Boosted catalytic activity by metal-oxide interface in porous single-crystalline niobium oxide monoliths

Domain: chemistry
Published: 2026-01-07
Editorial outcome: major_revision

Abstract
Introducing and stabilizing oxygen vacancies in the lattice of oxide support materials has been a huge challenge to boost the catalytic activity in redox reaction. Herein, we fabricate porous single-crystalline Nb2O5 monoliths at the centimeter scale, then we introduce the oxygen vacancies in lattice by reduction treatment and stabilize the oxygen vacancy defects by the ordered lattice. We then deposit Pt clusters at surface in the porous microstructures to construct an interfacial system and we show the significantly enhanced surface oxygen exchange coefficient. As a case study, we demonstrate the complete CO oxidation with air at 110 °C and 30,000 mL g-1 h-1 conditions, following the Mars-van Krevelen mechanism, with no visible performance attenuation after a continuous operation of ~500 h. At 60,000 mL g-1 h-1 and 110 °C, the CO conversion rate decreases to 83.8% and ultimately remains 76.3% after 185 h of long-term operation.

Introduction
Porous single crystals are a new type of porous material at the macroscale, which combine the advantages of porosity and single crystallinity in a monolith. The properties of these porous single-crystalline (PSC) materials can be further tailored by controlling their unique structural features, making them ideal catalyst supports because of their high specific surface areas and good chemical and thermal stabilities1. The clear surface is continuous in the porous microstructures, with clear stepped atoms at the inner surface in the porous microstructures, further engineering the electronic structure of the well-defined surface structure and leading to a more controllable interaction between the adsorbed substance and the active site at the surfaces2.

Niobium oxide (Nb2O5) usually serves as a solid acid catalyst and unique Lewis acid sites and Brønsted acid sites are observed at the surface3,4. The Nb2O5 shows high acid strength and is usually utilized as a heterogeneous catalyst support in the dehydration reaction and hydrodeoxygenation reaction. Oxygen vacancies usually play a key role in enhancing the catalytic performance in the redox reaction. However, its reducibility to form oxygen vacancies in the lattice remains underexplored. To date, only a limited number of studies have leveraged the exceptional properties of Nb2O5 to create oxygen vacancies5,6. In previous studies, the ability to generate oxygen vacancies in metal oxides has been shown to be extremely beneficial for catalytic applications. Oxygen vacancies usually facilitate the gas-phase oxygen recompletion and rapid catalyst surface charge transfer in heterogeneous catalysis, and therefore they are considered to be one of the most effective ways to improve catalytic performance7–11. Porous single-crystalline (PSC) Nb2O5 monoliths, with well-defined surfaces capable of generating active surfaces, show great potential owing to the synergistic effect of their interconnected porous structure and single-crystalline framework, which can introduce oxygen defects and stabilize them in the lattice following proper reduction treatment. These unique structures have inherent mechanical and thermal stability, which is conducive to the rapid diffusion of reactant species and products through a three-dimensional percolation pathway12. Therefore, the PSC Nb2O5 monoliths would demonstrate high catalytic performance and thermal durability when they are used as catalyst supports in the catalytic redox reaction13–15.

Catalytic oxidation usually requires the activation of oxygen at the active site at the catalyst surface16–19. However, the competitive adsorption of different reactants may hinder the chemisorption of oxygen, resulting in high operating temperatures for these oxidation reactions, such as the CO oxidation with air20,21. In the process, interfacial systems show the greatest potential to achieve efficient catalysts for CO oxidation reaction by using oxide supports with oxygen non-stoichiometry to facilitate the surface reactions22. Pt clusters are known to efficiently form active metal-oxide interfaces that can effectively improve CO oxidation reactions23,24. The loading of Pt clusters on the surfaces of PSC Nb2O5 monoliths would produce well-defined interface structures, which would facilitate the identification and engineering of active sites on the active metal-oxide interfaces25,26.

In this work, we fabricate centimeter-scale PSC Nb2O5 monoliths with Pt clusters deposited on the surface to form an interfacial system for enhancing catalytic CO oxidation. Notably, we achieve the complete oxidation of CO with air at 110 °C, with no visible degradation observed even after ~500 h of continuous operation. The current work will provide a new line of thought for the preparation of novel catalysts enriched with oxygen vacancies by confining oxygen-vacancy-rich and well-defined active structures at the surface for enhancing catalytic activity and stability.

Results
We grow PSC Nb4N5 monoliths from NaNbO3 single crystals using a solid-phase transformation method in an NH3 atmosphere27. We then grow PSC Nb2O5 monoliths by directly transforming the PSC Nb4N5 monoliths in oxygen atmosphere at elevated temperature. Supplementary Fig. 1a, b shows the X-ray diffraction (XRD) patterns of the NaNbO3 single crystals with the facet of (001) and (010), respectively. Supplementary Fig. 1c, d shows the c-axis and b-axis channels for removing the sodium and oxygen atoms from the lattice. Accordingly, we successfully grow PSC Nb4N5 monoliths with (002) facet from the NaNbO3 single crystals with both (100) and (010) crystal facets. In Supplementary Fig. 1e, f, the transformation of Nb4N5 to Nb2O5 is an oxidation process that involves the replacement of nitrogen with oxygen in the lattice in the phase transformation process. In Supplementary Fig. 1g, h, the polyhedral model demonstrates the lattice reconstruction process, ultimately leading to the growth of PSC Nb2O5 monoliths from PSC Nb4N5 monoliths. In this process, PSC Nb4N5 monoliths function as parent single crystals to grow porous single crystals.

Figure 1a shows the XRD patterns of PSC (002) Nb4N5 monoliths and PSC (001) Nb2O5 monoliths, confirming their single crystal characteristic even though they are porous architectures. Figure 1b, c shows scanning electron microscopy (SEM) images of the <002> oriented PSC Nb4N5 and <001> oriented PSC Nb2O5, respectively. Microscopic morphological characterization indicates that the pores in PSC Nb2O5 monoliths are larger than those in PSC Nb4N5 monoliths at the same scale, and a similar difference in internal pore density is also observed. As shown in Supplementary Fig. 2, we further conduct multiple measurements to determine the specific surface area and average pore size of PSC Nb2O5 monoliths. We observe that the PSC Nb2O5 monoliths exhibit a specific surface area of ~5.8–6.3 m2 g−1 and an average pore size of ~18–22 nm. The specific surface area of PSC Nb2O5 monoliths is slightly higher than that of PSC Nb4N5 monoliths. More pores are present within PSC Nb2O5 monoliths which is in good accordance with the SEM analysis.

Supplementary Fig. 3 shows the microstructure morphology of the sliced sample within sets b, c and d at the various magnification scales. These images clearly demonstrate that PSC Nb2O5 monoliths produced via the lattice reconstruction strategy that involves nitridation and re-oxidation exhibit a uniform distribution of pore channels and a good internal pore structure. The sliced samples remain intact with no fragments detached, indicating that the single-crystalline skeletons have reasonable mechanical strength. Supplementary Fig. 4 shows a magnified view of the sliced sample and we use the spherical aberration corrected transmission electron micrograph (STEM) and high-resolution transmission electron microscopy (HRTEM) images to investigate the skeleton and surface in the PSC Nb2O5 monoliths. This analysis omits some of the larger pores at several microns that are created by the curtain effect during slicing. The coexistence of twisted surfaces and pore channels can be clearly observed in the PSC Nb2O5 monoliths, further demonstrating the single-crystalline features of the skeletons in the porous microstructures. Supplementary Fig. 5 and Fig. 1d show the selected areas of electron diffraction (SAED) patterns of the sliced sample, again confirming the single crystallinity across different regions. The regular diffraction spots indicate that the overall lattice remains ordered even at different locations. The microstructure of the PSC Nb2O5 monoliths is analyzed using Cs-corrected HRTEM (Cs-HRTEM) in Fig. 1e. The results further confirm the single-crystalline nature of the interconnected Nb2O5 skeletons within the porous microstructure.

