication that the Pt clusters in both catalysts remained accessible after reaction. This assessment was consistent with the direct HAADF-STEM observation of similar mean particle sizes after reaction. However, the predominant Pt0 species were present in the spent 0.3Pt/(TiO2-T-500) catalyst, while the Ptδ+ species were predominant in the spent 0.3Pt/(TiO2-A) catalyst (Supplementary Fig. S4). This observation suggested that the hydroxyl groups constructed on the support induced the significant changes in the electronic structure of Pt species in the absence of size effects.

The formation of Pt0 species induced by hydroxyls for enhanced CO activation
To thoroughly investigate the influence of hydroxyls on the electronic structure of active metals, the H2 pretreatment process prior to the reaction was taken into consideration, which might induce changes in the catalyst structure. Having ruled out the influence of H2 reduction temperature on hydroxyl groups and H2O desorption (Supplementary Fig. S15a, b), the temperature-programmed reduction by H2 (H2-TPR, Fig. 2a) showed that the significant decrease in the reduction temperature of the 0.3Pt/(TiO2-T-500) catalyst compared to 0.3Pt/(TiO2-A). This elucidated that the construction of surface hydroxyls on the TiO2-T-500 support was beneficial to the reduction of catalyst, which was further evidenced by the higher hydrogen consumption observed in 0.3Pt/(TiO2-T-500) catalyst (Supplementary Fig. S15c). According to the Pt 4f XPS spectra, the Pt species in the fresh 0.3Pt/(TiO2-T-500) and 0.3Pt/(TiO2-A) catalysts exhibited Pt2+ species at 72.5 eV and 72.3 eV, respectively (Supplementary Fig. S16)39,40. After H2 pretreatment, the Pt in the 0.3Pt/(TiO2-A) catalyst showed the binding energy of 71.4 eV, corresponding to Ptδ+ (Fig. 2b)41,42. In contrast, the binding energy for the 0.3Pt/(TiO2-T-500) catalyst shifted down by 0.7 eV to 70.8 eV, which likely correlated with the presence of Pt043. This result was consistent with the superior reducibility of the 0.3Pt/(TiO2-T-500) catalyst compared to 0.3Pt/(TiO2-A), facilitating the reduction of Pt2+ to Pt0 during H2 treatment. Furthermore, the XANES profile at Pt L3 edge spectra revealed the lower white-line intensity for 0.3Pt/(TiO2-T-500) compared to 0.3Pt/(TiO2-A) (Supplementary Fig. S17), which indicated that the Pt species in 0.3Pt/(TiO2-T-500) possessed the higher 5d electron density, corresponding to the more Pt0 sites44. However, considering the poor signal-to-noise ratio and interference from H* adsorption under H2 atmosphere, this result could not fully represent the exact state of Pt species under the WGS reaction, which could only imply a stronger tendency for Pt species in 0.3Pt/(TiO2-T-500) to be in the metallic state compared to that in 0.3Pt/(TiO2-A). Moreover, in situ DRIFTS experiments with CO adsorption showed that the weak reducibility of 0.3Pt/(TiO2-A) catalyst resulted in the presence of Pt2+ and Ptδ+ (0<δ<2) species, observed at 2101 cm−1 and 2080 cm−1, respectively45,46. In contrast, while the Pt2+ species disappeared in the 0.3Pt/(TiO2-T-500) catalyst, a new band appeared at 2049 cm−1. Its red shift relative to the Ptδ+ band in 0.3Pt/(TiO2-A) was associated with its assignment to Pt0 species, consistent with literature and electronic effects46–50. While we acknowledge that band positions can also be influenced by factors such as particle size and CO coverage, the observed trend across the sample series, combined with the supporting HAADF-STEM images, XPS and XANES data, leads us to attribute the dominant effect to the modification of the Pt electronic state. Overall, the observed trends were consistent with a mechanistic interpretation wherein support hydroxylation promoted the formation of Pt species with the more metallic electronic character.

During the subsequent WGS reaction, the active metal typically served as the adsorption and activation site for the reactant molecule CO. In situ DRIFTS experiments revealed the Pt0 species in 0.3Pt/(TiO2-T-500) and the Ptδ+ species in 0.3Pt/(TiO2-A) formed during the H2 pretreatment, which remained under WGS reaction condition (Supplementary Fig. S18). To explore the adsorption capability of CO molecules on Pt species with different electronic states in the two catalysts, Ar atmosphere was switched from WGS reaction atmosphere in the in situ DRIFTS experiment (Fig. 2d, e). The Ptδ+ species in 0.3Pt/(TiO2-A) catalyst showed limited affinity for CO adsorption, with nearly completed desorption occurring within 3 minutes under Ar gas (Fig. 2d). For 0.3Pt/(TiO2-T-500) catalyst, in addition to the bridged CO signal at 1950 cm−1 originating from the metal-support interface, CO linear adsorption on the masked Pt0 sites at 2064 cm−1 emerged during Ar purging, which were closer to the interfacial sites compared to the Pt0 at 2043 cm−1 (Fig. 2e)47,49. Notably, the interfacial signal at 2064 cm−1 remained red-shifted compared to the Ptδ+ signal at 2080 cm−1 in 0.3Pt/(TiO2-A), indicating that the interfacial Pt sites in the 0.3Pt/(TiO2-T-500) catalyst possessed higher electron density, consistent with the state of Pt0 clusters. The persistence of CO adsorption strength for the two kinds of Pt0 species in the 0.3Pt/(TiO2-T-500) catalyst after 10 min of Ar gas purging indicated that the Pt0 induced by surface hydroxyls exhibited the stronger CO adsorption capability (Fig. 2f). Moreover, the enhanced binding of CO on the 0.3Pt/(TiO2-T-500) catalyst was further evidenced by the CO desorption temperature in the CO-TPD experiment (Supplementary Fig. S19), which was 30 °C for 0.3Pt/(TiO2-A) and significantly lower than the 65 °C observed for 0.3Pt/(TiO2-T-500). Furthermore, the kinetic orders of CO for the 0.3Pt/(TiO2-T-500) catalyst was 0.07 at 220 °C and 0.27 at 250 °C, which was one-third of the value for the 0.3Pt/(TiO2-A) catalyst at 220 °C and half of their value at 250 °C (Fig. 2g and Supplementary Fig. S20). The decrease in the CO reaction order further provided evidence for the significantly enhanced adsorption capability of CO molecules by Pt0 species in the 0.3Pt/(TiO2-T-500) catalyst.

It has been reported that the electronic structure of Pt species in the WGS reaction has been a subject of considerable controversy45,51. To accurately elucidate the activation capability of CO by Pt species with different electronic structures, in situ DRIFTS experiments were employed at 250 °C, involving switching between CO and Ar or Ar+H2O for adsorption and desorption steps. For the 0.3Pt/(TiO2-A) catalyst, after eliminating interference from surface oxygen on the gaseous CO2 signal (Supplementary Fig. S21), Ar and Ar+H2O atmosphere was switched from CO adsorption (Fig. 2h and Supplementary Fig. S22). The CO adsorbed on the oxidized Ptδ+ species of 0.3Pt/(TiO2-A) catalyst showed similar desorption rates under both Ar+H2O and Ar atmospheres and the concurrent decrease in the gaseous CO2 signal, which indicated that Ptδ+ species was not the efficient catalytic site. In contrast, the CO adsorbed on both the Pt0 species in the 0.3Pt/(TiO2-T-500) catalyst at 2064 cm−1 and at 2043 cm−1 exhibited the significantly accelerated consumption rate under Ar+H2O purging compared to Ar purging, accompanied by the gaseous CO2 signal that initially increased and subsequently decreased (Fig. 2i and Supplementary Fig. S23). This indicated that CO adsorbed on Pt0 sites reacted with H2O and generated additional CO2. As the adsorbed CO on Pt0 was progressively consumed, the production of CO2 gradually diminished and eventually vanished upon complete purging. These results collectively pointed to the superior ability of Pt0 in activating CO molecules. In addition, the CO on the Pt0 species near the interface at 2064 cm−1 was completely consumed after 200 s, and correspondingly, CO2 was no longer generated. Meanwhile, the CO signal on the Pt0 away from the interface at 2043 cm−1 remained present, but continued injection of H2O could not generate additional CO2 (Supplementary Fig. S24). These results revealed that the Pt0 closer to the interface was more active in activating CO molecules. It was noteworthy that in bimolecular redox reactions, instantaneous dynamic changes in the oxidation state of active sites at the interface were ubiquitous. DFT calculations and Bader charge analysis revealed the charge on the Pt atom in the Pt0-O-Tiv structure changed from −0.8|e| to +0.01|e| during the water dissociation process, indicating the formation of the Ptδ+-OH-Ti structure (Supplementary Fig. S25 and Table S2). This observation aligned with the dynamic evolution of the oxidation state of Pt species at the interface during the reaction.

The participation of hydroxyls in the reaction to generate oxygen vacancies
Generally, the activation and dissociation of H2O molecule was commonly regarded as the rate-determining step in the WGS reaction, which could be substantiated by H/D kinetic isotope effect (KIE) experiments (Supplementary Fig. S26)7. In the association mechanisms of the WGS reaction, surface hydroxyls, formed through H2O dissociation, served as active intermediates that react with CO to generate products52. Therefore, it was crucial to confirm the reactivity of surface hydroxyls constructed on the support of 0.3Pt/(TiO2-T-500) catalyst during the reaction. As shown in Fig. 3a, CO-TPR measurement after H2 treatment was conducted to monitor the H2 generation. Upon CO injection, the H2 signal for 0.3Pt/(TiO2-T-500) appeared at 166 °C, which was not only lower than the H2 formation temperature in the 0.3Pt/(TiO2-A) catalyst, but also showed the significant increase in the amount of H2 generated. This results indicated that the surface hydroxyls constructed on the catalyst could be directly consumed by CO to form products. To further elucidate the participation behavior of surface hydroxyls of 0.3Pt/(TiO2-T-500) in the reaction, mass spectrometry was performed under different conditions with continuous operation (Fig. 3b). Firstly, the WGS reaction condition was implemented to track the consumption of reactants and the formation of products. At 125 °C, the rapid CO consumption occurred before the reaction initiation, accompanied by the simultaneous formation of CO2 and H2. This phenomenon might originate from the participation of surface hydroxyls on the 0.3Pt/(TiO2-T-500) catalyst in the reaction, which was further evidenced by the fact that the 0.3Pt/(TiO2-A) catalyst exhibited no H2 production before the reaction initiation (Supplementary Fig. S27). Following the WGS reaction, it was observed that there was an absence of H2 generation after the injection of H2O, which excluded the presence of the redox pathway52,53. After a prolonged high-temperature drying process under Ar atmosphere to remove surface moisture, the temperature programmed surface reaction (TPSR) experiment was conducted. As injecting CO, the distinct signals of CO2 and H2 with the ratio of 2:1 were exhibited, which indicated the association mechanism of the catalyst following H2O dissociation forming hydroxyls as active intermediates (Supplementary Fig. S28a). The similar reaction mechanism was also followed by 0.3Pt/(TiO2-A) catalyst (Supplementary Fig. S28b). This further demonstrated the crucial role of surface hydroxyls in the efficient progress of WGS reactions.

Given that the consumption of surface hydroxyls constructed on the catalyst by CO occurred prior to the onset of the reaction, it is imperative to reveal the role of the consumption in surface structure of the catalysts. Firstly, in situ Raman spectroscopy was conducted (Fig. 3c). Upon switching from H2 to CO, the Eg peak of the 0.3Pt/(TiO2-T-500) catalyst exhibited the blue shift of 7 cm−1, while that in the 0.3Pt/(TiO2-A) catalyst remained unchanged54,55. A plausible explanation for this difference was that the reaction between CO and the surface hydroxyls of the 0.3Pt/(TiO2-T-500) catalyst not only generated the products but also facilitated the creation of oxygen vacancies. In addition, in situ infrared spectroscopy at low temperature (−130 °C) was employed by detecting Ti sites after treatment under various conditions at 300 °C (Fig. 3d). The two peaks located at 2179 cm−1 and 2164 cm−1 appeared after H2 pretreatment, which were attributed to unsaturated Ti5C sites (denoted as Ti1) and Pt-O(H)-Ti interfacial sites (denoted as Ti2), respectively56,57. The ratio of the peak areas of Ti2 to Ti1 sites (Ti2/Ti1) was used to qualitatively represent the content of hydroxyls. Subsequently, the catalyst was further treated with CO at 300 °C and then cooled down to −130 °C for testing. It was found that the Ti2/Ti1 ratio decreased from 0.43 to 0.31, indicating that CO consumed the surface hydroxyls. Simultaneously, the peak intensity at 2203 cm−1, attributed to Ti4C sites, increased significantly, which indicated the increase in oxygen vacancies on the TiO2 surface56,57. The above results provided insight into the correlation between the consumption of surface hydroxyl groups by CO and the facilitated formation of oxygen vacancies. After the WGS reaction, the signal of Pt-O(H)-Ti interfacial sites re-emerged abundantly, which was likely attributable to the surface hydroxyls formed via H2O dissociation during the reaction. Consistent with this, the post-reaction O1s XPS spectra and ATR-IR measurements likewise showed enhanced signals associated with hydroxyl species (Supplementary Fig. S29). Moreover, the weakening signal of the Ti4C and unsaturated Ti5C sites, along with the formation of new saturated Ti5C sites (denoted as Ti3)56,57, indicated that oxygen vacancies might be replenished by hydroxyls generated from water dissociation. Afterward, the post-reaction catalyst was also treated with CO. The Pt-O(H)-Ti interfacial sites peak weakened and the Ti4C and unsaturated Ti5C sites peaks increased, which was attributed to the consumption of hydroxyl groups by CO and the concomitant formation of oxygen vacancies. A reasonable model to explain these observations was that the consumption of hydroxyl groups by CO, whether initially present or formed during the WGS reaction, suggested a link to the formation of oxygen vacancies. Furthermore, the EPR results manifested that the 0.3Pt/(TiO2-T-500) catalyst did not exhibit significant defects after H2 pretreatment (Supplementary Fig. S30), while the substantial number of defects emerged following the WGS reaction (Fig. 3e). And the quantity of these defects was significantly higher compared to the 0.3Pt/(TiO2-A) catalyst. Given the similar size of the Pt species in both catalysts, the variation in oxygen vacancy concentration could be rationalized by the differing levels of surface hydroxylation, which was consistent with the observed correlation between hydroxyl consumption and defect formation.

Furthermore, insights were gained into the behavior of water dissociation on the surface of the 0.3Pt/(TiO2-T-500) catalyst using isotopic experiments. The catalyst was first subjected to CO-TPR aimed at removing hydroxyl groups. Subsequently, H218O was introduced for 20 min. Upon switching back to the CO flow, signals for C16O18O were detected by both in situ DRIFTS and mass spectrometry (Supplementary Fig. S31 and S32). This observation suggested the possibility that H2O dissociated on the catalyst surface. Moreover, 0.3Pt/(TiO2-T-500) with more defects exhibited the greater capacity for H2O dissociation, as evidenced by the fact that the reaction order of H2O at both 250 °C and 290 °C was lower than that of 0.3Pt/(TiO2-A) catalyst (Fig. 3f and Supplementary Fig. S33). However, the present experiments unfortunately could not confirm the exact active site for H2O dissociation. Moreover, given the dynamic nature of hydroxyl groups under reaction conditions, their precise role could not be unambiguously assigned to individual steps. Taken together, a plausible framework could be inferred by integrating all available data, namely, that the hydroxyl-tuning strategy resulted in an optimal catalyst concurrently exhibiting higher oxygen vacancy signatures and the greater capacity for water activation.

The enhanced WGS reaction performance by the construction of hydroxyls
The comprehensive optimization of both the electronic structure of the active metal and the surface structure of the support oxide by surface hydroxyl groups has been clearly revealed through the above results, which was summarized in the schematic diagram in Fig. 4a. On one hand, surface hydroxyls facilitated the reduction of the catalyst, thereby forming Pt0 species that enhanced the adsorption and activation of CO molecules. On the other hand, surface hydroxyls were directly consumed by CO during the reaction, which promoted the formation of oxygen vacancies that enhanced the dissociation of H2O molecules. Therefore, in contrast to the singular focus on optimizing the state of Pt species or the TiO2 surface structure reported in the literature, surface hydroxyls specifically achieved the simultaneous enhancement in the activation capability for both reactant molecules in the WGS reaction, thereby working in combination to maximize the catalytic performance.

The WGS reaction was evaluated under the product free gas (2% CO/10% H2O/N2). The catalytic activity of 0.3Pt/(TiO2-T-500) catalyst was significantly higher than that of 0.3Pt/(TiO2-A) catalyst, whose CO conversion approached nearly 100% at 250 °C (Fig. 4b). The combined evidence from ICP-MS quantification, XPS analysis, and thorough support washing ruled out the contribution of residual Na and Cl from synthesis to the observed activity enhancement (Supplementary Fig. S34 and Table S3). The similar enhanced the performance was also exhibited by catalysts with Pt loadings of 0.1 wt.% and 0.5 wt.% (Supplementary Fig. S35). Moreover, the WGS reaction activity was improved with increasing Pt loading from 0.1 wt.% to 0.3 wt.% on TiO2-T-500, while further increase of Pt loading to 0.5 wt.% led to inferior activity, which might be caused by saturation of the Pt active site (Supplementary Fig. S36). Thus, 0.3Pt/(TiO2-T-500) sample turned out as the ideal catalyst, which established the apparent advantage of reaction rate at 225 °C and 250 °C compared to other catalyst systems in the literature (Fig. 4c and Supplementary Table 4). In particular, the catalytic activity of 0.3Pt/(TiO2-T-500) catalyst reached 1.7×104 μmol·gPt−1·s−1 at 250 °C, which was more than twice that of the previously reported Pt/TiO2 catalysts. Moreover, the 0.3Pt/(TiO2-T-500) catalyst exhibited the TOF nearly twofold higher than that of the reference 0.3Pt/(TiO2-A) catalyst and advantages over other Pt-based catalysts reported in the literature (Supplementary Table 5). It should be noted that these value were derived via normalization using the uncertain dispersion estimate, which was subject to the inherent assumptions (1:1 CO:Pt stoichiometry) and potential interference. Assuming that the CO chemisorption measurements were comparable for the both catalysts, the observation of a markedly higher TOF indicated a potentially greater intrinsic activity of the active sites on the TiO2-T-500 support. The apparent activation energies (Ea) obtained from the Arrhenius plots showed the similar Ea values of 0.3Pt/(TiO2-T-500) and 0.3Pt/(TiO2-A) catalysts (Supplementary Fig. S37), which suggested the two samples followed the identical reaction mechanism, consistent with the results of TPSR experiment. Furthermore, the long-term stability test of 0.3Pt/(TiO2-T-500) catalysts was examined that there was no deactivation with 70 h, which also possessed remarkable cyclic stability during the rising and cooling between 250 °C and 300 °C (Fig. 4d). Correspondingly, Pt 4f XPS spectra indicated the slight further reduction of the Pt species during the long-time reaction (Supplementary Fig. S38). In contrast, the 0.3Pt/(TiO2-A) catalyst exhibited the gradual increase in activity as the reaction progressed, eventually stabilizing after 20 h, although its final activity remained lower than that of the 0.3Pt/(TiO2-T-500) catalyst. This phenomenon originated from the enhanced electron density of Pt species, as evidenced by the peak shifting to lower binding energy in the post-stability Pt 4f XPS characterization (Supplementary Fig. S39). This further confirmed the crucial role of inducing Pt0 formation for the enhancement of catalytic performance.

