Unleashing the power of zero-valent platinum single atoms for enhancing low-temperature oxygen activation

Domain: physics
Published: 2026-03-02
Editorial outcome: major_revision

Abstract
Developing efficient catalysts for low-temperature O2 activation is critical for energy-efficient heterogeneous catalysis, yet designing highly active and accessible active sites remains a formidable challenge. Here, we construct a new type of zero-valent platinum single atoms (Pt0 SAs) on two-dimensional Co3O4 through a feasible low-temperature reduction strategy. By eliminating oxygen coordination, we induce strong Pt−Co electronic interactions and optimize the Pt 5d band center, promoting electron donation that strengthens O2 activation. In contrast, conventional high-valent Pt4+ SAs, which rely on oxygen vacancy formation, exhibits weaker O2 activation. Consequently, Pt0 SAs achieves a 9.3-fold higher turnover frequency in toluene oxidation than does the Pt4+ SAs at 140 °C (the temperature at which a toluene conversion efficiency of 90% is achieved). This work highlights electronic modulation in optimizing O2 activation and affords a strategy for designing highly efficient zero-valent single atom catalysts.

Introduction
Thermal catalytic oxidation offers an efficient and economical strategy for eliminating toxic volatile organic compounds (VOCs)1, major pollutants that are detrimental to atmospheric quality and human health2–4. Enhancing catalyst performance at low temperatures hinges on improving the O2 activation capacity, which broadens the operational window and conserves energy5. Effective O2 activation typically requires electron-rich surface sites. While noble metal nanoparticles inherently possess zero-valent sites with good O2 activation ability6, many remain encapsulated and underutilized. Conversely, noble metal single-atom catalysts (SACs), despite their high degree of atomic utilization7,8, often feature coordinated saturation, forming electron-deficient high-valent metal centers9,10 that impede O2 activation. Therefore, the development of highly efficient and atomically economical active sites is imperative to unlock the full O2 activation potential of noble metals.

The construction of zero-valent noble metal single atoms (SAs) is a promising solution to the above issue. Recent studies have highlighted the unique advantages of zero-valent SAs in activating small molecules. For example, Yao et al. observed dynamically detached Pt SAs from a nitrogen–carbon support that exhibited near-zero-valent electronic properties during the hydrogen evolution reaction, where the high 5d electron density of Pt facilitated H2O activation11. Similarly, Lu et al. stabilized zero-valent Pd SAs on boron-doped carbon nitride. These Pd SAs can enhance metal–support orbital hybridization on the substrate through synergistic interactions with adjacent boron atoms, inducing an upward shift in the Pd 4d orbitals, which promoted electron back-donation for efficient H–H bond cleavage12. These findings demonstrate that the d-orbital electronic structure of zero-valent SAs favors reactant adsorption and activation, providing a compelling rationale for exploring the potential of zero-valent SAs in O2 activation.

Reducing the degree of oxygen coordination around the noble metal center is feasible approach to construct zero-valent SAs. Ren et al. developed a rapid heat treatment (RTT) method in an inert atmosphere to obtain highly dispersed Pt SAs on Fe2O3. By increasing the RTT temperature from 500 to 600 °C, the Pt–O coordination number was reduced, and Pt–Fe coordination occurred, lowering the Pt valence to +0.5613. Furthermore, Chen et al. fabricated zero-valent Pt SAs on the CeO2 (100) facet by coordinating Pt with two O atoms and one Ce atom, whereas positively charged Pt on the CeO2 (110) facet coordinated to four oxygen atoms14. However, the aforementioned high-temperature reduction and crystal facet regulation approaches still face challenges in terms of cost-effectiveness and practical operability.

Here, we introduce a facile low-temperature H2 reduction strategy to construct zero-valent Pt SAs. This method circumvents the issue of Pt aggregation into nanoparticles that may occur during high-temperature H2 reduction15,16. The key to our approach is the use of two-dimensional (2D) metal oxide support, which can provide abundant atomic defects17 for anchoring highly dispersed SAs18,19. Critically, the inherent unsaturated metal–oxygen coordination of this support renders lattice oxygen (Olat) more labile, facilitating removal under mild reduction conditions to prevent atomic agglomeration20. Building upon our previously developed defect-rich 2D Co3O4 support21,22, we synthesized zero-valent Pt SAs using low-temperature (180 °C) H2 reduction, substantially reducing the synthesis difficulty for zero-valent Pt SAs compared to current approaches. For comparative purposes, high-valent Pt SAs were prepared via air treatment. Comprehensive characterization and density functional theory (DFT) calculations elucidated the geometric and electronic structure of the zero-valent Pt sites. Insitu techniques and DFT further unveiled the mechanism by which zero-valent Pt SAs enhances low-temperature O2 activation and toluene (a model VOC) oxidation. These findings underscore the unique capability of the developed zero-valent Pt SAs to integrate the advantages of both Pt nanoparticles (efficient oxygen activation) and Pt SAs (high utilization efficiency).

Results
Construction and identification of zero-valent Pt SACs
The morphology of the Co3O4 support was characterized using electron microscopy. Scanning electron microscopy (SEM) (Supplementary Fig. 1a) and transmission electron microscopy (TEM) (Supplementary Fig. 1b) reveal a nanoflower-like structure composed of ultrathin nanosheets. The atomic force microscopy (AFM) image (Supplementary Fig. 1c) confirm the 2D nature of these nanosheets, with a thickness of ~2 nm. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) reveals the presence of abundant surface defects (Supplementary Fig. 1d, e) and atomic vacancies (Supplementary Fig. 1f), providing anchoring sites for Pt SA dispersion.

The Pt SA precursor (Pt–P/Co3O4) was prepared via ethanol impregnation on 2D/Co3O4, followed by air oxidation to obtain Pt–A/Co3O4 and H2 reduction to obtain Pt–H/Co3O4. The reduction process was investigated by constant-temperature H2 temperature programmed reduction (H-TPR) (Supplementary Fig. 2a). The peak observed during heating process corresponds to Pt2+ reduction23, while the peak emerging during constant-temperature process originates from the removal of ligands from the Pt(NH3)4(NO3)2 precursor, verified by a control experiment of replacing Pt precursor with Pt(NO3)2 (Supplementary Fig. 2b). The residual H2 consumption is attributed to the facilitated reduction of Co3O4, driven by the hydrogen spillover effect from the newly reduced Pt species24. For comparison, the reduction effect on the Olat of Co3O4 is quite weak (Supplementary Fig. 2c), indicating that the reduced Pt can strongly interact with Co3O4. Moreover, the optimal reduction duration was evaluated. Supplementary Fig. 3 shows that only appropriate removal of Olat can contribute to catalytic performance.

SEM (Supplementary Fig. 4) and TEM images (Supplementary Fig. 5) illustrate that Pt–A/Co3O4, Pt–H/Co3O4 and Co3O4-H retain the ultrathin nanosheet morphology of pristine Co3O4. X-ray diffraction (XRD) patterns (Supplementary Fig. 6) of all the samples match those of spinel Co3O4 (PDF#42-1467), with minor peak broadening observed in Pt–H/Co3O4 due to Olat depletion. In addition, no peak attributed to Pt nanoparticles is detected, which is due to the low Pt loading amount (approximately 0.6 wt%, as measured by inductively coupled plasma–mass spectrometry (ICP–MS)) or high Pt dispersibility. To confirm this, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of CO adsorption was performed. Peaks at approximately 2090 cm−1 for Pt–A/Co3O4 and approximately 2080 cm−1 for Pt–H/Co3O4 are observed in Fig. 1a, which correspond to the CO that adsorbed linearly on isolated Pt atoms25,26, suggesting that both samples are Pt SACs. In addition, the two different peak positions suggest different single-atom coordination27. HAADF-STEM (Fig. 1b, c) and high-resolution energy dispersive spectroscopy (EDS) mapping (Fig. 1d, e) images verify the uniform distribution of Pt SAs on the surface lattices of both Pt–A/Co3O4 and Pt–H/Co3O4. Moreover, the Pt 4f X-ray photoelectron spectroscopy (XPS) spectra (Fig. 1f) reveal Pt4+ dominance in Pt–A/Co3O4. Conversely, Pt–H/Co3O4 is dominated by Pt0, with its Pt 4f binding energy closely matching that of zero-valent Pt nanoparticles supported on Co3O4 (Supplementary Fig. 7). These results confirm the successful synthesis of high-valent and zero-valent Pt SAs (Pt4+ SA and Pt0 SA), respectively.

To elucidate the local coordination of Pt SAs, we initially attempted X-ray absorption fine structure (XAFS) spectroscopy at the Pt L3-edge. However, the intense fluorescence background from the abundant Co atoms in the Co3O4 support overwhelmingly masked the weak signal from the low-loading Pt, making the Pt signal undetectable. Consequently, we employed DFT calculations and high-resolution HAADF-STEM to resolve the Pt coordination structure. Our previous studies demonstrated that the 2D Co3O4 surface possessed abundant cobalt vacancies, including octahedral and tetrahedral vacancies (VCoOh and VCoTe) and oxygen vacancies with dicoordination (VOII) and tricoordination (VOIII)28, which served as potential anchoring sites for Pt SAs. The Co3O4 (110) facet was selected for analysis because of the distinguishable positions of octahedral Co (CoOh), tetrahedral Co (CoTe) and oxygen atoms in the HAADF-STEM images (Supplementary Fig. 8). Furthermore, DFT calculations were performed on Co3O4 (110)-A and (110)-B facets, incorporating three distinct vacancy types in each (A-VCoOh, A-VCoTe, A-VOIII, B-VCoOh, B-VOII and B-VOIII, respectively; Supplementary Fig. 9). The calculations results indicate that Pt exhibits the lowest binding energy when it occupies a Co vacancy on the (110)-B facet (B-VCoOh-Pt, Supplementary Fig. 10), forming a surface OII-Pt-OIII site. In this configuration, Pt coordinates with two surface O and two subsurface O atoms (Fig. 1g). In addition, Bader charge analysis reveals that the Pt atom in the OII-Pt-OIII site also exhibits the highest charge, which is in accordance with the high Pt valence state of Pt–A/Co3O4.

To simulate reduction treatment, O atoms near the Pt atom in the B-VCoOh-Pt model were successively removed. The energies of oxygen vacancy formation (EOVs) upon removal of one O atom from the OII-Pt-OIII site (yielding the B-VCoOh-Pt-ROII and B-VCoOh-Pt-ROIII models, respectively; Supplementary Fig. 11a, b) are lower than those for the OII-CoOh-OIII site in the Co3O4 model (Supplementary Fig. 11c, d), indicating enhanced Olat reactivity, which is consistent with the constant-temperature H2-TPR results. The Bader charge of Pt in the B-VCoOh-Pt-ROII and B-VCoOh-Pt-ROIII models are +0.81|e| and +0.80|e|, respectively, which are higher than those of the zero-valence Pt state of Pt–H/Co3O4. Further removal of two oxygen atoms (B-VCoOh-Pt-R2O, Supplementary Fig. 12a) still results in a positive Pt Bader charge (+0.40|e|). Moreover, removing one subsurface O atom connected to Pt in the B-VCoOh-Pt-R2O model can obtain the B-VCoOh-Pt-R3OU model (Supplementary Fig. 12b) and B-VCoOh-Pt-R3OD model (Supplementary Fig. 12c) with Pt Bader charge of +0.10|e| and 0|e|, respectively, among which the latter matches that of the Pt0 SA in Pt–H/Co3O4. In this configuration, Pt coordinates with one subsurface O, one subsurface CoOh, and one tertiary surface CoOh atom (Fig. 1g). The DFT-predicted Pt location and its surrounding Co atoms correspond well with the respective atoms in the high-resolution HAADF-STEM image (Fig. 1h), where the bright Pt SA signal aligns precisely with an octahedral site, as illustrated by the contrast profile (Fig. 1i). Further validation comes from the vibrational frequencies of adsorbed CO. The peaks obtained by theoretical calculation (Supplementary Fig. 13) at 2079 cm−1 (Pt4+ SA) and 2070 cm−1 (Pt0 SA) exhibit the same qualitative trend in position as observed experimentally (Fig. 1a). This consistency strongly supports the DFT-predicted coordination environment of Pt SAs. Moreover, DFT calculation (Supplementary Fig. 14) reveal that the binding energy of Pt0 SA is comparable to the Pt cohesive energy (−5.5 eV), indicating its sufficient thermodynamic stability29,30.

Catalytic performance of toluene oxidation
As shown in Fig. 2a, Pt–H/Co3O4 exhibits superior catalytic performance, with T10, T50, T90, and T100 values (corresponding to the evaluation temperatures for the conversion of toluene into CO2 (η) with efficiencies of 10%, 50%, 90%, and 100%, respectively) of 130, 136, 140 and 150 °C, respectively. In contrast, Pt–A/Co3O4 requires higher temperatures (T10 = 142 °C, T50 = 153 °C, T90 = 160 °C, and T100 = 170 °C, respectively), whereas the Co3O4 support alone demonstrates markedly inferior performance (T10 = 190 °C, T50 = 207 °C, T90 = 220 °C, and T100 = 240 °C). These results indicate that Pt0 SA sites significantly enhance the catalytic performance. In addition, Co3O4-H prepared by H2 reduction shows only a marginal improvement over pristine Co3O4 (Supplementary Fig. 15), indicating that reduction treatment alone does not substantially enhance the catalytic performance.

Furthermore, the apparent activation energy (Ea) values are calculated (Supplementary Fig. 16) and follows the order of Co3O4 (101.8 kJ/mol) > Pt–A/Co3O4 (69.3 kJ/mol) > Pt–H/Co3O4 (54.3 kJ/mol), which is consistent with their catalytic performance at low temperature. Additionally, the specific surface area normalized reaction rate (rs) at 125 °C (At this temperature, η < 10%), derived from characterization of N2 adsorption and desorption (Supplementary Fig. 17 and Supplementary Table 1), demonstrates that Pt–H/Co3O4 exhibits a 41.8-fold higher rs than does Pt–A/Co3O4 (Fig. 2b). Moreover, the turnover frequency (TOF) of Pt–H/Co3O4 is 9.3-fold higher than that of Pt–A/Co3O4 at 125 °C, underscoring the superior catalytic efficiency of Pt0 SA sites over Pt4+ SA sites.

The catalytic stability of Pt–H/Co3O4 with the optimal performance was further investigated. As shown in Fig. 2c, its toluene conversion efficiency remains at 90% after 48 h of reaction at 140 °C. Subsequently, post-reaction XPS (Supplementary Fig. 18) and HAADF-STEM (Supplementary Fig. 19) analyses also confirm that Pt0 SAs retain their zero-valent state and atomic dispersion. In addition, the T90 and T100 of Pt–H/Co3O4 remains stable during five consecutive test cycles, respectively (Supplementary Fig. 20). Moreover, Pt–H/Co3O4 also possesses remarkable moisture resistance at T100, maintaining near-complete toluene conversion into CO2 (100%, 97%, and 95%) at different relative humidity (RH) levels of 20%, 50%, and 80%, respectively (Fig. 2d). Impressively, Pt–H/Co3O4 outperforms previously reported SACs and noble metal nanoparticles supported on cobalt-based catalysts for toluene oxidation (Supplementary Table 2 and Table 3), demonstrating its exceptional catalytic performance at low temperature.

Electronic metal–support interaction (EMSI) and local atomic structure
Investigating the EMSI and local atomic structure of active sites is critical for understanding the electronic and geometric configurations that underpin the enhanced catalytic performance upon Pt SA loading. X-ray absorption near-edge structure (XANES) spectra of the Co K-edge were obtained to probe the modulation of the electronic Co structure caused by loading Pt SAs. Figure 3a reveals that the near-edge absorption thresholds adhere to the trend of Co3O4 > Pt–A/Co3O4 > Co3O4-H > Pt–H/Co3O4. A lower absorption threshold implies a reduced valence state31, indicating that both Pt SA loading and H2 reduction can decrease the Co valence state. This finding is corroborated by XPS result (all data have been corrected by C 1s spectra, Supplementary Fig. 21), where deconvolution of Co 2p XPS spectra (Fig. 3b) into the Co3+ and Co2+ components revealed a Co3+/Co2+ ratio consistent with the trend in the XANES data (Supplementary Table 4). For Co3O4-H, the reduction in Co valence derives from the H2 reduction of surface Co3+. For Pt SACs, the decrease in Co valence likely arises from the EMSI between the Pt SAs and Co3O4. To verify this inference, the B-VOIII-Pt, B-VCoOh-Pt-R3OD, and B-VOIII models are applied to represent Pt–A/Co3O4, Pt–H/Co3O4, and Co3O4, respectively. The charge density difference (Fig. 3c) suggests that both types of Pt SAs cause local electron rearrangement of the coordinated atoms. For Pt0 SA, local electrons are enriched between the Pt atom and the coordinated Co atoms in subsurface and tertiary layers, whereas Pt4+ SA exhibit electron depletion near Pt and electron enrichment around the coordinated oxygen.