The elemental mapping characterization of the sliced samples present in Fig. 1f reveals the absence of any additional elements, indicating the complete transformation of PSC Nb4N5 monoliths to PSC Nb2O5 monoliths in the solid-solid phase transformation. The top layer at the surface in PSC Nb2O5 monoliths is confirmed to be Nb together with O atoms, as evidenced by the high sensitivity low energy ion scattering spectroscopy (HS-LEISS) results presented in Fig. 1g. Figure 1h shows the differential charge distribution of the Nb-O coordination structure, highlighting the electron-deficient active center and indicating a distinct charge transfer from the Nb atom to the O atom at the surface in PSC Nb2O5 monoliths. Charge transfer from the metal to oxygen in the metal-oxygen bond usually occurs because of the difference in the electronegativities. The PSC Nb2O5 monoliths are further characterized by X-ray photoelectron spectroscopy (XPS) analysis in Fig. 1i, revealing Nb elemental peaks corresponding to Nb5+ states, along with oxygen elemental peaks associated with the presence of lattice oxygen (OI) and adsorbed oxygen (OIII).

Supplementary Fig. 6a shows the XRD spectra of a heterogeneous junction structure where Nb4N5 and Nb2O5 co-exist in the sample which is prepared by controlling the transformation time. To better understand the transformation process, we conduct the energy dispersive spectroscopy (EDS) elemental analysis of the sample with a shorter oxidation time in Supplementary Fig. 6b. The results indicate that, in PSC Nb4N5 monoliths with a short reaction time, a small amount of oxygen enter the sample to replace nitrogen. Based on the experimental conditions explored, the oxidation time of the nitride precursors in the reaction should be at least 0.5 h to achieve the complete conversion of PSC Nb4N5 monoliths to prepare PSC Nb2O5 monoliths. We further ground PSC Nb2O5 monoliths into powder and then conduct the XRD test to determine the crystalline phase in Supplementary Fig. 6c. The result conforms with JCPDS card PDF#30-0873, indicating an orthorhombic crystal system with a space group of Pbam (55) and a dotting constant of 6.175 Å × 29.175 Å × 3.93 Å <90.0° × 90.0° × 90.0°> for T-Nb2O5. As shown in Supplementary Fig. 6d, EDS analysis of PSC Nb2O5 monoliths reveals the presence of only Nb and O, with no other elements detected, further confirming the complete conversion of PSC Nb4N5 monoliths to PSC Nb2O5 monoliths. Supplementary Fig. 7 shows the SEM images of the upper and lower surfaces of the incompletely transformed heterostructured samples. PSC Nb2O5 monolith in white and PSC Nb4N5 monoliths in black highlight the coexisting phases at the interface.

Figure 2a–c show the HAADF-STEM images of the twisted surfaces at different scales. Analysis of the atomic distribution reveals the <200> and <0100> crystallographic orientations, with atomic spacing d of approximately 0.308 and 0.292 nm, respectively. The surface structure exhibits an identical lattice orientation around the pores, with lattice distortion present in the thickness of ~1–3 atomic layers. Figure 2d–f shows HAADF-STEM images of a flat area at various scales near another pore locations, revealing lattice orientations of <151> and <230>, with atomic spacing d of approximately 0.288 and 0.294 nm, respectively. The overall average atomic spacing in this region is smaller than that at the upper location. In summary, the primary difference between the two atomic arrangement diagrams is the degree of lattice distortion, which can vary across different twisted surfaces and is relatively larger near the pore channel. This results in a slightly larger atomic spacing, which allows the lattice oxygen of PSC Nb2O5 monolith to be activated more easily than that of other Nb2O5 materials, thereby enhancing catalytic performance.

Despite the slight lattice distortion at the twisted surface, the single-crystalline structure maintains the typical lattice ordering characteristics. The twisted surface not only ensures the high catalytic activity but also facilitates the interactions between the adsorbed substances and the well-defined surface structure. To engineer oxygen vacancies, the PSC Nb2O5 monolith is reduced by placing it in a reaction chamber at 750 °C with a hydrogen-argon flow rate of 50 mL min−1 for 10 h. Figure 2g shows the XRD pattern, with Nb2O5-H representing the sample prepared after reduction. The intensity of the diffraction peaks in the reduced sample is lower than that of the unreduced sample, primarily because of the structural defects in the reduced sample, which not only decrease the intensity of the diffraction peaks but also shift the positions. A spherical differential electron micrograph of the reduced PSC Nb2O5 monolith is shown in Supplementary Fig. 8a, indicating that the atomic arrangement remains largely regular; however, some areas of inhomogeneity can still be observed in the lattice structure. Analysis in the transverse and oblique directions in Supplementary Fig. 8b clearly shows that the intensity of the lattice atomic arrangement changes from strong to weak and then back to strong, which can be attributed to the presence of atomic defects in the reduced PSC Nb2O5 monolith, resulting in the formation of oxygen vacancies confined in the lattice.

To verify the presence of oxygen vacancies in the reduced PSC Nb2O5 monolith, the sample is subjected to the test of electron paramagnetic resonance (EPR) that detects unpaired electrons to determine oxygen vacancies. As shown in Supplementary Fig. 9, the pure-phase sample is measured against the reduced sample, yielding g-factor of 2.002 that indicate the presence of oxygen vacancies28. Figure 2h shows a continuously twisted surface around the pore, where the lattice orientation remains consistent when viewed from a fixed orientation. Figure 2i shows the differential charge density of the twisted surface structure, indicating that the top layer is in an electron-deficient state, which facilitates the reception of electrons during C-O activation.

We construct an interfacial system by depositing a Pt cluster at the skeleton surface in the PSC Nb2O5 monoliths. The content of Pt at 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.7 wt%, 1 wt%, and 4 wt% is determined by using inductively coupled plasma (ICP) analysis in Supplementary Fig. 10, with the average values from three tests yielding values of 0.13 wt%, 0.45 wt%, 0.60 wt%, 0.84 wt%, 0.98 wt% and 3.35 wt%, respectively. HAADF-STEM images characterization of PSC Nb2O5 monoliths with different amounts of loaded Pt is presented in Fig. 3a–c. The HAADF-STEM images of the PSC Nb2O5 monolith with 3.35 wt% Pt content at different scales show that, owing to the excessive amount of loaded Pt atoms, clusters finally form on the surface, by stacking and arranging Pt atoms into layers and resulting in a cluster or particle state. Supplementary Fig. 11 shows the HRTEM images of the PSC Nb2O5 monolith with 0.60 wt%, 0.84 wt%, and 0.98 wt% Pt, respectively, showing an increase in the number of loaded atoms. Pt clusters form into particles with crystal spacing d = 0.23 nm, suggesting that these particles correspond to the (111) orientation of Pt, and based on the original field of view, the particles are uniformly distributed across the entire surface of the PSC Nb2O5 monolith.