Methods
Preparation of TiO2 nanotube and subsequent thermal treatment process
The preparation of the TiO2 tube involved using a hydrothermal technique within Teflon-lined stainless-steel autoclaves37,58. In a standard synthesis procedure for the support, 28 g of NaOH (sourced from Sinopharm) was dissolved in 70 mL of deionized water, resulting in a 10 mol/L solution. Subsequently, 2 g of commercial anatase TiO2 (obtained from Macklin, with the particle size of 25 nm, referred to as TiO2-A) was introduced into the solution and stirred for 1 h at room temperature. Following this, the mixture was subjected to heating at 130 °C for a duration of 24 h. Post-hydrothermal synthesis, the freshly formed precipitates were isolated by filtration and then washed using deionized water and 2 L of a 0.2 M HCl (Sinopharm) aqueous solution, followed by another round of washing with deionized water. The resultant material was then dried in air at 120 °C for 18 h and subsequently ground using a mortar. From this point forward, the TiO2 tube was designated as TiO2-T-UC. Subsequently, the TiO2-T-UC powder was heated in a tube furnace at a rate of 2 °C/min to 200 °C, 400 °C, 500 °C, 600 °C and 800 °C, respectively, and maintained at each temperature for 8 h. The resulting samples were denoted as TiO2-T-t (t = 200, 400, 500, 600, 800), respectively. The TiO2-T-wash-500 catalyst was prepared following an identical procedure to that of TiO2-T-500, with the modification that after washing with 2 L of HCl, the solid was further washed with 5 L of high-purity water. The reference commercial anatase was also heated in a tube furnace at a rate of 2 °C/min to 500 °C for 8 hours before use.

Preparation of various Pt/TiO2 catalysts
The platinum−titanium catalysts were prepared according to the wet impregnation (IM) method. First, 0.2 g of TiO2 powers was added to 20 mL high purity water and dispersed uniformly under vigorous stirring. After stirring the mixture for 30 min, a designed amount of chloroplatinic acid (H2PtCl6) solution (0.19 mol/L) was added into the above slurry. The mixture was heated to 90 °C in an oil bath with continuous stirring to facilitate drying. The obtained catalysts were labeled as xPt/(TiO2-A), xPt/(TiO2-T-UC) and xPt/(TiO2-T-t). The symbol x denotes the weight percentage of metallic Pt on the support, which are 0.1, 0.3, and 0.5 wt%.

Inductively coupled plasma mass spectrometry (ICP-MS)
ICP-MS analysis was performed using the NexION 1000G instrument. The solid catalysts were completely digested using the high-concentration hydrofluoric acid (HF). Approximately 4 mg of the solid catalyst powder was completely digested in 2 mL of HF and subsequently diluted to a final volume of 100 mL. A 10 mL aliquot of this solution was then transferred to a new volumetric flask and diluted again to 100 mL. The resulting solution was used for ICP-MS analysis. The instrument detection limit for the ICP-MS was 50 ppt. By converting this value relative to the initial mass of the catalyst, the corresponding detection limit for elemental content in the solid catalyst is 0.00125 wt.%.

Temperature-programmed reduction with H2 (H2-TPR)
H2-TPR experiments were performed using a Builder PCSA-1000 instrument. Prior to the test, the catalysts (30 mg, 20−40 mesh) were pretreated under Ar at 120 °C for 30 min, followed by switching to 5% H2/Ar. After the baseline was stabilized in hydrogen, the temperature was increased from room temperature to 500 °C at a rate of 10 °C·min−1.

Temperature programmed reduction with CO (CO-TPR)
All these experiments were performed on a lab-made reactor. The catalyst was first pretreated in a 5% H2/Ar atmosphere for 30 min, then cooled to room temperature, followed by purging with the Ar atmosphere. Subsequently, the atmosphere was switched to 2% CO/Ar, and the temperature was ramped up to 800 °C at a rate of 2 °C/min while simultaneously collecting data.

In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS)
In situ DRIFTS experiments was conducted using a Bruker Vertex 70 FTIR spectrometer equipped with a mercury-cadmium-telluride (MCT) detector. The sample cell (Harrick) featured CaF2 windows and a heating cartridge. To enable rapid gas switching without dead volume, an electronically controlled quick-switching system was employed. About 20 mg of the sample was filled into the reaction cell and underwent pretreatment in a 5% H2/Ar atmosphere before any tests were conducted. The spectra were recorded with an integration time of 30 s and a resolution of 4 cm−1, while the background was taken in pure N2. For the CO adsorption experiment, after the H2 pretreatment, the 2% CO/He gas was introduced into the reaction cell at 25 °C. Subsequently, the temperature was raised to 250 °C, and the 2% CO/10% H2O/Ar gas mixture was introduced into the system. After the WGS reaction, the temperature was lowered to room temperature, and 2% CO/He gas was reintroduced. For the CO adsorption−desorption experiments at 250 °C, the catalyst was exposed to 2% CO/He for 10 min, after which it was purged with N2 and a mixture of N2 and H2O, respectively. Upon reaching a new temperature, a fresh background measurement was taken in pure N2.

In-situ infrared spectroscopy in the transmission mode
In-situ infrared spectroscopy was carried out in a UHV apparatus by an FTIR spectrometer Bruker Vertex 70 (v) with a multichambered ultrahigh vacuum system. The catalyst underwent four different pretreatment methods. Firstly, the sample was pretreated with H2 in the sample cell at 300 °C and dropped to –130 °C directly. Secondly, the sample was pretreated in the sample cell with H2 at 300 °C, followed by the switch to CO atmosphere for further treatment, and then cooled down to –130 °C. Thirdly, the sample underwent the WGS reaction treatment in the reactor, then it was transferred to the sample cell and directly cooled down to –130 °C. Lastly, the sample underwent the WGS reaction treatment in the reactor, then it was transferred to the sample cell and further treated with CO at 300 °C, followed by cooling down to –130 °C. After the completion of the aforementioned pretreatments and cooling down to –130 °C, adsorption was performed by passing 1×10−1 mbar CO accompanied by data collection.

X-ray photoelectron spectroscopy (XPS)
The XPS measurements were carried out on a Thermo Scientific ESCALAB Xi+ XPS spectrometer (Thermo Fisher) with Al Kα radiation (15 kV, 20 mA). Each spectrum was energy-calibrated using the C 1s signal at 284.8 eV as a reference.

Raman test
All the ex situ and in situ Raman spectra were acquired by using a Raman microscope system (HORIBA JY) with laser excitation at 473 nm. In the in-situ Raman experiment, the sample was first pretreated with H2 at 300 °C for 30 min, during which data was collected. Subsequently, the atmosphere was switched to CO, and after maintaining the CO atmosphere for another 30 minutes, data collection was performed.

Catalytic tests
The WGS reaction of platinum-titanium catalysts was conducted in a fixed-bed reactor. 100 mg of the samples (20−40 mesh) was placed inside and pretreated with a 5% H2/Ar gas mixture (70 mL·min−1) at 300 °C for 30 min. Following this, a mixed gas (2% CO/10% H2O/Ar) was flowed through to carry out the reaction at a gas hourly space velocity of 42,000 mL·gcat−1·h−1. The outlet gas compositions of CO and CO2 were analyzed online on a Gasboard 3500 IR spectroscopy (Wuhan Sifang Company, China). The CO conversion was defined by the following formula:
XCO = (ninCO − noutCO) / ninCO × 100 (1)
The reaction rates were evaluated by varying the catalyst mass and the flow rate of the reactant gas under conditions where the CO conversion remained below 15%, which were calculated by the following formula:
r = F × XCO / m (2)
where F was the molar flow rate of CO in mol·h−1 and m was the mass of Pt in the fixed bed.
The TOF value was defined by the following formula:
TOF = r × MPt / DPt (3)
where MPt was the molar weight of Pt and DPt was the dispersion of Pt calculated from the results of CO chemisorption by assuming that the stoichiometric ratio of adsorbed CO/Pt is 1.
During the stability test, the gas mixture was continuously supplied to the fixed-bed reactor at 250 °C for 70 h. Simultaneously, the conversion data were continuously monitored at gas hourly space velocities of 84,000 mL·gcat−1·h−1. Moreover, the conversion data during the 70 h process of supplying gas to a fixed-bed reactor while alternating between 250 °C and 300 °C was also recorded. An ice trap was employed to condense the unreacted water following the reactor tube. The concentrations of CO and CO2 in the outlet gas were monitored using an infrared gas analyzer (Gasboard-3100, manufactured by Wuhan Sifang Company, China). The apparent activation energy (Ea) was determined using the same apparatus as for testing the catalytic performance mentioned earlier. A suitable quantity of Pt-supported catalyst was loaded into the reactor, and the temperature and gas flow rate were adjusted to maintain the CO conversion within the range of 5 to 15%. The outlet gas was then analyzed with an infrared gas analyzer (Gasboard-3100, Wuhan Sifang Company, China).