Bader charge analysis of the surface and subsurface Co atoms of the B-VOIII-Pt, B-VCoOh-Pt-R3OD, and B-VOIII models (Supplementary Fig. 22) indicates that Pt loading and H2 reduction result mainly in a decrease in the average valence of the subsurface Co atoms, whereas the average valences of Co atoms on the Pt–H/Co3O4 and Pt–A/Co3O4 surfaces increase (Fig. 3d). In general, an increase in the valence of surface CoOh is conducive to the chemical adsorption of toluene32, implicating that loading Pt SA can facilitate this process. Projected density of electronic states (DOS) analysis further reveals the EMSI effects. Figure 3e reveals that the d band center of the 5d orbital of Pt0 SA is closer to the Fermi level than that of Pt4+ SA, which is consistent with the lower Pt valence state in Pt–H/Co3O4 relative to Pt–A/Co3O433. In addition, both Pt–H/Co3O4 and Pt–A/Co3O4 have obvious d-orbital occupation near the Fermi level, signifying a strong EMSI between the Pt SAs and Co3O411. Furthermore, the 3d orbital of the two coordinated Co atoms strongly hybridizes with the 5d orbital of the Pt0 SA, but the overlap with the 2p orbital of the coordinated O atom is weaker (Supplementary Fig. 23a). In addition, the d band center of these two coordinated Co atoms is reduced in contrast with that of Co3O4 (Supplementary Fig. 23b), proving that the abundant electrons around Pt are derived from the Pt–Co interaction (formation of Pt–Co bond) after the removal of partially coordinated oxygen atoms34.

Extended X-ray absorption fine structure (EXAFS) was utilized to identify the variation in Co coordination. The peaks located at 1.47, 2.45, and 3.00 Å in the Fourier transform (FT) Co K-edge k3χ spectra (Fig. 3f) are attributed to Co–O coordination, octahedral Co3+–Co3+ coordination (CoOh–CoOh) and tetrahedral Co2+–Co coordination (CoTe–Co, including CoTe–CoTe and CoTe–CoOh), respectively35. The fitting results (Supplementary Fig. 24 and Supplementary Table 5) indicate that the Co–O, CoOh–CoOh, and CoTe–Co coordination of Pt–A/Co3O4 decreased slightly compared with that of Co3O4, suggesting that the Pt4+ SA leads to a small increase in lattice disorder and oxygen vacancy, which is consistent with the reduced Ea of the OII-Pt-OIII site relative to that of the OII-CoOh-OIII site. In Co3O4-H, the pronounced decrease in Co–O coordination is due to the removal of coordinated oxygen atoms via H2 reduction. Moreover, the Co−O distance increases and the attenuation of CoTe–Co coordination is greater than that of CoTe–CoTe, implying preferential oxygen removal from CoOh–O sites. Notably, Pt–H/Co3O4 has the lowest Co–O, CoOh–CoOh and CoTe–Co coordination, which is consistent with highly active Olat that facilitates extensive oxygen vacancy formation and induces pronounced surface lattice disorder during H2 reduction36. This substantial reduction in Co coordination in Pt–H/Co3O4 provides a structural foundation for the formation of Pt–Co bonds. Furthermore, the HAADF-STEM images (Supplementary Fig. 25) directly visualize the lattice-disordered structures surrounding the Pt SAs in both Pt–A/Co3O4 and Pt–H/Co3O4. Wavelet transform analysis of the Co K-edge (Supplementary Fig. 26) also provides atomic-scale insight, revealing a systematic decrease in Co-Co and Co–O coordination signal intensity in the order of Co3O4 > Pt–A/Co3O4 > Co3O4-H > Pt–H/Co3O4, which is consistent with the FT-EXAFS results. Collectively, these findings may indirectly suggest that Pt0 SA in Pt–H/Co3O4 possesses less oxygen coordination.

Oxygen activation mechanism
Both the characterization and DFT calculations reveal that the Pt0 SA site in Pt–H/Co3O4 exhibits optimal O2 activation potential. To verify this, the O 1s XPS spectra was acquired at room temperature, and the peaks could be deconvolved into two components (Supplementary Fig. 27), assigned to Olat and surface-absorbed reactive oxygen species (Oads)37. The Oads/Olat value of Pt–H/Co3O4 follows the trend of Co3O4 < Pt–A/Co3O4 < Co3O4-H < Pt–H/Co3O4 (Supplementary Table 4). Co3O4-H benefits from H-induced oxygen vacancies to promote O2 activation, whereas Pt–A/Co3O4 with Pt4+ SAs and marginally increased the surface oxygen vacancies exhibits weaker enhancement of O2 activation. In contrast, Pt–H/Co3O4, featuring a Pt0 SA demonstrate the highest level of reactive oxygen species (ROS) generation. Further insights were obtained via H-TPR (Supplementary Fig. 28). For Co3O4, the reduction peaks at 220–320 and 320–500 °C correspond to Co3+−O and Co2+−O reduction, respectively. Upon Pt SA loading, these peaks shift to lower temperatures, indicating enhanced O reactivity. In addition, a new reduction peak (100–250 °C) emerges only for Pt–H/Co3O4 and is attributed to surface ROS reduction38,39. Similarly, O2 temperature-programmed desorption (O-TPD) spectra (Supplementary Fig. 29) reveals the O2 adsorption capabilities of Pt–A/Co3O4 and Pt–H/Co3O4. The peak in the range of 120–200 °C corresponds to the desorption of surface Oads, while the peak around 200–450 °C is assigned to the desorption of surface Olat40. Notably, the intensity of the surface Oads peak for Pt–H/Co3O4 is significantly stronger, suggesting its superior O2 activation capability. Electron paramagnetic resonance (EPR) analysis using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) trapping under O2-saturated conditions (Fig. 4a) further confirms that the strongest superoxide/peroxide signal intensity for Pt–H/Co3O4. While DMPO-EPR cannot distinguish superoxide from peroxide41, subsequent DFT calculations would address this issue.

To elucidate the effect of low-temperature elevation (spanning the T10, T50 and T90 of Pt SACs) on O2 activation, quasi-in situ XPS characterization was performed in an O2 atmosphere. Both Pt–A/Co3O4 (Fig. 4b) and Pt–H/Co3O4 (Fig. 4c) display increasing Oads/Olat ratios with elevating temperature, with the ratio for Pt–H/Co3O4 being consistently higher at each temperature point (Supplementary Fig. 30), confirming its stronger O2 activation capability. Notably, the Olat peak shifts to a higher binding energy for both catalysts, indicating electron depletion around the Olat and the weakened electronic interaction between Co and the O atom, which demonstrates the Olat activation during the heating process42. Based on the preceding analysis, the O2 activation in Pt–H/Co3O4, stems from its highest degree of lattice disorder (Fig. 3f), whereas in Pt–A/Co3O4, it arises from the enhanced reactivity of the O-Pt4+–O site compared to the O-CoOh–O site (Supplementary Fig. 11). Given that the weak O2 activation ability of isolated Pt4+ SA site alone cannot explain the markedly enhanced low-temperature activity of Pt–A/Co3O4 over Co3O4, it is proposed that the actual O2 activation site in Pt–A/Co3O4 is oxygen vacancies (PtOh–OV) associated with Pt4+ SAs, which formed by the removal of activated Olat from O-Pt4+–O site and exhibit stronger O2 activation capacity than those oxygen vacancies near Co atoms (CoOh–OV). This hypothesis is further supported by subsequent DFT calculations.

O2 adsorption was modeled on B-VCoOh-Pt, B-VCoOh-Pt-ROII, B-VCoOh-Pt-R3OD, and B-OV models, simulating O2 adsorption on Pt4+ SA, PtOh–OV, Pt0 SA, and CoOh–OV sites, respectively. Charge density difference analysis (Fig. 4d–f and Supplementary Fig. 31) reveals electron transfer from all surfaces to the adsorbed O2, confirming its activation. The calculated O2 adsorption energy (Eads, O2) values follow the order of Pt4+ SA (−0.9 eV) < CoOh–OV (−1.2 eV) < PtOh–OV (−1.5 eV) < Pt0 SA (−3.1 eV), with corresponding O=O bond lengths (LO=O) of 1.33, 1.37, 1.39 and 1.45 Å, respectively. Thus, O2 is activated as a superoxide on the oxygen vacancy and Pt4+ SA and as a peroxide on the Pt0 SA43. Pt0 SA exhibits the strongest O2 activation capability, as evidenced by its largest Eads, O2 and longest O=O bond length. Based on the above analysis, the CoOh–OV, PtOh–OV, and Pt0 SA serve as the O2 activation sites for Co3O4, Pt–A/Co3O4, and Pt–H/Co3O4, respectively. The electron localization function (ELF) is applied to resolve the differences in the geometric and electronic properties of activated O2 at different active sites, where the electron localization also follow the order of Pt4+ SA < CoOh–OV < PtOh–OV < Pt0 SA, indicating that the Pt0 SA possesses the highest covalent character upon its interaction with absorbed O2. As shown in Fig. 4g, Pt–H/Co3O4 has an upshifted d band center relative to that of Pt–A/Co3O4, which facilitates easier delocalization of Pt electrons into antibonding orbitals during O2 adsorption, strengthening the interaction of the O2pπ* band of O2 for activation44. Consequently, the O2 chemisorbed on the Pt0 SA exhibits strengthened overlap between the 2p orbital of O2 and the 5d orbital of Pt than does PtOh–OV. This overlap shifts closer to the Fermi level for Pt0 SA (Fig. 4h), further evidencing its enhanced O2 activation45,46. Additionally, analysis of the Pt 5d orbitals before and after O2 adsorption reveals significant electron loss in the dxy, dyz, and dxz orbitals of the Pt0 SA (Supplementary Fig. 32), which spatially align with the 2pπ* orbital of O2. Subsequent DFT calculations (Supplementary Fig. 33) revealed that the dissociation process for O2 adsorbed on Pt0 SA site is thermodynamically more favorable, exhibiting an energy barrier 0.4 eV lower than that at the PtOh–OV SA site. This further demonstrates the superior O2 activation capability of Pt0 SA sites.

Catalytic mechanism of toluene oxidation
On the basis of the above analysis, loading Pt SA on 2D Co3O4 surface and reducing the valence state of Pt can enhance O2 activation to greatly promote catalytic performance at low temperatures. To elucidate the origin of this enhancement, we investigated the toluene transformation pathways of Pt–A/Co3O4, Pt–H/Co3O4, and Co3O4 using in situ DRIFTS at T10, T50, and T90 (Fig. 5a–c). For Co3O4, the key peaks include benzyl alcohol stretching vibrations (1000–1200 cm−1)47; the C–O (1300 cm−1) and C=O (1250 cm−1) stretching vibrations of maleic anhydride species48; the stretching vibrations of the aromatic ring skeleton (1520 and 1598 cm−1)49,50; the asymmetric (1410 cm−1) and symmetric (1550 cm−1) vibrations of benzoate51; and the C=O stretching vibrations of benzaldehyde (1473, 1489 and 1652 cm−1)52. The accumulation of these intermediates begins at T10 but slows at T50 and T90, indicating accelerated consumption at higher temperatures. The Pt SACs exhibit similar trends but display three additional peaks: a second stretching vibration of the aromatic ring skeleton (1489 cm−1)53, suggesting altered toluene adsorption at Pt sites; the C−O stretching vibration of phenolate (1215 cm−1)54; and the C=O stretching vibration of benzoquinone (1705 cm⁻¹)55. These observations indicate that Pt SAs modify toluene adsorption and intermediate formation. Analysis of the reaction tailgas by thermal desorption-gas chromatography-mass spectrometry (TD-GC/MS) at T10, T50, and T90 (Supplementary Fig. 34) reveals trace amounts of gaseous intermediates (acetaldehyde, acetic acid, ethanol, acetone, ethyl acetate, and benzene) alongside toluene. Less intense gaseous intermediate signals are observed with the Pt SACs compared with Co3O4, indicating accelerated intermediate depletion and minimal atmospheric release, and the strongest benzene signal from Co3O4 also suggests a different ring-opening pathway for benzoic acid compared to Pt SACs.

Subsequently, toluene adsorption was investigated to explore the possibility that its altered adsorption could lead to an adjustment of the reaction pathway. In toluene TPD-MS characterization, the toluene signal between 60–220 °C corresponds to the physical adsorption of toluene (Fig. 5d) and the CO2 signal appearing between 200 and 450 °C arises from the reaction of chemically adsorbed toluene with surface Olat (Fig. 5e)56,57. Notably, the toluene adsorption capacity is significantly enhanced after Pt SA loading, among which Pt–H/Co3O4 exhibits the largest chemisorption amount. Further, in situ DRIFTS spectra (Supplementary Fig. 35) indicate that both Pt–A/Co3O4 and Pt–H/Co3O4 exhibit new vibrations of the aromatic ring skeleton and phenol compared with Co3O4, indicating that the toluene adsorption configuration still changes with no coexisting O2. DFT calculations (Supplementary Fig. 36) demonstrate the increased toluene adsorption energy (Eads, T) on the Pt SACs, with the aromatic ring positioned closer to the CoOh sites. This geometry is more likely to facilitate the interaction of methyl H and ring H atoms with Pt SA-activated ROS. In contrast, the toluene methyl groups adsorb may farther from the ROS on bare Co3O4, leading to the reaction path change upon Pt SA loading.

Kinetic analysis was conducted to further elucidate the toluene oxidation mechanism (Supplementary Fig. 37). The experimental data were fitted using kinetic models corresponding to the Langmuir–Hinshelwood (L–H), Eley–Rideal (E–R), and Mars-van Krevelen (MvK) mechanisms (Supplementary Table 6). The results indicate that the apparent reaction order for toluene is negative, which is inconsistent with both E–R and MvK models, while the L–H model provides a good fit fitting degree, indicating that the L–H mechanism is dominant at low reaction temperatures. Complementary insights were obtained from toluene temperature programmed surface reaction (TPSR) with 18O labeling (Supplementary Fig. 38) over Pt–H/Co3O4. Below 160 °C, signals corresponding to C16O18O and C18O2 are detected, consistent with the complete toluene oxidation by activated O2. The emergence of C16O18O likely originates from isotopic exchange effect58,59, instead of direct oxidation by Olat, as C16O2—which arises from oxidation by activated Olat—is only observed above 160 °C. Together, these results demonstrate that toluene oxidation at low temperatures proceeds predominantly via the L–H mechanism, with ROS derived primarily from O2 activation.

Based on the above findings, DFT calculations were performed to investigate the relative energy variation during toluene oxidation over Pt–H/Co3O4 and Co3O4, aiming to demonstrate that this novel toluene conversion pathway occurring on Pt–H/Co3O4 is more conducive to enhancing catalytic activity. As shown in Fig. 5f, the oxidation pathway from toluene to benzoic acid proceeds via identical intermediates (benzyl alcohol and benzaldehyde) on both Co3O4 and Pt–H/Co3O4. Thereafter, the reaction pathways diverge markedly. For Pt–H/Co3O4, the transformation proceeds sequentially through salicylic acid, phenol, hydroquinone, p-benzoquinone, maleic acid, and finally maleic anhydride (Supplementary Figs. 39 and 40). In contrast, the pathway on Co3O4 involves benzene, cyclohexadienone, 1-butynal, and cis-1,4-butenedial before yielding maleic anhydride (Supplementary Figs. 41 and 42). Maleic anhydride is then oxidized to small VOCs and ultimately mineralized into CO2 and H2O. Figure 5g illustrates that, compared to Co3O4, the distinct reaction route on Pt–H/Co3O4 reduces the relative energy by 2.1 eV for the methyl oxidation process (toluene to benzoic acid, steps 1–6) and by an additional 1.3 eV for the subsequent ring-opening process (benzoic acid to maleic anhydride, steps 6–21). Therefore, the intermediate conversion on Pt–H/Co3O4 is more exothermic, thereby underpinning its superior low-temperature catalytic performance.

Methods
Catalyst preparation
Co3O4 was synthesized by a solvothermal method. First, 24 mL of ethanol, 84 mL of ethylene glycol, and 14 mL of deionized H2O were mixed. Then, 1.16 g of Co(NO3)2·6H2O was dissolved in the mixed solution, followed by the addition of 0.42 g of hexamethylenetetramine (HMT) and 0.6 g of polyvinylpyrrolidone (PVP) K30. The resulting mixture was subsequently stirred for 30 min and transferred into a Teflon-lined stainless steel autoclave to react at 180 °C for 18 h. Finally, the obtained material was washed and dried at 100 °C to obtain the precursor, which was calcined in air at 300 °C for 3 h and then in N2 at 300 °C for an additional 3 h.