As the loaded Pt content increases to form particles, some visible Pt particles become encapsulated by the carrier owing to the presence of strong metal–support interactions, thereby embedding them within the single-crystalline porous oxide to form a Pt/NbOx interface. This structure endows the catalyst with high thermal stability. However, because Pt behaves similarly to absorbed CO, the catalytic activity of this catalyst is significantly compromised29. In general, increasing the amount of loaded Pt results in the formation of larger particles under reducing conditions. However, owing to its stable oxygen vacancies, PSC Nb2O5 monolith would limit the generation of large particles to some extent. Consequently, increasing the amount of loaded Pt leads to a uniform distribution across the surface in the PSC Nb2O5 monolith, which therefore would improve the catalytic activity toward CO oxidation. Figure 3d shows the elemental mapping of the PSC Nb2O5 monolith with the surface featuring Pt clusters, illustrating the distribution of nanoscale Pt clusters in the porous microstructure.

Figure 3e shows a differential charge density map of the surface structure with Pt clusters, indicating charge transfer from Pt to O, which effectively activates the lattice oxygen linked to Pt at the surface. Figure 3f shows the HS-LEISS of PSC Nb2O5 monolith with the Pt at 3.35 wt%. Notably, Pt primarily exists in a state of clusters or particles. The Ne spectrum show the Pt signals in addition to Nb signals, indicating that Pt is stably loaded on the surface. The HS-LEISS for the PSC Nb2O5 monoliths with other loading amounts of Pt are shown in Supplementary Fig. 12, where all spectra reveal the presence of Pt on the surface of PSC Nb2O5 monolith. As can be seen in Fig. 3g, the signal of Pt-3L is weaker than that of the Pt foil, which suggests that the Pt in the PSC Nb2O5 monoliths is mainly in the reduced state (Pt0). And the PSC Nb2O5 monoliths with different Pt loading contents exhibit almost the same characteristics. With the presence of Pt in the form of nanoparticles or clusters, surface dangling bonds and low-coordinated atoms may lead to a change in the density distribution of the electronic states, thus weakening the intensity of the characteristic peaks30,31. The presence of a small amount of oxidized state Pt leads to a slight shift of the near-side energy to higher energies.

Figure 3h shows the Fourier transform (FT) of the extended X-ray absorption fine structure (EXAFS) spectra for the PSC Nb2O5 monoliths with loaded Pt. The shape of the curve of the reduced Pt/Nb2O5 sample is similar to that of Pt0. The bond length of Pt-Pt is approximately 2.7 Å, indicating the presence of a Pt-Pt bond in the sample and confirming that Pt is in the metallic state on the surface of the PSC Nb2O5 monolith. It is also observed that the Pt-O bond is present in the curve, indicating the presence of partially oxidized Pt in the form of Pt2+ in the clusters. The Raman spectra of the PSC Nb2O5 monoliths loaded with Pt clusters exhibit a high-intensity broadband centered at approximately 670–690 cm−1 in Fig. 3i, which corresponds to the characteristic vibrational peaks of the coexistence of NbO6 and NbO7. This result aligns with the literature on the T-Nb2O5 spectrum, and the absence of nitrogen characteristic peaks on the surface suggests complete transformation32. Because of its sensitivity to the structure and chemical bonding of metal oxides, Raman spectroscopy is well-suited for investigating defects caused by doping or oxygen vacancies. A partial enlargement of the Raman profile is shown in Supplementary Fig. 13, where the peak value shifts to the left from 685 to 675 cm−1 with increasing Pt loading content, indicating that the number of oxygen vacancies increases and that the lower Nb–O bond level leads to a longer Nb-O bond length in reduced states.

Figure 4a shows the results of CO oxidation experiments with the Pt loading contents, indicating that the temperature required for the complete conversion of CO to CO2 remarkably decreases at higher loading contents. At a loading of 3.35 wt% and a space velocity of 30,000 mL g−1 h−1, the complete conversion temperature finally reaches approximately 110 °C, while the complete conversion is not achieved by using PSC Nb2O5 monoliths without Pt loading even at 300 °C. Figure 4b shows that PSC Nb2O5 monoliths loaded with 3.35 wt% of Pt loading demonstrates the outstanding durability, owing to the structural stability of the single-crystalline features in the porous microstructure. We therefore observe the complete CO conversion even after a continuous operation of ~500 h under the operation condition of high space velocity. As shown in Fig. 4c, the metal-oxide interfacial system in the PSC Nb2O5 monoliths significantly increases the surface oxygen exchange coefficient, which further suggests that the fast dynamic equilibrium of surface defect reaction of Ox + 2h• ⇌ V••O + 1/2 O2 effectively facilitate the activation of lattice oxygen. This is pretty favorable for enhancing the catalytic oxidation of CO with air in the interfacial system in PSC Nb2O5 monoliths. Moreover, this relationship between the surface oxygen exchange coefficient and the surface Pt loading contents further confirm the effectiveness of the localized structures of metal-oxide interfacial system in activating lattice oxygen in the PSC Nb2O5 monoliths. Supplementary Fig. 14 shows the EXAFS spectra of the PSC Nb2O5 monoliths with 3.35 wt% of Pt loading at different temperatures under the flow of CO gas. The EXAFS indicates that the Nb K-edge and scattering distance (R) generally remain identical for the PSC Nb2O5 monoliths with 3.35 wt% of Pt loading before and after CO adsorption at different temperatures, which suggests the structural stability of PSC Nb2O5 monoliths.

To analyze the catalytic effect of PSC Nb2O5 monoliths with different Pt loading contents, in situ infrared measurements have been conducted to assess the adsorption and activation for CO at different temperatures. As shown in Fig. 4d, the main adsorption peak of PSC Nb2O5 monoliths loaded with 3.35 wt% Pt is located at approximately 2090 cm−1, which indicates the linear adsorption at the interfacial system. The adsorption peaks shift relatively to blue region when the temperature ranges from low to high temperatures, indicating that Pt is positively charged, while the intensity of the adsorption of CO gradually increases with increasing temperature. The peaks at approximately 2175 cm−1 can be primarily attributed to CO gas. Figure 4e shows the position of the adsorption peaks for CO2 generation from PSC Nb2O5 monoliths with 3.35 wt% of Pt loading content. The intensities of the peaks increase with increasing temperature, indicating that the interfacial system exhibits higher activity in catalytic oxidation of CO at higher temperatures. A higher operation temperature promotes faster oxidation of CO by effectively activating the lattice oxygen linked to the Pt clusters in the interfacial system at the surface. As shown in Supplementary Fig. 15, the linear adsorption is also observed because the main adsorption peaks locate at approximately 2070–2090 cm−1 for the Pt-loaded PSC Nb2O5 monoliths, which is also validated by the relative blue shift of the adsorption peaks at high temperatures. Another set of plots shows the position of the adsorption peaks during the CO2 production for the PSC Nb2O5 monoliths with 3.35 wt% of Pt loading content. The peak intensity increases with the rise in temperature, indicating that the interaction between CO molecules and the active lattice oxygen atoms present on the surface becomes stronger at high temperatures, and the desorption amount of CO2 also increases accordingly.

In Fig. 4f and Supplementary Fig. 16, XPS results of the Pt-loaded PSC Nb2O5 monoliths after reduction treatment reveal that the elemental peaks of Nb are nearly identical. Each of the O peaks consists of lattice oxygen (OI), oxygen vacancies (OII) and adsorbed oxygen (OIII) with binding energies of approximately 529.8, 531.0 and 532.3 eV, respectively. This further provides the evidence of the presence of oxygen vacancies in the lattice. Pt has peaks in two states, Pt0 and Pt2+, and although some of the Pt is oxidized, but most of the Pt remains in the metallic state, with the Pt0 peak dominating the curve. Based on the EXAFS, XPS, in situ FTIR results, we consider the IR bands centered at 2070–2090 cm−1 to represent CO molecules adsorbed on Pt clusters.