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This manuscript addresses the role of surface hydroxyls in modulating the catalytic behavior of Pt/TiO2 systems for the water-gas shift (WGS) reaction. While the overarching topic is of high relevance, particularly regarding metal-support interactions and dynamic surface chemistry, the manuscript contains several conceptual oversimplifications, grammatical issues, and unsupported conclusions that must be addressed before publication.\n\n1. Conceptual Framing and Literature Context\n\"Supported metal-oxide catalysts have garnered attention due to their ability to form efficient catalytic interfaces through metal-support interactions, where the active metal and the support collectively activate different reactant molecules\"\nThis opening sentence suggests that the primary reason for using supported metal catalysts is to facilitate bifunctional activation (e.g., metal vs. support activating distinct molecules). This is misleading. The dominant reason for employing oxide supports is typically related to dispersion and thermal/mechanical stability, not inherently bifunctional activation. Furthermore, reference 8 does not support this bifunctional claim.\n\"Pt/TiO2, as a typical catalyst\"\nWhat is meant by \"typical catalyst\"? This phrasing is vague and should be clarified. Typical in what context? WGS? Hydrocarbon reforming?\n\"which frequently is the rate-determining step of the WGS reaction\"\nPlease provide references to support this assertion regarding the RDS of WGS.\n\"the electron-deficient Pt sites formed in the Ptδ+-Ov-Ti3+ structure accordingly due to the electronic metal-support interaction (EMSI)\"\nThe term \"EMSI\" must be defined more clearly. What is the specific electron transfer or orbital overlap occurring here? Why invoke a formal term like EMSI without clarifying the mechanism or providing a reference?\n\"exhibit the inadequate adsorption capacity for CO molecules, leading to limited WGS reaction activity\"\nIf so, isn’t that the role of the Pt nanoparticles themselves? Please reconcile the contradiction here: if Ptδ+ is inactive, why does that affect the role of Pt0 nanoparticles, which are present?\n\"to match the abundant defect structure\"\nClarify what structure is being referred to. It appears to be the TiO2 support, not the Pt.\n\"loss of abundant active sites\"\nWhy? Is this a geometrical equivalency argument or an adsorption energy-driven rationale? Please clarify. Also consider size effects in CO adsorption: very small Pt particles do not bind CO efficiently (see https://doi.org/10.1021/ja058282w).\n\"provides a guarantee for preserving the size of the\"\nThis is too strong. No treatment \"guarantees\" particle size preservation.\n\"on TiO2 facilitate hydrogen spillover has been clearly proposed35,36.\"\nPlease clarify the direction of hydrogen spillover.\n\"is capable of directly reacting with CO adsorbed on Pt0 sites.\"\nGrammar: \"are capable\"\n\"precise regulation of the hydroxyl group content is essential, as their effectiveness is not always positively correlated with their content40,41.\"\nWhy? What are the competing mechanisms that reduce catalytic effectiveness at high hydroxyl coverage?\n\"The obtained electron-rich Pt0 species was revealed\"\nGrammar: \"were revealed\"\n\"hydroxyl groups during the subsequent reaction acted as active intermediates\"\nAdsorption and reaction intermediacy is not the same as catalytic activity. Please do not conflate.\n\"This work achieved the comprehensive enhancement in the activation capability of reactant molecules in\"\nHow much? Please be quantitative. What is the observed improvement? Compared to what literature benchmarks?\n\"hydroxyl content on the support to obtain the target Pt/TiO2 catalyst was shown in Figure 1a.\"\nGrammar: \"is shown\"\n2. Language and Clarity\nThe introduction is relatively well-written, but the remainder of the manuscript suffers from frequent grammatical errors and awkward phrasing. Just 2 quick examples:\n• \"Commercial anatase (denoted as TiO2-A) as precursor was hydroxylated by... which denoted as\".\n• \"The surface structure of modified TiO2 and its effects on the state of supported Pt species need to be clearly characterized\".\n3. Experimental Issues and Data Interpretation\nFTIR Spectra:\n• The materials appear extremely wet in the FTIR results in Fig S2. All samples should be dried (preferably >100 °C) prior to spectral acquisition to allow proper comparison of hydroxyl features and FTIR spectra for all samples should be shown.\nClaims of Pt Encapsulation:\n• The conclusion that Pt is \"embedded\" in the TiO2 lattice is based on a single triangular particle image (Supplementary Figs. S3, S4). This is insufficient. Support this claim with catalytic activity suppression or CO chemisorption data to show surface-area loss.\n• Figure S4 only presents a narrow IR range. No comparison with other samples is shown. The term \"used\" is ambiguous; please clarify whether this means spent catalyst.\nFigure 1d – Volcano Plot:\n• 4 data points are insufficient to define a volcano curve. Error bars are missing (everywhere in the article; please add). Lines should be described in the caption and justified physically.\nRedundancy and Missing Information:\n• Figure 1f is redundant with 1d.\n• Figure 1e should show TGA of samples treated at 200 and 800 °C.\n• Figure S7 does not convincingly show a significant difference in OH groups. The conclusion of \"significantly more abundant\" is not justified.\nParticle Size and Dispersion:\n• No average particle size data are provided for any sample in Figure 1. If particle size changes, so will activity, regardless of hydroxyl concentration.\n• Provide HAADF-STEM with statistical analysis (>100 particles), histograms, and support with chemisorption data to report surface exposure.\n• Report TOF values.\nTPR Analysis:\n• The H2-TPR data (Fig. 2a) do not prove hydrogen spillover. Lower reduction temperatures can also arise from water loss or hydroxyl dehydrogenation. FTIR suggests the material is wetter, not necessarily more reducible.\n• Assigning changes in reducibility to Pt species alone (e.g., Pt2+ → Pt0) without structural or XAS data is speculative.\nXPS Data:\n• The XPS spectra (Fig. 1c) show minimal differences. Claims of electron-rich Pt0 formation are not distinguishable from noise. Additional XAS data are needed.\nCO Adsorption / DRIFTS Interpretation:\n• The assignment of bands to Pt0 vs. Ptδ+ is highly tentative.\n• CO-TPD experiments only support stronger binding, not overall \"adsorption capability.\"\n\"CO adsorbed on the electron-deficient Ptδ+ species\"\nAgain, this assignment rests on uncertain XPS data.\n\"In contrast, for the 0.3Pt/(TiO2-T-500) catalyst... CO2 products... Fig. 2i\"\nThis claim is highly questionable. Figure 2h shows a CO2 peak for the \"A\" sample that is larger than that for the \"T-500\" sample. The conclusion that CO2 is not formed on the A sample is unsubstantiated. Under Ar, no desorption curves are provided for CO, which complicates interpretation. It is also very plausible that the T-500 sample simply adsorbs CO more strongly due to particle size differences.\nReaction Mechanism Claims:\n\"This corresponded to the conclusion that oxygen vacancies were formed by the consumption of surface hydroxyls by CO during the reaction...\"\nAgain, this could also be due to differences in particle size or suboxide shell formation. Particle sizes must be reported for all fresh and spent catalysts.\nOverall\nThis study explores a timely and important topic, but currently suffers from overinterpretation of spectroscopic data, lack of rigorous controls, and incomplete physical characterization. Stronger claims about site-specific activity or electronic structure require corroboration by XAS, chemisorption, and particle size analysis. Many conclusions are not fully supported by the presented data.\nSubstantial revisions are necessary before this manuscript can again be considered for publication in Nature Communications.", "reviewer_2": "Jia and coauthors present a compelling strategy for enhancing the catalytic performance of supported metal-oxide catalysts by modulating the electronic structure of active sites through surface hydroxyl groups. This work convincingly demonstrates the formation of electron-rich Pt⁰ clusters (~2 nm) on hydroxylated TiO₂, in contrast to conventional Pt^δ+-Ov-Ti³⁺ interfacial structures. This modification not only enhances CO adsorption and activation but also couples with hydroxyl-assisted oxygen vacancy formation to promote H₂O dissociation, leading to synergistic improvement in the water-gas shift (WGS) reaction. The mechanistic insights provided into how surface hydroxyl groups contribute both to the electronic modulation of Pt and the dynamic restructuring of the oxide support are novel and significant. I find the study well-structured and impactful; however, I suggest the authors provide additional experimental or theoretical validation of the proposed Pt⁰-hydroxyl interaction mechanism and quantify the contribution of each step (CO adsorption vs. H₂O dissociation) to the overall WGS enhancement.\n1. Why is there such a large shift (~0.7 eV) in the O1s binding energy of lattice oxygen (O_latt.) in TiO2-T-UC compared to TiO2-T-500 and TiO2-A? Please explain the origin of this significant difference.\n2. The statement “However, excessive surface hydroxyls caused the supported Pt species to be completely embedded in the TiO2 support lattice during the WGS reaction, resulting in the loss of active metal sites (Supplementary Fig. S3 and S4)” requires quantitative data or literature support. Only two STEM images alone are not sufficient to support such a conclusion. A statistical comparison of the post-reaction STEM data between TiO2-T-500 and the hydroxyl-rich sample would help clarify how the OH content influences the embedding or migration of Pt species.\n3. The frequent mention of “OH content of TiO2-T-500 (1.3 mmol g⁻¹)” gives the impression that the value may have been selectively emphasized. Please consider adjusting Figure 1 to avoid repetitive or potentially misleading data presentation.\n4. Please provide the WGS reaction conditions in the legend of Figure 1, especially those corresponding to Figure 1d. This information is necessary for clarity and reproducibility.\n5. The interpretation of Pt 4f spectra in Figure 2c requires further clarification. Specifically, 0.3Pt/(TiO2-T-500) predominantly shows metallic Pt⁰ species, while 0.3Pt/(TiO2-A) mainly exhibits Pt²⁺ or Pt⁴⁺ states. The orange peaks in both XPS spectra are currently labeled as Pt⁰, but the binding energy difference between them (~0.7 eV) is too large to be attributed to the same oxidation state. Please clarify the specific assignments of each deconvoluted peak.\n6. The phrase “the formation of electron-rich Pt⁰ species” is somewhat inappropriate. It may be unnecessary to emphasize \"electron-rich,\" as the main point is the formation of metallic Pt⁰ species. There is no clear evidence that these Pt⁰ species are more electron-enriched than typical Pt⁰, as indicated by the XPS results in Figure 2c.\n7. In the in situ DRIFTS spectra of the 0.3Pt/(TiO2-A) catalyst, why does the CO₂ signal appear at the very beginning (Figure S14), while for 0.3Pt/(TiO2-T-500) the signal is much weaker or absent? This suggests that the Ptδ⁺–OH–Ti⁴⁺ interfacial sites in the former are highly reactive initially, rapidly oxidizing CO to CO₂. Please discuss this. Also, how should we interpret the volcano-shaped curve of CO₂ formation in Figure 2i? A clear explanation is needed in the text.\n8. As the authors state, “These results revealed that the electron-rich Pt⁰ closer to the interface was more active in activating CO molecules.” However, is it possible that the “Pt⁰ near the interface” is in fact the Ptδ⁺ species located at the Ptδ⁺–OH–Ti⁴⁺ interface, rather than fully metallic Pt⁰? This may involve dynamic transformation between Ptδ⁺ and Pt⁰ driven by OH consumption and water dissociation during the reaction. Consider using DFT simulations and valence state calculations to further support this hypothesis.\n9. In Figure 3b, the CO₂ and H₂ signals during the second CO injection are significantly weaker than those during the first injection. This indicates that the interfacial OH species regenerated via water dissociation are less abundant than the native surface OH species originally present on the catalyst. What could be the reason? Is it due to structural changes in the catalyst or sintering of the Pt nanoparticles?\n10. After the long-term stability test, how does the Pt 4f XPS spectrum of the 0.3Pt/(TiO2-T-500) catalyst compare with the fresh sample? Are there any notable changes in the oxidation state of Pt species?\n11. Based on the above concerns, I would like to recommend the publication of this work in Nature Communications."}, "author_response": "Responses to the Reviewers’ Comments and the Corresponding Revisions\nReviewer #1:\nComment: This manuscript addresses the role of surface hydroxyls in modulating the\ncatalytic behavior of Pt/TiO systems for the water-gas shift (WGS) reaction. While the\n2\noverarching topic is of high relevance, particularly regarding metal-support\ninteractions and dynamic surface chemistry, the manuscript contains several\nconceptual oversimplifications, grammatical issues, and unsupported conclusions that\nmust be addressed before publication.\nResponse: We sincerely appreciate the reviewer for the careful reading of the\nmanuscript and the constructive comments, which have greatly helped us improve the\nquality of the work. We have carefully revised the entire manuscript and provided more\ncomprehensive evidence. We hope this revised version can be accepted to Nature\nCommunications.\n1. Conceptual Framing and Literature Context\nComment 1: \"Supported metal-oxide catalysts have garnered attention due to their\nability to form efficient catalytic interfaces through metal-support interactions, where\nthe active metal and the support collectively activate different reactant molecules\"\nThis opening sentence suggests that the primary reason for using supported metal\ncatalysts is to facilitate bifunctional activation (e.g., metal vs. support activating\ndistinct molecules). This is misleading. The dominant reason for employing oxide\nsupports is typically related to dispersion and thermal/mechanical stability, not\ninherently bifunctional activation. Furthermore, reference 8 does not support this\nbifunctional claim.\nResponse: We sincerely appreciate the professional comments of the reviewer. Indeed,\nas the reviewer rightly pointed out, supported metal–oxide catalysts have attracted\nextensive attention owing to their high dispersion and stability of metals. This\n1\nviewpoint has been revised and showed on Page 3, lines 5−6 in the revised\nmanuscript (highlight in yellow).\nMoreover, for gas-phase reactions involving two distinct reactant molecules, such\nas the water gas shift (WGS) reaction, catalysis at a single type of active site is often\ninsufficient. The synergistic effect of multiple catalytic sites is required to facilitate the\nreaction. In supported metal-oxide catalysts, when the reducible oxide serves as the\nsupport, the synergistic effect between the active metal and oxygen vacancies becomes\ncrucial. Shen et al. investigated the realistic structure of the Cu/CeO catalyst and its\n2\nstructure-activity relationship in the WGS reaction. In their study, Cu clusters provide\nCu+ sites for effective CO adsorption, while oxygen vacancies on the CeO surface\n2\ndissociate H O into hydroxyl species (Chen, A. et al. Nat. Catal. 2019, 2, 334−341).\nv\nsite for the WGS reaction, where CO adsorption and H O dissociation occur at the Pt0\n2\nsites and oxygen vacancies, respectively (Li, Y. et al. Nat. Common. 2021, 12, 914). In\nour work, Pt0 sites in the clusters function to adsorb CO, while a high density of oxygen\nvacancies formed in situ during the reaction efficiently cleaves H O. This similarly\n2\nunderscores the important role of synergistic sites in the activation of reactant\nmolecules within supported metal-oxide catalysts. Therefore, we have added the\ncorresponding description on Page 3, lines 6−7 (highlight in yellow), with citations\nto the aforementioned literature as 3 and 4.\nComment 2: \"Pt/TiO , as a typical catalyst\"\nTypical in what context? WGS? Hydrocarbon reforming?\nResponse: We are grateful to the reviewer for the constructive comment. Pt/TiO\n2\nsystem stands as an exemplary catalytic system that has been extensively\ninvestigated in a variety of pivotal reactions, including the water gas shift reaction,\nCO oxidation, hydrogenation, and hydrocarbon reforming (Iida, H. et al. Appl.\nM. et al. ACS Cent. Sci. 2022, 8, 1633–1645; Zhao, H. et al. ACS Appl. Mater.\nInterfaces 2018, 10, 36954–36960; Chen, J. et al. Nat. Commun. 2023, 14, 1–12; Hu,\nX. et al. Angew. Chem. Int. Ed. 2025, 64, e202419103; He, C. et al. Angew. Chem. Int.\nEd. 2024, 136, e202412308). We have revised the manuscript on Page 3, lines 8−10\n(highlight in yellow). The relevant references have been cited as 5−8.\nComment 3: \"which frequently is the rate-determining step of the WGS reaction\"\nPlease provide references to support this assertion regarding the RDS of WGS.\nResponse: We thank the reviewer for the valuable suggestion. Accordingly, we have\nnow cited three references (Mavrikakis, M. et al. J. Am. Chem. Soc. 2008, 130,\n1402−1414; Odriozola, J. A. et al. ACS Catal. 2024, 14, 14947−14957; Wei, M. et al.\nACS Catal. 2019, 9, 2707−2717.), which provide compelling evidence from both DFT\ncalculations and experiments, confirming that H O dissociation acts as the rate-\n2\ndetermining step in the water gas shift reaction. The relevant references have been\ncited as 11−13.\nComment 4: \"the electron-deficient Pt sites formed in the Ptδ+-O -Ti3+ structure\nv\naccordingly due to the electronic metal-support interaction (EMSI)\"\nThe term \"EMSI\" must be defined more clearly. What is the specific electron transfer\nor orbital overlap occurring here? Why invoke a formal term like EMSI without\nclarifying the mechanism or providing a reference?\nResponse: We sincerely thank the reviewer for this insightful comment. The electronic\nmetal-support interaction (EMSI) primarily refers to the electron transfer between the\nsupport and the supported metal. The formation of the Ptδ⁺-O -Ti3+ structure in Pt/TiO\nv 2\nsystems involves electron transfer from Pt to TiO , thereby generating electron-\n2\n3\ndeficient Ptδ⁺ species. The electron transfer induced by EMSI has been consider as an\nestablished phenomenon in the literatures (Dong, Y. et al. ACS Cent. Sci. 2022, 8,\n1633−1645; Jiang, J. et al. Angew. Chem. Int. Ed. 2025, 64, e202419103; Yang, Q. et\nal. Common. Chem. 2021, 4, 54).\nThe corresponding description has been revised on Page 3, lines 10−12\n(highlight in yellow). We have cited these works as references 6, 9, and 10. Once\nagain, we thank the reviewer for the professional and thorough suggestions.\nComment 5: \"exhibit the inadequate adsorption capacity for CO molecules, leading to\nlimited WGS reaction activity\"\nIf so, isn’t that the role of the Pt nanoparticles themselves? Please reconcile the\ncontradiction here: if Ptδ+ is inactive, why does that affect the role of Pt0 nanoparticles,\nwhich are present?\nResponse: We thank the reviewers for the constructive comments. In Pt/TiO -based\n2\ncatalyst systems, it is generally accepted that the interfacial sites serve as the active\ncenters for the reaction (Gao, M. et al. ACS Cent. Sci. 2022, 8, 1633−1645; Xiong, H.\net al. J. Am. Chem. Soc. 2025, 147, 38204−38214.). For nanoparticle catalysts, Pt0\nspecies that are distant from the interface are generally catalytically inert and function\nprimarily as spectators during the reaction. Moreover, the electronic structure of the\ninterfacial sites often plays a key role in determining the catalytic performance.\nHowever, due to the electronic metal–support interaction (EMSI) between Pt and TiO ,\n2\nelectrons at the interface tend to transfer from Pt species to TiO , resulting in the\n2\nformation of Ptδ+–O –Ti3+ interfacial sites. Although such interfacial sites facilitate the\nv\nformation of unsaturated Ti3+ and oxygen vacancies, thereby enhancing H O\n2\ndissociation, the electron-deficient Ptδ+ species exhibit limited ability for CO activation.