Pt SACs supported by Co3O4 were prepared by a low-temperature H2 reduction strategy. First, 0.3 g of 2D Co3O4 was dispersed into 20 mL of ethanol by stirring for 10 min. Meanwhile, an aqueous solution of Pt(NH3)4(NO3)2 (1.25 mg/mL) was added to 10 mL of ethanol. This mixture was then rapidly added to the Co3O4 dispersion system and stirred vigorously for 2 h, followed by aging for 2 h. Finally, the precursor reaction system was dried at 60 °C to obtain the precursor of the Pt SACs (named Pt–P/Co3O4). Pt SACs containing oxidized Pt (named Pt–A/Co3O4) were synthesized by calcining Pt–P/Co3O4 in air at 250 °C for 2 h. Whereas, Pt SACs containing reduced Pt (named Pt–H/Co3O4) were obtained by multiple gas treatments. Specifically, Pt–P/Co3O4 was first purged by Helium flow for 15 min and then treated with 5% H2/Ar flow at 180 °C for 60 min. Finally, the sample was treated with 1% O2/Ar flow at 250 °C for 30 min. To evaluate the effect of H2 reduction on Co3O4, H2 reduction of Co3O4 was performed under the same conditions as those used for Pt–H/Co3O4, and the resulting sample was named Co3O4-H.

Catalyst characterizations
XRD was conducted using an X’Pert Pro powder diffractometer (PANalytical Corp., Netherlands), and Raman spectroscopy was performed using an inVia confocal Raman microscope (Renishaw, UK). ICP–MS was conducted on an Agilent 725 (Agilent, USA). SEM was conducted using a MIRA microscope (TESCAN, Czech Republic) equipped with a Quantax EDS (Bruker, USA), and AFM was performed using a MultiMode 8-HR (Bruker, Germany). TEM was conducted using a JEM-2100F transmission electron microscope (JEOL, Japan), and N2 adsorption and desorption studies were conducted using an ASAP 2460 N2-adsorption apparatus (Micromeritics, Norcross, GA, USA). Aberration-corrected STEM was performed in the HAADF mode using a JEM-ARM200F microscope (JEOL), and XPS was performed using an Escalab Xi+ spectrometer (Thermo Fisher Scientific, USA). XAFS spectrum was collected at the 4B9A beamline in the Beijing Synchrotron Radiation Facility. EPR was conducted using a ELEXSYS E500 spectrometer (Bruker, Germany). H2-TPR was performed using a PCA-1200 (Biaode, China). O2-TPD was conducted on an AutoChem II 2950HP (Micromeritics, USA). Toluene TPSR with 18O isotopic labeling and Toluene TPD was tested on a chemisorption analyzer (Belcat II, Japan) with mass spectrometer (Belmass II, Japan). In situ DRIFTS was performed using a VERTEX 70 FT-IR spectrometer (Bruker, Germany). TD-GC/MS was performed using a 7890B GC-5977B MSD (Agilent, USA).

Catalytic performance evaluation
The activity of catalytic oxidation of toluene was evaluated in a fixed-bed reactor, which was composed of two identical stainless-steel tubes with 6-mm diameter, one with quartz wool placed in the middle as a test tube to support the catalyst, and the other as a bypass tube to regulate the reactant gas. Both stainless steel tubes were mounted in a programmed heating furnace. During the dynamic test, 100 ppm of toluene with a total gas flow of 100 mL min−1 was obtained by diluting toluene standard gas with air (relative humidity is adjustable) and passed into the bypass tube at 120 °C. After that, the gas flow was switched to the test tube to pass through 0.1 g of 40–60 mesh catalyst with a gaseous hourly space velocity (GHSV) of 60,000 h−1. Detailed calculation methods for conversion efficiency (η), Ea, rs, TOF and reaction order are provided in the Supplementary Information Appendix.