Furthermore, we investigate the active species in CO oxidation catalyzed with different Pt loading contents. Electron Paramagnetic Resonance (EPR) analysis has been performed to detect the unpaired electron originating from the oxygen vacancies in the PSC Nb2O5 monoliths. The number of oxygen vacancies present in PSC Nb2O5 monoliths can be quantitatively compared based on the variations in the intensity of the EPR spectrum. As shown in Fig. 4g, the spectra of PSC Nb2O5 monoliths loaded with different Pt loading contents exhibit a sharp peak with a g-factor of 2.002, corresponding to the paramagnetic signal of surface oxygen vacancies associated with the superoxide ion (O2−) generated by the adsorption of atmospheric oxygen onto the surface. Notably, the peak intensity increases with increasing the Pt loading content and finally reaches the highest peak intensity for PSC Nb2O5 monoliths with the 3.35 wt% of Pt loading content. In addition, the EPR data provide direct spectroscopic evidence for the presence of oxygen vacancies in Pt-loaded PSC Nb2O5 monoliths, aligning with the H2-temperature-programmed reduction (H2-TPR) results as shown in Supplementary Fig. 17. The activation energy for CO oxidation is approximately 46–56 kJ mol−1 for Pt-loaded PSC Nb2O5 monoliths as shown in Fig. 4h. The HAADF-STEM image in Supplementary Fig. 18 shows the similar sizes of Pt clusters, further validating the thermal stability of interfacial system in the PSC Nb2O5 monoliths.

In the catalytic oxidation of CO with air, the reaction mechanism follows the Mars-van Krevelen (MvK) mechanism33–35. In the process, the CO adsorbs onto the Pt clusters in interfacial system with the presence of oxygen vacancies in the PSC Nb2O5 monoliths, and the oxygen from the reactive gas enters the oxygen vacancies to form lattice oxygen. As the temperature increases, the lattice oxygen linked to Pt in interfacial system becomes effectively activated. Subsequently, the CO reacts with the lattice oxygen to form CO2 which is then desorbed, allowing oxygen from the gas to recharge the lattice to form lattice oxygen. Further, the transition state for the oxidation of CO at the Pt/Nb2O5 interface is determined by the calculation of density functional theory (DFT). The potential energy diagram is shown in Fig. 4i. The adsorption energy of CO on the Pt/Nb2O5 interface structure is approximately 1.59 eV, while the reaction energy barrier for the formation of CO2 by the combination of the lattice oxygen connected to the Pt clusters and CO is approximately 0.72 eV. This indicates that the reaction between CO and the lattice oxygen at this interface has a high possibility. We further conduct the XPS and Raman tests after the long-term reaction to validate the stability of the Pt-loaded PSC Nb2O5 monoliths as shown in Supplementary Fig. 19, 20. We observe that the Pt-loaded PSC Nb2O5 monoliths generally remain unchanged before and after the reaction test as seen in Supplementary Fig. 19, thus indicating the outstanding stability originating from the structural feature of single crystallinity and porosity in a monolith. In Supplementary Fig. 20, the peaks at 244 and 321 cm−1 in the Raman spectra belong to the bending mode of the Nb-O-Nb bond in the orthorhombic T-Nb2O5 structure, whereas the broadband at 675 cm−1 is due to the coexistence of two different types of niobium coordination (NbO6 and NbO7) in the crystal structure36. In Supplementary Fig. 21, We evaluate the long-term stability assessment under high-temperature conditions of 110 °C combined with higher WHSV. First, we evaluated the CO conversion rate of the catalyst at different WHSV values by increasing the WHSV at 110 °C. As shown in Supplementary Fig. 21a, the CO conversion rate decreased from 100% to 83.83% as the WHSV increased from 30,000 mL g-1 h-1 to 60,000 mL g-1 h-1 at 110 °C. Subsequently, in Supplementary Fig. 21b, the long-term stability of Pt/PSC Nb2O5 was tested for 185 h under conditions of 110 °C and 60,000 mL g-1 h-1. The conversion rate decreased by 9%, ultimately reaching 76.3%. Pt/PSC Nb₂O₅ catalysts exhibit excellent durability.

In conclusion, we grow PSC Nb2O5 monoliths at the centimeter scale while we introduce oxygen vacancies in lattice by reduction and then stabilize the oxygen vacancies in lattice by the ordered structure. We then deposit Pt clusters at the surface in the porous microstructures to construct an interfacial system and we show the significantly enhanced surface oxygen exchange coefficient that contributes to the effective activation of lattice oxygen. We show the remarkably improved catalytic activity in the Pt cluster-decorated interfacial system in the PSC Nb2O5 monoliths. We achieve the complete conversion of CO at 110 °C and 30,000 mL g-1 h-1 conditions, with no visible performance degradation being observed even after a continuous operation for ~500 h. We believe that the current work will provide a new line of thought for the preparation of novel catalysts enriched with oxygen vacancies at the surface for enhancing the catalytic activity as well as the stability.

Methods
Synthesis
By using molten salt method, the appropriate amount of Nb2O5 and Na2CO3 and excess WO3 or B2O3 are mixed in a certain ratio in a platinum crucible, and finally placed in a furnace with the temperature set above 1260 °C. During the growth process, the temperature is raised and kept at a constant temperature for 10 h. The powder in the crucible is being observed until it forms a molten state, and the control temperature is lowered to 960 °C for 2 h. At this time, a transparent crystal surface could be clearly seen in the crucible, and then it starts to crystallize at a slow rate of 2 °C h−1. Then the temperature is cooled to room temperature at 10 °C/min to obtain NaNbO3 crystals. NaNbO3 crystals are used as precursors for the growth of PSC Nb4N5 monoliths using a lattice reconstruction strategy. The NaNbO3 crystals oriented with (001) and (010) planes are placed in ammonia gas at a flow rate of 200–350 ml min−1 at a pressure of 200–760 Torr at 800–950 °C for 50–100 h to obtain PSC Nb4N5 monoliths. We then grow PSC Nb2O5 monoliths by converting PSC Nb4N5 monoliths using a lattice reconstruction strategy. The temperature of 600 °C and a pressure of 200–760 Torr are required for the gradual oxidation in an O2/Ar mixture at a flow rate of 60–500 ml min−1 for 0.5–6 h to obtain grow PSC Nb2O5 monoliths. We use impregnation method to load Pt in PSC Nb2O5 monoliths. We use H2PtCl6 as the Pt precursor and prepare solutions with different concentrations of H2PtCl6 for Pt loadings of 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.7 wt%, 1 wt% and 4 wt%, respectively.

Characterization
We use a field emission scanning electron microscope (FE-SEM) (SU-8010) to observe the microstructure of the samples. The facet orientation is characterized by X-ray diffractometry (XRD, Cu-Kα, Miniflex 600). The elemental content is analyzed using ICP-AES with utlima-2 (France. JY). Raman spectra are obtained by Labram HR evolution Raman spectroscopy (Horiba Jobin Yvon). The lattice structure is analyzed using Cs-TEM (FEI Titan 3 G2 60–300). The chemical state of the elements is determined by XPS (ESCALAB 250Xi). XAFS measurements are carried out on the 1W1B beamline of the Beijing Synchrotron Radiation Facility (BSRF). In situ EXAFS is tested at the Shanghai Synchrotron Radiation Facility (SSRF) BL05U beamline. High sensitivity low energy ion scattering spectroscopy (HS-LEISS, Qtac100, ION-TOF) is used to examine the atomic termination layers of the samples. Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) measurements are performed on an infrared spectrometer (Bruker VERTEX70). Surface oxygen exchange coefficient tests are performed using the electrical conductivity relaxation (ECR) method. EPR spectra are acquired on a spectrometer (Bruker Biospin GMBH E500 10/12) to identify oxygen vacancies in the interfacial system.