\nThis limitation hinders effective matching with the enhanced H O dissociation\n2\ncapability, thus restricting further improvement in the WGS reaction activity. Therefore,\nit is essential to modulate the electronic structure of Pt species at the interface. This\n4\nwould enable the formation of O –Ti3+ sites to improve H O dissociation, while\nv 2\nsimultaneously maintaining the interfacial Pt species in the metallic state, thereby\nfacilitating more effective activation of CO molecules and synergistically enhancing\nthe WGS reaction activity.\nIn summary, the insufficient activation of CO by the interfacial Ptδ+ species does\nnot affect the Pt0 sites located away from the interface, which typically act as spectators.\nRather, our objective is to strategically modulate the structure of the interfacial sites,\nwhich are recognized as the active centers, to further enhance their CO activation\ncapability. This would allow it to better match the high H O dissociation activity,\n2\nthereby maximizing the overall performance of the WGS reaction. The corresponding\ndescription has been revised on Page 3, lines 12−16 in the revised manuscript\n(highlight in yellow).\nComment 6: \"to match the abundant defect structure\"\nClarify what structure is being referred to. It appears to be the TiO support, not the Pt.\nengineering abundant defect structures on the TiO support surface. To provide greater\n2\nspecificity, the relevant discussion has been updated to “to match the abundant defect\nstructure on the TiO surface” on Page 3, lines 18−19 in the revised manuscript\n2\n(highlight in yellow).\nComment 7: \"loss of abundant active sites\"\nWhy? Is this a geometrical equivalency argument or an adsorption energy-driven\nrationale? Please clarify. Also consider size effects in CO adsorption: very small Pt\nparticles do not bind CO efficiently (see https://doi.org/10.1021/ja058282w).\nResponse: We are grateful to the reviewer for the insightful comment, which helps to\nclarify the underlying mechanism. The loss of active sites with increased particle size\n5\nis primarily a geometrical equivalency argument (Ge, S. et al. ACS Catal. 2024, 14,\n2532-2544). The primary reason is the decrease in the dispersion and the specific\nsurface area of the Pt species as their size increases. Smaller nanoparticles have a higher\nproportion of their total atoms exposed on the surface, which can function as active\nsites. As the particles grow, a larger fraction of atoms resides in the particle bulk,\nbecoming inaccessible for catalysis, which is regarded as the underlying cause of\nabundant active site loss. Certainly, as the reviewer rightly points out, catalytic activity\nis not monotonically increased with decreasing particle size. When the metal species\nbecome extremely small (e.g., < 1 nm), the formation of positively charged metal sites\nis promoted (Leendert Bezemer, G. et al. J. Am. Chem. Soc. 2006, 128, 3956-3964).\nThis electron deficiency suppresses the crucial π-backdonation from the metal d-\norbitals to the 2π* anti-bonding orbital of CO, thereby reducing the strength of the Pt–\nCO bond and consequently weakening CO adsorption. Therefore, precise regulation\nof the electronic structure of Pt sites while controlling the size of metal species is\nessential yet challenging. The corresponding description has been shown in the\nrevised manuscript on Page 3, lines 21−26 (highlight in yellow). The corresponding\nreferences have been cited as 15 and 16.\nComment 8: \"provides a guarantee for preserving the size of the\"\nThis is too strong. No treatment \"guarantees\" particle size preservation.\nResponse: We highly appreciate the reviewer's valuable comments. We have revised to\n\"contributes to maintaining the size of the active metals\" on Page 4, lines 2−3\n(highlight in yellow).\nComment 9: \"on TiO facilitate hydrogen spillover has been clearly proposed35,36.\"\nthe direction of hydrogen spillover is from the metal sites to the support surface\nand have modified the manuscript accordingly on Page 4, line 4.\nComment 10: \"is capable of directly reacting with CO adsorbed on Pt0 sites.\"\nGrammar: \"are capable\"\nResponse: We appreciate the reviewer's careful comment and apologize for our mistake.\nWe have corrected it on Page 4, line 8.\nComment 11: \"precise regulation of the hydroxyl group content is essential, as their\neffectiveness is not always positively correlated with their content40,41.\"\nWhy? What are the competing mechanisms that reduce catalytic effectiveness at high\nhydroxyl coverage?\nResponse: We thank the reviewer for the constructive comment. In catalysis, the\ninfluence of surface hydroxyl groups does not follow a trend of monotonic\nimprovement. An optimal coverage exists, which must be evaluated on a case-by-case\nbasis for different catalytic systems. Firstly, the exposure of active sites can be hindered\nby strong metal–hydroxyl interactions. For instance, studies on Ru catalysts have\nshown that the strong affinity for adsorbed hydroxyls poisons the active sites and\ndegrades performance. This issue can be addressed by introducing SnO , which\n2\ncompetes with Ru for OH adsorption, thereby effectively mitigating the site poisoning\n(Zhang, J. et al. Angew. Chem. Int. Ed. 2022, 61, e202209486). Moreover, hydroxyl\ngroups can alter the oxidation state and dispersion of the active metal. However, the\nstate of metal species induced by the high hydroxyl coverage is not necessarily the most\ncatalytically active. As demonstrated by the work of Li et al. (Li et al., J. Am. Chem.\nSoc. 2025, 147, 30326−30338), the content of surface hydroxyls can be tailored to\ncontrol the size of Ag on Al O . They found that the high hydroxyl coverage anchors\n2 3\noptimal performance for the C H -SCR reaction, it exhibited negligible activity in both\n3 6\nC H epoxidation and NH -SCO reactions. In contrast, the lower hydroxyl coverage\n2 4 3\nfacilitated the formation of Ag nanoparticles, which was proved to be the most active\nfor the latter reactions. This finding clearly illustrates that no positive correlation exists\nbetween surface hydroxyl content and catalytic activity, as different reactions require\ndistinct state of active site. Therefore, the hydroxyl content must be strategically tuned\nto achieve optimal performance for the specific catalytic reaction. Based on the two\npoints above, we have revised the manuscript on Page 4, line 11−16 (highlight in\nyellow). And we have cited the aforementioned references as 34 and 35. Once again,\nwe thank the reviewer for the insightful comments.\nComment 12: \"The obtained electron-rich Pt0 species was revealed\"\nGrammar: \"were revealed\"\nResponse: We appreciate the reviewer's thorough comment and apologize for the\nmistake. The manuscript has been revised accordingly, as indicated on Page 4, line\n19.\nComment 13: \"hydroxyl groups during the subsequent reaction acted as active\nintermediates\"\nAdsorption and reaction intermediacy is not the same as catalytic activity. Please do\nnot conflate.\nResponse: We sincerely thank the reviewer for the insightful comment. We agree with\nthe reviewer that strengthened reactant adsorption at the individual site and the presence\nof reaction intermediates cannot be solely interpreted as direct evidence for enhanced\ncatalytic activity. In our work, the hydroxyl groups constructed on the catalyst surface\n8\nnot only function as intermediates, reacting with CO to form CO , but, more importantly,\n2\ntheir consumption during the reaction concurrently generates abundant oxygen\nvacancies. These vacancies subsequently serve as active sites for H O dissociation.\nenhanced H O dissociation capability synergizes with the strong adsorption and\n2\nactivation of CO molecules on Pt0 sites, thereby collectively promoting the observed\nincrease in the reaction rate. To avoid any confusion, we have revised the relevant\ntext in the revised manuscript on Page 4, lines 20−23 (highlight in yellow).\nComment 14: \"This work achieved the comprehensive enhancement in the activation\ncapability of reactant molecules in\"\nHow much? Please be quantitative. What is the observed improvement? Compared to\nwhat literature benchmarks?\nResponse: We appreciate the reviewer's professional comment. Generally, the\nimprovement in the activation capability of reactant molecules corresponds to the\nincrease in the catalytic reaction rate. The turnover frequency (TOF) defines the\nintrinsic activity per active site and can serve to quantify the activation capability of the\nactive sites towards reactant molecules. As presented in Table R1-1, the 0.3Pt/(TiO -T-\n2\n500) catalyst exhibited the TOF nearly twice that of the reference 0.3Pt/(TiO -A)\n2\ncatalyst. Meanwhile, this TOF value demonstrated the clear advantage over those\nreported for other Pt-based catalysts in the literature. These results indicated that the\n0.3Pt/(TiO -T-500) catalyst possess an enhanced capability for activating reactant\n2\nmolecules. In addition, the qualitative assessment of reactant activation capability is\nalso widely employed, where the value of the reaction order can represent the activation\ncapacity for reactant molecules. As shown in Figure R1-1a and b, at both 250 and\n290 °C, the H O reaction order of the 0.3Pt/(TiO -T-500) catalyst showed the 20%\n2 2\nreduction compared to the 0.3Pt/(TiO -A) reference. This observed reduction suggested\n2\nthe improvement in the H O activation. Similarly, the CO reaction order for the\n2\n0.3Pt/(TiO -T-500) catalyst is also approximately half that of the 0.3Pt/(TiO -A)\n2 2\n9\ncatalyst at both 250 °C and 220 °C, indicating the enhanced CO activation capability\n(Figure R1-1c and d).\nTo more clearly demonstrate the enhanced activation of reactant molecules, we\nhave now quantified this improvement using the reaction rate and TOF value in the\nrevised manuscript. The text has been revised on Page 4, line 23−26 (highlight in\nyellow). The Table R1-1 has been shown as Table S4 in supplementary information.\nThe Figure R1-1a has been shown as Figure 3f in the revised manuscript. The\nFigure R1-1b has been shown as Figure S31 in supplementary information. The\nFigure R1-1c has been shown as Figure 2g in the revised manuscript. The\nFigure R1-1d has been shown as Figure S20 in supplementary information.\nTable R1-1. Comparison of reaction rate and TOF values for WGS reaction over\nvarious catalysts at 250 °C.\nRate\nSamples\nTOF (s-1) Reference\n(mol ·g -1·h-1)\nco Pt\n0.3Pt/(TiO -T-500) 62.7 6.15 This work\n2\n0.3Pt/(TiO -A) 31.4 3.54 This work\nPt-4Na/TiO 7.74 1.39\n2\n123-132.\nChen, Y. et al. ACS Catal. 2018,\nPt/FeO 17.2 0.93\nx\n8, 859−868.\nPanagiotopoulou, P. et al. Catal.\nPt/Al O 0.35 0.02\n2 3\nToday 2007, 127, 319-329.\nPierre, D. et al. Top. Catal. 2007,\nPt/CeO 1.71 0.17\nx\n46, 363-373.\nZhai, Y. et al. Science 2010, 329,\nPt=Na/SiO 4.32 0.24\n2\n1633-1636.\n2 2 2\n(a) 250 °C and (b) 290 °C. (c−d) CO reaction orders of 0.3Pt/(TiO -T-500) and\n2\n0.3Pt/(TiO -A) at (c) 250 °C and (d) 220 °C.\nwas shown in Figure 1a.\"\nGrammar: \"is shown\"\nResponse: We sincerely appreciate the reviewer's careful review and apologize for the\nmistake. The manuscript has been revised accordingly on Page 5, line 3.\n2. Language and Clarity\nThe introduction is relatively well-written, but the remainder of the manuscript suffers\nfrom frequent grammatical errors and awkward phrasing. Just 2 quick examples:\n11\n• \"Commercial anatase (denoted as TiO -A) as precursor was hydroxylated by... which\n2\ndenoted as\".\n• \"The surface structure of modified TiO and its effects on the state of supported Pt\n2\nspecies need to be clearly characterized\".\nResponse: We are grateful for the reviewer's meticulous and expert suggestions on the\nwording and expression. The two specific examples of language issues highlighted by\nthe reviewer have been addressed as follows: (1) \" Commercial anatase (denoted as\nTiO -A) was hydrothermally treated with the highly concentrated NaOH solution\n2\n(10 mol/L), followed by washing with HCl solution.\" and (2) \" It was imperative to\nelucidate the surface structure of the modified TiO and the chemical state of the\n2\nsupported Pt species.\" on Page 5, lines 4−8. Furthermore, we have performed the\ncomprehensive revision throughout the revised manuscript.\n3. Comments about Experimental Issues and Data Interpretation\nComment 1: FTIR Spectra: The materials appear extremely wet in the FTIR results in\nFig S2. All samples should be dried (preferably >100 °C) prior to spectral acquisition\nto allow proper comparison of hydroxyl features and FTIR spectra for all samples\nshould be shown.\nResponse: Thanks for reviewer’s valuable suggestions. The drying temperature for the\nTiO -T-UC support has been increased from the initial 80 °C to 120 °C and maintained\n2\nfor 18 hours. As shown in Figure R1-2a, the TGA results indicated that the mass loss\nbelow 200 °C was reduced, suggesting that the increased drying temperature facilitated\nthe removal of physically adsorbed H O. Above 200 °C, the mass loss showed no\n2\nsignificant change, demonstrating that the surface hydroxyl groups are preserved. FT-\nIR analysis revealed the slight decrease in the OH signal after drying at 120 °C, which\nremained significantly stronger than that of the TiO -A support (Figure R1-2b).\n12\nwas observed that the intensity of the OH signal gradually decreased with increasing\ncalcination temperature of the supports, further demonstrating that the calcination\ntemperature plays a regulatory role in the surface hydroxyl content.\nWe have updated the data for TiO -T-UC dried at 120 °C from Figures R1-2a\n2\nand b to Figure S2 in the supplementary information. The corresponding\ndescription in the method section has been revised to \"dried in air at 120 °C for 18\nhours\" on Page 17, line 26 in the revised manuscript (highlight in yellow).\nMoreover, the Figure R1-2c has been shown as Figure S9b in the supplementary\ninformation.\nFigure R1-2. (a) TGA curves of TiO -T-UC at 80 °C and 120 °C. (b) The attenuated\n2\ntotal reflectance-infrared spectroscopy (ATR-IR) of TiO -T-UC at 80 °C and 120 °C\n2\nand TiO -A. (c) The attenuated total reflectance-infrared spectroscopy (ATR-IR) of\n(1) The conclusion that Pt is \"embedded\" in the TiO lattice is based on a single\n2\ntriangular particle image (Supplementary Figs. S3, S4). This is insufficient. Support\nthis claim with catalytic activity suppression or CO chemisorption data to show\nsurface-area loss.\n0.3Pt/(TiO -T-UC) was measured to be 4.9 μmol·g −1·s−1 at 250 °C, which represented\n2 cat\nthe significant decrease compared to the 0.3Pt/(TiO -A) catalyst with the non-\n2\nhydroxylated support (Figure R1-3). When the TiO -T-UC support was calcined at\n2\n500 °C followed by subsequent Pt loading, superior catalytic activity was achieved.\nThis result corresponded to the HAADF-STEM observations, indicating that the\nencapsulation of Pt particles led to the suppression of the catalytic activity. Additionally,\nCO pulse chemisorption experiments were performed on the spent catalysts (Table R1-\n2). The results revealed that the 0.3Pt/(TiO -A) and 0.3Pt/(TiO -T-500) catalysts\n2 2\nexhibited comparable CO uptake, which was significantly greater than that of the\n0.3Pt/(TiO -T-UC) catalyst. This indicated that the Pt species in 0.3Pt/(TiO -T-UC)\n2 2\nwere covered, thereby losing their CO adsorption capacity. This conclusion was\nconsistent with the trends observed in catalytic activity, HAADF-STEM images and in\nsitu DRIFTS results. The Figure R1-3 was shown as Figure S5 in the supplementary\ninformation. The Table R1-2 was shown as Table S1 in the supplementary\ninformation. The corresponding description has been added in the revised\nmanuscript on Page 5, lines 17−19 (highlight in yellow).\nFigure R1-3. The reaction rate of 0.3Pt/(TiO -A), 0.3Pt/(TiO -T-UC) and 0.3Pt/(TiO -\n2 2 2\nT-500) catalysts at 250 °C.\n2 2\nand 0.3Pt/(TiO -T-500) catalysts.\nDispersion\n(μmol/g)\n0.3Pt/(TiO -A) 7.4 48.1 %\n2\n0.3Pt/(TiO\n2\n-T-UC) 2.9 18.8 %\n0.3Pt/(TiO\n2\n-T-500) 8.5 55.2 %\n(2) Figure S4 only presents a narrow IR range. No comparison with other samples is\nshown. The term \"used\" is ambiguous; please clarify whether this means spent catalyst.\nResponse: We thank the reviewer for the valuable suggestions. The CO adsorption\nresults from in situ DRIFTS spectra for the three samples after the WGS reaction are\npresented in Figure R1-4. The results showed that the 0.3Pt/(TiO -A) catalyst exhibited\n2\ndistinct signals corresponding to Pt2+ and Ptδ⁺ species. In contrast, the CO adsorption\nsignals for Pt0 species were nearly absent in the 0.3Pt/(TiO -T-UC) catalyst, which was\n2\nattributed to the encapsulation of Pt species by the support. Furthermore, upon the\nadjustment of the hydroxyl group content on the support, pronounced signals of Pt0\nspecies re-emerge in the 0.3Pt/(TiO -T-500) catalyst, which demonstrated the exposure\n2\nof the Pt species. The comparison among the three samples provided further evidence\nfor the encapsulation of Pt species by the support in the 0.3Pt/(TiO -T-UC) catalyst.\ncorresponding description has been added in the revised manuscript on Page 5,\nlines 17−19 (highlight in yellow).\nIn addition, the term \"used\" in this manuscript means spent catalyst, which was\nindeed ambiguous. Therefore, in accordance with the suggestion of the reviewer, we\n15\nhave replaced \"used\" with \"spent\" throughout the revised manuscript. We thank the\nreviewer again for the expert comment.\nFigure R1-4. In situ DRIFTS spectra of the CO adsorption for the spent 0.3Pt/(TiO -\n2 2\nComment 3: Figure 1d – Volcano Plot: 4 data points are insufficient to define a volcano\ncurve. Error bars are missing (everywhere in the article; please add). Lines should be\ndescribed in the caption and justified physically.\nResponse: We thank the reviewer for the insightful comments. The reaction rates of\ncatalysts with supports calcined at 400 °C and 600 °C have been added to Figure\nR1-5. It was observed that the Pt-based catalyst supported on TiO -T calcined at 500 °C\n2\nexhibited the optimal catalytic activity. However, the divergent catalytic activities\nexhibited by the Pt catalysts supported on TiO -T calcined at different\n2\ntemperatures were influenced by the combination of factors. Firstly, the surface\nhydroxyl content progressively decreased with increasing calcination temperature,\nwhich was confirmed by TGA and ATR-IR results (Figure R1-6). Furthermore, the\nexposure of Pt species and their particle size also varied with the calcination\ntemperature of the support. As shown in Figure R1-7a, the catalysts with supports that\nwere untreated retained their nanotubular morphology after the WGS reaction.\nouter walls of the nanotubes, resulting in the non-uniform size distribution. In addition\nto the inadequate exposure of active sites for Pt particles located within the nanotube\ninterior, those on the external surfaces were also found to be embedded within the tube\nwalls. These masked sites collectively contribute to the suppression of WGS activity.\nWhen the support was calcined at 200 °C, the majority of the nanotubes were retained\n(Figure R1-7b). Similarly to the 0.3Pt/(TiO -T-UC) catalyst, Pt particles were\n2\nincorporated into both the interior and the outer walls of these nanotubes, which\nhindered the exposure of active sites. In contrast to 0.3Pt/(TiO -T-UC), a portion of the\n2\nnanotubes in the 0.3Pt/(TiO -T-200) catalyst collapsed, forming layered sheet-like\n2\nstructures. Although the Pt particles supported on these structures still exhibited a non-\nuniform size distribution, this morphological change increased the number of exposed\nPt sites to absorb the CO molecules (Figure R1-8), thereby leading to a slight\nenhancement in the WGS activity. As shown in Figure R1-9, when the calcination\ntemperature of the support was increased to 400 °C, the TiO nanotubes underwent\n2\ncomplete collapse, transforming into the sheet-like morphology. This transformation\nwas accompanied by a progressive increase in the size of the supported Pt particles with\nrising calcination temperature of TiO support, which was attributed to the loss of\n2\nsurface hydroxyl groups and the consequent weakening of their anchoring effect on the\nPt species. Therefore, Figure R1-5, which showed the variation of catalyst reaction\nrate with support calcination temperature, served to identify the optimal\ncalcination temperature of 500 °C. Since the volcano-shaped trend lacks physical\nsignificance, we have removed the line. The Figure R1-5 has been shown as Figure\n1c in the revised manuscript. The Figure R1-6, R1-7, R1-8 and R1-9 has been\nshown as Figure S9, S7, S8 and S10 in the supplementary information, respectively.