Theoretical calculations
Detailed information regarding DFT calculations is given in the Supplementary Information Appendix.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This manuscript, “Unleashing the power of zero-valent platinum single atoms for enhancing low-temperature oxygen activation,” reports the synthesis of zero-valent Pt single atoms (Pt⁰ SAs) on Co₃O₄ and their superior activity in toluene oxidation. The topic is of potential relevance to single-atom catalysis and oxygen activation chemistry. However, the central claim—that isolated zero-valent Pt atoms are stable and catalytically active under oxidative reaction conditions—is not convincingly supported by the presented data. Several critical pieces of experimental evidence are missing or internally inconsistent. Therefore, I cannot recommend this manuscript for publication in its current form.\n1. The authors claim to have obtained atomically dispersed Pt⁰ species, yet no Pt L₃-edge EXAFS data are provided. Only Co K-edge EXAFS results are shown (Supplementary Fig. 19 and Table 5), which merely reflect the local coordination of the Co₃O₄ support.Pt L₃-edge EXAFS is essential to verify the absence of Pt–Pt scattering and to quantify Pt–O coordination. Without such data, the claim of “zero-valent Pt single atoms” remains speculative. The authors even acknowledge that the Pt-edge signal was too weak to detect, which further undermines their structural assignment.\n2. The catalytic reaction studied—oxidation of toluene to CO₂ in air—is highly oxidative. Under these conditions, zero-valent Pt atoms are expected to oxidize rapidly to Pt²⁺/Pt⁴⁺ or sinter into metallic nanoparticles.The authors assert that Pt⁰ species remain stable after 48 h based on XPS (Supplementary Fig. S16). However, XPS cannot distinguish single atoms from metallic clusters, and the Pt⁰ signal may well originate from aggregated Pt nanoparticles formed during reaction. No post-reaction HAADF-STEM or Pt-edge EXAFS data are provided to confirm atomic dispersion after catalysis.\n3. According to the authors’ own DFT calculations (Supplementary Fig. S9), the zero-valent Pt configuration exhibits relatively low binding energy and poor thermodynamic stability on the Co₃O₄ surface. This theoretical finding contradicts the experimental claim that Pt⁰ SAs are stably anchored and remain intact after long-term oxidation. The discrepancy is neither discussed nor rationalized.\n4. The authors use Bader charge and DOS analyses to differentiate Pt valence states. Although the results qualitatively indicate a lower oxidation state for Pt in Pt-H/Co3O4 than in Pt-A/Co3O4, the quantitative evidence is insufficient to justify the assignment of oxidation states (Pt4+ vs. Pt0). Therefore, explicit use of these experimental-determined valence in the theoretical discussion (e.g., in Fig. 4 and Supplementary Figs. 12 and 26) should be avoided. Furthermore, only an upward shift of the d-band center is not sufficient proof of metallic character—it merely reflects a reduction in the effective oxidation state of the Pt center.\n5. I am skeptical about the reported differences in O₂ adsorption energies at various sites (Fig. 4). From Pt4+ to Pt0, the O–O bond length increases by only 0.12 Å, yet the adsorption energy decreases by as much as 2.2 eV. It is questionable whether O₂ activation would exhibit such a steep potential energy surface. Suggest the author to perform transition state calculations to simulate the complete potential energy surface, rather than relying solely on static adsorption comparisons.\n6. This manuscript proposes a new \"benzene ring opening pathway\", but does not provide the reaction energy or potential barrier diagram. The author should at least perform DFT calculations on some key steps to facilitate a thermodynamic comparison between the proposed approach and traditional approaches.\n7. There are some formatting issues in the article, such as the abbreviation of ROS not being given its full name when it first appears, and the full name of TOF should be Turnover Frequency instead of Turnover Rate", "reviewer_2": "In this study, the authors constructed a zero-valent Pt single-atom catalyst anchored on 2D Co3O4 via a simple low-temperature reduction strategy, which demonstrated promising performance in catalytic oxidation of toluene. Moreover, the work comprehensively employed multiple characterization techniques and theoretical calculations to elucidate the geometric/electronic structure of the zero-valent Pt single atoms and the mechanism by which they enhance O2 activation. This research provides a new strategy for designing efficient zero-valent single-atom catalysts and offers valuable insights into the role of electronic modulation in catalytic oxidation. I believe the manuscript can be accepted after addressing the following issues:\n1. The specific surface area-normalized reaction rate (rₛ) should also be calculated at reaction temperatures with conversion efficiencies below 10%.\n2. It is recommended to rename the oxygen and toluene adsorption energies as Eads, O2 and Eads, T, respectively, to avoid confusion.\n3. The caption of Supplementary Fig. 7 is incorrect. Furthermore, please clarify how the positions of octahedral Co (CoOh), tetrahedral Co (CoTe), and oxygen atoms are distinguished in the HAADF-STEM image.\n4. The yellow and purple circles in Supplementary Fig. 20 lack corresponding annotations.\n5. The labeling of intermediate species in Supplementary Fig. 29 is incomplete; please supplement it accordingly.", "reviewer_3": "This work successfully constructed a zerovalent platinum single-atom catalyst (Pt0 SAs) on two-dimensional Co3O4 through an innovative low-temperature H2 reduction strategy, overcoming the electronic limitations of traditional high-valent single-atom catalysts in O2 activation. The study systematically reveals that the Pt0 sites enhance electron transfer capability by optimizing the d-band center, significantly improving the low-temperature toluene oxidation performance, thus providing valuable insights for the valence state regulation of single-atom catalysts. The experimental design is rigorous, combining in-situ characterization and theoretical calculations, demonstrating strong innovation and application potential. However, the data analysis in some parts of the manuscript has room for improvement, and the validation of certain viewpoints overly relies on theoretical simulations, lacking reliable experimental evidence. Therefore, based on the high standards of Nature Communications, it is recommended that the authors undertake a major revision before further consideration for publication.\n1. The authors devote considerable length in the initial sections to discussing the catalyst synthesis process, which is crucial to the zerovalent single-atom structure they emphasize. However, all related data are presented in the Supporting Information. It is recommended to optimize the figure composition appropriately by moving some key data to the main text.\n2. The full XPS survey scan and the C 1s spectrum used for calibration must be provided. To better confirm the valence state information, it is advised to supplement the data with a reference sample of metallic Pt particles formed after over-reduction.\n3. The caption for Figure S7 is incorrect, as it is not XRD data.\n4. The authors propose that O atoms around Pt are removed during the H2 treatment. Was the H2 consumption calculated to provide quantitative or semi-quantitative support for this inference?\n5. The Pt structure is the core claim of the work but lacks sufficient experimental evidence. Generally, at this loading level, the Pt EXAFS information should be obtainable. It is recommended to re-attempt obtaining the Pt coordination structure information. Alternatively, provide atomic-resolution image intensity analysis to substantiate how the precise structural information in Figure 1g was determined.\n6. The authors explored O activation capability via quasi-in-situ XPS, stating that the Pt-H catalyst has stronger activation ability. However, in my opinion, the trend shown in the S24 data does not strongly support this claim. Furthermore, using the shift of the lattice oxygen signal to prove surface electronic information is not convincingly demonstrated in the figures, and this part of the discussion needs refinement. Similarly, all spectra should be presented with their corresponding C 1s calibration spectra, as XPS data analysis can be highly subjective.\n7. Multiple rounds of catalytic testing are needed to verify the stability of the catalytic structure. Additionally, long-term stability tests should be conducted at conversion levels below the thermodynamic equilibrium conversion. The data in Fig. 2c, nearing 100% conversion, cannot convincingly demonstrate structural stability. Moreover, the final data point indicates noticeable deactivation behavior.\n8. Attributing the enhanced Raman signal intensity in S25 to lattice oxygen activation is unsubstantiated and lacks rigor. Raman signal intensity is difficult to interpret directly, as it is strongly influenced by and often coincidental due to laser focusing on the solid sample surface. The authors should analyze the Raman results cautiously, and the discussion must be supported by reliable literature evidence.\n9. Oxygen storage capacity measurement experiments should be supplemented to differentiate the oxygen adsorption capabilities of the two catalysts.\n10. Relevant kinetic experiments, such as determining reaction orders and performing 18O isotope tracing, should be added.\n11. The IR spectra presented in Fig. 5 are overly cluttered, making effective comparison of differences difficult. It is recommended to optimize the presentation to clearly highlight the key distinctions between the different samples.\n12. The current mechanism discussion fails to clearly identify the rate-determining step in the overall pathway. According to TCD results, the Pt-A catalyst exhibits a stronger toluene adsorption capacity, which the authors posit is the core reason for the enhanced performance over Co3O4. However, the main catalyst itself shows weak adsorption capacity. The reasons for this should be analyzed.\n13. The discussion of the mechanism is unclear. The respective roles and functions of Ov (oxygen vacancies), Co3O4, and Pt sites are not explicitly discussed.\n14. The core concept of this manuscript proposes \"zerovalent platinum single atoms\" to address the electronic deficiency of high-valent SAs in O2 activation. However, the introduction section needs to strengthen the discussion regarding the unique advantages of \"zerovalent SAs\" and how this work distinguishes itself from existing research."}, "author_response": "Response to Reviewers’ Comments\nManuscript number: NCOMMS-25-77796\nTitle: Unleashing the power of zero-valent platinum single atoms for enhancing low-temperature oxygen activation\nResponse to reviewer 1\nComments: This manuscript, “Unleashing the power of zero-valent platinum single atoms for enhancing low-temperature oxygen activation,” reports the synthesis of zero-valent Pt single atoms (Pt0 SAs) on Co O and their superior activity in toluene oxidation. The topic is of potential relevance to single-atom catalysis and oxygen activation chemistry. However, the central claim—that isolated zero-valent Pt atoms are stable and catalytically active under oxidative reaction conditions—is not convincingly supported by the presented data. Several critical pieces of experimental evidence are missing or internally inconsistent. Therefore, I cannot recommend this manuscript for publication in its current form.\nResponse: We sincerely thank you for your time and effort in evaluating our manuscript and for providing constructive comments. We acknowledge the concerns raised regarding the microstructure and stability of zero-valent Pt single atoms. Based on these valuable suggestions, we have performed additional experimental characterizations and theoretical calculations to address the identified issues. We hope that our detailed responses and revisions will be satisfactory.\n1. The authors claim to have obtained atomically dispersed Pt0 species, yet no Pt L -edge EXAFS data are provided. Only Co K-edge EXAFS results are shown (Supplementary Fig. 19 and Table 5), which merely reflect the local coordination of the Co O support. Pt L₃-edge EXAFS is essential to verify the absence of Pt–Pt scattering and to quantify Pt–O coordination. Without such data, the claim of “zero-valent Pt single atoms” remains speculative. The authors even acknowledge that the Pt-edge signal was too weak to detect, which further undermines their structural assignment.\nResponse: Thanks for your critical and insightful comment. We fully agree that Pt L -edge EXAFS would be the most direct technique to verify the local coordination environment of Pt species. However, we acknowledge the inherent technical challenge in acquiring Pt L -edge EXAFS data for our specific system. The intense fluorescence background from the abundant Co atoms (73.4 wt.%) in the Co O support overwhelmingly masks the weak signal from the low-loading Pt (0.6 wt.%), making it difficult to extract usable EXAFS result for reliable fitting even after optimizing measurement parameters, despite multiple attempts at different synchrotron facilities, such as Beijing Synchrotron Radiation Facility (BSRF), Hefei Light Source (HLS), and most recently Shanghai Synchrotron Radiation facility (SSRF, The testing process is shown in the Fig. R1).\nFig. R1 | The XAFS testing of the sample at SSRF.\nTo address this limitation, we have made a comprehensive set of complementary characterizations and theoretical calculations to address this point rigorously in the absence of direct EXAFS data. HAADF-STEM (Fig. 1g, h) confirms the presence of isolated Pt atoms on the Co O support for both Pt-H/Co O and Pt-A/Co O samples, ruling out Pt clusters. The in situ DRIFTS spectra of CO adsorption (Fig. 1a) reveal distinct linear adsorption peaks, confirming that Pt species in both samples exist as single atoms (SAs) with different coordination structures. In addition, XPS analysis (Fig. 1f) indicates that Pt in Pt-H/Co O and Pt-A/Co O exhibits predominantly zero-valent and +4 oxidation states, respectively—a direct consequence of their distinct SA coordination environments. Considering that Pt-A/Co O is prepared under oxidative conditions, whereas Pt-H/Co O is obtained via 5% H reduction followed by treatment in 1% O , we infer that the Pt SAs in Pt-A/Co O likely possess high O atom coordination, while those in Pt-H/Co O may be coordinated by fewer O atoms along with Co atoms from the support.\nGuided by these combined characterization results, we performed DFT calculations to model the plausible coordination structures of the two types of single atoms. Based on the analysis of Pt binding energies and Bader charges analysis, a Pt4+ SA configuration could be reasonably represented by a Pt atom coordinated with four O atoms, whereas a Pt0 SA model was best described by a Pt atom coordinated with one O atom and two Co atoms (Fig. 1g). In addition, the DFT-optimized Pt0 SA is located at the Co site of the Co O Oh support, which aligns well with the atomic positions observed in the high-magnification HAADF-STEM image (Fig. 1h, i). Furthermore, we simulated the CO adsorption infrared spectra (Supplementary Fig. 12) based on these two structural models. The simulated peak positions show good agreement with the in situ DRIFTS spectra of CO adsorption data, providing strong theoretical validation for the proposed coordination environments. These results validate the reasonableness of the DFT calculations.\nFig. 1 | Construction of zero-valent Pt SACs. a, In situ CO DRIFTS of Pt-A/Co O and Pt-H/Co O . b, c, HAADF-STEM images of Pt-A/Co O (b) and Pt-H/Co O (c). d, e, EDS mapping images of Pt-A/Co O (d) and Pt-H/Co O (e). f, Pt 4f XPS spectra of Pt-A/Co O and Pt-H/Co O . g, Local coordination structure of Pt4+ SA and Pt0 SA. h, HAADF-STEM image of a Pt0 SA on the Co O (110) facet in Pt-H/Co O . The inset shows the DFT-calculated location of the Pt⁰ SA. Pt0 SA is marked by an orange circle, and the surrounding Co atoms are indicated by blue hexagons. i, Line profile of the Pt0 SA.\nSupplementary Fig. 13 | DFT-calculated IR spectra of CO adsorbed on Pt4+ SA site and Pt0 SA site.\nMoreover, our proposed coordination for Pt0 SA aligns with reports of low-valent Pt SAs from Zhang Tao's group. For instance, in the Fe O -supported Pt SA system, EXAFS fitting indicates a coordination number of 1.8 for Pt-O and 0.8 for Pt-Fe, with a corresponding Pt valence state of +0.56 (Nat. Commun. 2019, 10, 4500); in the CeO -supported Pt SA system, Pt coordinated with two O atoms and one Ce atom exhibited a zero-valent state, whereas Pt coordinated with four O atoms showed a +4 state (J. Catal. 2022, 415, 174).\nBased on the comprehensive analysis above, while the coordination structure of Pt0 SA in Pt-H/Co O cannot be directly determined from EXAFS alone, we integrate evidence from HAADF-STEM, in situ DRIFTS of CO adsorption, XPS, DFT calculations, and relevant literature reports. This supports our assignment of Pt0 SA with a likely coordination involving one O atom and two Co atoms.\nWe have added the local coordination structure of Pt4+ SA into Fig. 1g to provide a clear comparison with that of Pt0 SA. Furthermore, in Fig. 1h, we have included the DFT determined coordination of Pt0 SA, highlighting its good agreement with the atomic arrangement in the high-resolution HAADF-STEM image. The corresponding description has been added revised version of the manuscript now includes this description in Lines 134137, 149150, and 169172 of the revised Manuscript.\nLines 134137\nHowever, the intense fluorescence background from the abundant Co atoms in the Co O support overwhelmingly masked the weak signal from the low-loading Pt, making the Pt signal undetectable.\nLines 149150\nIn this configuration, Pt coordinates with two surface O and two subsurface O atoms (Fig. 1g).\nLines 169172\nThe DFT-predicted Pt location and its surrounding Co atoms correspond well with the respective atoms in the high-resolution HAADF-STEM image (Fig. 1h), where the bright Pt SA signal aligns precisely with an octahedral site, as illustrated by the contrast profile (Fig. 1i).\n2. The catalytic reaction studied—oxidation of toluene to CO in air—is highly oxidative. Under these conditions, zero-valent Pt atoms are expected to oxidize rapidly to Pt2+/Pt4+ or sinter into metallic nanoparticles. The authors assert that Pt0 species remain stable after 48 h based on XPS (Supplementary Fig. S16). However, XPS alone cannot reliably distinguish between single atoms and clusters/nanoparticles. In response to your suggestion, we have performed HAADF-STEM characterization on the Pt-H/Co O catalyst after the long-term stability test. As shown in Fig. R2, Pt SAs still remain highly dispersed, confirming their structural stability under the reaction conditions. Additionally, as mentioned in the response to comment 1, it is challenging to detect the EXAFS signal of Pt. We sincerely apologize for being unable to provide the post-reaction Pt-edge EXAFS data. Nevertheless, by integrating the post-reaction HAADF-STEM and post-reaction XPS results, which indicate that the valence state of Pt in Pt-H/Co O remains zero, it is reasonable to infer that the coordination structure of Pt0 SA remains stable.\nFig. R2 | HAADF-STEM images of Pt-H/Co O after the long-term catalytic stability test.\nWe have included Fig. R2 as Supplementary Fig. 19 in the revised Supplementary Information and added corresponding discussion in Lines 212–214 of the revised Manuscript.\nLines 212214\nSubsequently, post-reaction XPS (Supplementary Fig. 18) and HAADF-STEM (Supplementary Fig. 19) analyses also confirm that Pt0 SAs retain their zero-valent state and atomic dispersion.\n3. According to the authors’ own DFT calculations (Supplementary Fig. S9), the zero-valent Pt configuration exhibits relatively low binding energy and poor thermodynamic stability on the Co O surface. This theoretical finding contradicts the experimental claim that Pt0 SAs are stably anchored and remain intact after long-term oxidation. The discrepancy is neither discussed nor rationalized.\nResponse: Thank you for your thoughtful comment. We appreciate the opportunity to clarify this point. Supplementary Fig. 9 presents the binding energies of Pt atoms at different vacancy sites (VCo , VCo , VO , and VO ), which are calculated to identify the most plausible coordination environment for Pt4+ SA. We found that when Pt atom occupies the VCo site, it exhibits the lowest binding energy and the highest Bader charge value (Supplementary Fig. 10d), corresponding to its high oxidation state.