Catalytic test
The catalytic tests are carried out at atmospheric pressure in a tubular reaction system with a flow-through quartz micro-reactor with an inner diameter of 5 mm. PSC Nb2O5 monoliths with a diameter of less than 5 mm and a thickness of less than 1 mm is loaded repeatedly as a catalyst and then preheated at 300 °C for 3 h in a 5% H2/Ar air stream. The reaction products are analyzed using an on-line gas chromatograph (GC) (Shimadzu GC-2014) equipped with FID and TCD detectors and a 30 m long CP-poraplot Q packed column. The reaction gas, consisting of 1% CO and 99% air, is introduced into the reactor at a flow rate of 50 sccm. In situ EXAFS experiments use the same gas as the catalytic reaction, and the gas flow rate is 20 sccm.

Theoretical calculations
Density Functional Theory (DFT) calculations are performed using the Vienna Ab Initio Simulation Software Package (VASP 6.3.2) code37,38. The generalized gradient approach (GGA) and Perdew–Burke–Ernzerhof (PBE) functional are used to describe exchange and correlation. Projected Augmented Wave (PAW) method is used to describe the interaction between nuclear and valence electrons. The transition states are searched using the climbing image nudged elastic band method (CI-NEB) and confirmed by the vibrational frequency analysis. The plane wave cut-off is set to 520 eV. The energies and residual forces are converged to 10−5 eV and 0.02 eV Å−1 during electron and geometry optimization. The optimized lattice parameters of Nb2O5 crystal are a = 6.175 Å, b = 29.175 Å, c = 3.93 Å with a 5 × 1 × 8 k-point grid. A p(2 × 1) superstructure of surface is used for the slab models. A supercell surface model of Nb2O5 decorated with a tetrahedral Pt cluster was constructed to investigate the mechanism of CO oxidation. A 20 Å vacuum area is used to avoid interaction between the plate and its repeated images for these models. A 2 × 1 × 1 k-point grid is used for the models for sampling in the Brillouin zone. The Gibbs free energy change (ΔG) at T = 383 K is calculated as ΔG = ΔE + ΔZPE - TΔS, where ΔE is the total energy difference obtained from DFT calculations, ΔZPE represents the zero-point energy correction derived from vibrational frequency analysis, and ΔS is the entropy change.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This study successfully demonstrates the fabrication of centimeter-scale PSC Nb₂O₅ monoliths decorated with Pt clusters, achieving complete CO oxidation at 110°C with stable performance over 500 hours. The deposition of Pt clusters onto PSC Nb₂O₅ monoliths leads to the formation of well-defined interfacial structures, significantly enhancing catalytic efficiency. Furthermore, the study reveals a notable improvement in the surface oxygen exchange coefficient, which contributes to the remarkable catalytic activity of the Pt cluster-decorated interfacial system.\n\nThe experimental work presented is highly intriguing, and the Nb₂O₅ monoliths fabricated in this study could make a valuable contribution to the field of heterogeneous catalysis. However, several points require clarification before the paper can be accepted. Below are my detailed comments and questions:\n1. The concept of oxygen vacancy engineering in Pt/oxide nanocatalysts is well-established, with numerous studies reporting similar strategies. Relevant prior works, such as those by For example, Y. Li et al. ACS Catal. 12, 9, 4906–4917 (2022); S. B. T. Tran et al. Journal of Catalysis 375, 124-134 (2019); H. Qin et al. Molecular Catalysis, 546, 113267 (2023) ; Y. Zheng et al. J. Mater. Chem. A, 2022,10, 14171-14186; H. Choi et al. Catal. Sci. Technol. 11, 1698-1708 (2021, should be cited to acknowledge previous contributions and contextualize the current investigation.\n2. The Pt 4f peaks in Figure 4f appear unusual. It would be helpful to clarify whether the full width at half maximum (FWHM) of these peaks remains consistent or if an additional peak is present. Additionally, the figure should clearly differentiate between raw data and fitted curves to enhance readability and interpretation.\n3. Pt nanoparticles in the 2-3 nm size range are highly susceptible to oxidation during CO oxidation, which can significantly impact catalytic activity. However, the oxidation states of Pt are not sufficiently discussed in the XPS analysis presented in Figure 4f. A more thorough discussion is needed, potentially incorporating insights from in-situ EXAFS experiments. Furthermore, post-reaction XPS analysis should be provided to reveal the chemical states of Pt after CO oxidation, offering a clearer understanding of catalyst stability under operating conditions.", "reviewer_2": "The manuscript presents a novel approach to enhancing the catalytic activity of Nb2O5 by introducing and stabilizing oxygen vacancies through a reduction treatment, along with the deposition of Pt clusters on the surface. The authors report a significant improvement in the surface oxygen exchange coefficient and demonstrate complete CO oxidation at 110 °C with high stability. However, several aspects of the paper need improvement before it can be accepted for publication in Nature Communications. The specific comments are as follows:\n(1) The importance of this work is not adequately emphasized, particularly in the introduction. The authors should strengthen this point.\n(2) The mechanism of the catalyst for CO oxidation has not been explored or discussed in the manuscript.\n(3) There is a lack of characterization of the catalysts after the reaction, which should be addressed.\n(4) The authors provide numerous electron microscopy images to characterize their catalyst. However, there are several inaccuracies in the labeling of these images. For example, in Figure 2, the images should be labeled as HAADF-STEM instead of HRTEM. Additionally, in Figure 3d, while HRTEM or BF-STEM is presented, HAADF-STEM should be used if available, as it allows for better identification of Pt species and facilitates comparison with EDS maps.\n(5) In Figure 2, the authors indicate an enlarged area using a cycle, but the enlarged area in the images is actually rectangular.\n(6) The authors should combine the XANES spectra to facilitate a comparison of the Pt-L3 white line intensity, rather than spacing them out. (see doi.org/10.1038/s41467-021-23696-7; doi.org/10.1021/jacs.3c10659).\n(7) In Figure 4h, the activation energies should be fitted with a solid line instead of a broken line; otherwise, the accuracy of the activation energy values is questionable."}, "author_response": "Response to reviewers\nReviewer #1\nThis study successfully demonstrates the fabrication of centimeter-scale PSC Nb₂O₅\nmonoliths decorated with Pt clusters, achieving complete CO oxidation at 110 °C with\nstable performance over 500 hours. The deposition of Pt clusters onto PSC Nb₂O₅\nmonoliths leads to the formation of well-defined interfacial structures, significantly\nenhancing catalytic efficiency. Furthermore, the study reveals a notable improvement\nin the surface oxygen exchange coefficient, which contributes to the remarkable\ncatalytic activity of the Pt cluster-decorated interfacial system.\n\nThe experimental work presented is highly intriguing, and the Nb₂O₅ monoliths\nfabricated in this study could make a valuable contribution to the field of\nheterogeneous catalysis. However, several points require clarification before the paper\ncan be accepted. Below are my detailed comments and questions.\nAnswer: Many thanks for your comments. We have further conducted supplementary\nexperiments to strengthen our work. We have carefully revised this manuscript\naccording to your suggestions and we hope the revised version would merit the\npublication in Nature Communications.\n1. The concept of oxygen vacancy engineering in Pt/oxide nanocatalysts is\nwell-established, with numerous studies reporting similar strategies. Relevant prior\nworks, such as those by For example, Y. Li et al. ACS Catal. 