\nThe corresponding description has been added on Page 5, lines 20−27 (highlight\nin yellow).\nIn addition, error bars have been incorporated into the reported values for the\nreaction rates (Figure R1-5), reaction orders (Figure R1-10), and Ea (Figure R1-11).\nFigure R1-10b has been shown as Figure S31 in supplementary information. The\nFigure R1-10c has been shown as Figure 2g in the revised manuscript. The Figure\nR1-10d has been shown as Figure S20 in supplementary information. Figure R1-\n11 has been shown as Figure S34 in supplementary information.\nFigure R1-5. WGS reaction rate at 250 °C as the function of calcination temperature\nof TiO -T support, with the optimum at 500 °C.\n2\n2\ndifferent thermal treatment temperature.\nFigure R1-7. The aberration-corrected HAADF-STEM images and the size statistics\nof the spent (a) 0.3Pt/(TiO -T-UC) and (b) 0.3Pt/(TiO -T-200) catalyst.\n2 2\nFigure R1-8. In situ DRIFTS spectra of the CO adsorption for the spent 0.3Pt/(TiO -T-\n2\nof the spent (a) 0.3Pt/(TiO -T-400), (b) 0.3Pt/(TiO -T-500), (c) 0.3Pt/(TiO -T-600) and\n2 2 2\n(d) 0.3Pt/(TiO -T-800) catalyst.\n2\n2 2\n250 °C and (b) 220 °C. The H O reaction order of 0.3Pt/(TiO -T-500) and 0.3Pt/(TiO -\n2 2 2\nA) at (a) 250 °C and (b) 290 °C.\nFigure R1-11. Activation energy (E ) for 0.3Pt/(TiO -A) and 0.3Pt/(TiO -T-500)\na 2 2\ncatalysts.\n(1) Figure 1f is redundant with 1d.\nResponse: We thank the reviewer for the thoughtful suggestion. The original Figure 1f\nhas been replaced with a plot of the reaction rate as a function of the support calcination\ntemperature, which now appeared as Figure 1c in the revised manuscript.\nFurthermore, the original Figure 1d revealed that the hydroxylated TiO -T calcined at\n2\n500 °C, which exhibited optimal catalytic performance after supporting Pt species,\nretained the higher concentration of surface hydroxyl groups compared to the anatase\nTiO -A precursor. This demonstrated that the two-step hydroxylation–thermal\n2\ntreatment process applied to TiO -A successfully produced the TiO -T-500 support with\n2 2\nthe optimal hydroxyl content, thereby resulting in superior WGS activity after Pt\nloading. The original Figure 1d has been shown as Figure 1e in the revised\nmanuscript.\n(2) Figure 1e should show TGA of samples treated at 200 and 800 °C.\nResponse: We thank the reviewer for the careful comments. The surface hydroxyl\ncontent of the supports calcined at different temperatures was measured by TGA. It was\nfound that the mass loss above 200 °C gradually decreased with increasing calcination\ntemperature, indicating the reduction in surface hydroxyl groups. Therefore, the TGA\nresults for the 200 °C and 800 °C samples, along with those of other calcination\ntemperatures, are summarized in Figure R1-12. After identifying 500 °C as the optimal\nsupport calcination temperature based on the highest catalytic activity, the hydroxyl\ncontents on TiO -T-500 and the precursor anatase TiO -A were compared (Figure R1-\n2 2\n13). The results demonstrated that a certain amount of hydroxyl groups remained on\nthe TiO -T-500 support, and this amount was higher than that on the TiO -A\n2 2\nsupport. Figure R1-12 has been shown as Figure S9a in supplementary\ninformation. Figure R1-13a and b has been shown as Figure 1d and e in the revised\n22\nmanuscript. The corresponding description has been updated on Page 5, lines 23,\n24 and Page 7, lines 1−3 in the revised manuscript (highlight in yellow).\nFigure R1-12. TGA curves of various TiO under different thermal treatment\n2\ntemperature.\nFigure R1-13. (a) TGA curves of TiO -A and TiO -T-500 supports. (b) The hydroxyl\n2 2\ncontent of TiO -A and TiO -T-500 supports determined from TGA measurements.\n2 2\n(3) Figure S7 does not convincingly show a significant difference in OH groups. The\nconclusion of \"significantly more abundant\" is not justified.\nResponse: We thank the reviewer for the timely comments. The peak area of the HD\nsignal in the H–D exchange experiment was representative of the surface hydroxyl\ngroup concentration. As shown in Figure R1-14b, TiO -T-500 exhibited the larger HD\n2\nsignal peak area compared to TiO -A, indicating the higher abundance of surface\n2\nhydroxyl groups on TiO -T-500. As correctly noted by the reviewer, the difference in\n2\nthe integrated H-D exchange signal intensities between the two supports should not be\ndescribed as \"significantly\". Accordingly, the statement in the revised manuscript has\nbeen changed to: \"the hydroxyl groups on TiO -T-500 were more abundant than\n2\nthose on TiO -A.\" To further compare the hydroxyl group concentration on the two\n2\nsupports, ATR-IR results demonstrated that TiO -T-500 exhibited the more intense\n2\nhydroxyl signal compared to TiO -A (Figure R1-14c). Figure R1-14 has been shown\n2\nas Figure S11 in supplementary information and the corresponding description\nhas been added on Page 7, lines 3−5 in the revised manuscript (highlight in yellow).\nFigure R1-14. (a) HD evolution profiles during the H−D exchange of TiO -A and TiO -\n2 2\nT-500. (b) OH contents samples determined from the peak area of H−D curves\nnormalized by support mass. (c) ATR-IR of TiO -A and TiO -T-500.\n2 2\nComment 5: Particle Size and Dispersion:\n(1) No average particle size data are provided for any sample in Figure 1. If particle\nsize changes, so will activity, regardless of hydroxyl concentration.\nResponse: We thank the reviewer for the expert comments. For the hydroxylated TiO -\n2 2\nnanotubular morphology led to the coverage of Pt active sites, resulting in lower\n24\ncatalytic activity (Figure R1-7 and R1-8). When the calcination temperature of the\nsupport exceeds 400 °C, the nanotubes completely collapse into the sheet-like\nmorphology, leading to full exposure of the Pt sites. However, with the further increase\nin the calcination temperature, the decreasing hydroxyl group concentration weakened\nthe anchoring ability for the Pt species, leading to the gradual increase in Pt particle\nsize (Figure R1-9). Thus, the observed variation in catalytic activity of the Pt-based\ncatalysts with support calcination temperature results from the collective\ninfluence of multiple factors, including surface hydroxyl content, the exposure of\nPt species, and particle size. Consequently, the Figure R1-5 displaying the catalyst\nreaction rate as a function of support calcination temperature served to identify\nthe optimal thermal treatment conditions for the hydroxylated support.\nThe 0.3Pt/(TiO -T-500) catalyst, with the support calcined at 500 °C, exhibited the\n2\noptimal catalytic performance and was therefore selected as the primary subject for\ncomparison with 0.3Pt/(TiO -A), which used non-hydroxylated anatase TiO as the\n2 2\nsupport. As shown in Figure R1-15−R1-17, HAADF-STEM characterization revealed\nthat in the fresh 0.3Pt/(TiO -T-500) catalyst, Pt species primarily coexisted as single\n2\natoms and clusters, which was consistent with the state of Pt species in the fresh\n0.3Pt/(TiO -A) catalyst. After the WGS reaction, aggregation of Pt species occurred in\n2\nboth catalysts. Statistical analysis of Pt species indicated that the average Pt particle\nsize in the spent 0.3Pt/(TiO -T-500) catalyst was 1.6 nm, which was quite similar to the\n2\n1.7 nm observed in the spent 0.3Pt/(TiO -A) catalyst (Figure R1-18). Moreover, CO\n2\nchemisorption measurements revealed that the dispersions of the spent 0.3Pt/(TiO -T-\n2\n500) and 0.3Pt/(TiO -A) catalysts were 48.1 % and 55.2 %, respectively. This result\n2\ndemonstrated that the Pt species in both catalysts exhibited the similar dispersion (Table\nR1-2). Given the comparable Pt particle size and dispersion in the 0.3Pt/(TiO -T-500)\n2\nand 0.3Pt/(TiO -A) catalysts, the difference in their catalytic performance was primarily\n2\nattributed to the distinct concentration of surface hydroxyl groups on the respective\nsupports, which critically influences both the electronic structure of the Pt species and\nthe surface properties of the support. Figure R1-15 has been shown as Figure 1f−k in\n25\nthe revised manuscript. Figure R1-16− R1-18 has been shown as Figure S12−14 in\nsupplementary information. Table R1-2 has been shown as Table S1 in\nsupplementary information. The corresponding description has been revised on\nPage 5, lines 25−27 and Page 7, lines 9−19 in the revised manuscript (highlight in\nyellow).\nFigure R1-15. (a−f) Aberration-corrected HAADF-STEM images of the fresh (a)\n0.3Pt/(TiO -T-500) and (b) 0.3Pt/(TiO -A) catalyst.\n2 2\n(c−f) Aberration-corrected\nHAADF-STEM images of the spent (c, d) 0.3Pt/(TiO -T-500) and (e, f) 0.3Pt/(TiO -A)\n2 2\ncatalyst.\n0.3Pt/(TiO -T-500).\n0.3Pt/(TiO -A).\n2\n2\n0.3Pt/(TiO -A) catalysts.\n2 2\nand 0.3Pt/(TiO -T-500) catalysts.\nDispersion\n(μmol/g)\n0.3Pt/(TiO -A) 7.4 48.1 %\n2\n0.3Pt/(TiO\n2\n-T-UC) 2.9 18.8 %\n0.3Pt/(TiO\n2\n-T-500) 8.5 55.2 %\n(2) Provide HAADF-STEM with statistical analysis (>100 particles), histograms, and\nsupport with chemisorption data to report surface exposure.\nResponse: We appreciate the constructive comments from the reviewer. HAADF-\nSTEM images of the spent 0.3Pt/(TiO -T-500) and 0.3Pt/(TiO -A) catalysts have been\n2 2\nprovided (Figure R1-15−R1-17), along with particle size statistics (Figure R1-18). The\nresults showed that the average particle sizes of the two catalysts are 1.6 nm and 1.7\n2\nnm, respectively. In addition, CO chemisorption experiments conducted after the\nreaction revealed that the Pt dispersions in the 0.3Pt/(TiO -T-500) and 0.3Pt/(TiO -A)\n2 2\ncatalysts are 48.1% and 55.2%, respectively (Table R1-2). These findings indicated that\nthe Pt species in both catalysts exhibit similar particle sizes and dispersion.\n(3) Report TOF values.\nResponse: We thank the reviewers for the professional comments. The TOF values of\nthe 0.3Pt/(TiO -T-500) and 0.3Pt/(TiO -A) catalysts were 6.15 s−1 and 3.54 s−1,\n2 2\nrespectively, indicating that the activity per Pt site in the 0.3Pt/(TiO -T-500) catalyst\n2\nwas higher than that in the 0.3Pt/(TiO -A) catalyst (Table R1-1). Table R1-1 has been\n2\nshown as Table S4 in supplementary information. The corresponding calculation\nformula has been added into the revised manuscript on Page 20, lines 9−17. The\ncorresponding description has been added on Page 16, lines 14−16 in the revised\nmanuscript (highlight in yellow).\nComment 6: TPR Analysis:\n(1) The H -TPR data (Fig. 2a) do not prove hydrogen spillover. Lower reduction\n2\ntemperatures can also arise from water loss or hydroxyl dehydrogenation. FTIR\nsuggests the material is wetter, not necessarily more reducible.\nResponse: We thank the reviewer for the insightful comments. To exclude the potential\ninfluence of H O desorption during the heating process on the decrease in the reduction\n2\npeak temperature, H -TPR coupled with mass spectrometry was performed on both\n2\ncatalysts (Figure R1-19a). The results indicated that the hydrogen consumption\ntemperature of the 0.3Pt/(TiO -T-500) catalyst remained lower than that of 0.3Pt/(TiO -\n2 2\nA). Moreover, no significant H O signal was detected simultaneously with the H\n2 2\nconsumption peaks. This observation was likely attributable to the fact that both\nsupports were calcined at 500 °C and subsequently the catalyst pretreated at 120 °C\n29\nunder the Ar atmosphere prior to the H -TPR measurements. The findings\n2\ndemonstrated that the lower reduction temperature did not arise from the water\nloss. Furthermore, the TiO -T-500 and TiO -A supports exhibited negligible TCD\n2 2\nsignals during H -TPR analysis (Figure R1-19b). This indicated that the surface\n2\nhydroxyl groups did not consume H , thereby ruling out the possibility that the lower\n2\nreduction temperature was caused by dehydrogenation of hydroxyl groups.\nSubsequently, we further quantified the H consumption from the H -TPR results\n2 2\nof the two catalysts (Figure R1-19c). It was found that the actual H consumption of the\n2\n0.3Pt/(TiO -T-500) catalyst exceeded the theoretical H consumption of the Pt species,\n2 2\nwhereas the actual H consumption of 0.3Pt/(TiO -A) was less than its theoretical Pt\n2 2\nconsumption. Although this evidence could not directly prove the occurrence of\nhydrogen spillover, it clearly demonstrated that the Pt species in the 0.3Pt/(TiO -T-500)\n2\ncatalyst activated the support, thereby leading to enhanced reducibility.\nThe Figure R1-19 has been shown as Figure S15 in the supplementary\ninformation and the corresponding description has been added on Page 7, lines\n27−28 and Page 8, lines 3−4 in the revised manuscript (highlight in yellow).\nFigure R1-19. (a) H -TPR profiles of the 0.3Pt/(TiO -T-500) and 0.3Pt/(TiO -A)\n2 2 2\nsamples characterized by mass spectrometry. (b) H -TPR profiles of TiO -T-500 and\n2 2\nTiO -A support. (c) H consumption calculated from the results in H -TPR profiles of\n2 2 2\nthe 0.3Pt/(TiO -T-500) and 0.3Pt/(TiO -A) samples.\n2 2\n30\n(2) Assigning changes in reducibility to Pt species alone (e.g., Pt2+ → Pt0) without\nstructural or XAS data is speculative.\nResponse: We are grateful to the reviewer for the constructive comments. To confirm\nthe evolution of Pt species during H reduction, structural characterization was\n2\nperformed. According to the Pt 4f XPS spectra, the Pt species in both the 0.3Pt/(TiO -\n2\neV, which was assigned to Pt2+ species (Figure R1-20a and b). After H pretreatment,\n2\nas shown in Figure R1-20c, the Pt in the 0.3Pt/(TiO -A) catalyst showed the binding\n2\nenergy of 71.4 eV, corresponding to Ptδ⁺. In contrast, the binding energy for the\n0.3Pt/(TiO -T-500) catalyst shifted down by 0.7 eV to 70.8 eV, indicating the presence\n2\nof Pt0 species. This result demonstrated the superior reducibility of the 0.3Pt/(TiO -T-\n2\n500) catalyst compared to 0.3Pt/(TiO -A), facilitating the reduction of Pt2+ to Pt0 during\n3 2\nfurther carried out (Figure R1-21). Despite the relatively poor signal-to-noise ratio of\nthe Pt/TiO catalysts due to the low Pt loading (0.3 wt%), both catalysts were observed\n2\nthat white-line intensity was close to that of Pt foil, indicating the reduction of Pt species\nunder the H atmosphere. Furthermore, the white-line intensity of 0.3Pt/(TiO -A) was\n2 2\nhigher than that of 0.3Pt/(TiO -T-500). This white-line intensity was proportional to\n2\nthe transition probability of 2p electrons to unoccupied 5d orbitals (Rossi, G. et al. Phys.\nRev. B 1983, 27, 5154–5157). The higher white-line intensity corresponded to the\ngreater number of unoccupied 5d states and the lower 5d-electron density, thus\nindicating the higher oxidation state of Pt species in 0.3Pt/(TiO -A).\ninformation. Figure R1-20c has been revised in Fig. 2b in the revised manuscript.\nFigure R1-21 has been shown as Figure S17 in the supplementary information.\nThe corresponding description has been added on Page 8, lines 5−12 and 17−21\nlines in the revised manuscript (highlight in yellow). The corresponding reference\nwas cited as 50 in the revised manuscript.\n2\n0.3Pt/(TiO -A) samples. (c) The Pt 4f XPS for 0.3Pt/(TiO -T-500) and 0.3Pt/(TiO -A)\n2 2 2\nsamples after H pretreatment.\n3 2\nComment 7: XPS Data: The XPS spectra (Fig. 1c) show minimal differences. Claims\nof electron-rich Pt0 formation are not distinguishable from noise. Additional XAS data\nare needed.\nResponse: We thank the reviewer for the insightful comment. In situ XANES\nprofile at Pt L edge under the H pretreatment was further carried out (Figure R1-21).\n3 2\nDespite the relatively poor signal-to-noise ratio of the Pt/TiO catalysts due to the low\n32\nunder H flow was still distinguishable. Compared with 0.3Pt/(TiO -A), 0.3Pt/(TiO -\n2 2 2\nT-500) exhibited the weaker white-line intensity, indicating that Pt species in\n0.3Pt/(TiO -T-500) possessed higher 5d electron density. It was noteworthy that the\n2\nwhite-line intensity of the Pt species in 0.3Pt/(TiO -A) was nearly identical to that of\n2\nintensity than Pt foil. We must elucidate the reason for the low white-line intensity\nof the Pt species occurred in both catalysts.\n(1) As the measurements were performed under the H flow, the Pt L -edge white-line\n2 3\nintensity decreased and the edge of 0.3Pt/(TiO -T-500) shifted to higher energy relative\n2\nto Pt foil, suggesting the H adsorption on Pt species modulated the Pt electronic state\nand decreased the unoccupied 5d states (Gorczyca, A. et al. Angew. Chem. Int. Ed. 2014,\n53, 12426–12429). Such hydrogen adsorption was also considered to be present in the\n0.3Pt/(TiO\n2\n-A) sample. This accounted for the consistently low white line intensity\nobserved in both catalysts. Nevertheless, 0.3Pt/(TiO -T-500) exhibited an even lower\n2\nwhite line intensity than 0.3Pt/(TiO -A), indicating the presence of a greater number of\n(2) XANES results reflect the averaging effect over the bulk structure of the metal\nspecies, unlike XPS and DRIFTS spectra, which can distinguish the specific states of\ndifferent sites in the surface structure of the metal species. Therefore, the XANES\nresults fail to reflect the accurate state of the surface structure of the metal species.\n(3) Given the low Pt loading, the catalysts underwent approximately 2 hours of data\nacquisition during the XANES measurements, during which the Pt species were\ncontinuously reduced under the H flow. This was further corroborated by in situ\n2\nattributed to Pt0 and Ptδ+, respectively, were observed for the 0.3Pt/(TiO -A) catalyst\n2\n(Figure R1-22). These signals might have been averaged in the XANES spectra,\nresulting in a white-line intensity similar to that of Pt foil. However, since the catalysts\nwere only reduced in H atmosphere for 30 minutes prior to the actual reaction, the\n2\n33\ncurrent XANES results did not fully represent the state of the Pt species under real\nreaction conditions.\nBased on the above three points, the Pt species in the two catalysts cannot be\nunambiguously identified from the XANES results. However, it can be concluded\nthat the Pt sites in the 0.3Pt/(TiO -T-500) catalyst possessed the lower oxidation\n2\nstate compared to those in 0.3Pt/(TiO -A).\n30 scanning cycles were performed (Figure R1-20c). The results consistently revealed\nthe shift in the binding energy of Pt species from 71.4 eV in the 0.3Pt/(TiO -A)\n2\ncatalyst to 70.8 eV in the 0.3Pt/(TiO -T-500) catalyst, which was attributed as Pt0\n2\nspecies, indicating the increase in electron density of Pt species in 0.3Pt/(TiO -T-\n2\n500).\nFigure R1-20c has been revised in Figure 2b in the revised manuscript. Figure\nR1-21 has been shown as Figure S17 in the supplementary information. The\ncorresponding description has been added on Page 8, lines 7−12 and 17−21 in the\nrevised manuscript (highlight in yellow).\nFigure R1-22. In situ DRIFTS spectra at 300 °C of (a) 0.3Pt/(TiO -A) and (b)\n2\n0.3Pt/(TiO -T-500) after H pretreatment for 2 hours.\n2 2\nComment 8: CO Adsorption / DRIFTS Interpretation:\n(1) The assignment of bands to Pt0 vs. Ptδ+ is highly tentative.\nassignment of adsorbed species to specific metal sites based solely on in situ DRIFTS\nspectra can be challenging and requires careful justification. We have now strengthened\nour assignment by providing the more comprehensive discussion based on established\nliterature and well-understood electronic effects.\n1. Support from Literature: Our assignment was supported by the literature on CO\nadsorption on Pt-based catalysts. Many studies using combined techniques such as in\nsitu DRIFTS and XAS spectra have reported that the linearly adsorbed CO on Pt0 sites\ntypically appears in the region of 2030-2070 cm−1, while CO adsorbed on Ptδ⁺ sites was\nobserved at higher wavenumbers, typically 2070-2095 cm−1. Additionally, the\nadsorption signal at 1950 cm⁻1 was attributed to bridge-bonded CO on the interface\nbetween metallic Pt clusters and the support (Dessal, C. et al. ACS Catal. 2019, 9,\n5752−5759; Zhou, Y. et al. ACS Catal. 2016, 6, 7799−7809; Qiao, B. et al. Nat. Chem.\n2011, 3, 634−641; Resasco, J. et al. J. Am. Chem. Soc. 2020, 142, 169−184). Based on\nthe aforementioned literature, the CO adsorption band observed at 2080 cm⁻1 in the in\nsitu DRIFTS of the 0.3Pt/(TiO -A) catalyst was assigned to Ptδ⁺ species, whereas the\n2\nsignals at 2064 cm⁻1, 2043 cm⁻1, and 1965 cm⁻1 for the 0.3Pt/(TiO -T-500) catalyst\n2\nwere attributed to Pt0 clusters.