\nSupplementary Fig. 10 | d, B-VCo -Pt model of locating Pt atom on Co vacancy and corresponding Pt atom binding energy (ΔE) and Bader charge of Pt.\nAs for thermodynamic stability, it is generally assessed by comparing the binding energy of SA with its cohesive energy. If the binding energy of SA is lower than or comparable to its cohesive energy, it is considered stable against clustering (Energy Environ. Sci. 2021, 14, 3455). According to the literature (Nat. Commun. 2024, 15, 8216), the cohesive energy of Pt is -5.5 eV. Supplementary Fig. 9d shows that the binding energy of Pt4+ SA in the octahedral site configuration is -7.9 eV, confirming its good stability. We have further calculated the binding energy of Pt0 SA (Fig. R3), which is –5.5 eV and equal to the cohesive energy of Pt, indicating that Pt0 SA is also sufficiently stable. Moreover, post-reaction characterizations such as XPS (Supplementary Fig. 10) and HAADF-STEM (Fig. R2) analyses consistently confirm that Pt0 SAs retain their atomic dispersion and zero-valent state after long-term toluene oxidation (detailed analysis please refer to the response to comment 2), corroborating the DFT calculations.\nFig. R3 | The binding energy (ΔE) and Bader charge of Pt0 SA.\nWe have included Fig. R3 as a new Supplementary Fig. 14 in the revised Supplementary Information and added related discussion on Pt stability in Lines 176–179 of the revised Manuscript.\nLines 176179\nMoreover, DFT calculation (Supplementary Fig. 14) reveal that the binding energy of Pt0 SA is comparable to the Pt cohesive energy (-5.5 eV), indicating its sufficient thermodynamic stability29,30.\n4. The authors use Bader charge and DOS analyses to differentiate Pt valence states. Although the results qualitatively indicate a lower oxidation state for Pt in Pt-H/Co O than in Pt-A/Co O , the quantitative evidence is insufficient to justify the assignment of oxidation states (Pt4+ vs. Pt0). Therefore, explicit use of these experimental-determined valence in the theoretical discussion (e.g., in Fig. 4 and Supplementary Figs. 12 and 26) should be avoided. Furthermore, only an upward shift of the d-band center is not sufficient proof of metallic character—it merely reflects a reduction in the effective oxidation state of the Pt center.\nResponse: Thank you for this insightful comment. Our analysis of Pt oxidation states is primarily based on experimental XPS data (Fig. 1f), which clearly shows that the predominant Pt species in Pt-H/Co O is Pt0, whereas Pt-A/Co O features mainly Pt4+.\nThe Bader charge and DOS calculations were performed to provide a theoretical understanding of how the distinct coordination environment in Pt-H/Co O stabilizes the zero-valent state, rather than to independently quantify oxidation states.\nFig. 1 | f, Pt 4f XPS spectra of Pt-A/Co O and Pt-H/Co O .\nWe also sincerely appreciate your clarification that an upward shift of the d band center does not necessarily indicate metallic character, but rather reflects a decrease in the effective oxidation state of Pt. Accordingly, we have revised our interpretation of the d band center shift in Lines 256258 of the revised Manuscript.\nLines 256258\nFig. 3e reveals that the d band center of the 5d orbital of the Pt0 SA is closer to the Fermi level than that of the Pt4+ SA, which is consistent with the lower Pt valence state in Pt-H/Co O relative to Pt-A/Co O 33.\n5. I am skeptical about the reported differences in O adsorption energies at various sites (Fig. 4). From Pt4+ to Pt0, the O–O bond length increases by only 0.12 Å, yet the adsorption energy decreases by as much as 2.2 eV. It is questionable whether O activation would exhibit such a steep potential energy surface. Suggest the author to perform transition state calculations to simulate the complete potential energy surface, rather than relying solely on static adsorption comparisons.\nResponse: Thank you for this valuable suggestion. The variation in O adsorption energy arises not only from the change in O–O bond length, but more fundamentally from the difference of adsorption site and adsorption configuration (Nat. Commun. 2025, 16, 7451; Nat. Commun. 2025, 16, 7847). Therefore, the differences in adsorption energies can be attributed to the distinct coordination environments of the Pt4+ and Pt0 SA sites, as well as to the different O adsorption sites and O–O bond lengths involved.\nTaking into account that there is no transition state between gaseous O and chemisorbed O , we have followed your suggestion and performed additional DFT calculations for the transition state from chemisorbed O to dissociated reactive O atoms. As shown in Fig. R4, the dissociation process for O adsorbed on Pt0 SA site is thermodynamically more favorable, with its energy barrier being 0.4 eV lower than that at the Pt -OV site, further demonstrating the superior O activation performance of Pt0 SA site.\nFig. R4 | a, b, The dissociation energy and energy barrier of O adsorbed on Pt -OV (a) and Pt0 SA site (b).\nWe have included Fig. R4 as Supplementary Fig. 33 in the Supplementary Information and added the corresponding description in Lines 368–371 of the revised Manuscript.\nLines 368371\nSubsequent DFT calculations (Supplementary Fig. 33) revealed that the dissociation process for O adsorbed on Pt0 SA site is thermodynamically more favorable, exhibiting an energy barrier 0.4 eV lower than that at the Pt -OV SA site. This further demonstrates the superior O activation capability of Pt⁰ SA sites.\n6. This manuscript proposes a new \"benzene ring opening pathway\", but does not provide the reaction energy or potential barrier diagram. The author should at least perform DFT calculations on some key steps to facilitate a thermodynamic comparison between the proposed approach and traditional approaches.\nResponse: Thank you for this constructive suggestion. We have performed comprehensive DFT calculations to provide a quantitative thermodynamic comparison of the reaction pathways, as recommended.\nBased on in situ DRIFTS results (Figs. 5a–c), the catalytic oxidation of toluene over Pt SACs yields unique intermediates including phenol and benzoquinone, while TD-GC/MS analysis reveals the strongest signal of benzene intermediate over Co O (Supplementary Fig. 34). In addition, both Pt SACs and Co O also share common intermediates including benzyl alcohol, benzaldehyde, benzoic acid, and maleic anhydride. This suggests that the conversion pathway from benzoic acid to maleic anhydride is altered when Pt SAs are supported on Co O . Specifically, over Pt SACs, benzoic acid transforms into maleic anhydride via phenol and benzoquinone, whereas over Co O it may proceed through benzene before ring opening to yield maleic anhydride.\nFig. 5 | a–c, In situ DRIFTS of toluene adsorption on Co O (a), Pt-A/Co O (b) and Pt-H/Co O (c).\nSupplementary Fig. 34 | a–c, TDGC/MS signals of toluene oxidation of Co O (a), Pt-A/Co O (b) and Pt-H/Co O (c).\nTo demonstrate that this novel toluene conversion pathway occurring on Pt SACs is thermodynamically more favorable, we have performed DFT calculations to investigate the relative energy variation during toluene oxidation to maleic anhydride by using the B-VCo -Pt-R3O (representing Pt-H/Co O ) and the B-VO model (representing Co O ).\nBased on extensive DFT optimizations, the primary reaction intermediates identified over Pt-H/Co O include benzyl alcohol, benzaldehyde, benzoic acid, salicylic acid, phenol, hydroquinone, p-benzoquinone, and maleic anhydride (Figs. R5, 6). In contrast, over Co O , the key intermediates comprise benzyl alcohol, benzaldehyde, benzoic acid, benzene, cyclohexadienone, glyoxal, oxalic acid, 1-butynal, and cis-1,4-butenedial (Figs. R7, 8).\nFig. R5 | The specific adsorption configurations of reaction intermediates corresponding to Steps 1–6 in the methyl oxidation process (from toluene to benzoic acid) on B-VCo -Pt-R3O model (representing Pt-H/Co O ).\nFig. R6 | The specific adsorption configurations of reaction intermediates corresponding to Steps 7–21 in aromatic ring-opening process (from benzoic acid to maleic anhydride) on B-VCo -Pt-R3O model (representing Pt-H/Co O ).\nFig. R7 | The specific adsorption configurations of reaction intermediates corresponding to Steps 1–6 in the methyl oxidation process (from toluene to benzoic acid) on B-VO model (representing Co O ).\nFig. R8 | The specific adsorption configurations of reaction intermediates corresponding to Steps 7–21 in aromatic ring-opening process (from benzoic acid to maleic anhydride) on B-VO model (representing Co O ).\nThe resulting energy profiles (Fig. R9) clearly show that the pathway on Pt-H/Co O is significantly more exothermic than that on Co O . Specifically, the methyl oxidation step (toluene → benzoic acid) is lowered by 2.1 eV, and the subsequent aromatic ring-opening step (benzoic acid → maleic anhydride) is lowered by 1.3 eV on Pt-H/Co O relative to Co O . These results illustrate that the significantly improved low-temperature catalytic performance of Pt SACs originates from the new reaction pathway, which substantially lowers the relative energy for intermediate conversion compared to the conventional route on Co O .\nFig. R9 | Comparative relative energy profiles for toluene oxidation into maleic anhydride on Pt-H/Co O and Co O .\nWe have included Figs. R5–R8 as Supplementary Figs. 39–42 in the revised Supplementary Information and Fig. R9 as Fig. 5g. Corresponding descriptions about reaction mechanism have been added to the revised Manuscript in Lines 442–458.\nLines 442458\nBased on above findings, DFT calculations were performed to investigate the relative energy variation during toluene oxidation to maleic anhydride over Pt-H/Co O and Co O , aiming to demonstrate that this novel toluene conversion pathway occurring on Pt-H/Co O is more conducive to enhancing catalytic activity. As shown in Fig. 5f, the oxidation pathway from toluene to benzoic acid proceeds via identical intermediates (benzyl alcohol and benzaldehyde) on both Co O and Pt-H/Co O . Thereafter, the reaction pathways diverge markedly. For Pt-H/Co O , the transformation proceeds sequentially through salicylic acid, phenol, hydroquinone, p-benzoquinone, maleic acid, and finally maleic anhydride (Supplementary Figs. 39, 40). In contrast, the pathway on Co O involves benzene, cyclohexadienone, 1-butynal, and cis-1,4-butenedial before yielding maleic anhydride (Supplementary Figs. 41, 42). Fig. 5g illustrates that, compared to Co O , the distinct reaction route on Pt-H/Co O reduces the relative energy by 2.1 eV for the methyl oxidation process (toluene to benzoic acid, Steps 1-6) and by an additional 1.3 eV for the subsequent ring-opening process (benzoic acid to maleic anhydride, Steps 6-21). Therefore, the intermediate conversion on Pt-H/Co O is more exothermic, thereby underpinning its superior low-temperature catalytic performance.\n7. There are some formatting issues in the article, such as the abbreviation of ROS not being given its full name when it first appears, and the full name of TOF should be Turnover Frequency instead of Turnover Rate.\nResponse: Thank you for pointing out these formatting issues. We have already made adjustment in Lines 308310 and Lines 207209 of the revised Manuscript.\nLines 308310\nIn contrast, Pt-H/Co O , featuring a Pt0 SA and abundant oxygen vacancies demonstrates the highest level of reactive oxygen species (ROS) generation.\nLines 207209\nMoreover, the turnover frequency (TOF) of Pt-H/Co O is 9.3-fold higher than that of Pt-A/Co O at 125 °C, underscoring the superior catalytic efficiency of Pt0 SA sites over Pt4+ SA sites.\nResponse to reviewer 2\nComments: In this study, the authors constructed a zero-valent Pt single-atom catalyst anchored on 2D Co O via a simple low-temperature reduction strategy, which demonstrated promising performance in catalytic oxidation of toluene. Moreover, the work comprehensively employed multiple characterization techniques and theoretical calculations to elucidate the geometric/electronic structure of the zero-valent Pt single atoms and the mechanism by which they enhance O activation. This research provides a new strategy for designing efficient zero-valent single-atom catalysts and offers valuable insights into the role of electronic modulation in catalytic oxidation. I believe the manuscript can be accepted after addressing the following issues:\nResponse: We sincerely appreciate you for the positive evaluation of our work and the time dedicated to reviewing our manuscript. We are glad that our research is recognized for its strategy and insights. In response to the valuable suggestions provided, we have carefully addressed each of the raised issues to further improve the quality of the manuscript. We hope that our detailed revisions and responses will meet with your approval.\n1. The specific surface area-normalized reaction rate (rₛ) should also be calculated at reaction temperatures with conversion efficiencies below 10%.\nResponse: We really appreciate your helpful suggestion. We have calculated rₛ at 125 °C, where the conversion efficiency is below 10%. As shown in Fig. R10, the rₛ value of Pt-H/Co O (3.01×10-10) is 41.8 times higher than that of Pt-A/Co O (0.072×10-10).\nFig. R10 | r and TOF of Pt-A/Co O and Pt-H/Co O at 125 °C\nFig. R10 has been added to the revised Manuscript as the new Fig. 2b. The corresponding description has been added in Lines 203–207 of the revised Manuscript\nLines 203207:\nAdditionally, the specific surface area normalized reaction rate (r ) at 125 °C (At this temperature, η < 10%), derived from characterization of N adsorption and desorption (Supplementary Fig. 17 and Supplementary Table 1), demonstrates that Pt-H/Co O exhibits a 41.8-fold higher r than does Pt-A/Co O (Fig. 2b).\n2. It is recommended to rename the oxygen and toluene adsorption energies as E , and E , respectively, to avoid confusion.\nResponse: Thanks for your meaningful comment. According to your suggestions, we have renamed the oxygen energy and toluene adsorption energy as E and E . The corresponding revisions are located in Lines 347350 and 415-417 of the revised manuscript.\nLines 347350:\nThe calculated O adsorption energy (E ) values follow the order of Pt4+ SA (-0.9 eV) < Co -OV (-1.2 eV) < Pt -OV (-1.5 eV) < Pt0 SA (-3.1 eV), with corresponding O=O bond lengths (L ) of 1.33 Å, 1.37 Å, 1.39 Å and 1.45 Å, respectively.\nLines 415417:\nDFT calculations (Supplementary Fig. 36) demonstrate the increased toluene adsorption energy (E ) on the Pt SACs, with the aromatic ring positioned closer to the Co sites.\n3. The caption of Supplementary Fig. 7 is incorrect. Furthermore, please clarify how the positions of octahedral Co (Co ), tetrahedral Co (Co ), and oxygen atoms are distinguished in the HAADF-STEM image.\nResponse: Thank you for pointing out this error. We have added the structural model of the Co O (110) facet in Supplementary Fig. 7 (now Supplementary Fig. 8) to illustrate how to distinguish the positions of octahedral Co (Co ), tetrahedral Co (Co ), and oxygen atoms in the HAADF-STEM image. The caption of Supplementary Fig. 8 has been updated accordingly as follows:\nSupplementary Fig. 8 | a, High-magnification HAADF-STEM image of the 2D Co O support. b, Top view of the structural model for the Co O (110). Octahedral Co (Co ), tetrahedral Co (Co ), and oxygen atoms are marked by blue, cyan, and red circles, respectively.\nBy comparing the HAADF-STEM image with the structural model, it can be observed that the Co atoms marked with blue circles (Co ) are located at the octahedral sites of the spinel structure, while the Co atoms marked with cyan circles are situated at the tetrahedral sites (Co ) of the spinel structure. Although O atoms are not clearly visible in the HAADF-STEM image, their locations (marked by red circles) between Co and Co can be inferred accordingly.\n4. The yellow and purple circles in Supplementary Fig. 20 lack corresponding annotations.\nResponse: Thank you for pointing out the missing labels. The purple circle in Supplementary Fig. 20a (now Supplementary Fig. 25a) highlights the lattice disorder surrounding the high-valence Pt single atom in Pt-A/Co O , while the yellow circle in Supplementary Fig. 20b (now Supplementary Fig. 25b) marks the lattice disorder around the zero-valent Pt SA in Pt-H/Co O . We have added the corresponding annotations to the caption of Supplementary Fig. 20 as shown below:\nSupplementary Fig. 25 | a, b, HAADF-STEM images of Pt-A/Co O (a) and Pt-H/Co O (b). The purple circle highlights the lattice disorder surrounding the high-valence Pt single atom in Pt-A/Co O , while the yellow circle marks the lattice disorder around the zero-valent Pt SA in Pt-H/Co O .\n5. The labeling of intermediate species in Supplementary Fig. 29 is incomplete; please supplement it accordingly.\nResponse: Thank you for pointing this out. Based on your suggestion, we have supplemented and revised the annotation of intermediate species in all TD-GC/MS spectra to provide clearer visualization and to better highlight the key differences in intermediate species between Pt SACs and Co O .\nSupplementary Fig. 34 | a–c, TDGC/MS signals of toluene oxidation of Co O (a), Pt-A/Co O (b) and Pt-H/Co O (c).\nResponse to reviewer 3\nComments: This work successfully constructed a zerovalent platinum single-atom catalyst (Pt0 SAs) on two-dimensional Co O through an innovative low-temperature H reduction strategy, overcoming the electronic limitations of traditional high-valent single-atom catalysts in O activation. The study systematically reveals that the Pt0 sites enhance electron transfer capability by optimizing the d-band center, significantly improving the low-temperature toluene oxidation performance, thus providing valuable insights for the valence state regulation of single-atom catalysts. The experimental design is rigorous, combining in-situ characterization and theoretical calculations, demonstrating strong innovation and application potential. However, the data analysis in some parts of the manuscript has room for improvement, and the validation of certain viewpoints overly relies on theoretical simulations, lacking reliable experimental evidence. Therefore, based on the high standards of Nature Communications, it is recommended that the authors undertake a major revision before further consideration for publication.\nResponse: We would like to express our sincere gratitude to you for the highly positive and constructive comments on our work, as well as for the significant time and effort dedicated to the review process. In response to your valuable suggestions, we have carefully addressed the specific issues raised, with particular emphasis on strengthening the connection between theoretical calculations and experimental results to more clearly elucidate the microstructure of developed catalyst and reaction mechanism. We hope that our detailed responses and revisions will meet with your satisfaction.\n1. The authors devote considerable length in the initial sections to discussing the catalyst synthesis process, which is crucial to the zerovalent single-atom structure they emphasize. However, all related data are presented in the Supporting Information. It is recommended to optimize the figure composition appropriately by moving some key data to the main text.\nResponse: We are grateful for your valuable advice. We have added the local coordination structure of Pt4+ SA into Fig. 1g to provide a clear comparison with that of Pt0 SA. Furthermore, in Fig. 1h, we have included the DFT calculation results of Pt0 SA located on the Co O (110) facet model. It can be seen that the Pt0 SA and its surrounding Co atoms in the model correspond well with the respective atoms in the high-resolution HAADF-STEM image, thereby demonstrating the plausibility of the proposed coordination structure of Pt0 SA.\nFig. 1 | Construction of zero-valent Pt SACs. a, In situ CO DRIFTS of Pt-A/Co O and Pt-H/Co O . b, c, HAADF-STEM images of Pt-A/Co O (b) and Pt-H/Co O (c). d, e, EDS mapping images of Pt-A/Co O (d) and Pt-H/Co O (e). f, Pt 4f XPS spectra of Pt-A/Co O and Pt-H/Co O . g, Local coordination structure of Pt4+ SA and Pt0 SA. h, HAADF-STEM image of a Pt0 SA on the Co O (110) facet in Pt-H/Co O . The inset shows the DFT-calculated location of the Pt⁰ SA. Pt0 SA is marked by an orange circle, and the surrounding Co atoms are indicated by blue hexagons. i, Line profile of the Pt0 SA.