12, 9, 4906–4917 (2022);\nS. B. T. Tran et al. Journal of Catalysis 375, 124-134 (2019); H. Qin et al. Molecular\nCatalysis, 546, 113267 (2023); Y. Zheng et al. J. Mater. Chem. A, 2022,10,\n14171-14186; H. Choi et al. Catal. Sci. Technol. 11, 1698-1708 (2021), should be\ncited to acknowledge previous contributions and contextualize the current\ninvestigation.\nAnswer: Thank you very much and we have cited the relevant work in revision. Yes,\nthe concept of oxygen vacancy engineering is useful to regulate the catalytic activity\nand many pioneer scientists have made significant contribution in past years. Here, we\nfabricate centimeter-scale porous single-crystalline Nb₂O₅ monoliths decorated with\nPt clusters, and we reveal a notable improvement in the surface oxygen exchange\ncoefficient, which therefore contributes to the remarkably enhanced catalytic activity\nof the Pt cluster-decorated interfacial system for complete CO oxidation at 110 °C\nwith stable performance over 500 hours of continuous operation in our work.\n2. The Pt 4f peaks in Figure 4f appear unusual. It would be helpful to clarify whether\nthe full width at half maximum (FWHM) of these peaks remains consistent or if an\nadditional peak is present. Additionally, the figure should clearly differentiate between\nraw data and fitted curves to enhance readability and interpretation.\nto the figures. We have refitted the Pt 4f peak in Figure 4f in revision. There are\ndominant Pt0 together with Pt2+ peaks present and their FWHM remain consistent at\n1.18 and 1.7 eV, respectively. In addition, a clear distinction has been made between\nthe raw data and the fitted curve in the figure.\nFigure 4 (f) XPS of PSC Nb O monolith decorated with 3.35 wt% Pt cluster.\n2 5\nFigure S16. XPS of PSC Nb O monoliths at different loading Pt amounts.\n2 5\n3. Pt nanoparticles in the 2-3 nm size range are highly susceptible to oxidation during\nCO oxidation, which can significantly impact catalytic activity. However, the\noxidation states of Pt are not sufficiently discussed in the XPS analysis presented in\nFigure 4f. A more thorough discussion is needed, potentially incorporating insights\nfrom in-situ EXAFS experiments. Furthermore, post-reaction XPS analysis should be\nprovided to reveal the chemical states of Pt after CO oxidation, offering a clearer\nunderstanding of catalyst stability under operating conditions.\nAnswer: Thank you very much for your comments and we have further carried out\nsupplementary experiments in revision. We have fully discussed the XPS data and\nEXAFS data in revision. In the XPS of Figure 4f, the Pt has peaks in two states,\nincluding Pt0 and Pt2+. We observe that most of the Pt remains in the metallic state\nwith the Pt0 peak dominating in the figure but some of the Pt is partially oxidized in\nthe form of Pt2+. In the EXAFS in Figure 3g, the signal of sample Pt-3L is weaker\nthan that of the platinum foil, which suggests that the platinum in the samples is\nmainly in the reduced state Pt⁰, and the six samples, shown in the Figure 3h, exhibit\nalmost the same characteristics. The shape of the curve of the reduced Pt/Nb O\n2 5\nsample is similar to that of Pt0. The bond length of Pt-Pt is approximately 2.7 Å,\n2\nindicating the presence of a Pt-Pt bond in the sample and confirming that Pt is in the\nmetallic state on the surface of the PSC Nb O monolith. It is also observed that the\n2 5\nPt-O bond is present in the curve, indicating the presence of partially oxidized Pt in\nthe form of Pt2+ in the clusters. In addition, from the post-reaction XPS as shown in\nthe following figure, it can be seen that the catalyst generally remains unchanged\nbefore and after the reaction, thus indicating the chemical stability of the catalyst.\nFigure 4f and Figure S18. XPS comparison of PSC Nb O monoliths decorated with\n2 5\n3.35 wt% Pt clusters before and after reaction.\nReviewer #2\nThe manuscript presents a novel approach to enhancing the catalytic activity of Nb O\n2 5\nby introducing and stabilizing oxygen vacancies through a reduction treatment, along\nwith the deposition of Pt clusters on the surface. The authors report a significant\nimprovement in the surface oxygen exchange coefficient and demonstrate complete\nCO oxidation at 110 °C with high stability. However, several aspects of the paper\nneed improvement before it can be accepted for publication in Nature\nCommunications. The specific comments are as follows:\nAnswer: Many thanks for your comments. We have carefully revised this manuscript\naccording to your suggestions.\n1. The importance of this work is not adequately emphasized, particularly in the\nintroduction. The authors should strengthen this point.\nAnswer: Many thanks for your comments. We have revised introduction to emphasize\nthe importance of this work. The current work will provide a new line of thought for\nthe preparation of novel catalysts enriched with oxygen vacancies by confining\noxygen-vacancy-rich, well-defined active structures to the surface to activate lattice\noxygen.\n2. The mechanism of the catalyst for CO oxidation has not been explored or discussed\nin the manuscript.\nAnswer: Many thanks for your comments. We have added the discussion of the\nreaction mechanism in revision. The reaction mechanism follows the Mars-van\nKrevelen (MvK) mechanism 33-35. In the reaction process, CO adsorbs on the Pt\n3\ncluster at the surface of Pt/Nb O , due to the presence of oxygen vacancies, while the\n2 5\noxygen in the reacting gas enters the oxygen vacancies in lattice and forms lattice\noxygen. The lattice oxygen linked to Pt at the surface is effectively activated.\nSubsequently, CO reacts with the lattice oxygen to form carbon dioxide, which is\ndesorbed while the oxygen in the gas re-enters the lattice to form lattice oxygen.\n33. Zhang J, et al. Advances in CO catalytic oxidation on typical noble metal\ncatalysts: Mechanism, performance and optimization. Chem Eng J 495, 153523\n(2024).\n34. Kim H, Lee H, Henkelman G. CO oxidation mechanism on CeO -supported Au\n2\nnanoparticles. J Am Chem Soc 134, 1560-1570 (2012).\n35. Widmann D, et al. How Temperature Affects the Mechanism of CO Oxidation on\nAu/TiO : A Combined EPR and TAP Reactor Study of the Reactive Removal of\n2 2\n(2016).\n3. There is a lack of characterization of the catalysts after the reaction, which should\nbe addressed.\nAnswer: Many thanks for your comments and we have conducted supplementary\nexperiments in revision. The Raman and XPS images in Figures S18 and S19\nillustrate that there is no visible change in structure features of the PSC Nb O\n2 5\nmonoliths after the long-term reaction. The 244, 321 cm-1 in Figure S19 belong to the\nbending mode of the Nb-O-Nb bond in the orthorhombic T-Nb O structure, and the\n2 5\nbroad band at 675 cm-1 is due to the coexistence of two different types of niobium\ncoordination (NbO and NbO ) in the crystal structure.\n6 7\nFigure S18. XPS after reaction of PSC Nb O monolith decorated with 3.35 wt% Pt\n2 5\nclusters.\n2 5\nPt clusters.\n4. The authors provide numerous electron microscopy images to characterize their\ncatalyst. However, there are several inaccuracies in the labeling of these images. For\nexample, in Figure 2, the images should be labeled as HAADF-STEM instead of\nHRTEM. Additionally, in Figure 3d, while HRTEM or BF-STEM is presented,\nHAADF-STEM should be used if available, as it allows for better identification of Pt\nspecies and facilitates comparison with EDS maps.\nAnswer: Many thanks. The labelling of the images in the text has been corrected and\nin Figure 2 the image labelling has been changed to HAADF-STEM and changed in\nthe text. Also, in Figure 3d it has been changed to HAADF-STEM.\nFigure 3 (d) Elemental mapping of PSC Nb O monolith with Pt clusters on the\n2 5\nsurface.\n5. In Figure 2, the authors indicate an enlarged area using a cycle, but the enlarged\narea in the images is actually rectangular.\nAnswer: Many thanks. The markings in the figure have been corrected.\nFigure 2 HAADF-STEM of twisted surfaces at different scales and locations.\n5\n6. The authors should combine the XANES spectra to facilitate a comparison of the\nPt-L3 white line intensity, rather than spacing them out.