\n2. Electronic Effect: The blue shift in the CO adsorption band from Pt0 to Ptδ+ is\nattributed to the electronic effects governing CO chemisorption. The Ptδ+ site, being\nelectron-deficient, has the reduced capacity for π-back-donation from its d-orbitals to\nthe 2π* anti-bonding orbital of the CO molecule. This weakened back-donation results\nin the stronger C-O bond, which corresponds to a larger force constant (k). According\nto Hooke's law (eq 1), the force constant k is proportional to the vibrational frequency\n(ν) and wavenumber (ṽ) in the corresponding DRIFTS spectra (Zhang, R. et al. ACS\nCatal. 2020, 10, 14722−14731). Therefore, the higher frequency band we assigned to\nPtδ⁺ in the 0.3Pt/(TiO -A) catalyst and Pt0 in the 0.3Pt/(TiO -T-500) was fully consistent\n2 2\nwith this widely accepted model.\n35\n1 𝑘\nṽ = √ eq 1\n2πc 𝜇\nṽ represents the wavenumber; k represents the force constant; μ represents the\nreduced mass of the vibrational system.\nThe corresponding description has been added on Page 8, lines 14–17, Page 9,\nlines 14 and Page 10, lines 1–6. The corresponding reference has been cited as\n45−49.\n(2) CO-TPD experiments only support stronger binding, not overall \"adsorption\ncapability.\"\nResponse: We thank the reviewer for their valuable comment. We have revised to “the\nenhanced binding of CO on the 0.3Pt/(TiO -T-500) catalyst” in the revised\n2\nmanuscript on Page 10, line 9 (highlight in yellow).\nComment 9: \"CO adsorbed on the electron-deficient Ptδ+ species\", Again, this\nassignment rests on uncertain XPS data.\nResponse: We thank the reviewer for the valuable comments. In situ XANES\nprofile at Pt L edge under the H pretreatment was further carried out (Figure R1-21). Despite\n3 2\nthe relatively poor signal-to-noise ratio of the Pt/TiO catalysts due to the low Pt loading\n2\n(0.3 wt%), the difference in white-line intensity between the two catalysts under H\n2\nflow was still distinguishable. Compared with 0.3Pt/(TiO -T-500), 0.3Pt/(TiO -A)\n2 2\nexhibited the higher white-line intensity, indicating that Pt species in 0.3Pt/(TiO -\nof the Pt species in 0.3Pt/(TiO -A) was nearly identical to that of Pt foil, and by\n2\ncomparison, 0.3Pt/(TiO\n2\n-T-500) exhibited the weaker white-line intensity than Pt foil.\nWe must elucidate the reason for the low white-line intensity of the Pt species\noccurred in both catalysts.\n36\n(1) As the measurements were performed under the H flow, the Pt L -edge white-line\n2 3\nintensity decreased and the edge of 0.3Pt/(TiO -T-500) shifted to higher energy relative\n2\nto Pt foil, suggesting the H adsorption on Pt species modulated the Pt electronic state\nand decreased the unoccupied 5d states (Gorczyca, A. et al. Angew. Chem. Int. Ed. 2014,\n53, 12426–12429). Such hydrogen adsorption was also considered to be present in the\n0.3Pt/(TiO -A) sample, thereby reducing the observed white line intensity.\n2\n(2) XANES results reflect the averaging effect over the bulk structure of the metal\nspecies, unlike XPS and DRIFTS spectra, which can distinguish the specific states of\ndifferent sites in the surface structure of the metal species. Therefore, the XANES\nresults fail to reflect the accurate state of the surface structure of the metal species.\n(3) Given the low Pt loading, the catalysts underwent approximately 2 hours of data\nacquisition during the XANES measurements, during which the Pt species were\ncontinuously reduced under the H flow. This was further corroborated by in situ\n2\nattributed to Pt0 and Ptδ+, respectively, were observed for the 0.3Pt/(TiO -A) catalyst\n2\n(Figure R1-22). These signals might have been averaged in the XANES spectra,\nresulting in a white-line intensity similar to that of Pt foil. However, since the catalysts\nwere only reduced in H atmosphere for 30 minutes prior to the actual reaction, the\n2\ncurrent XANES results did not fully represent the state of the Pt species under real\nreaction conditions.\nBased on the above three points, the Pt species in the two catalysts cannot be\nunambiguously identified from the XANES results. However, it can be concluded\nthat the Pt sites in the 0.3Pt/(TiO -A) catalyst possessed the higher oxidation state\n2\ncompared to those in 0.3Pt/(TiO -T-500).\neffectively improved the signal-to-noise ratio (Figure R1-20c). The results showed the\nbinding energy of Pt species at 71.4 eV in the 0.3Pt/(TiO -A) catalyst and 70.8 eV\n2\nin the 0.3Pt/(TiO -T-500) catalyst, which provided stronger evidence that the\n2\n37\n0.3Pt/(TiO -A) catalyst exhibited Ptδ⁺ species, while the 0.3Pt/(TiO -T-500) catalyst\n2 2\ncontains Pt0 species.\nComment 10: \"In contrast, for the 0.3Pt/(TiO -T-500) catalyst... CO products... Fig.\n2 2\n2i\", This claim is highly questionable. Figure 2h shows a CO peak for the \"A\" sample\n2\nthat is larger than that for the \"T-500\" sample. The conclusion that CO is not formed\n2\non the A sample is unsubstantiated. Under Ar, no desorption curves are provided for\nCO, which complicates interpretation. It is also very plausible that the T-500 sample\nsimply adsorbs CO more strongly due to particle size differences.\nResponse: We thank the reviewer for the professional comments. To identify the origin\nof the gaseous CO signal observed during in situ DRIFTS measurements, mass\n2\nspectrometry was employed to monitor the catalytic behavior during temperature-\nprogrammed WGS reactions. As shown in Figure R1-23, both catalysts exhibited rapid\nconsumption of reactant CO molecules before the occurrence of the WGS reaction.\nHowever, a notable difference was observed. The 0.3Pt/(TiO -A) catalyst produced\n2\nonly CO without H , indicating that abundant surface oxygen on the catalyst facilitated\n2 2\nthe reaction with CO at relatively low temperatures to form CO , rather than involving the\n2 2\nthe gaseous CO signal detected by in situ DRIFTS during the CO adsorption for\n2\n0.3Pt/(TiO -A) originated from CO formed by the reaction between CO and surface\n2 2\noxygen.\nTo eliminate the influence of surface oxygen on the 0.3Pt/(TiO -A) catalyst,\n2\nmultiple CO adsorption and purging experiments were conducted during in situ\nDRIFTS testing. As shown in Figure R1-24, the gaseous CO signal progressively\n2\nweakened with successive CO adsorption cycles and nearly disappeared after the fourth\ncycle, indicating that surface oxygen was effectively removed. Therefore, after four CO\nadsorption cycles, switching experiments involving CO and Ar or Ar+H O were\n2\nperformed again. As shown in Figure R1-25, at 250 °C, the CO adsorption peak on Ptδ+\nspecies of 0.3Pt/(TiO -A) gradually diminished under Ar purging, and upon re-\n2\nadsorption of CO, the CO signal at 2080 cm⁻1 re-emerged. Subsequently, as shown in\nFigure R1-26a, upon switching to the Ar+H O atmosphere, the CO adsorption peak\n2\n38\nsimilarly diminished gradually, with the decay rate consistent with that observed under\npure Ar purging. Meanwhile, the concurrent decrease in the gaseous CO signal\n2\noccurred. In contrast, for the 0.3Pt/(TiO -T-500) catalyst, the CO signal corresponding\n2\nto Pt0 species decayed significantly faster under the Ar + H O atmosphere than under\n2\npure Ar, accompanied by the gaseous CO signal that initially increased and\n2\nsubsequently decreased (Figure R1-26b). This indicated that CO adsorbed on Pt0 sites\nreacted with H O, generating additional CO . As the adsorbed CO on Pt0 was\n2 2\nprogressively consumed, the production of CO gradually diminished and eventually\n2\nvanished upon complete purging. These results collectively demonstrated the superior\nability of Pt0 species in activating CO molecules.\nIn summary, the time-dependent CO desorption curves under the Ar\natmosphere are summarized in Figure R1-26a (right). Figure R1-24 has been\nshown as Figure S21 in the supplementary information. Figure R1-25 has been\nshown as Figure S22 in the supplementary information. Figure R1-26 has been\nshown as Figure 2h and 2i in the revised manuscript. The corresponding\ndescription has been added on Page 10, lines 22–29 and Page 11, lines 1–5.\nFigure R1-23. The catalytic behavior of (a) 0.3Pt/(TiO -A) and (b) 0.3Pt/(TiO -T-500)\n2 2\nduring the heating process of the water gas shift (WGS) reaction.\nDRIFTS spectroscopy of 0.3Pt/(TiO -A) catalyst at 250 °C.\nCO re-adsorption over 0.3Pt/(TiO -A) catalyst at 250 ºC.\n2 2\nA) and (b) 0.3Pt/(TiO -T-500) at 250 °C. Right: the intensity of CO adsorption on Pt\n2\nsites upon Ar+H O and Ar purging as function of time.\n2\noxygen vacancies were formed by the consumption of surface hydroxyls by CO during\nthe reaction...\" Again, this could also be due to differences in particle size or suboxide\nshell formation. Particle sizes must be reported for all fresh and spent catalysts.\nResponse: We thank the reviewer for the perceptive comments. The HAADF-STEM\nimages of the fresh and spent 0.3Pt/(TiO -T-500) and 0.3Pt/(TiO -A) catalysts were\n2 2\npresented in Figure R1-27. It was found that Pt species in both fresh catalysts primarily\nexisted as the mixture of single atoms and clusters. After the WGS reaction, these\nspecies aggregated to form Pt clusters in both catalysts. According to particle size\nstatistics, the average sizes of the Pt clusters in the spent 0.3Pt/(TiO -T-500) and\n2\n0.3Pt/(TiO -A) catalysts were approximately 1.6 nm and 1.7 nm, respectively, which\n2\nindicated that the Pt clusters in both catalysts exhibited similar dimensions (Figure R1-\n28). Therefore, the disparity in the concentration of oxygen vacancies between the two\nspent catalysts originated from the difference in their surface hydroxyl concentrations.\nThese hydroxyl groups were consumed by CO during the reaction, consequently\nleading to the formation of oxygen vacancies. The corresponding description has\nbeen added on Page 14, lines 13–17 in the revised manuscript (highlight in yellow).\n0.3Pt/(TiO -T-500) and (b) 0.3Pt/(TiO -A) catalyst.\n2 2\n(c−f) Aberration-corrected\nHAADF-STEM images of the spent (c, d) 0.3Pt/(TiO -T-500) and (e, f) 0.3Pt/(TiO -A)\n2 2\ncatalyst.\nFigure R1-28. The size statistics of the spent 0.3Pt/(TiO -T-500) and 0.3Pt/(TiO -A)\n2 2\ncatalysts.\nComment 12: Overall. This study explores a timely and important topic, but currently\nsuffers from overinterpretation of spectroscopic data, lack of rigorous controls, and\nincomplete physical characterization. Stronger claims about site-specific activity or\nelectronic structure require corroboration by XAS, chemisorption, and particle size\nanalysis. Many conclusions are not fully supported by the presented data. Substantial\nrevisions are necessary before this manuscript can again be considered for publication\nin Nature Communications.\nResponse: We thank the reviewer for the valuable comments. We have conducted the\nadditional experiments as suggested, including X-ray absorption spectroscopy (XAS),\nCO chemisorption, particle size analysis and so on. Current results demonstrated that,\nwith the size effect ruled out, the presence of surface hydroxyl groups on the\nsupport modulated the electronic structure of the supported Pt species, leading to\n42\nthe formation of 2 nm Pt0 clusters, which promoted the adsorption and activation\nof CO molecules. The description of the spectral results has been revised accordingly.\nWe believe these revisions have significantly improved the quality of the manuscript\nand hope that the manuscript now can be considered for publication in Nature\nCommunications.\ncatalytic performance of supported metal-oxide catalysts by modulating the electronic\nstructure of active sites through surface hydroxyl groups. This work convincingly\ndemonstrates the formation of electron-rich Pt0 clusters (~2 nm) on hydroxylated TiO ,\n2\nin contrast to conventional Ptδ+-Ov-Ti3+ interfacial structures. This modification not\nonly enhances CO adsorption and activation but also couples with hydroxyl-assisted\noxygen vacancy formation to promote H O dissociation, leading to synergistic\n2\nimprovement in the water-gas shift (WGS) reaction. The mechanistic insights provided\ninto how surface hydroxyl groups contribute both to the electronic modulation of Pt and\nthe dynamic restructuring of the oxide support are novel and significant. I find the study\nwell-structured and impactful; however, I suggest the authors provide additional\nexperimental or theoretical validation of the proposed Pt0-hydroxyl interaction\nmechanism and quantify the contribution of each step (CO adsorption vs. H O\n2\ndissociation) to the overall WGS enhancement.\nResponse: We would like to extend our sincere gratitude to the reviewer for the careful\nreading of our manuscript and the insightful comments. We have carefully addressed\neach point and made corresponding revisions to the manuscript. We hope that our\nresponses and the revised manuscript will meet your expectations.\nComment 1: Why is there such a large shift (~0.7 eV) in the O binding energy of lattice\n1s\noxygen (O_latt.) in TiO -T-UC compared to TiO -T-500 and TiO -A? Please explain the\n2 2 2\norigin of this significant difference.\nResponse: We thank the reviewer for the valuable comment. We attribute the higher O\n1s binding energy of the lattice oxygen in TiO -T-UC, compared to TiO -T-500 and\n2 2\nTiO -A, primarily to its fundamentally different crystal structure and local chemical\n2\nenvironment of oxygen. Based on the combined analysis of XRD patterns (Figure R2-\n1) and relevant literature, the synthesized TiO -T-UC support was identified as H Ti O ,\n2 2 3 7\nwhich exhibited the layered structure distinct from the anatase phase of TiO -T-500 and\n2\n2\nstructure inherently contained structural hydroxyl groups (-OH) and might incorporate\ninterlayer water molecules. The O–H bonds within the structure exhibit the significant\nelectronegativity difference. Hydrogen atoms withdrew electron density from oxygen\natoms, thereby reducing the local electron density around the oxygen. This electronic\nenvironment results in the higher O 1s XPS binding energy compared to that of the Ti–\nO–Ti structure in anatase TiO . The corresponding description has been added on\ncorresponding reference has been cited as 38.\nFigure R2-1. The XRD patterns of the TiO -A, TiO -T-UC and TiO -T-500 supports.\n2 2 2\nComment 2: The statement “However, excessive surface hydroxyls caused the\nsupported Pt species to be completely embedded in the TiO support lattice during the\nS4)” requires quantitative data or literature support. Only two STEM images alone are\nnot sufficient to support such a conclusion. A statistical comparison of the post-reaction\nSTEM data between TiO -T-500 and the hydroxyl-rich sample would help clarify how\n2\nthe OH content influences the embedding or migration of Pt species.\nResponse: We thank the reviewer for the constructive comment. In order to provide the\nquantitative data, CO chemisorption experiments were performed on the spent catalysts\n45\n(Table R2-1). The results revealed that the 0.3Pt/(TiO -A) and 0.3Pt/(TiO -T-500)\n2 2\ncatalysts exhibited comparable CO uptake. In contrast, the 0.3Pt/(TiO -T-UC) catalyst\n2\nexhibited the significant decrease in CO uptake, which indicated that the Pt species in\n0.3Pt/(TiO -T-UC) were covered, thereby losing their CO adsorption capacity.\n2\nsupport, the morphology of catalyst and the location of the Pt species were investigated\nusing HAADF-STEM imaging. As shown in Figure R2-2a, the 0.3Pt/(TiO -T-UC)\n2\ncatalyst retained its nanotubular morphology even after the WGS reaction.\nInterestingly,\nthe Pt species were distributed both on the inner and outer walls of the nanotubes,\nresulting in the non-uniform size distribution. In addition to the inadequate exposure of\nactive sites for Pt particles located within the nanotube interior, those on the external\nsurfaces were also found to be embedded within the tube walls. These encapsulated\nsites suppress the adsorption of CO molecules. When the support was calcined at 200 °C,\nthe majority of the nanotubes were retained (Figure R2-2b). Similarly to the\n0.3Pt/(TiO -T-UC) catalyst, Pt particles were incorporated into both the interior and the\n2\nouter walls of these nanotubes, which hindered the exposure of active sites. In contrast\nto 0.3Pt/(TiO -T-UC), a portion of the nanotubes in the 0.3Pt/(TiO -T-200) catalyst\n2 2\ncollapsed, forming layered sheet-like structures. Although the Pt particles supported on\nthese structures still exhibited a non-uniform size distribution, this morphological\nchange increased the number of exposed Pt sites to absorb the CO molecules (Figure\nR2-3). These results demonstrated that the tubular morphology of TiO\n2\n-T-UC led to the\nencapsulation of the supported Pt species. In contrast, the TiO -T-500 support\n2\ncompletely collapsed into the sheet-like structure, which allowed the Pt species to\nbecome exposed after the reaction, thereby enhancing CO adsorption (Figure R2-4).\nIn summary, the tubular morphology of TiO -T-UC led to the encapsulation\n2\nof the supported Pt species. Once the tubular structure of TiO collapsed upon\n2\nthermal treatment, the Pt species become exposed. Table R2-1 was shown as Table\nS1 in the supplementary information. Figure R2-2 and R2-3 has been shown as\nFigure S7 and S8 in the supplementary information. Figure R2-4 has been shown\n46\nas Figure 1h and 1i in the revised manuscript. The corresponding description has\nbeen added on Page 5, lines 16–22 in the revised manuscript (highlight in yellow).\nTable R2-1. The CO uptake and Pt dispersion of 0.3Pt/(TiO -A), 0.3Pt/(TiO -T-UC)\n2 2\nand 0.3Pt/(TiO -T-500) catalysts.\nDispersion\n(μmol/g)\n0.3Pt/(TiO -A) 7.4 48.1 %\n2\n0.3Pt/(TiO\n2\n-T-UC) 2.9 18.8 %\n0.3Pt/(TiO\n2\n-T-500) 8.5 55.2 %\nFigure R2-2. The aberration-corrected HAADF-STEM images and the size statistics\nof the spent (a) 0.3Pt/(TiO -T-UC) and (b) 0.3Pt/(TiO -T-200) catalyst.\n2 2\n0.3Pt/(TiO -T-500) catalyst.\n2\nthe impression that the value may have been selectively emphasized. Please consider\nadjusting Figure 1 to avoid repetitive or potentially misleading data presentation.\nResponse: We appreciate the reviewer for thoughtful suggestions. To avoid potential\nover-emphasis and misinterpretation by readers, we have removed the relevant data\nfrom Figure R2-5. Instead, the figure now simply annotated that the TiO -T-500 support\n2\npossessed the higher concentration of hydroxyl groups compared to TiO -A. Figure\ndescription has been added on Page 7, lines 2–3 in the revised manuscript\n(highlight in yellow).\n2 2\nfrom TGA measurements.\nComment 4: Please provide the WGS reaction conditions in the legend of Figure 1,\nespecially those corresponding to Figure 1d. This information is necessary for clarity\nand reproducibility.\nResponse: We sincerely thank the reviewer for the attentive comments. The reaction\nrates of the catalysts with supports calcined at different temperatures were presented in\nFigure R2-6. The tests were conducted at 250 °C under the reaction atmosphere\ncomposed of 2% CO/10% H O/N . This information has now been added in the\n2 2\nlegend on Page 6, lines 4−6 (highlight in yellow). We appreciate the reviewer for the\nvaluable comments again.\nof TiO -T support, with the optimum at 500 °C. Reaction condition: 2% CO/10%\n2 2\nComment 5: The interpretation of Pt 4f spectra in Figure 2c requires further\nclarification. Specifically, 0.3Pt/(TiO -T-500) predominantly shows metallic Pt⁰ species,\n2\nwhile 0.3Pt/(TiO -A) mainly exhibits Pt²⁺ or Pt⁴⁺ states. The orange peaks in both XPS\n2\nspectra are currently labeled as Pt⁰, but the binding energy difference between them\n(~0.7 eV) is too large to be attributed to the same oxidation state. Please clarify the\nspecific assignments of each deconvoluted peak.\nResponse: We thank the reviewer for the valuable comments. According to the\nliterature, in Pt 4f XPS spectra, peaks at binding energies above 74 eV were typically\nattributed to Pt4+, while those between 72-73 eV were generally assigned to Pt2+ (Lei,\nH. et al. Angew. Chem. Int. Ed. 2025, e202509239; Wang, H. et al. ACS Catal. 2023,\n13, 10500−10510). This indicated that both catalysts contained Pt2+ species but no Pt4+.\nFurthermore, the peaks in the 70-71 eV range were commonly ascribed to Pt0, whereas\nthose between 71-72 eV were usually attributed to Ptδ+ species (Tang, N. et al. ACS\nal. ACS Appl. Mater. Interfaces 2021, 13, 52193−52201). Therefore, the Pt species in\nthe 0.3Pt/(TiO -T-500) catalyst were predominantly in the metallic Pt0 state, while in\n2\nthe 0.3Pt/(TiO -A) catalyst, the Pt species existed mainly as Ptδ+ species. The\n2\nreassigned XPS spectra was now presented in Figure R2-7 and have been showed\nin the revised manuscript as Figure 2b. The corresponding description has been\nadded on Page 8, lines 7–10 in the revised manuscript (highlight in yellow) and the\nrelevant references have been cited as 41−43.