\n2. The full XPS survey scan and the C 1s spectrum used for calibration must be provided. To better confirm the valence state information, it is advised to supplement the data with a reference sample of metallic Pt particles formed after over-reduction.\nResponse: We sincerely appreciate this valuable suggestion. Following your comment, we have included the full XPS survey spectra and the corresponding C 1s spectra (Fig. R10) of Pt-A/Co O , Pt-H/Co O , Co O and Co O -H as Supplementary Fig. 21 in the revised Supplementary Information. All XPS results are calibrated using the C 1s peak at 284.8 eV for charge correction.\nFig. R10 | a, b, XPS survey (a) and C 1s XPS (b) spectra of Pt-A/Co O , Pt-H/Co O , Co O , and Co O -H.\nAdditionally, to further verify the Pt valence state in Pt-H/Co O , a reference sample (labeled as Pt-NP/Co O ) has been prepared by loading 0.6 wt.% Pt nanoparticles onto 2D Co O support via a borohydride reduction method—a common approach for synthesizing zero-valent Pt nanoparticles (with H PtCl ·6H O serving as the Pt precursor). The Pt 4f XPS spectrum of Pt-NP/Co O (Fig. R11) confirms the presence of Pt0. Notably, the binding energy positions (71.6 eV and 74.6 eV) of the Pt 4f in Pt-NP/Co O closely align with those observed in Pt-H/Co O (71.8 eV and 74.7 eV).\nThis comparative spectrum has been included as Supplementary Fig. 7 in the revised Supplementary Information. Relevant descriptions have been added in Lines 127–132 in the revised Manuscript.\nFig. R11 | a–c, Pt 4f XPS (a), XPS survey (b) and C 1s XPS spectra (c) of Pt-NP/Co O . All XPS results are calibrated using the C 1s peak at 284.8 eV for charge correction. Pt-NP/Co O was prepared by loading 0.6 wt.% Pt nanoparticles onto 2D Co O support via the borohydride reduction method—a common approach for synthesizing zero-valent Pt nanoparticles (with H PtCl ·6H O serving as the Pt precursor).\nLines 127132\nMoreover, the Pt 4f X-ray photoelectron spectroscopy (XPS) spectra (Fig. 1f) reveal Pt4+ dominance in Pt-A/Co O . Conversely, Pt-H/Co O is dominated by Pt0, with its Pt 4f binding energy closely matching that of zero-valent Pt nanoparticles supported on Co O (Supplementary Fig. 7). These results confirm the successful synthesis of high-valent and zero-valent Pt SAs (Pt0 SA and Pt4+ SA), respectively.\n3. The caption for Figure S7 is incorrect, as it is not XRD data.\nResponse: Thank you for pointing out this error. We have added the structural model of the Co O (110) facet in Supplementary Fig. 7 (now Supplementary Fig. 8) to illustrate how to distinguish the positions of octahedral Co (Co ), tetrahedral Co (Co ), and oxygen atoms in the HAADF-STEM image. The caption of Supplementary Fig. 8 has been updated accordingly as follows:\nSupplementary Fig. 8 | a, High-magnification HAADF-STEM image of the 2D Co O support. b, Top view of the Co O (110)-B facet model. Octahedral Co (Co ), tetrahedral Co (Co ), and oxygen atoms are marked by blue, cyan, and red circles, respectively.\n4. The authors propose that O atoms around Pt are removed during the H treatment. Was the H consumption calculated to provide quantitative or semi-quantitative support for this inference?\nResponse: Thank you for your valuable feedback. To quantitatively analyze the Pt reduction process during H treatment, we have performed H -TPR measurements using CuO as a reference. According to the stoichiometric relationship, the complete reduction of 1 mol CuO standard consumes 1 mol H (CuO + H → Cu + H O). From the H -TPR profile of CuO (Fig. R12), we calibrated that each unit integrated area corresponds to 1.08 × 10-8 mol H consumed.\nBy integrating the Pt reduction peak (Supplementary Fig. 2a) and applying the above calibration, we found that the reduction of Pt (loading: 3.08 × 10-6 mol) actually consumed 6.74 × 10-5 mol H . This value is significantly higher than the theoretical maximum H consumption required solely for Pt reduction (6.16 × 10-6 mol). This discrepancy is attributed to hydrogen spillover, induced by the strong electronic metal–support interaction between reduced Pt species and the Co O support, which promotes extensive reduction of lattice oxygen in Co O (Angew. Chem. Int. Ed. 2022, 61, e202208237; Nano Res. 2023, 16, 6507). Thus, the Pt reduction peak also contains contributions from Co O reduction.\nAs the concentration of reduced Pt species increases and stabilizes, the resulting hydrogen spillover effect also reaches a steady state, which in turn leads to the stabilization of Co O reduction signal. For comparison, Co O support alone exhibits a much weaker Co O reduction signal (Supplementary Fig. 2c).\nAlthough the hydrogen spillover effect prevents the quantitative determination of Pt reduction alone, the markedly higher H consumption provides indirect evidence for the strong interaction between Pt and Co O .\nFig. R12 | H -TPR spectra of CuO standard.\nSupplementary Fig. 2 | a–c, Constant-temperature H -TPR spectra of Pt-P/Co O (a), Pt-PN/Co O (b), and Co O (c).\nBased on above analysis, we have optimized the discussion on the strong interaction between reduced Pt and Co O in Lines 101109 of the revised manuscript.\nLines 101109\nThe peak observed during heating process corresponds to Pt2+ reduction23, while the peak emerging during constant-temperature process originates from the removal of ligands from the Pt(NH ) (NO ) precursor, verified by a control experiment of replacing Pt precursor with Pt(NO ) (Supplementary Fig. 2b). The residual H consumption is attributed to the facilitated reduction of Co O , driven by the hydrogen spillover effect from the newly reduced Pt species24. For comparison, the reduction effect on the O of lat Co O is quite weak (Supplementary Fig. 2c), indicating that the reduced Pt can strongly interact with Co O .\n5. The Pt structure is the core claim of the work but lacks sufficient experimental evidence. Generally, at this loading level, the Pt EXAFS information should be obtainable. It is recommended to re-attempt obtaining the Pt coordination structure information. Alternatively, provide atomic-resolution image intensity analysis to substantiate how the precise structural information in Figure 1g was determined.\nResponse: We are grateful for your valuable advice. We fully agree that Pt L -edge EXAFS would be the most direct technique to verify the local coordination environment of Pt species. However, we acknowledge the inherent technical challenge in acquiring Pt L -edge EXAFS data for our specific system. The intense fluorescence background from the abundant Co atoms (73.4 wt.%) in the Co O support overwhelmingly masks the weak signal from the low-loading Pt (0.6 wt.%), making it difficult to extract usable EXAFS result for reliable fitting even after optimizing measurement parameters, despite multiple attempts at different synchrotron facilities, such as Beijing Synchrotron Radiation Facility (BSRF), Hefei Light Source (HLS), and most recently Shanghai Synchrotron Radiation facility (SSRF, The testing process is shown in the Fig. R1).\nFig. R1 | The XAFS testing of the sample at SSRF.\nTo address this limitation, we have made a comprehensive set of complementary characterizations and theoretical calculations to address this point rigorously in the absence of direct EXAFS data. HAADF-STEM (Fig. 1g, h) confirms the presence of isolated Pt atoms on the Co O support for both Pt-H/Co O and Pt-A/Co O samples, ruling out Pt clusters. The in situ DRIFTS spectra of CO adsorption (Fig. 1a) reveal distinct linear adsorption peaks, confirming that Pt species in both samples exist as single atoms (SAs) with different coordination structures. In addition, XPS analysis (Fig. 1f) indicates that Pt in Pt-H/Co O and Pt-A/Co O exhibits predominantly zero-valent and +4 oxidation states, respectively—a direct consequence of their distinct SA coordination environments. Considering that Pt-A/Co O is prepared under oxidative conditions, whereas Pt-H/Co O is obtained via 5% H reduction followed by treatment in 1% O , we infer that the Pt SAs in Pt-A/Co O likely possess high O atom coordination, while those in Pt-H/Co O may be coordinated by fewer O atoms along with Co atoms from the support.\nGuided by these combined characterization results, we performed DFT calculations to model the plausible coordination structures of the two types of single atoms. Based on the analysis of Pt binding energies and Bader charges analysis, a Pt4+ SA configuration could be reasonably represented by a Pt atom coordinated with four O atoms, whereas a Pt0 SA model was best described by a Pt atom coordinated with one O atom and two Co atoms (Fig. 1g). In addition, the DFT-optimized Pt0 SA is located at the Co site of the Co O Oh support, which aligns well with the atomic positions observed in the high-magnification HAADF-STEM image (Fig. 1h, i). Furthermore, we simulated the CO adsorption infrared spectra (Supplementary Fig. 12) based on these two structural models. The simulated peak positions show good agreement with the in situ DRIFTS spectra of CO adsorption data, providing strong theoretical validation for the proposed coordination environments. These results validate the reasonableness of the DFT calculations.\nFig. 1 | Construction of zero-valent Pt SACs. a, In situ CO DRIFTS of Pt-A/Co O and Pt-H/Co O . b, c, HAADF-STEM images of Pt-A/Co O (b) and Pt-H/Co O (c). d, e, EDS mapping images of Pt-A/Co O (d) and Pt-H/Co O (e). f, Pt 4f XPS spectra of Pt-A/Co O and Pt-H/Co O . g, Local coordination structure of Pt4+ SA and Pt0 SA. h, HAADF-STEM image of a Pt0 SA on the Co O (110) facet in Pt-H/Co O . The inset shows the DFT-calculated location of the Pt⁰ SA. Pt0 SA is marked by an orange circle, and the surrounding Co atoms are indicated by blue hexagons. i, Line profile of the Pt0 SA.\nSupplementary Fig. 13 | DFT-calculated IR spectra of CO adsorbed on Pt4+ SA site and Pt0 SA site.\nMoreover, our proposed coordination for Pt0 SA aligns with reports of low-valent Pt SAs from Zhang Tao's group. For instance, in the Fe O -supported Pt SA system, EXAFS fitting indicates a coordination number of 1.8 for Pt-O and 0.8 for Pt-Fe, with a corresponding Pt valence state of 0.56 (Nat. Commun. 2019, 10, 4500); in the CeO -supported Pt SA system, Pt coordinated with two O atoms and one Ce atom exhibited a zero-valent state, whereas Pt coordinated with four O atoms showed a +4 state (J. Catal. 2022, 415, 174).\nBased on the comprehensive analysis above, while the coordination structure of Pt0 SA in Pt-H/Co O cannot be directly determined from EXAFS alone, we integrate evidence from HAADF-STEM, in situ DRIFTS of CO adsorption, XPS, DFT calculations, and relevant literature reports. This supports our assignment of Pt0 SA with a likely coordination involving one O atom and two Co atoms.\nWe have added the local coordination structure of Pt4+ SA into Fig. 1g to provide a clear comparison with that of Pt0 SA. Furthermore, in Fig. 1h, we have included the DFT determined coordination of Pt0 SA, highlighting its good agreement with the atomic arrangement in the high-resolution HAADF-STEM image. The corresponding description has been added revised version of the manuscript now includes this description in Lines 134137, 149150, and 169172 of the revised Manuscript.\nLines 134137\nHowever, the intense fluorescence background from the abundant Co atoms in the Co O support overwhelmingly masked the weak signal from the low-loading Pt, making the Pt signal undetectable.\nLines 149150\nIn this configuration, Pt coordinates with two surface O and two subsurface O atoms (Fig. 1g).\nLines 169172\nThe DFT-predicted Pt location and its surrounding Co atoms correspond well with the respective atoms in the high-resolution HAADF-STEM image (Fig. 1h), where the bright Pt SA signal aligns precisely with an octahedral site, as illustrated by the contrast profile (Fig. 1i).\n6. The authors explored O activation capability via quasi-in-situ XPS, stating that the Pt-H catalyst has stronger activation ability. However, in my opinion, the trend shown in the S24 data does not strongly support this claim. Furthermore, using the shift of the lattice oxygen signal to prove surface electronic information is not convincingly demonstrated in the figures, and this part of the discussion needs refinement. Similarly, all spectra should be presented with their corresponding C 1s calibration spectra, as XPS data analysis can be highly subjective.\nResponse: We sincerely thank the reviewer for their valuable advice. Upon careful re-examination, we agree that the original description stating “Pt-H/Co O exhibits a greater enhancement magnitude” is imprecise. To facilitate a clearer comparison, we have summarized the peak-fitting results of the quasi-in situ O 1s XPS spectra (previously Supplementary Fig. 24) in a new figure (Fig. R13a, now Supplementary Fig. 30a). The data clearly show that the O /O ratios for both Pt-A/Co O and Pt-H/Co O increase with temperature elevation, and Pt-H/Co O exhibits a higher rati at each tested temperature, providing stronger evidence of its superior O activation capacity.\nThe upward shift in binding energy in XPS is a well-established spectral feature indicating reduced electron density around the atom, reflecting a change in its chemical coordination. In our system, the upward shift of O 1s binding energy corresponds to a weaker Co–O interaction, which reduces electron donation from Co to O, leading to elongated or even broken Co–O bonds and the possible formation of oxygen vacancies. The decrease in electron density around O thus signifies O activation. This interpretation is consistent with previous reports (e.g., Feng et al., Angew. Chem. Int. Ed. 2019, 58, 11720). Regarding the concurrent increase in O peak intensity, we acknowledge that this is likely due to the desorption of surface contaminants (e.g., hydrocarbons, physisorbed H O) during heating, which enhances the overall O 1s signal, and therefore may not directly correlate with O activation.\nBased on the above discussion, we have replaced the original Supplementary Fig. 24 with Fig. R13 as the new Supplementary Fig. 30, which also includes the corresponding XPS survey spectra and C 1s XPS spectra. The relevant discussion has been revised accordingly (Lines 325342 in the revised manuscript) to present a more coherent and reasonable interpretation of the quasi-in situ XPS results.\nFig. R13 | a, The O /O value of quasi-in situ XPS spectra of O absorption under heating over Pt-A/Co O and Pt-H/Co O . b, c, XPS survey spectra of Pt-A/Co O (b) and Pt-H/Co O (c). d, e, C 1s XPS spectra of Pt-A/Co O (d) and Pt-H/Co O (e). All XPS results are calibrated using the C 1s peak at 284.8 eV for charge correction.\nLines 325342\nTo elucidate the effect of low-temperature elevation (spanning the T , T and T of Pt SACs) on O activation, quasi-in-situ XPS characterization was performed in an O atmosphere. Both Pt-A/Co O (Fig. 4b) and Pt-H/Co O (Fig. 4c) display increasing O /O ratios with elevating temperature, with the ratio for Pt-H/Co O being consistently higher at each temperature point (Supplementary Fig.30), confirming its stronger O activation capability. Notably, the O peak shifts to a higher binding energy for both catalysts, indicating electron depletion around the O and the weakened electronic interaction between Co and O atom, which demonstrates the O activation during the heating process42. Based on the preceding analysis, the O activation in Pt-H/Co O , stems from its highest degree of lattice disorder (Fig. 3f), whereas in Pt-A/Co O , it arises from the enhanced reactivity of the O -Pt -O site compared to the O -Co -O site (Supplementary Fig. 11). Given that the weak O activation ability of isolated Pt4+ SA site alone cannot explain the markedly enhanced low-temperature activity of Pt-A/Co O over Co O , it is proposed that the actual O activation site in Pt-A/Co O is oxygen vacancies (Pt –OV) associated with Pt4+ SAs, which formed by the removal of activated O from O -Pt -O site and exhibit stronger O activation capacity than those oxygen vacancies near Co atoms (Co -OV). This hypothesis is further supported by subsequent DFT calculations.\n7. Multiple rounds of catalytic testing are needed to verify the stability of the catalytic structure. Additionally, long-term stability tests should be conducted at conversion levels below the thermodynamic equilibrium conversion. The data in Fig. 2c, nearing 100% conversion, cannot convincingly demonstrate structural stability. Moreover, the final data point indicates noticeable deactivation behavior.\nResponse: We are grateful for your valuable advice. We have performed additional cycling tests to evaluate the catalytic durability of Pt-H/Co O . As shown in Fig. R14, the T and T of Pt-H/Co O remain stable around 140 °C and 150 °C during five consecutive test cycles, respectively.\nFig. R14 | The catalytic performance of Pt-H/Co O for toluene oxidation during cycle tests.\nFurthermore, as you rightly pointed out, a stability test conducted near full conversion (T ) may not adequately reflect structural robustness. Thus, we have conducted a long-term stability test at T , which aligns with common practice in the literature for toluene oxidation stability assessments (ACS Catal. 2023, 13, 14792; ACS Catal. 2023, 13, 3444; Environ. Sci. Technol. 2022, 56, 16249). As presented in Fig. R15, the toluene conversion efficiency of Pt-H/Co O remains at 90% after 50 h of continuous reaction. These results confirm the excellent catalytic stability of Pt-H/Co O .\nFig. R14 | Long-term catalytic stability of Pt-H/Co O at T .\nWe have included Fig. R14 as Supplementary Fig. 20 in the revised Supplementary Information and incorporated Fig. R15 into the revised Manuscript as the new Fig. 2c. Additionally, the corresponding description of catalytic stability has been updated in Lines 211212 and Lines 214216 of the revised Manuscript.\nLines 211212\nAs shown in Fig. 2c, its toluene conversion efficiency remains at 90% after 48 h of reaction at 140 °C.\nLines 214216\nIn addition, the T and T of Pt-H/Co O remain stable during five consecutive test cycles, respectively (Supplementary Fig. 20).\n8. Attributing the enhanced Raman signal intensity in S25 to lattice oxygen activation is unsubstantiated and lacks rigor. Raman signal intensity is difficult to interpret directly, as it is strongly influenced by and often coincidental due to laser focusing on the solid sample surface. The authors should analyze the Raman results cautiously, and the discussion must be supported by reliable literature evidence.\nResponse: We sincerely thank you for this valuable and professional comment, which has significantly strengthened the quality of our work. We fully acknowledge that Raman signal intensity is a semi-quantitative parameter susceptible to various factors. As rightly pointed out, in addition to laser focusing conditions, changes in surface roughness or morphology of sample induced by thermal effects, the desorption of surface adsorbates (such as H O or organic contaminants) during heating can also significantly alter the signal collection efficiency. Therefore, we fully agree with your perspective that directly correlating the intensity enhancement with O activation lacks rigor and could be misleading.\nMore importantly, our central conclusion regarding the activation of surface O on the catalyst is already well supported by multiple surface-sensitive techniques, including Quasi-in situ XPS, O -TPD, and toluene-TPD (detailed analysis please refer to the response to comment 6, 9, and 12), which provide direct and reliable evidence. In contrast, Raman spectra primarily probe the bulk lattice vibrations, making its direct correlation with the activation of surface O comparatively weaker.\nConsidering the above points, and to ensure the utmost rigor of our conclusions, we have decided to remove the discussion and conclusions related to in situ Raman results from the revised Manuscript. Our analysis now focuses exclusively on the more direct and robust characterization techniques mentioned above.\n9. Oxygen storage capacity measurement experiments should be supplemented to differentiate the oxygen adsorption capabilities of the two catalysts.\nResponse: Thanks for your valuable advice. We have performed O temperature-programmed desorption (O -TPD) measurements on Pt-A/Co O and Pt-H/Co O to further compare the O adsorption capabilities of the two catalysts. As shown in Fig. R15, the peak in the range of 120–200 °C corresponds to the desorption of surface adsorbed reactive oxygen species (O ), while the peak around 200–500 °C is assigned to the desorption of surface lattice oxygen (O ). Notably, the intensity of the surface O peak for Pt-H/Co O is significantly stronger than that of Pt-A/Co O , indicating its superior O adsorption and activation capacity.