\n(see doi.org/10.1038/s41467-021-23696-7; doi.org/10.1021/jacs.3c10659).\nAnswer: Many thanks. We have added the discussion and we have cited the reference.\nWe have also contacted the scientist at Shanghai Synchrotron Radiation Facility to\nvalidate the discussion in revision. As shown in Figure 3g, XANES spectra have been\ncombined to facilitate comparison of Pt-L3 white line intensities. The sample Pt-L3\nsignal is weaker than that of the Pt foil, indicating that Pt is predominantly in the\nreduced state (Pt0) in the sample, and that Pt exists in the form of nanoparticles or\nclusters, where the surface dangling bonds and low-coordinated atoms may lead to a\nchange in the density distribution of the electronic states, weakening the intensity of\nthe characteristic peaks at the near edge. The presence of a small amount of oxidized\nstate Pt leads to a slight shift of the near-side energy to higher energies.\nFigure 3 (g) XANES of PSC Nb O monoliths with Pt clusters on the surface.\n2 5\n7. In Figure 4h, the activation energies should be fitted with a solid line instead of a\nbroken line; otherwise, the accuracy of the activation energy values is questionable.\nAnswer: Many thanks. In Figure 4h, the activation energies have been fitted with a\nstraight line before, only the results presented are misleading and have been corrected\nin the figure.\nFigure 4 (h) Activation energies of CO oxidation by using PSC Nb O monoliths\n2 5\ndecorated with different loading contents of Pt cluster.\n6"}, {"round": 2, "reviewer_comments": {"reviewer_1": "I read the reply letter, and the revised manuscript carefully, and I feel that my comments and concerns were properly addressed, therefore, I suggest the paper be accepted as it is.", "reviewer_2": "I appreciate the authors’ revision. However, several key issues remain that require further attention:\n1) While the author has added a discussion on the catalyst’s mechanism for CO oxidation, the manuscript still lacks experimental evidence to substantiate this discussion.\n2) The stability of CO oxidation should not be assessed under 100% CO conversion, as the present data may overestimate the catalysts’ stability. The author could lower the CO conversion below 100% by improving the WHSV to reassess the stability.\n3) There are still some minor issues in the revised manuscript. For example, “HAADF-STEM of” should be corrected to “HAADF-STEM image of”. It is recommended that the authors have others review the manuscript for detailed issues to meet the journal’s requirements."}, "author_response": "Response to reviewers\nReviewer #1 (Remarks to the Author):\nI read the reply letter, and the revised manuscript carefully, and I feel that my comments\nand concerns were properly addressed, therefore, I suggest the paper be accepted as it\nis.\nAnswer: Many thanks for your comments. We further conduct supplementary research\nto improve the manuscript and enhance the quality.\nReviewer #2 (Remarks to the Author):\nI appreciate the authors’ revision. However, several key issues remain that require\nfurther attention:\nAnswer: Many thanks for your comments. We further conduct supplementary\nexperimental and theoretical research to strengthen the work.\n1) While the author has added a discussion on the catalyst’s mechanism for CO\noxidation, the manuscript still lacks experimental evidence to substantiate this\ndiscussion.\nAnswer: Many thanks for your comments. The combination of in situ FTIR and DFT\ncalculation is generally utilized to investigate the catalytic mechanism for CO oxidation.\nIn revision, we conduct supplementary research to strengthen the mechanistic study.\nAs shown in Figure 4d, the main adsorption peak of PSC Nb O monoliths loaded with\n2 5\n3.35 wt% Pt is located at approximately 2090 cm-1, which indicates the linear\nadsorption at the interfacial system. The adsorption peaks shift relatively to blue region\nwhen the temperature ranges from low to high temperatures, indicating that Pt is\npositively charged, while the intensity of the adsorption of CO gradually increases with\nincreasing temperature. The peaks at approximately 2175 cm-1 can be primarily\nattributed to CO gas. Figure 4e shows the position of the adsorption peaks for CO\n2\ngeneration from PSC Nb O monoliths with 3.35 wt% of Pt loading content. The\n2 5\nintensities of the peaks increase with increasing temperature, indicating that the\ninterfacial system exhibits higher activity in catalytic oxidation of CO at higher\ntemperatures. A higher operation temperature promotes faster oxidation of CO by\neffectively activating the lattice oxygen linked to the Pt clusters in the interfacial system\nat the surface.As shown in Figure S15, the linear adsorption is also observed because\nthe main adsorption peaks locate at approximately 2070-2090 cm-1 for the Pt-loaded\nPSC Nb O monoliths, which is also validated by the relative blue shift of the\n2 5\nadsorption peaks at high temperatures. Another set of plots shows the position of the\nadsorption peaks during the CO production for the PSC Nb O monoliths with 3.35\n2 2 5\nwt% of Pt loading content. The peak intensity increases with the rise in temperature,\nindicating that the interaction between CO molecules and the active lattice oxygen\n1\natoms present on the surface becomes stronger at higher temperatures, and the\ndesorption amount of CO also increases accordingly.\n2 5\ndetermined by density functional theory (DFT). The potential energy diagram is shown\nin Figure 4i. The adsorption energy of CO on the Pt/Nb O interface structure is\n2 5\napproximately 1.59 eV, while the reaction energy barrier for the formation of CO by\n2\nthe combination of the lattice oxygen connected to the Pt clusters and CO is\napproximately 0.72 eV. This indicates that the reaction between CO and the lattice\noxygen at this interface has a high possibility. Combining situ FTIR and DFT\ncalculations, we believe that in the process of catalytic oxidation of CO on Pt/Nb O\n2 5\nfollows the MvK mechanism.\nFigure 4(d, e). In situ FTIR of CO oxidation with air using PSC Nb O monoliths decorated with\n2 5\n3.35 wt% Pt cluster.\nFigure S15. In situ FTIR of PSC Nb O monoliths at different loading Pt amounts.\n2 5\nFigure 4i. The potential energy diagram of CO oxidation including surface intermediates and\ntransition states.\n2\n2) The stability of CO oxidation should not be assessed under 100% CO conversion, as\nthe present data may overestimate the catalysts’ stability. The author could lower the\nCO conversion below 100% by improving the WHSV to reassess the stability.\nAnswer: Many thanks for your comments. We refer to some literature and find that the\nCO oxidation reaction is generally evaluated for its stability in terms of complete\nconversion1, 2, 3. Furthermore, we evaluate the catalytic performance of the catalyst\nunder different WHSV. We discover that as the WHSV increases to 60,000 mL g-1 h-1,\nthe complete oxidation temperature finally rise to 180 °C. We also evaluate the long-\nterm stability at 40,000 mL g-1 h-1 and 60,000 mL g-1 h-1. After approximately 150 hours\nof testing, the catalytic performance remains generally unchanged.\nFigure S21. Comparison and long-term testing of the CO oxidation performance of 3.35 wt% Pt\ncluster-loaded PSC Nb O monoliths at different WHSV.\n2 5\n1. Chen J, et al. Reverse oxygen spillover triggered by CO adsorption on Sn-doped\nPt/TiO for low-temperature CO oxidation. Nat Commun 14, 3477 (2023).\n2\n2. Voskanyan AA, Tsui C-KJ, Chan K. Durable ruthenium oxide/ceria catalyst with\nultralarge mesopores for low-temperature CO oxidation. J Catal 382, 155-164\n(2020).\n3. Yang W, et al. High-performance and long-term stability of mesoporous Cu-doped\nTiO microsphere for catalytic CO oxidation. J Hazard Mater 403, 123630 (2021).\n2\n3) There are still some minor issues in the revised manuscript. For example, “HAADF-\nSTEM of” should be corrected to “HAADF-STEM image of”. It is recommended that\nthe authors have others review the manuscript for detailed issues to meet the journal’s\nrequirements.