\nFigure R2-7. Ex situ Pt 4f XPS for 0.3Pt/(TiO -T-500) and 0.3Pt/(TiO -A) samples\n2 2\nafter H pretreatment.\ninappropriate. It may be unnecessary to emphasize \"electron-rich,\" as the main point\nis the formation of metallic Pt0 species. There is no clear evidence that these Pt0 species\nare more electron-enriched than typical Pt0, as indicated by the XPS results in Figure\n2c.\nResponse: We thank the reviewer for this professional comment. In the revised\nmanuscript, we have amended the phrasing to \"Pt0 clusters\", including both the\ntitle and the main text.\n2\nsignal is much weaker or absent? This suggests that the Ptδ+–OH–Ti4+ interfacial\nsites in the former are highly reactive initially, rapidly oxidizing CO to CO₂. Please\ndiscuss this. Also, how should we interpret the volcano-shaped curve of CO₂ formation\nin Figure 2i? A clear explanation is needed in the text.\nResponse: We thank the reviewer for the professional comments. Since the generation\nof H could not be detected by in situ DRIFTS, we employed mass spectrometry to\n2\nmonitor the catalytic behavior during the heating process of the water gas shift (WGS)\nreaction. As shown in Figure R2-8, both catalysts exhibited rapid consumption of\nreactant CO molecules before the occurrence of the WGS reaction. However, a notable\ndifference was observed. The 0.3Pt/(TiO -A) catalyst produced only CO without H ,\n2 2 2\nindicating that abundant surface oxygen on the catalyst facilitated the reaction with CO\nat relatively low temperatures to form CO , rather than involving the Ptδ+–OH–Ti4+\n2\nstructure. In contrast, the 0.3Pt/(TiO -T-500) catalyst generated both CO and H ,\n2 2 2\ndemonstrating that the reaction between Pt0-OH and CO occurred. Therefore, the\ngaseous CO signal detected by in situ DRIFTS during the CO adsorption for\n2\n0.3Pt/(TiO -A) originated from CO formed by the reaction between CO and surface\n2 2\noxygen.\nTo eliminate the influence of surface oxygen on the 0.3Pt/(TiO –A) catalyst,\n2\nmultiple CO adsorption and purging experiments were conducted during in situ\nDRIFTS testing. As shown in Figure R2-9, the gaseous CO signal progressively\n2\nweakened with successive CO adsorption cycles and nearly disappeared after the fourth\ncycle, indicating that surface oxygen was effectively removed. Therefore, after four CO\nadsorption cycles, switching experiments involving CO and Ar or Ar+H O were\n2\nperformed again. As shown in Figure R2-10, at 250 °C, the CO adsorption peak on Ptδ+\nspecies of 0.3Pt/(TiO -A) gradually diminished under Ar purging, and upon re-\n2\nadsorption of CO, the CO signal at 2080 cm⁻1 re-emerged. Subsequently, as shown in\nFigure R2-11a, upon switching to the Ar+H O atmosphere, the CO adsorption peak\n2\n52\nsimilarly diminished gradually, with the decay rate consistent with that observed under\npure Ar purging. Meanwhile, the concurrent decrease in the gaseous CO signal\n2\noccurred. In contrast, for the 0.3Pt/(TiO -T-500) catalyst, the CO signal corresponding\n2\nto Pt0 species decayed significantly faster under the Ar + H O atmosphere than under\n2\npure Ar, accompanied by the gaseous CO signal that initially increased and\n2\nsubsequently decreased (Figure R2-11b). This indicated that CO adsorbed on Pt0 sites\nreacted with H O, generating additional CO . As the adsorbed CO on Pt0 was\n2 2\nprogressively consumed, the production of CO gradually diminished and eventually\n2\nvanished upon complete purging. These results collectively demonstrated the superior\nability of metallic Pt0 in activating CO molecules.\nFigure R2-9 has been shown as Figure S21 in the supplementary information.\nFigure R2-10 has been shown as Figure S22 in the supplementary information.\nFigure R2-11 has been shown as Figure 2h and 2i in the revised manuscript. The\ncorresponding description has been added on Page 10, lines 22–29 and Page 11,\nlines 1–5.\nFigure R2-8. The catalytic behavior of (a) 0.3Pt/(TiO -A) and (b) 0.3Pt/(TiO -T-500)\n2 2\nduring the heating process of the water gas shift (WGS) reaction.\nDRIFTS spectroscopy of 0.3Pt/(TiO -A) catalyst at 250 °C.\nCO re-adsorption over 0.3Pt/(TiO -A) catalyst at 250 ºC.\n2 2\nA) and (b) 0.3Pt/(TiO -T-500) at 250 °C. Right: the intensity of CO adsorption on Pt\n2\nsites upon Ar+H O and Ar purging as function of time.\n2\ncloser to the interface was more active in activating CO molecules.” However, is it\npossible that the “Pt⁰ near the interface” is in fact the Ptδ⁺ species located at the Ptδ⁺–\nOH–Ti⁴⁺ interface, rather than fully metallic Pt0? This may involve dynamic\ntransformation between Ptδ⁺ and Pt0 driven by OH consumption and water dissociation\nduring the reaction. Consider using DFT simulations and valence state calculations to\nfurther support this hypothesis.\nResponse: We thank the reviewer for the valuable comments. In bimolecular redox\nreactions, the instantaneous dynamic change of the active site oxidation state was\nubiquitous (Li, Y. et al. Nat. Common. 2021, 12, 914). To reveal the dynamic changes\nin the state of Pt sites during the reaction, DFT calculations and Bader charge analysis\nwere performed (Figure R2-12 and Table R2-2). As shown in Figure R2-12a, we\nsuccessfully constructed an eight-atom Pt cluster on the TiO (101) surface and removed\n2\nthe oxygen atom at the interface bonded to the Pt atom to create an oxygen vacancy\n1\n(Vo). Analysis of the Bader charge revealed a value of -0.8 |e| for the Pt atom,\n1\nindicating that the Pt atom was most likely in the metallic state. Therefore, the active\n1\nstructure identified in our experiments, denoted as Pt0–O –Ti, has been successfully\nv\nmodeled. During the water dissociation process, the oxygen vacancy was filled by the\n-OH group, and the Bader charge of Pt changes to +0.01 |e|, confirming the formation\n1\nof the Ptδ+–OH–Ti structure (Figure R2-12b). Notably, the other H* atom bonds from\nH O dissociation with a surface oxygen atom to form a new -OH group. Concurrently,\n2\nthe Bader charge of the adjacent Pt atom decreased from +0.25 |e| to +0.14 |e|.\nobservation clearly demonstrated the dynamic evolution of the oxidation state of Pt\nspecies at the interface during the reaction. Figure R2-12 has been shown as Figure\nS25 in the supplementary information. Table R2-2 has been shown as Table S2 in\nthe supplementary information. The corresponding description has been added on\nPage 11, lines 10–16 (highlight in yellow).\ncluster 2\ncatalysts (a) with the oxygen vacancy and (b) after the H O dissociation.\ncluster 2\ncatalysts with the oxygen vacancy and after the H O dissociation.\nPt atoms After H O\ndissociation\nPt1 -0.80 0.01\nPt2 0.09 -0.27\nPt3 0.21 0.04\nPt4 -0.10 -0.10\nPt5 -0.04 0.06\nPt6 0.02 0.06\nPt7 0.25 0.14\nPt8 -0.10 -0.11\nsignificantly weaker than those during the first injection. This indicates that the\ninterfacial OH species regenerated via water dissociation are less abundant than the\nnative surface OH species originally present on the catalyst. What could be the reason?\nIs it due to structural changes in the catalyst or sintering of the Pt nanoparticles?\nResponse: We thank the reviewer for the attentive comments. The substantial and\nsustained production of CO and H observed in the first stage (0−65 min) was\n2 2\nattributed to the simultaneous introduction of CO and H O. During this stage, H O\n2 2\nunderwent continuous dissociation, while CO reacted to form CO and H . In the fifth\n2 2\nstage (the second CO injection), however, only CO was introduced, which could only\nreact with the hydroxyl groups generated during the pre-hydroxylation process of the\nprevious stage. Without additional replenishment of H O, the production of CO and\n2 2\nH in this stage was consequently relatively limited. We have annotated the Stage I\n2\nreaction atmosphere (CO + H O) in Figure R2-13 to provide readers with a clearer\n2 2\nunderstanding of the gas conditions during each stage. The Figure R2-13 has been\nupdated as Figure 3b in the revised manuscript.\nFigure R2-13. (a, b) In situ DRIFTS spectra of Ar+H O purging over (a) 0.3Pt/(TiO -\n2 2\nA) and (b) 0.3Pt/(TiO -T-500) at 250 °C. Right: the intensity of CO adsorption on Pt\n2\nsites upon Ar+H O and Ar purging as function of time.\n2\n0.3Pt/(TiO -T-500) catalyst compare with the fresh sample? Are there any notable\n2\nchanges in the oxidation state of Pt species?\nResponse: We thank the reviewer for the constructive comments. As shown in Figure\nR2-14a, the Pt species in the fresh 0.3Pt/(TiO -T-500) catalyst existed as Pt2+. However,\n2\nafter the long-time stability test, the catalyst was predominantly composed of Pt0\nspecies, indicating the reduction of Pt species during the reaction (Figure R2-14b).\nNotably, the H -treated 0.3Pt/(TiO -T-500) catalyst exhibited peaks at 70.8 eV and 72.2\n2 2\neV, attributed to Pt0 and Pt2+ species respectively (Figure R2-15). After the long-term\nstability test, the Pt0 peak further shifted to the lower binding energy of 70.4 eV and the\nPt2+ species were further reduced to Ptδ⁺, appearing at 71.2 eV. These results\ndemonstrated that the Pt species in 0.3Pt/(TiO -T-500) also underwent further reduction\n2\nduring the WGS reaction. Figure R2-14a has been shown as Figure S16a in the\nsupplementary information. Figure R2-14b has been shown as Figure S35 in the\nsupplementary information. Figure R2-15 has been shown as Figure 2b in the\nrevised manuscript. The corresponding description has been added on Page 16,\nlines 22–24 (highlight in yellow).\nFigure R2-14. The Pt 4f XPS spectra of the 0.3Pt/(TiO -T-500) catalyst (a) before\n2\nreaction and (b) after the 60 h stability test.\n2 2\nH pretreatment.\nof this work in Nature Communications.\nResponse: We thank the reviewer for the constructive and positive comments on our\nwork, which were very valuable for improving the quality of our manuscript. We have\nthoroughly revised the manuscript accordingly. We hope that the revised manuscript is\nnow suitable for publication in Nature Communications.\nReviewer #1:\nComment 1: The authors have revised their manuscript and the central idea remains\nthat tuning the hydroxyl population on TiO has two coupled effects: it biases reduced\nactivation, and it promotes oxygen-vacancy generation during turnover in a way that\nenhances water activation. The overall narrative is coherent and, at a high level,\nplausible for WGS on reducible oxides. I also find the materials handle conceptually\nappealing and potentially useful: deliberate hydroxyl regulation via a titanate-derived\nroute and controlled calcination to reach an apparent optimum hydroxyl content at\n500 °C. The optimization itself is one of the more convincing aspects of the work,\nparticularly because the authors acknowledge that excessive hydroxylation can lead to\nPt encapsulation in the uncalcined nanotubular precursor and they relate that state to\nsuppressed CO uptake and suppressed activity for the hydroxyl-rich TiO -T-UC sample,\n2\nrather than relying on microscopy alone.\nThe revision is strengthened by the addition of TOFs, chemisorption-derived\ndispersions, reaction orders, and additional spectroscopy. The reported performance\ndifferences are nontrivial and persist after normalization to accessible Pt sites as the\nauthors define them. In particular, the revised manuscript reports a rate of 62.7 mol\nCO\ng −1 h−1 and a TOF of 6.15 s−1 for 0.3Pt/(TiO -T-500) at 250 °C, compared with 31.4\nPt 2\nmol g −1 h−1 and 3.54 s−1 for 0.3Pt/(TiO -A). The authors also state that the two\nCO Pt 2\ncatalysts show similar apparent activation energies and therefore likely follow the same\noverall mechanism, which is an important and appropriate framing that supports a\nrate-enhancement claim rather than a claim of a fundamentally new pathway.\nResponse: We ’thank the reviewer for the valuable comments, which have undoubtedly\nhelped improve the logical flow and evidential support of the manuscript.\nComment 2: My main concern is that key mechanistic statements still read more\ncertain than the current evidence warrants. In several places the manuscript relies on\n1\nchains of observations that are mutually consistent but not uniquely discriminating, and\nthe conclusions drift from “consistent with” toward “demonstrated”. This is most\nevident in the assignment of Pt0 versus Ptδ+. The assignment is still based primarily on\nCO-DRIFTS band positions and small XPS shifts, supported by an in situ Pt L -edge\n2\nlimitations here, including signal-to-noise constraints at 0.3 wt% and the fact that the\nmeasurement conditions are not operando WGS. The chemical rationale offered for the\nDRIFTS shift (reduced back-donation on electron-deficient Ptδ+ leading to higher CO\nstretching frequency) is reasonable, but it does not resolve the core ambiguity: on\nPt/TiO , CO band positions can be influenced by oxidation state as well as particle size,\n2\ncoverage, ensemble effects, and interfacial geometry.\nResponse: We thank the reviewer for this important comment, which helps us sharpen\nthe scientific narrative. We have revised the manuscript throughout to more carefully\nreflect the supportive, rather than demonstrative, role of the spectroscopic data. Key\nchanges include:\n1. Replacing verbs like “demonstrated” or “proved” with “suggested,” “indicated,”\n“pointed to”, “was associated with”, or “was consistent with” in sections discussing\nPt electronic state. The corresponding changes have been made on page 9, line 14 and\n28; page 12, line 15 and 25 of the revised manuscript (highlight in yellow).\n2. We added explicit discussions on the inherent limitations of the characterization\ntechniques employed. Specifically, for the in situ XANES data acquired under H , we\n2\nnow clearly state on Page 9, lines 16−23 (highlight in yellow): \"Considering the poor\nsignal-to-noise ratio and interference from H* adsorption under H atmosphere,\n2\nthis result could not fully represent the exact state of Pt species under the WGS\nreaction, which could only imply a stronger tendency for Pt species in 0.3Pt/(TiO -\n2\n-A).\" Regarding\nthe in situ DRIFTS results, we have incorporated the necessary caution on Page 9, line\n29 and Page 10, lines 1−3: \"While we acknowledge that band positions can also be\ninfluenced by factors such as particle size and CO coverage, the observed trend\n2\nacross the sample series, combined with the supporting HAADF-STEM images,\nXPS and XANES data, leads us to attribute the dominant effect to the modification\nof the Pt electronic state.\"\n3. Finally, our overall conclusion has been reframed with appropriate caution on Page\n10, lines 3−5 (highlight in yellow): \"Overall, the observed trends were consistent\nwith a mechanistic interpretation wherein support hydroxylation promoted the\nformation of Pt species with the more metallic electronic character.\"\nOverall, incorporating the reviewer's valuable comment has allowed us to present\na more coherent and cautious mechanistic discussion that connects the experimental\ntrends while acknowledging the boundaries of the current evidence, which has greatly\nstrengthened the manuscript.\nComment 3: The authors have added post-reaction HAADF-STEM statistics and CO\nchemisorption on spent catalysts, and the mean sizes appear similar after reaction\n(about 1.6–1.7 nm). However, the chemisorption table shows dispersions that are not\nidentical (about 55.2% for TiO -T-500 versus 48.1% for TiO -A in the provided dataset).\n2 2\nWith such low metal loading, this difference is not obviously negligible, and it matters\nbecause the chemisorption-derived site count is being used both to normalize activity\n(TOF) and to support mechanistic interpretation. If the claim is that intrinsic site\nquality changes, the manuscript would benefit from a clearer demonstration that CO\nuptake and dispersion estimates are robust and not systematically biased by support-\ndependent spillover, readsorption, or differences in CO binding strength that could\naffect the inferred site count. At minimum, the authors should temper conclusions that\nhinge critically on dispersion-derived normalization and explicitly discuss the\nuncertainty and assumptions.\nResponse: We sincerely thank the reviewer for the valuable comment regarding the\nrobustness of CO chemisorption for site counting. We fully acknowledge the reviewer's\nconcern that factors such as support-dependent spillover, readsorption dynamics, or\ndifferences in CO binding strength could, in principle, introduce systematic bias into\n3\nthe measured CO uptake and the derived dispersion, especially at such low metal\nloadings. However, we wish to emphasize that even if the absolute site counts are\nsubject to such a bias, the relative comparison between the two catalysts remains valid\nand highly informative. The key observation is that while the dispersion of 0.3Pt/TiO -\n2\npronounced discrepancy strongly suggests an intrinsic difference in the catalytic quality\nof the Pt sites induced by the TiO supports.\nother factors on dispersion estimates must be carefully considered. However, it is\nextremely difficult to precisely eliminate the contribution of these intertwined factors\nto the total CO signal with currently accessible techniques. Therefore, in line with the\nreviewer's suggestion for a minimum revision, we have chosen to fundamentally\nreframe our discussion and conclusions to explicitly discuss the uncertainty and\nassumptions, rather than relying on potentially ambiguous additional measurements.\nOur revisions focus on the following key points, which we believe strengthen the\nmanuscript significantly:\n1. Explicit discussion of limitations: We have added a dedicated discussion explicitly\nstating the assumptions and potential limitations of CO chemisorption for site\nquantification in the section discussing dispersion and TOF.\n2. Tempered language and focus on trends: We have revised the text to temper the\nconclusions regarding TOF: “Assuming that the CO chemisorption measurements\nwere comparable for both catalysts, the observation of a markedly higher TOF\nindicated a potentially greater intrinsic activity of the active sites on the TiO -T-\n2\n500 support” The mechanistic claim was now pivoted to emphasize the relative trend\nof activity enhancement.\nThe corresponding description has been revised on Page 8, lines 18−23 and\nPage 18, lines 10−17 of the revised manuscript (highlight in yellow).\nComment 4: The second major mechanistic pillar, that hydroxyl consumption by CO\ngenerates oxygen vacancies that become the dominant loci for water dissociation,\nis\n4\nintriguing and not unreasonable, but it is still somewhat over-interpreted. The revision\nlinks vacancy formation to EPR changes after WGS and to Ti-related spectral features\ninterpreted as vacancy signatures, and then links “more vacancies” to “better water\nactivation” through reaction orders and a kinetic isotope effect. The reported KIE of\nroughly 1.65 upon substituting D O for H O indicates that O–H activation is kinetically\n2 2\nrelevant, but it does not uniquely identify the elementary step, nor does it establish that\nvacancies created specifically by hydroxyl consumption are the operative active sites\nfor that step. Moreover, the manuscript also states that hydroxyl signals increase after\nreaction due to water dissociation and adsorption, implying that hydroxyls are\ncontinuously regenerated during WGS. In such a dynamic system it is important to\ndistinguish hydroxyls as spectators, hydroxyls as true intermediates on the main\ncatalytic cycle, and hydroxyls as part of a parallel redox process that modulates defect\npopulations without being kinetically dominant. At present the evidence is consistent\nwith the proposed picture, but causality remains incompletely established. I would\ntherefore ask for at least one genuinely discriminating experiment or, alternatively, a\nmore conservative mechanistic framing. Suitable discriminating experiments could\ninclude isotope tracing (for example H ^18O, C^18O, or ^18O-enriched supports) to\n2\ndetermine whether oxygen in CO derives predominantly from water, lattice oxygen, or\n2\nhydroxyl oxygen under the relevant catalyst states, or operando measurements that\ncorrelate a quantitative defect metric with instantaneous rate under controlled\nperturbations.