\nFig. R15 | O -TPD spectra of Pt-A/Co O and Pt-H/Co O .\nWe have included Fig. R15 as Supplementary Fig. 29 in the revised Supplementary Information, and the corresponding description has been added in Lines 315–319 of the revised Manuscript.\nLines 315319\nSimilarly, O temperature-programmed desorption (O -TPD) spectra (Supplementary Fig. 29) reveals the O adsorption capabilities of Pt-A/Co O and Pt-H/Co O . The peak in the range of 120–200 °C corresponds to the desorption of surface O , while the peak around 200–450 °C is assigned to the desorption of surface O 40. Notably, the intensity of the surface O peak for Pt-H/Co O is significantly stronger.\n10. Relevant kinetic experiments, such as determining reaction orders and performing 18O isotope tracing, should be added.\nResponse: We appreciate your valuable suggestion. In response, we have conducted additional kinetic experiments and toluene-TPSR measurements with 18O labeling on the Pt-H/Co O sample to further clarify the reaction mechanism.\nFor kinetic experiments, we measured toluene conversion under varying toluene partial pressures (at fixed O partial pressure) and varying O partial pressures (at fixed toluene partial pressure) in the low-temperature range. This temperature range was selected to ensure conversion remained below 15%, thereby minimizing the influence of diffusion on the reaction rate. As shown in Fig. R16, toluene conversion decreases with increasing toluene partial pressure and increases with elevated O partial pressure.\nFig. R16 | a, b, The catalytic performance of Pt-H/Co O at low-temperature range with different toluene (a) and O (b) partial pressures.\nSubsequently, the apparent reaction orders for toluene and oxygen were determined using the power-law model (Equation 1):\nr = kP αP β\nwhere r refers to the reaction rate, k refers to the apparent rate constant, P refers to the toluene partial pressure, P refers to the oxygen partial pressure, α refers to the apparent reaction order of toluene, and β refers to the apparent reaction order of oxygen.\nTaking the logarithm of Equation 1 gives Equation 2:\nlnr = lnk + αlnP + βlnP\nBy fixing P and linearly fitting lnr versus lnP , the slope yields α (Fig. R17a). Similarly, by fixing P and linearly fitting lnr versus lnP , the slope gives β (Fig. R17b). The calculated average values in the low-temperature range are α = −0.86 and β = 0.63, respectively.\nFig. R17 | a, b, The apparent reaction order of toluene (a) and O (b) partial pressures at low-temperature range.\nFurthermore, kinetic models corresponding to three typical toluene catalytic oxidation mechanisms—Langmuir–Hinshelwood (L–H), Eley–Rideal (E–R), and Mars–van Krevelen (MvK) (Table R1)—were applied to fit the experimental data. Given that the apparent reaction order for toluene is negative (α<0), which is inconsistent with the kinetic models of both the E–R and MvK mechanisms, the L–H kinetic model was selected for nonlinear fitting under fixed P (Fig. R18a) and P (Fig. R18b) conditions. The results showed strong agreement, indicating that the L–H mechanism is dominant at low reaction temperatures.\nTable R1. Kinetic model formula of L-H, E-R, and MvK mechanism.\nKinetic simplified equation simplified equation\nreaction rate equation\nmodel for fix P for fix P\nL-H 𝑟 = 𝑘 𝑘 𝑘 𝑃 𝑃 / (1+𝑘 𝑃 +𝑘 𝑃 )2\nE-R 𝑟 = 𝑘 𝑘 𝑃 𝑃 / 1+𝑘 𝑃\nMvK 𝑟 = 𝑘 𝑘 𝑃 𝑃 / 9𝑘 𝑃 +𝑘 𝑃\nWhere k , k , k refer to the reaction rate constant, toluene adsorption rate constant and O adsorption constant respectively. P and P refer to the partial pressure of toluene and oxygen, respectively. For E-R kinetic models, the first model supposes that the catalytic reaction takes place between adsorbed O and toluene in the gas phase; the second model supposes that the catalytic reaction takes place between adsorbed toluene and O in the gas phase.\nFig. R18 | a, b, The fitting curves of r versus toluene (a) and O (b)partial pressure based on L–H kinetic model at low-temperature range.\nMoreover, toluene-TPSR results with 18O labeling (Fig. R19) show that C16O18O and C18O signals appear in the low-temperature range (80–160 °C), which arise from the complete oxidation of toluene by activated O . The presence of C16O18O may be attributed to the isotopic exchange effect between activated 18O (by Pt0 SA) and surface O during heating (Catal. Commun. 2023, 179, 106687; Phys. Chem. Chem. Phys., 2025, 27, 8467) rather than from toluene oxidation by O , since C16O —resulting from the toluene oxidation by O — emerges only above 160 °C. Additionally, the aforementioned kinetic experiments also indicate that toluene oxidation in the low-temperature region is not consistent with the MvK mechanism.\nFig. R19 | Toluene-TPSR spectra with 18O labeling of Pt-H/Co O .\nBased on these two sets of experimental evidence, it can be concluded that toluene oxidation on Pt-H/Co O predominantly follows the L–H mechanism in the low-temperature range, with ROS mainly originating from the activation of gaseous O .\nThese results have been included in the Supplementary Information as Supplementary Fig. 37 (Figs. R16-18), Supplementary Fig. 38 (Fig. R19), and Supplementary Table 6 (Table R1), and corresponding descriptions have been added in Lines 427–441 of the revised Manuscript.\nLines 427441:\nKinetic analysis was conducted to further elucidate the toluene oxidation mechanism (Supplementary Fig. 37). The experimental data were fitted using kinetic models corresponding to the Langmuir–Hinshelwood (L–H), Eley–Rideal (E–R), and Mars–van Krevelen (MvK) mechanisms (Supplementary Table 6). The results indicate that the apparent reaction order for toluene is negative, which is inconsistent with both E–R and MvK models, while the L–H model provides a good fit fitting degree, indicating that the L–H mechanism is dominant at low reaction temperatures. Complementary insights were obtained from toluene-TPSR with 18O labeling (Supplementary Fig. 38). Below 160 °C, signals corresponding to C16O18O and C18O are detected, consistent with the complete toluene oxidation by activated O . The emergence of C16O18O likely originates from isotopic exchange effect58,59, instead of direct oxidation by O , as C16O —which arises from oxidation by activated O —is only observed above 160 °C. Together, these results demonstrate that toluene oxidation at low temperatures proceeds predominantly via the L–H mechanism, with ROS derived primarily from O activation.\n11. The IR spectra presented in Fig. 5 are overly cluttered, making effective comparison of differences difficult. It is recommended to optimize the presentation to clearly highlight the key distinctions between the different samples.\nResponse: Thank you for this pointing out. Following your suggestion, we have revised the annotation of reactive intermediates in all in situ DRIFTS spectra (Fig. 5a–c and Supplementary Fig. 35) to provide clearer visualization and to better highlight the key differences in reaction intermediates between Pt SACs and Co O .\nFig. 5 |a–c, In situ DRIFTS of toluene adsorption on Co O (a), Pt-A/Co O (b) and Pt-H/Co O (c).\nSupplementary Fig. 35 | a–c, In situ DRIFTS of toluene adsorption on Co O (a), Pt-A/Co O (b)and Pt-H/Co O (c).\n12. The current mechanism discussion fails to clearly identify the rate-determining step in the overall pathway. According to TCD results, the Pt-A catalyst exhibits a stronger toluene adsorption capacity, which the authors posit is the core reason for the enhanced performance over Co O . However, the main catalyst itself shows weak adsorption capacity. The reasons for this should be analyzed.\nResponse: We sincerely appreciate the reviewer’s insightful comments. After careful re-examination, we recognize that the description of the toluene adsorption results may have been unclear, leading to potential misunderstanding. We have revisited the toluene-TPD-MS profiles (Fig. R20a) and note that, in addition to the toluene MS signal, the CO MS signal can also be used to assist in evaluating the toluene adsorption capacity. The toluene signal in the range of 60–220 °C corresponds to the physical adsorption of toluene (Fig. R17a) and the CO signal appearing between 200–450 °C arises from the reaction of chemically adsorbed toluene with surface O (Fig. R20b) (Environ. Sci. Technol. 2023, 57, 20053; ACS Catal. 2024, 14, 4340). Although Pt-H/Co O exhibits slightly less physisorbed toluene than Pt-A/Co O , it demonstrates stronger chemical adsorption of toluene. In contrast, Co O support shows markedly weaker capacity for both physisorption and chemisorption of toluene.\nFig. R20 | a, b, Toluene (a) and CO (b) MS signal of toluene-TPD-MS of Co O , Pt-A/Co O and Pt-H/Co O .\nDFT calculation results (Supplementary Fig. 36) also suggest that the increased toluene adsorption energy (E ) on Pt-A/Co O and Pt-H/Co O relative to the Co O support with the aromatic ring positioned closer to the Co site and Pt-H/Co O exhibits the strongest E . Therefore, combining toluene-TPD-MS and DFT results, it can be concluded that Pt-H/Co O possesses strongest toluene chemisorption capability, which likely correlates with its superior low-temperature catalytic performance.\nSupplementary Fig. 36 | a–c, Models of toluene adsorption on Co O (a), Pt-A/Co O (b) and Pt-H/Co O (c); d indicates the shortest distance between the aromatic ring and the Co site.\nTo address the concern that the current mechanism discussion fails to clearly identify the rate-determining step in the overall pathway, we conduct a more in-depth discussion by combining the result of in situ DRIFTS, TD-GC/MS and DFT calculations.\nBased on in situ DRIFTS results (Figs. 5a–c), the catalytic oxidation of toluene over Pt SACs yields unique intermediates including phenol and benzoquinone, while TD-GC/MS analysis reveals the strongest signal of benzene intermediate over Co O (Supplementary Fig. 34). In addition, both Pt SACs and Co O also share common intermediates including benzyl alcohol, benzaldehyde, benzoic acid, and maleic anhydride. This suggests that the conversion pathway from benzoic acid to maleic anhydride is altered when Pt SAs are supported on Co O . Specifically, over Pt SACs, benzoic acid transforms into maleic anhydride via phenol and benzoquinone, whereas over Co O it may proceed through benzene before ring opening to yield maleic anhydride.\nFig. 5 | a–c, In situ DRIFTS of toluene adsorption on Co O (a), Pt-A/Co O (b) and Pt-H/Co O (c).\nSupplementary Fig. 34 | a–c, TDGC/MS signals of toluene oxidation of Co O (a), Pt-A/Co O (b) and Pt-H/Co O (c).\nTo demonstrate that this novel toluene conversion pathway occurring on Pt SACs is thermodynamically more favorable, we have performed DFT calculations to investigate the relative energy variation during toluene oxidation to maleic anhydride by using the B-VCo -Pt-R3O (representing Pt-H/Co O ) and the B-VO model (representing Co O ).\nBased on extensive DFT optimizations, the primary reaction intermediates identified over Pt-H/Co O include benzyl alcohol, benzaldehyde, benzoic acid, salicylic acid, phenol, hydroquinone, p-benzoquinone, and maleic anhydride (Figs. R5, 6). In contrast, over Co O , the key intermediates comprise benzyl alcohol, benzaldehyde, benzoic acid, benzene, cyclohexadienone, glyoxal, oxalic acid, 1-butynal, and cis-1,4-butenedial (Figs. R7, 8).\nFig. R5 | The specific adsorption configurations of reaction intermediates corresponding to Steps 1–6 in the methyl oxidation process (from toluene to benzoic acid) on B-VCo -Pt-R3O model (representing Pt-H/Co O ).\nFig. R6 | The specific adsorption configurations of reaction intermediates corresponding to Steps 7–21 in aromatic ring-opening process (from benzoic acid to maleic anhydride) on B-VCo -Pt-R3O model (representing Pt-H/Co O ).\nFig. R7 | The specific adsorption configurations of reaction intermediates corresponding to Steps 1–6 in the methyl oxidation process (from toluene to benzoic acid) on B-VO model (representing Co O ).\nFig. R8 | The specific adsorption configurations of reaction intermediates corresponding to Steps 7–21 in aromatic ring-opening process (from benzoic acid to maleic anhydride) on B-VO model (representing Co O ).\nThe resulting energy profiles (Fig. R9) clearly show that the pathway on Pt-H/Co O is significantly more exothermic than that on Co O . Specifically, the methyl oxidation step (toluene → benzoic acid) is lowered by 2.1 eV, and the subsequent aromatic ring-opening step (benzoic acid → maleic anhydride) is lowered by 1.3 eV on Pt-H/Co O relative to Co O . These results illustrate that the significantly improved low-temperature catalytic performance of Pt SACs originates from the new reaction pathway, which substantially lowers the relative energy for intermediate conversion compared to the conventional route on Co O .\nFig. R9 | Comparative relative energy profiles for toluene oxidation into maleic anhydride on Pt-H/Co O and Co O .\nTherefore, we propose that the formation of benzoic acid and the altered conversion pathway of benzoic acid are likely the rate-determining steps, which lead to the substantial enhancement in catalytic performance of Pt-H/Co O over Co O . Since Pt-H/Co O and Pt-A/Co O share the same reaction intermediates, the optimal performance of Pt-H/Co O is likely associated with its superior low-temperature O activation ability, which facilitates the conversion of intermediates.\nWe have included Fig. R18 and Fig. R9 as new Fig. 5d, e and Fig. 5g in the revised Manuscript. In addition, we have added Figs. R5–R8 as Supplementary Figs. 39–42 in the revised Supplementary Information. Corresponding descriptions about toluene adsorption and reaction mechanism have been added to the revised Manuscript in Lines 405411 and Lines 442–458.\nLines 405411\nSubsequently, toluene adsorption was investigated to explore the possibility that its altered adsorption could lead to an adjustment of the reaction pathway. In toluene-TPD-MS characterization, the toluene signal between 60–220 °C corresponds to the physical adsorption of toluene (Fig. 5d) and the CO signal appearing between 200–450 °C arises from the reaction of chemically adsorbed toluene with surface O (Fig. 5e)56,57. Notably, the toluene adsorption capacity is significantly enhanced after Pt SA loading, among which Pt-H/Co O exhibits the largest chemisorption amount.\nLines 442458\nBased on above findings, DFT calculations were performed to investigate the relative energy variation during toluene oxidation to maleic anhydride over Pt-H/Co O and Co O , aiming to demonstrate that this novel toluene conversion pathway occurring on Pt-H/Co O is more conducive to enhancing catalytic activity. As shown in Fig. 5f, the oxidation pathway from toluene to benzoic acid proceeds via identical intermediates (benzyl alcohol and benzaldehyde) on both Co O and Pt-H/Co O . Thereafter, the reaction pathways diverge markedly. For Pt-H/Co O , the transformation proceeds sequentially through salicylic acid, phenol, hydroquinone, p-benzoquinone, maleic acid, and finally maleic anhydride (Supplementary Figs. 39, 40). In contrast, the pathway on Co O involves benzene, cyclohexadienone, 1-butynal, and cis-1,4-butenedial before yielding maleic anhydride (Supplementary Figs. 41, 42). Fig. 5g illustrates that, compared to Co O , the distinct reaction route on Pt-H/Co O reduces the relative energy by 2.1 eV for the methyl oxidation process (toluene to benzoic acid, Steps 1-6) and by an additional 1.3 eV for the subsequent ring-opening process (benzoic acid to maleic anhydride, Steps 6-21). Therefore, the intermediate conversion on Pt-H/Co O is more exothermic, thereby underpinning its superior low-temperature catalytic performance.\n13. The discussion of the mechanism is unclear. The respective roles and functions of O v (oxygen vacancies), Co O , and Pt sites are not explicitly discussed.\nResponse: Thank you for your valuable comment. Based on a series of in situ characterizations and newly supplemented DFT calculation results of the toluene catalytic oxidation pathway, we have now provided a more detailed and in-depth discussion regarding the roles of different active sites and the underlying reaction mechanism.\nIn Co O , oxygen vacancies (Co -OV) serve as sites for O adsorption and activation, while high-valence Co3+ at the octahedral sites (Co ) act as chemisorption centers for the aromatic ring of toluene (Environ. Sci. Technol. 2020, 54, 10342). For the two Pt SACs studied here, the Pt0 SA site exhibits the strongest capacity for O activation. Although Pt4+ SA in octahedral site (Pt ) itself shows weaker O activation capability than Co -OV, the Pt –OV configurations formed by O stripping around Pt at elevated temperatures exhibit superior O activation performance compared to the Co -OV site (Fig. 4 and Supplementary Fig. 31).\nIn addition, Fig. 3d indicates loading Pt SAs strengthens the electron-deficient nature of nearby surface Co (Lines 249255 in revised Manuscript). Synchronously, DFT calculations (Supplementary Fig. 35) demonstrate the increased toluene adsorption energy (E ) on the Pt SACs, with the aromatic ring positioned closer to the Co sites. This geometry is more likely to facilitate the interaction of methyl H and ring H atoms with Pt SA-activated ROS (Lines 417420 in revised Manuscript). These combined effects promote the initial steps of the toluene oxidation reaction.\nSubsequently, we performed DFT calculations to compare the toluene oxidation pathways over Co O and Pt0 SAC. The results indicate that, in the presence of Pt0 SA site, the conversion of toluene to benzyl alcohol, benzaldehyde, and benzoic acid becomes thermodynamically more favorable. Owing to the superior O activation capability and optimized toluene adsorption of Pt0 SA sites, its ROS interacts more strongly with both the methyl group and the aromatic ring of toluene. This alters the ring-opening pathway of benzoic acid—shifting from the route via benzoic acid → benzene → maleic anhydride (on Co O ) to benzoic acid → phenol → benzoquinone → maleic anhydride (on Pt0 SAC), which is thermodynamically more favorable (detailed analysis please refer to the response to comment 12). Consequently, a remarkable 80 °C decrease in T for toluene oxidation 90 is achieved compared to bare Co O .\nDiscussions on OV and Pt SA serving as O activation sites have been incorporated in Lines 352–354 of the revised Manuscript.\nLines 352354\nBased on the above analysis, the Co -OV, Pt -OV, and Pt0 SA serve as the O activation sites for Co O , Pt-A/Co O , and Pt-H/ Co O , respectively.\n14. The core concept of this manuscript proposes “zerovalent platinum single atoms” to address the electronic deficiency of high-valent SAs in O activation. However, the introduction section needs to strengthen the discussion regarding the unique advantages of “zerovalent SAs” and how this work distinguishes itself from existing research.\nResponse: We are grateful for your valuable advice. Following your advice, we have modified the final paragraph of the Introduction section (Lines 76–79 and Lines 82–86 in the revised manuscript) to highlight the unique aspects of the developed Pt0 SAC in terms of its preparation strategy and low-temperature O activation capacity compared to existing reports.\nLines 7679\nBuilding upon our previously developed defect-rich 2D Co O support21,22, we synthesized zero-valent Pt SAs using low-temperature (180 °C) H reduction, substantially reducing the synthesis difficulty for zero-valent Pt SAs compared to current approaches.\nLines 8286\nIn situ techniques and DFT further unveil the mechanism by which zero-valent Pt SAs enhances low-temperature O activation and toluene (a model VOC) oxidation. These findings underscore the unique capability of the developed zero-valent Pt SAs to integrate the advantages of both Pt nanoparticles (efficient oxygen activation) and Pt SAs (high utilization efficiency)."}, {"round": 2, "reviewer_comments": {"reviewer_1": "(1) There is still no direct experimental evidence demonstrating that the atomically dispersed Pt species observed by HAADF-STEM are in the 0 oxidation state. CO-DRIFTS can only confirm the presence of isolated Pt sites, but cannot determine the Pt valence state. Likewise, XPS is inherently incapable of distinguishing single atoms from sub-nanometer Pt clusters.\nThe authors justify their assignment by citing prior work from Zhang Tao’s group (Nat. Commun. 