\nAnswer: Many thanks for your comments. We have corrected the errors in the\nmanuscript.\n3"}, {"round": 3, "reviewer_comments": {"reviewer_2": "I recommend that this manuscript be accepted, provided that the real stability of the catalyst is assessed. Although the authors have indicated that the stability of the CO oxidation reaction is evaluated in terms of complete conversion in some literature, the contexts differ significantly between this work and those studies. For instance, in the first referenced study, stability was tested under SO2 conditions. Typically, CO oxidation in the presence of SO2 is challenging, leading to a rapid decline in activity compared to reactions conducted without SO2. Consequently, many studies only assess the stability of CO oxidation under SO2 conditions at 100% conversion, as other catalysts tend to exhibit diminished activity under such conditions, facilitating straightforward comparisons. In the second referenced study, while the initial activity of the CeRu-3 catalyst was tested at 100% conversion, it rapidly decreased to below 100%, allowing for an assessment of the catalyst’s real stability.\n\nIn contrast, this work examines a straightforward CO oxidation process without SO2 or H2O, yet the catalyst maintains a constant 100% conversion, which indicates saturation of activity. For instance, if we assume the catalyst has the potential for 500% CO conversion under these conditions, and this capability diminishes to 200% after 150 hours, it still only demonstrates a constant apparent conversion of 100% after that time. Therefore, the authors should consider lowering the CO conversion below 100% by increasing the WHSV to better reassess the stability.\n\nThe authors have indeed lowered the CO conversion below 100% by increasing the WHSV, as per my suggestion. However, I am unclear about why they subsequently raised the temperature to maintain a 100% CO conversion. The authors should focus on evaluating long-term stability at 110 °C with the higher WHSV. Even if the CO conversion decreases slightly, this information should be reported.\n\nPublishing this work in Nature Communications with only 100% CO conversion data could mislead other researchers. It may lead them to believe that evaluating stability based solely on complete conversion is acceptable, especially since they might reference this publication as a precedent."}, "author_response": "Response to reviewers\nReviewer #2 (Remarks to the Author):\n1. I recommend that this manuscript be accepted, provided that the real stability of the\ncatalyst is assessed. Although the authors have indicated that the stability of the CO\noxidation reaction is evaluated in terms of complete conversion in some literature, the\ncontexts differ significantly between this work and those studies. For instance, in the\nfirst referenced study, stability was tested under SO conditions. Typically, CO\n2\noxidation in the presence of SO is challenging, leading to a rapid decline in activity\n2\ncompared to reactions conducted without SO . Consequently, many studies only\n2\nassess the stability of CO oxidation under SO conditions at 100% conversion, as\n2\nother catalysts tend to exhibit diminished activity under such conditions, facilitating\nstraightforward comparisons. In the second referenced study, while the initial activity\nof the CeRu-3 catalyst was tested at 100% conversion, it rapidly decreased to below\n100%, allowing for an assessment of the catalyst’s real stability.\nIn contrast, this work examines a straightforward CO oxidation process without SO\n2\nor H O, yet the catalyst maintains a constant 100% conversion, which indicates\n2\nsaturation of activity. For instance, if we assume the catalyst has the potential for\n500% CO conversion under these conditions, and this capability diminishes to 200%\nafter 150 hours, it still only demonstrates a constant apparent conversion of 100%\nafter that time. Therefore, the authors should consider lowering the CO conversion\nbelow 100% by increasing the WHSV to better reassess the stability.\nThe authors have indeed lowered the CO conversion below 100% by increasing the\nWHSV, as per my suggestion. However, I am unclear about why they subsequently\nraised the temperature to maintain a 100% CO conversion. The authors should focus\non evaluating long-term stability at 110 °C with the higher WHSV. Even if the CO\nconversion decreases slightly, this information should be reported.\nPublishing this work in Nature Communications with only 100% CO conversion data\ncould mislead other researchers. It may lead them to believe that evaluating stability\nbased solely on complete conversion is acceptable, especially since they might\nreference this publication as a precedent.\nAnswer: Many thanks for your comments. We re-evaluated the long-term stability\nassessment under high-temperature conditions of 110 °C combined with higher\nWHSV operations. Firstly, we evaluated the CO conversion rate of the catalyst at\ndifferent WHSV values by increasing the WHSV at 110 °C. As shown in Figure S21a,\nthe CO conversion rate decreased from 100% to 83.83% as the WHSV increased from\n30,000 mL g⁻¹ h⁻¹ to 60,000 mL g⁻¹ h⁻¹ at 110°C. Subsequently, in Figure S21b, the\nlong-term stability of PSC Nb₂O₅ loaded with Pt was tested for 185 hours under\nconditions of 110°C and 60,000 mL g⁻¹ h⁻¹. The PSC Nb O₅ monoliths loaded with Pt\n2\nexhibit excellent durability even though slight decrease of ~9% is observed for the\nconversion rate under high WHSV of 60,000 mL g⁻¹ h⁻¹ at 110°C.\nmonoliths with 3.35 wt% Pt at different WHSV values at 110 °C.\n2"}, {"round": 4, "reviewer_comments": {"reviewer_2": "I thank the authors for their detailed response. In my opinion, the paper can now be accepted.\nHowever, before publication, the authors should revise the statement in the abstract: “As a case study, we demonstrate the complete CO oxidation with air at 110 °C with no visible performance attenuation after a continuous operation of ~500 hours.” According to their new data, the catalyst actually shows a ~9% decrease in activity within 80 hours, rather than “no visible performance attenuation.”\nIn addition, the current abstract is clear but somewhat too short and mainly describes the experimental steps. I recommend that the authors slightly expand it by adding the sentences summarizing the main mechanistic insight or structure-activity relationship associated with the interface and oxygen vacancies."}, "author_response": "Response to reviewers\nReviewer #2 (Remarks to the Author):\nI thank the authors for their detailed response. In my opinion, the paper can now be\naccepted. However, before publication, the authors should revise the statement in the\nabstract: “As a case study, we demonstrate the complete CO oxidation with air at 110 °C\nwith no visible performance attenuation after a continuous operation of ~500 hours.”\nAccording to their new data, the catalyst actually shows a ~9% decrease in activity\nwithin 80 hours, rather than “no visible performance attenuation.” In addition, the\ncurrent abstract is clear but somewhat too short and mainly describes the experimental\nsteps. I recommend that the authors slightly expand it by adding the sentences\nsummarizing the main mechanistic insight or structure-activity relationship associated\nwith the interface and oxygen vacancies.\nAnswer: Many thanks for your comments. Based on your suggestion, the abstract has\nbeen revised. As a case study, we demonstrate the complete CO oxidation with air at\n110 °C and 30,000 mL g⁻¹ h⁻¹ conditions，with no visible performance attenuation after\na continuous operation of ~500 hours. At 60,000 mL g⁻¹ h⁻¹ and 110 °C, the CO\nconversion rate decreased from 100% to 83.83%. After 185 hours of long-term testing,\nthe conversion rate declined by 9%, ultimately reaching 76.3%. In this study, we\ncombined experimental and computational methods to validate that the CO oxidation\nreaction mechanism follows the Mars-van Krevelen mechanism."}]

Decision letter