\nResponse: We sincerely thank the reviewer for the insightful and constructive critique\nof the mechanistic section of our manuscript. In response to this concern, we have\nconducted H 18O isotopic tracing experiments by in situ DRIFTS and mass\n2\nspectrometry. Firstly, the catalyst was first subjected to CO-TPR aimed at removing\nhydroxyl groups, as evidenced by the simultaneous generation of H and CO around\n2 2\n150 °C (Figure R1a). Subsequently, H 18O was introduced for 20 minutes. Upon\n2\nswitching back to the CO flow, signals for C16O18O and C18O18O were detected (Figure\nR1b). This observation suggested the possibility that H O dissociated on the catalyst\n2\n5\nsurface and the incorporation of its oxygen into the product. Meanwhile, the presence\nof C16O16O was indicative of reactions between CO and surface oxygen atoms or the\ninitially engineered hydroxyl groups. Moreover, during the same experiment by in situ\nDRIFTS, C16O18O was also detected, providing further evidence for the dissociation of\nH O on the catalyst surface (Figure R2). The corresponding description has been\n2\nadded on page 15, line 30 and page 16, line 1−5 in the revised manuscript (highlight\nin yellow). Figure R1 and R2 has been added as Figure S31 and S32 in the revised\nsupplementary information.\nHowever, while this result supported the occurrence of the water activation\nstep, it did not uniquely identify the atomic-scale origin of the active site whether\nit belongs exclusively to vacancies generated via hydroxyl consumption. Therefore,\nwe have chosen to adopt the reviewer's alternative suggestion and have\nimplemented a thorough revision towards a more conservative mechanistic\nframing. Key changes in the revised manuscript include:\n1. Reframing the narrative: The entire mechanistic discussion has been shifted from\na definitive \"demonstration\" to an inferential \"proposal of a self-consistent model.\"\nThe\ncore narrative now uses phrasing such as “A plausible explanation for this difference\nwas that…”, “The above results provided insight into the correlation between…\",\n“A reasonable model to explain these observations was that…” and so on.\n2. Stating observed correlations, weakening causal interpretation: We have\nreplaced statements that implied a mechanistic direction with direct statements of the\nobserved correlations. For instance, we now state: “The above results provided\ninsight into the correlation between the consumption of surface hydroxyl groups\nby CO and the facilitated formation of oxygen vacancies.”, “The consumption of\nhydroxyl groups by CO, whether initially present or formed during the WGS\nreaction, suggested a link to the formation of oxygen vacancies.” and “0.3Pt/(TiO -\n2\ncorresponding description has been revised on page 14, line 4; page 15, lines 9−10 and\n20−23 and page 16, lines 5−8 in the revised manuscript (highlight in yellow).\n6\n3. Explicit acknowledgement of limitations and system dynamics: A dedicated\nparagraph has been added outlining the limitations of the current evidence, including\nthe inability of the isotopic experiment to pinpoint the origin of the active site.\nFurthermore, given that hydroxyl groups are dynamic under reaction conditions, their\nprecise roles cannot be unambiguously assigned to individual steps, underscoring the\ncomplexity of the working catalyst surface. The corresponding description has been\nadded on page 16, lines 8−11 in the revised manuscript (highlight in yellow).\n4. Revised conclusion: The conclusion has been refocused from \"elucidating a\nmechanism\" to \"establishing a strong correlation and proposing a rational framework\nthat links hydroxyl chemistry to enhanced water activation capability.\" We now\nconclude that the hydroxyl-tuning strategy results in an optimal catalyst that\nconcurrently exhibits higher oxygen vacancy signatures and a greater capacity for\nwater activation. The corresponding description has been added on page 16,\nlines\n11−14 in the revised manuscript (highlight in yellow).\nFigure R1 (a) CO-TPR profiles of 0.3Pt/(TiO -T-500) after H pretreatment. The grey\n2 2\ndotted line represents the working temperature. (b) The generation of CO when\n2\ninjecting CO/Ar after H 18O dissociation at 250 °C.\n2\n2\n(a) H pretreatment and (b) subsequent H 18O treatment.\n2 2\nComment 5: A further concern is a plausible confound that is not convincingly\nexcluded. The hydroxylated support is produced using concentrated NaOH and acid\nwashing to form titanate intermediates before calcination. Trace residual sodium or\nchloride can measurably alter TiO2 surface chemistry, hydroxyl stability, vacancy\nformation energetics, and WGS kinetics, and these effects could mimic a “hydroxyl\nregulation” trend. Given that the manuscript compares performance against literature\nbenchmarks that include alkali-modified Pt/TiO2 systems, it becomes especially\nimportant to demonstrate that residual promoters are not contributing to the observed\nbehavior. If not already provided, elemental analysis such as ICP/OES (or similarly\nconvincing quantification) for Na and Cl on the final catalysts should be included,\nalong with a brief discussion of detection limits.\nResponse: We thank the reviewer for raising this critical point. This following study\nexamined the residual content of Na and Cl on the catalyst surface and ruled out their\ncontribution to the activity enhancement.\n1. Regarding the residual Na:\n8\n(1) For the analysis of Na residues, ICP-MS was employed (Table R1), which showed\nthat 0.3Pt/(TiO -T-500) catalyst contained 0.49 wt.% Na. In contrast, the Na content in\n2\nthe 0.3Pt/(TiO -A) catalyst was below the detection limit (<50 ppt). Relative to the mass\n2\nof the catalyst, this corresponded to a residual Na level of less than 0.00125 wt.%.\nThe\nresults indicated that Na indeed remained on the catalyst surface during the synthesis\nprocess.\n(2) To minimize residual ions, we implemented an intensive washing protocol using 5\nL of high-purity water for the titanate precursor. In the resulting catalyst, 0.3Pt/(TiO -\nefficacy of extensive washing for Na removal (Table R1). Notably, the washed catalyst,\n0.3Pt/(TiO -T-wash-500), matched the original 0.3Pt/(TiO -T-500) both in its high\n2 2\nWGS activity and in its ATR-IR hydroxyl signal profile, with both being superior to the\n0.3Pt/(TiO -A) catalyst (Figure R3a and b). This provided the understanding that the\n2\nactivity enhancement was not attributable to Na residues.\n(3) Furthermore, we also found that the residual Na content on the surface of the\n0.3Pt/(TiO -T-400) catalyst was at the similar level as that on the 0.3Pt/(TiO -T-500)\n2 2\ncatalyst (Table R1). However, the catalytic reaction rate of 0.3Pt/(TiO -T-500) was\n2\ntwice that of 0.3Pt/(TiO -T-400) (Figure R4). This further indicated that residual Na\n2\nwas not the source of the enhancement in catalytic performance.\n2. Regarding the residual Cl:\n(1) We clarify that standard ICP-OES/MS is not the optimal technique for accurate\nquantification of chloride anions due to poor sensitivity in the vacuum UV region and\nsignificant spectral interferences, which preclude reliable detection at the low ppm/ppb\nlevels relevant here. Thus, we could only perform a semi-quantitative assessment and\ntrend analysis of the Cl residues on the surfaces of different catalysts using Cl 2p XPS.\n2p\nAs shown in Table R1, Figure R3c and d, the signal of residual Cl on the catalyst\nsurfaces was weak. As indicated by semi-quantitative XPS analysis, the difference in\nCl content between 0.3Pt/(TiO -T-500) and 0.3Pt/(TiO -A) was within 0.2 wt.%.\n2 2\nattributed to residual Cl.\n(2) In addition, while chlorine residues can aid in catalyzing some organic reactions for\noxide-supported catalysts, for gas-phase reactions, chlorine species on the catalyst\nsurface typically exhibit strong binding to metal sites, thereby hindering the adsorption\nof reactant molecules and suppressing catalytic activity (Gracia, F. J. et al. J. Catal.\n2002, 209, 341–354; Bartholomew, C. H. et al. Appl. Catal. A: Gen. 2001, 212, 17–60;\nJardim, E. O. et al. J. Colloid Interface Sci. 2015, 443, 45–55). Therefore, the presence\nof Cl residues on the catalyst surface was not considered to be the source of enhanced\ncatalytic activity.\nIn summary, the above exclusion of the influence of Na and Cl on catalytic\nperformance has been added on page 17, lines 10−11 and page 18, lines 1 in the\nmanuscript and page 47, lines 5−24 in the Supporting Information (highlight in\nyellow). The Table R1 has been added as Supplementary Table 3 in the Supporting\nInformation. The Figure R3b, c, d has been added as Supplementary Fig. S34 in\nthe Supporting Information. In addition, we have added the ICP-MS test method\nand a brief analysis of the detection limits on page 20, lines 19−27 in the\nmanuscript (highlight in yellow).\nTable R1. Residual Na and Cl content on the catalyst surface\nSodium residue Chloride residue\nSamples\n(wt.%) a (wt.%) b\n0.3Pt/(TiO -T-500) 0.49 0.95\n2\n0.3Pt/(TiO -A) <LOD 0.81\n2\n0.3Pt/(TiO -T-500)-wash <LOD 1.07\n2\n0.3Pt/(TiO -T-400) 0.59 —\n2\na Determined by ICP-MS; LOD: limit of detection. The method LOD was 0.00125 wt.% for Na.\nb Determined by XPS;\n2 2 2\ndependent CO conversion of 0.3Pt/(TiO -T-500) and 0.3Pt/(TiO -A) and 0.3Pt/(TiO -\n2 2 2\nT-wash-500) catalysts for the WGS reaction. (c) The XPS survey and (d) Cl 2p spectra\nof the fresh 0.3Pt/(TiO -T-500), 0.3Pt/(TiO -A) and 0.3Pt/(TiO -T-wash-500) catalysts.\n2 2 2\nFigure R4 WGS reaction rate at 250 °C as the function of calcination temperature of\nTiO -T support, with the optimum at 500 °C. Reaction condition: 2% CO/10% H O/N .\n2 2 2\nApproximately half of the references in the manuscript are authored exclusively by\nChinese research groups, which is unusually high for a general catalysis paper in\nNature Communications. Many of these citations are used to support broad and well-\nestablished concepts such as metal–support interactions, hydroxyl effects, and defect-\nmediated water activation. At the same time, several foundational and widely\nrecognized contributions from the broader international literature are under-\nrepresented or absent. This includes classical frameworks for metal–support\ninteraction and reducible oxide chemistry, as well as established kinetic and\nmechanistic studies of WGS on Pt/TiO2. The current citation pattern risks giving the\nimpression that recent regional literature defines these concepts, rather than placing\nthe present work within the full historical and international context of the field. Such a\nbalance is problematic from a scholarly perspective, and I would strongly recommend\nthat the author balance the references to better reflect the breadth of prior work and to\nclearly acknowledge the foundational studies on which this manuscript builds.\nResponse: We thank the reviewer for this professional comment. Accordingly, we have\nsignificantly revised the reference list. Key foundational and international papers and\nreviews on water gas shift reaction (Ratnasamy, C et al. Catal. Rev. 2009, 51, 325-\n440); the various reactions employed in the Pt/TiO system (An, K. et al. Nano Lett.\n2\n2014, 14, 4907–4912; Kattel, S. et al. J. Catal. 2016, 343, 115–126; Bonanni, S. et al.\nJ. Am. Chem. Soc. 2014, 136, 8702–8707; Kalamaras, C. M. et al. J. Catal. 2009, 64,\n117–129) metal-support interactions (Tauster, S. J. et al. Science 1981, 211, 1121–\n1125; Campbell, C. T. Nat. Chem. 2012, 4, 597–598; van Deelen, T. W. et al. Nat. Catal.\n2019, 2, 955–970), reducible oxide chemistry (Wendt, S. et al. Science 2008, 320,\n1755–1759), defect-mediated water activation (Menetrey, M. et al. Surf. Sci. 2003,\n524, 49–62; Schaub, R. et al. Phys. Rev. Lett. 2001, 87, 266104-1−266104-4.), Surface\nfunctionalization of the support (Van Den Berg, R. et al. ACS Catal. 2015, 5, 4439–\n4448), hydroxyl effects (Gunasooriya, G. T. K. K. et al. ACS Catal. 2016, 6, 3660–\n12\n3664; Saavedra, J. et al. Science 2014, 345, 1599–1602; Parkinson, G. S. et al. Nat.\nMater. 2013, 12, 724–728.) and kinetic and mechanistic studies of WGS on Pt/TiO\n2\n(Kalamaras, C. M. et al. J. Catal. 2009, 64, 117–129; Azzam, K. G. et al. Appl. Catal.\nB Environ. 2008, 80, 129–140) have been added or replaced in the revised manuscript.\nThese references have been added to the revised manuscript as 1, 4−7, 9−13, 20−23,\nand 32 (highlight in yellow).\nComment 7: I would also like to comment on a conceptual statement made in the\nrebuttal, which appears to carry over implicitly into the revised mechanistic framing.\nThe authors state that “for gas-phase reactions involving two distinct reactant\nmolecules, such as the water–gas shift reaction, catalysis at a single type of active site\nis often insufficient.” As written, this statement remains misleading and introduces\nconceptual ambiguities that has not yet been fully resolved in the revised text. The\noverwhelming majority of heterogeneous catalytic reactions involve two or more\nreactants, and yet in many well-established systems the dominant chemistry occurs on\nmetal sites alone, even when multiple elementary steps and adsorbates are involved.\nMoreover, supported metal nanoparticles do not constitute a “single type of active site”\nin any strict sense, as they inherently present a distribution of terraces, edges, corners,\nand metal–support interfacial sites. While bifunctional or metal–support cooperative\nmechanisms certainly exist and are well documented for some reactions and materials,\nthey are not the general rule, and invoking them requires careful evidence rather than\nbroad generalization. I would therefore encourage the authors to revise the language\nin both the manuscript and the rebuttal to avoid implying that multi-reactant gas-phase\ncatalysis generally requires chemically distinct active sites on different phases. A more\naccurate framing would acknowledge that metal–support cooperation is one possible\nmechanistic motif for WGS on reducible oxides, but not an inherent requirement\ndictated simply by the presence of multiple reactants.\nResponse: We sincerely thank the reviewer for this professional correction, which has\nhelped us clarify a significant conceptual ambiguity. In the revised manuscript, we have\n13\ncompletely corrected this erroneous statement. The manuscript now describes metal–\noxygen vacancies synergy as one possible mechanism for the WGS reaction on\nreducible oxide–based catalysts. The corresponding part was on Page 3, lines 6−7 in\nthe revised manuscript (highlight in yellow).\nComment 8: Finally, the manuscript’s positioning still risks overselling novelty in a\nfield where the coupled roles of hydroxyls, defect chemistry, and metal electronic\nstructure in WGS have been discussed extensively. The work will be strongest if it is\npositioned around the specific and defensible contribution: a practical hydroxyl-\nregulation approach that yields a reproducible optimum and correlates with improved\nactivity, with a mechanistic interpretation that is consistent with multiple probes but not\nasserted as uniquely proven where it is not. In particular, the manuscript should avoid\nimplying that Pt L3-edge data under H2 pretreatment definitively establishes Pt surface\noxidation state under WGS conditions.\nResponse: We sincerely thank the reviewer for the guidance on positioning our work.\nTo avoid any overstatement of novelty, we have reframed the manuscript around the\nspecific and defensible contribution as suggested.\n1. Refocused abstract, discussion and the last first paragraph of introduction: We\nnow position our primary contribution as the development of a practical and\nreproducible hydroxyl-regulation strategy via titanate precursor calcination that\ndelivers an optimized and well-characterized catalyst. Supported by multiple\ncharacterizations, a mechanism interpretation is provided that rationalizes the role of\nhydroxyls in tuning the metal electronic state and the oxide surface structure. The\ncorresponding part was on Page 2, lines 1−14, Page 4, lines 17−26 and Page 19,\nlines 6−18 in the revised manuscript (highlight in yellow).\n2. Clarified mechanistic claims: Throughout the manuscript, we have replaced\ndefinitive language with cautious interpretations. Specifically, regarding the Pt L -edge\n3\ndata, we explicitly stated that the results obtained under H atmosphere could not fully\n2\nrepresent the exact state of Pt under WGS conditions, which could only imply a stronger\n14\ntendency for Pt species in 0.3Pt/(TiO -T-500) to be in the metallic state compared to\n2\nthat in 0.3Pt/(TiO -A). The corresponding description was added on Page 9, lines\n2\n19−23 in the revised manuscript (highlight in yellow).\nComment 9: Overall, the revision addresses several legitimate concerns and the\nperformance improvements, including TOF-normalized differences as presented, are\nsignificant. I believe the work can be suitable for Nature Communications provided that\nthe mechanistic claims are brought into tighter alignment with what is strictly\ndemonstrated, and that either a discriminating experiment is added to strengthen the\nhydroxyl-to-vacancy-to-water-activation causality or the mechanistic framing is\nthoroughly revised to be appropriately cautious. In addition, the manuscript should pre-\nemptively address residual-ion effects from the synthesis route with quantitative\nelemental analysis or equivalent evidence.\nResponse: We thank the reviewer for the positive assessment of our revisions and for\nthe clear pathway to further improvement. In response to the reviewer's comments, we\nhave made the following efforts to address the relevant concerns.\n1. Mechanistic claims aligned with evidence: We have thoroughly revised the\nmanuscript to bring all mechanistic interpretations into tighter alignment with the\ndemonstrated evidence. Language implying causation has been replaced with more\ncautious phrasing (e.g., “suggests,” “is consistent with,” “points to”), particularly\nregarding the states of Pt and the role of vacancies. The proposed mechanism is now\nexplicitly framed as a coherent model that best reconciles the collective data.\n2. Conservative mechanistic framing: We have adopted the suggested path of a\n“thoroughly revised and appropriately cautious mechanistic framing.” The narrative no\nlonger presents the hydroxyl–vacancy–water activation sequence as a proven causal\nchain, but as a self-consistent working model strongly supported by, and providing a\nrational explanation for, the full set of our observations.\n15\n3. Residual-ion effects addressed quantitatively: We combined evidence from ICP-\nMS quantification, XPS analysis, and thorough support washing ruling out the\ncontribution of residual Na and Cl from synthesis to the observed activity enhancement.\nOverall, we once again thank the reviewers for the professional and careful\ncomments, which substantially improved the quality of our manuscript. We hope\nthat our responses and revisions now meet the standards of Nature\nCommunications.\npublication of this work in Nature Communications.\nResponse: We thank the reviewer for the positive feedback on our work and for the\ntime invested. Your expert comments have been instrumental in enhancing the quality\nof the manuscript.\nReviewer #1:\nComment 1: The authors have now responded appropriately and substantively and\nhave largely addressed my concerns. Small residual things remain. E.g., the manuscript\nstill contains a few sentences that read more definitive than the new caveats warrant—\nfor example, language like “predominant Pt0 species were present...” and “suggested...\nin the absence of size effects” is still stronger than “consistent with”, given their own\nacknowledgement that CO-band positions can shift with coverage/geometry - but I\nbelieve this is acceptable.\nResponse: We sincerely thank the reviewers for their valuable time and professional\ncomments, which has significantly enhanced the quality of our manuscript."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have now responded appropriately and substantively and have largely addressed my concerns. Small residual things remain. E.g., the manuscript still contains a few sentences that read more definitive than the new caveats warrant—for example, language like “predominant Pt0 species were present...” and “suggested... in the absence of size effects” is still stronger than “consistent with”, given their own acknowledgement that CO-band positions can shift with coverage/geometry - but I believe this is acceptable."}, "author_response": "Response: We sincerely thank the reviewers for their valuable time and professional\ncomments, which has significantly enhanced the quality of our manuscript."}]

Decision letter