2019). However, this comparison is not appropriate. In that study, the claimed Pt species were low-valent (≈ +0.5) rather than truly zero-valent, and the reactions were conducted under hydrogenation (reducing) conditions, not under strongly oxidative environments. In contrast, the present manuscript explicitly claims Pt⁰ and studies toluene oxidation in air, which fundamentally contradicts chemical intuition.\nIn addition, there appears to be a possible labeling or conceptual error in Fig. 1g regarding the Pt⁴⁺ single-atom configuration, further weakening confidence in the proposed structural assignments.\n(2) The DFT calculations raise additional concerns. In Supplementary Fig. 13, the DFT-calculated CO vibrational frequencies show nearly perfect agreement with experiment, with deviations as small as ~9 cm⁻¹. This level of agreement is highly unrealistic.\nIt is well established that standard DFT functionals systematically overestimate vibrational force constants, leading to uniformly higher frequencies that normally require empirical scaling factors. The near-exact match reported here suggests either over-fitting or an unphysical cancellation of errors, and therefore cannot be considered reliable evidence supporting the proposed Pt coordination or oxidation state.\n(3) The post-reaction HAADF-STEM images obtained after long-term catalytic testing cannot support the existence of Pt⁰ single atoms. Under oxidative reaction conditions, any stable atomically dispersed Pt is far more likely to be high-valent Pt stabilized by multiple Pt–O bonds.\nThe DFT model proposed by the authors—where Pt is coordinated by only one O atom and two Co atoms—would only be thermodynamically plausible under strongly reducing conditions. A simple ab initio thermodynamic phase-diagram analysis would show that, at realistic oxygen chemical potentials, Pt should adopt higher oxygen coordination numbers.\nMoreover, the authors’ own results contradict their claim: Figure R4 shows that O₂ dissociation on the proposed Pt⁰ site is exothermic, implying a strong thermodynamic driving force for the formation of additional Pt–O bonds. This directly undermines the possibility of maintaining a low-coordination Pt⁰ configuration in an oxidative atmosphere.\n(4) Even in the work cited from Zhang Tao’s group (Nat. Commun. 2019), which was conducted under H₂-rich reducing environments, the lowest experimentally observed Pt–O coordination number was still ~2, and this conclusion was directly supported by Pt L₃-edge EXAFS spectra. In contrast, the present manuscript proposes an even lower Pt–O coordination under oxidative conditions, without any Pt-edge EXAFS evidence, which is chemically implausible and inconsistent with established experimental literature.\nIn summary, although the authors have added extensive additional data, the core claim of stable zero-valent Pt single atoms under oxidative reaction conditions remains fundamentally flawed. The arguments rely heavily on indirect characterization and DFT modeling, which are internally inconsistent and, in several cases, contradict basic thermodynamic expectations.\nThus, I still do not recommend publication in Nature Communications.", "reviewer_2": "The manuscript has been well improved after revision; all the queries have been addressed. It is recommended be published at the current status.", "reviewer_3": "The authors have modified the manuscript with care and responded to the reviewers' comments. I suggest accepting it."}, "author_response": "Response to Reviewers’ Comments\nManuscript number: NCOMMS-25-77796A\nTitle: Unleashing the power of zero-valent platinum single atoms for enhancing low-temperature oxygen activation\nResponse to reviewer 1\n1. There is still no direct experimental evidence demonstrating that the atomically dispersed Pt species observed by HAADF-STEM are in the 0 oxidation state. CO-DRIFTS can only confirm the presence of isolated Pt sites, but cannot determine the Pt valence state. Likewise, XPS is inherently incapable of distinguishing single atoms from sub-nanometer Pt clusters. The authors justify their assignment by citing prior work from Zhang Tao’s group (Nat. Commun. 2019). However, this comparison is not appropriate. In that study, the claimed Pt species were low-valent (≈ +0.5) rather than truly zero-valent, and the reactions were conducted under hydrogenation (reducing) conditions, not under strongly oxidative environments. In contrast, the present manuscript explicitly claims Pt0 and studies toluene oxidation in air, which fundamentally contradicts chemical intuition. In addition, there appears to be a possible labeling or conceptual error in Fig. 1g regarding the Pt4+ single-atom configuration, further weakening confidence in the proposed structural assignments.\nResponse: Thank you for your valuable comments. We fully acknowledge the inherent limitations of any single characterization technique (such as XPS or CO-DRIFTS) in unambiguously distinguishing atomic-scale structures and valence states. Therefore, the conclusions in our work are drawn from the cross-validation of multiple experimental techniques, rather than relying on any single dataset. As you correctly noted, CO-DRIFTS confirms the presence of isolated Pt sites (Fig. 1a), while XPS indicates the Pt species in Pt-H/Co O possess a zero-valent state (Fig. 1f). Futhermore, HAADF-STEM imaging (Fig. 1c) shows atomically dispersed Pt species. These results collectively support the conclusion that the Pt in Pt-H/Co O exists predominantly as zero-valent single atoms (Pt0 SAs).\nFig. 1 | a, In situ CO DRIFTS of Pt-A/Co O and Pt-H/Co O . c, HAADF-STEM images of Pt-H/Co O . f, Pt 4f XPS spectra of Pt-A/Co O and Pt-H/Co O .\nRegarding the reference to the work from Prof. Zhang Tao’s group (Nat. Commun. 2019, 10, 4500), we note your point that the reported Pt species (with coordination numbers of 1.8 for Pt–O and 0.8 for Pt–Fe) were characterized as low-valent (+0.56), not strictly zero-valent. In our previous response, we also cited another relevant study from the same group (J. Catal. 2022, 415, 174), where Pt coordinated with two O atoms and one Ce atom was identified as zero-valent. Our citation of these studies is intended to illustrate the general principle that low oxygen coordination combined with Pt–support metal bonding can synergistically stabilize low/zero-valent states, not meant as a direct comparison of coordination numbers. Our work is a further exploration aiming to feature strong Pt–Co bonds and even lower oxygen coordination, thereby stabilizing Pt0 SAs on 2D Co O .\nYou raised a valid concern that in Prof. Zhang Tao’s studies, the low-valent SAs were stabilized under reducing (hydrogenation) conditions, whereas classical thermodynamics would suggest that Pt0 is unstable under strongly oxidative environments. However, the catalytic surface is a dynamic system. In our study, the catalytic activity of Pt-H/Co O remains stable after 48 h of reaction in a toluene/air atmosphere at 140 °C (Fig. 2c). Post-reaction characterization shows that the Pt species retained a predominantly zero-valent according to XPS (Supplementary Fig. 18a) and remained atomically dispersed as confirmed by HAADF-STEM (Supplementary Fig. 19). These results demonstrate the operational stability of Pt0 SAs under our reaction conditions.\nFig. 2 | c, Long-term catalytic stability of Pt-H/Co O at T .\nSupplementary Fig. 18 | a, Pt 4f XPS spectrum of Pt-H/Co O after a long-term catalytic stability test.\nSupplementary Fig. 19 | HAADF-STEM images of Pt-H/Co O after a long-term catalytic stability test.\nMoreover, experimental evidence supports the presence of a strong electronic metal-support interaction (EMSI) between Pt and Co O . Co K-edge XANES (Fig. 3a) and XPS (Fig. 3 b) show a reduction in the Co oxidation state of Pt-H/Co O , indicating significant electronic interaction between Pt and Co. Furthermore, Co K-edge EXAFS (Fig. 3f) reveals a big decrease in the Co coordination number in Pt-H/Co O , providing structural basis for the formation of Pt–Co bonds. This strong interaction provides stable anchoring, preventing the agglomeration of Pt SAs.\nFig. 3 | a, b, Co K-edge XANES spectra (a) and Co 2p XPS spectra (b) of Pt-A/Co O , Pt-H/Co O , Co O , and Co O -H. f, Co K-edge FT k3𝜒 spectra of Pt-A/Co O , Pt-H/Co O , Co O and Co O -H.\nThe dynamic equilibrium process of the toluene catalytic oxidation can also explain the stability of Pt0 SAs. Our DFT calculations (Supplementary Fig. 33) show that O dissociation on Pt0 sites must overcome a distinct energy barrier. This implies that at relatively low reaction temperatures, O is more likely to initially adsorb molecularly as activated reactive oxygen species, which is indeed confirmed by our O -TPD (Supplementary Fig. 29) and EPR experiments (Fig. 4a). Reactive oxygen species do not form coordinating lattice oxygen with Pt0 SAs. As the temperature increases sufficiently to overcome the dissociation barrier, the resulting active oxygen atoms (O*) are rapidly consumed by the continuously fed toluene molecules, ultimately forming CO and H O. This process effectively prevents the coordination of O atoms with Pt0 SAs, allowing the active centers to regenerate within the catalytic cycle. Therefore, Pt0 SAs can remain dynamically stable under the specific conditions of toluene oxidation.\nSupplementary Fig. 33 | a, b, The dissociation energy (E ) and energy barrier of O adsorbed on Pt -OV (a) and Pt0 SA site (b).\nSupplementary Fig. 29 | O -TPD spectra of Pt-A/Co O and Pt-H/Co O .\nFig. 4 | a, EPR signals of DMPO-captured superoxide/peroxide.\nAdditionally, to address your concern about a possible misinterpretation of the Pt4+ SA configuration in Fig. 1g, we have modified it for better clarity. We now use ball-and-stick model specifically for the local Pt coordination structure of both Pt0 SA and Pt4+ SA, while representing the rest of the Co O structure with a wireframe model. This change aims to more clearly visualize the key structural differences in Pt coordination.\nFig. 1 | g, Local coordination model of Pt4+ SA and Pt0 SA. The coordination bonds of Pt with O and Co are highlighted in yellow.\n2. The DFT calculations raise additional concerns. In Supplementary Fig. 13, the DFT-calculated CO vibrational frequencies show nearly perfect agreement with experiment, with deviations as small as ~9 cm-1. This level of agreement is highly unrealistic. It is well established that standard DFT functionals systematically overestimate vibrational force constants, leading to uniformly higher frequencies that normally require empirical scaling factors. The near-exact match reported here suggests either over-fitting or an unphysical cancellation of errors, and therefore cannot be considered reliable evidence supporting the proposed Pt coordination or oxidation state.\nResponse: Thank you for your comment about DFT-calculated CO vibrational frequencies. We fully acknowledge the known limitations of DFT in accurately predicting vibrational frequencies, especially for complex systems such as CO chemisorbed on metal sites. It should be noted that the final frequency deviation in such systems results from the combined effects of multiple factors. On the one hand, the harmonic approximation and functional tend to systematically overestimate force constants; on the other hand, errors in describing metal-adsorbate bonds—especially d-π* back-donation—can independently lead to an underestimation of frequencies. In practice, these errors can partially cancel out in specific chemical environments, leading to calculated frequencies that may appear closer to or lower than experimental values (ACS Catal. 2017, 7, 6887; Nat. Commun. 2019, 10, 3808; Nat. Catal. 2020, 3, 824), which is not a result of intentional parameter adjustment.\nWe maintain that in surface catalysis calculations, the more reliable value of DFT often lies in relative comparisons between different models rather than in achieving perfect absolute agreement with experiment. Our calculations clearly show that the CO vibrational frequency on the Pt0 SA model is lower than that on the Pt4+ SA model, which is in full qualitative agreement with our experimental observation—namely, that the CO adsorption peak of Pt-H/Co O shifts to lower wavenumbers compared to that of Pt-A/Co O . This qualitative correspondence provides strong supporting evidence from theory for the essential difference in the coordination structure of Pt SA between the two catalysts.\nWe explicitly agree with your central concern that the absolute DFT-calculated frequencies should not be treated as a single or decisive piece of evidence for structural determination. In the manuscript, we have only used it as qualitative support. The foundational pillars of our conclusions remain the direct experimental evidence chain from in situ CO DRIFTS, XPS, HAADF-STEM, XAFS, and systematic catalytic performance tests.\nIn the revised manuscript (Lines 175–177), we have refined the description of the theoretically calculated CO adsorption frequencies to emphasize their qualitative agreement with the experimental trends, rather than a strict numerical match.\nLines 175177\nThe peaks obtained by theoretical calculation (Supplementary Fig. 13) at 2079 cm⁻¹ (Pt4+ SA) and 2070 cm-1 (Pt0 SA) exhibit the same qualitative trend in position as observed experimentally (Fig. 1a).\n3. The post-reaction HAADF-STEM images obtained after long-term catalytic testing cannot support the existence of Pt0 single atoms. Under oxidative reaction conditions, any stable atomically dispersed Pt is far more likely to be high-valent Pt stabilized by multiple Pt–O bonds. The DFT model proposed by the authors—where Pt is coordinated by only one O atom and two Co atoms—would only be thermodynamically plausible under strongly reducing conditions. A simple ab initio thermodynamic phase-diagram analysis would show that, at realistic oxygen chemical potentials, Pt should adopt higher oxygen coordination numbers. Moreover, the authors’ own results contradict their claim: Figure R4 shows that O dissociation on the proposed Pt0 site is exothermic, implying a strong thermodynamic driving force for the formation of additional Pt–O bonds. This directly undermines the possibility of maintaining a low-coordination Pt0 configuration in an oxidative atmosphere.\nResponse: Thanks for your valuable comments. Our study aims to demonstrate that, within a carefully designed catalytic system, kinetic factors and dynamic processes are equally crucial in governing the stability of the active centers. As noted in our response to Comment 1, we must first acknowledge the factual existence of atomically dispersed Pt0 SAs in the post-reaction sample, as directly confirmed by XPS (Supplementary Fig. 18) and HAADF-STEM (Supplementary Fig. 19) of the spent Pt-H/Co O . This observation necessitates an explanation that goes beyond static thermodynamics to consider the dynamic nature of the catalytic cycle.\nThe stability of Pt0 SAs arises from the synergy of two key factors: continuous consumption of reactive oxygen species and regeneration of the Pt0 active site. DFT calculations (Supplementary Fig. 33) confirm that O dissociation on Pt0 SA site is exothermic with a kinetic barrier. At lower temperatures, the molecular O chemisorbed on Pt0 SAs remains as reactive oxygen species rather than forming coordinating lattice oxygen, confirmed by our O -TPD (Supplementary Fig. 29) and EPR experiments (Fig. 4a). Under reaction conditions, these reactive oxygen species or the subsequently dissociated active oxygen atoms are rapidly consumed by the continuous flow of toluene molecules. This consumption step prevents the formation of O coordination, allowing the Pt site to undergo periodic regeneration, thereby maintaining the stability of Pt0 SAs in a dynamic equilibrium. Concurrently, the stability of Pt0 SAs is fundamentally anchored by a strong electronic metal-support interaction (EMSI). Co K-edge XANES (Fig. 3a) and Co 2p XPS (Fig. 3b) indicate significant electronic interaction between Pt and Co, and the pronounced local structural perturbation of the support revealed by Co K-edge EXAFS (showing the lowest Co coordination number of Pt-H/Co O , Fig. 3f) provides structure basis for Pt atoms coordinating with Co to form Pt–Co bond. It is precisely this strong interaction that provides the physical foundation for Pt0 SAs to resist irreversible structural evolution throughout the dynamic catalytic cycle.\n4. Even in the work cited from Zhang Tao’s group (Nat. Commun. 2019), which was conducted under H -rich reducing environments, the lowest experimentally observed Pt–O coordination number was still ~2, and this conclusion was directly supported by Pt L -edge EXAFS spectra. In contrast, the present manuscript proposes an even lower Pt–O coordination under oxidative conditions, without any Pt-edge EXAFS evidence, which is chemically implausible and inconsistent with established experimental literature.\nResponse: We sincerely appreciate your rigorous examination regarding the comparison with the cited literature. We would like to clarify again that our reference to the work of Prof. Zhang Tao’s group is intended to draw upon its core design principle—experimentally validated (including by EXAFS)—rather than to directly replicate its specific reaction conditions or coordination numbers. Their series of studies (from stabilizing Pt at approximately +0.56 to zero-valent) clearly demonstrate that fine-tuning the coordination environment (reducing oxygen coordination and introducing Pt–M bonds) enables the modulation of Pt oxidation states. Our work is a further exploration, which attempts to create an environment on 2D Co O that potentially features strong Pt–Co interactions and even lower oxygen coordination, thereby achieving stable Pt0 SAs.\nWe acknowledge that due to technical constraints, we are unable to obtain direct Pt L -edge EXAFS evidence. In surface science and catalysis, when direct probing is limited, converging multiple independent lines of complementary indirect evidence can also lead to a reliable conclusion. In this work, XPS (Supplementary Fig. 18) combined with HAADF-STEM (Supplementary Fig. 19) directly identifies the post-reaction Pt species as Pt0 SAs. Co K-edge XANES (Fig. 3a) and Co 2p XPS (Fig. 3b) reveal significant electronic interaction between Pt and Co, and the pronounced local structural perturbation of the support observed via Co K-edge EXAFS (Fig. 3f) provides experimental evidence for an interaction between Pt and the Co O lattice, supporting the model of Pt–Co bond formation. Moreover, the unique low-temperature O activation and toluene oxidation performance of Pt0 SAC (Pt-H/Co O ) are entirely consistent with the expected chemical behavior of an electron-rich Pt0 SA center.\nTherefore, the coordination model we propose is a self-consistent interpretation of the ensemble of experimental observations. Regarding your concern about the stability of Pt0 SAs under oxidative conditions, we have provided detailed explanations in our Responses to Comments 1 and 3: The stability of Pt0 SAs in our system originates from the continuous consumption of reactive oxygen species and the regeneration of the Pt0 active site within the dynamic catalytic cycle.\nBased on the above analysis, we have added a discussion on the experimental evidence of Pt–Co coordination in Lines 272273 of the revised manuscript.\nLines 272273\nThis substantial reduction in Co coordination in Pt-H/Co O provides a structural foundation for the formation of Pt–Co bonds.\nResponse to reviewer 2\nComments: The manuscript has been well improved after revision; all the queries have been addressed. It is recommended be published at the current status.\nResponse: We sincerely thank you for your positive and constructive evaluation of our revised manuscript. We are delighted to know that you find the manuscript well improved and that all questions have been addressed. Your recognition and recommendation for publication are greatly encouraging to us. Thank you once again for your valuable time and effort spent on reviewing our work.\nResponse to reviewer 3\nComments: The authors have modified the manuscript with care and responded to the reviewers' comments. I suggest accepting it.\nResponse: We thank you very much for your supportive comments and for acknowledging our careful modifications and detailed responses to your comments. We are truly grateful for your time, insightful suggestions throughout the review process, and for your final recommendation to accept the manuscript. Your expertise has been instrumental in improving the quality of our work."}]

Decision letter