Identifying and Engineering Active Sites at the Surface of Porous Single-Crystalline Oxide Monoliths to Enhance Catalytic Activity and Stability

Abstract

Open AccessCCS ChemistryRESEARCH ARTICLE1 Apr 2022Identifying and Engineering Active Sites at the Surface of Porous Single-Crystalline Oxide Monoliths to Enhance Catalytic Activity and Stability Guoming Lin, Hao Li and Kui Xie Guoming Lin Key Laboratory of Optoelectronic Materials Chemistry and Physics, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002 , Hao Li Key Laboratory of Optoelectronic Materials Chemistry and Physics, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002 and Kui Xie *Corresponding author: E-mail Address: [email protected] Key Laboratory of Optoelectronic Materials Chemistry and Physics, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002 Key Laboratory of Design and Assembly of Functional Nanostructures, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002 Fujian Science and Technology Innovation Laboratory for Optoelectronic Information of China, Fuzhou, Fujian 350108 Advanced Energy Science and Technology Guangdong Laboratory, Huizhou, Guangdong 116023 https://doi.org/10.31635/ccschem.021.202000740 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Identifying and engineering active sites play a key role in many catalytic reactions. Herein, we create well-defined surface structures through the growth of porous single-crystalline Mn3O4 and Mn2O3 monoliths at centimeter scale and confine atomically dispersed Pt ions in the lattice at the twisted surface to construct isolated active sites. The activation of lattice oxygen linked to isolated Pt ions is much more effective than the lattice oxygen linked to Mn ions in local structures, leading to an approximately seven- to eightfold enhancement of surface oxygen exchange coefficients for catalytic CO oxidation. The active structures of PtO1.5 and PtO1.4 confined at the well-defined surfaces contribute to the efficient activation of lattice oxygen linked to Pt ions in local structures in addition to the chemisorption of CO in the oxidation reaction. We demonstrate the complete CO oxidation with air at 65 °C without degradation being observed even after continuous operation of 300 h. Download figure Download PowerPoint Introduction Catalytic oxidation reactions require specific oxidant, either from O2 or other oxygen-containing oxidant, to accomplish the oxidation reactions in which the oxidants are chemically adsorbed and activated on active sites at catalyst surfaces.1–5 Activation of oxygen at the active sites that have unsaturated coordination structures, therefore, plays a key role to lower operation temperature in many catalytic oxidation reactions; however, the competitive adsorption of reactants blocks the chemisorption of oxygen and, hence, prohibits the activation of oxygen at the active sites.6–9 In this case, higher operation temperature is required to activate oxygen in these catalytic reactions. Activation of lattice oxygen at the surface of catalysts would provide an alternative to enhance the catalytic activity in oxidation reactions. The dynamic equilibrium of defect reaction between oxygen vacancy and adsorbed oxygen at the surface of catalyst would deliver a continuous supply of activated lattice oxygen for the oxidation reactions, leading to the reduction of the operation temperatures.10–12 Isolated sites with impurity ions are one of the ideal states of supported metal catalyst, which can uniformly distribute the metal ions on the surface of substrates. Isolated active sites are the center of catalytic activity in many heterogeneous reactions and would deliver high activity and high selectivity and provide a new solution to study the catalytic mechanisms.13–17 Three-way catalysis plays a key role in automotive catalysis in which lowering the operation temperature would be essential to minimize exhaust emissions. Currently preferred Pt-loaded oxide catalysts operate at a relatively high temperature of ∼150 °C to maintain the complete oxidation of CO with air. The strong chemisorption of CO molecules at the surface of Pt catalysts blocks the activation of oxygen, thus leading to the high operation temperatures in catalytic reactions.18–20 The activation of lattice oxygen linked to the active sites would be an alternative method to reduce operation temperature, but it remains a fundamental challenge to induce complete CO oxidation at lower temperatures. Porous single crystals combining both single-crystalline properties and interconnected pores would deliver a unique advantage to create well-defined structures at the twisted surfaces that are kinetically trapped. The large surface areas in the porous architectures would sufficiently host chemical reactions.21–23 The surface with clear top-layer atoms is therefore confined by the long-range ordering of lattice structures in the porous single-crystalline (PSC) architectures. The activation of lattice oxygen at the surface could be further manipulated through a surface engineering strategy such as element doping in the lattice. The well-defined surface structures thus provide an advantage for the construction and identification of active sites, which is expected to tailor the chemical interactions with adsorbed species through engineering the electronic structures at the surfaces. Here, the porous single crystals at centimeter scale are typical PSC monolithic catalysts. Traditional monolithic catalysts in polycrystalline states are mainly prepared from catalyst particles by mechanical forming and sintering. In contrast, PSC monoliths are in single-crystalline states with three-dimensional porous microstructures. They combine the advantages of the long-range ordering of lattice structures and the disordering of interconnected pores in a single-crystalline porous architecture. Therefore, they could deliver higher stability like bulk single crystals and higher activity like nanocrystals in catalysis. Transition-metal oxides such as manganese oxides (MnOx) are commonly used as catalyst substrates, which show various morphologies and phases, multiple 3d electron configurations, and broad ranges of oxygen storage capacities in catalytic oxidation reactions.24,25 The oxygen vacancies at the surface of MnOx are the main surface defects, and they can normally interact with metal species to construct the active sites or interfaces. In catalytic reactions, the dynamic equilibrium of oxygen nonstoichiometry simultaneously arises from the reversible defect reactions between the oxygen vacancy and adsorbed oxygen at surfaces, thus providing a unique opportunity to activate lattice oxygen at surfaces.26–28 The manipulation of active sites and their electronic structures at the well-defined surfaces would lead to controllable chemical interactions between the active sites and adsorbed species during the catalytic oxidation of CO with air.29–31 In this case, a reduced operation temperature is anticipated by precisely identifying and engineering active sites at the surface of PSC oxide monoliths to enhance the catalytic activity and stability. Here, we grow PSC Mn3O4 and Mn2O3 monoliths at centimeter scale to create well-defined surface structures and confine the atomically dispersed Pt at Mn sites in the lattice at the twisted surfaces to construct isolated active sites in the PSC architectures. We demonstrate the significantly enhanced activation of lattice oxygen linked to the isolated Pt ions in lattice in the local structures at the well-defined surfaces. Using PSC monoliths, we show the complete CO oxidation with air at 65 °C without degradation being observed even after operation for 300 h. Experimental Methods Crystal growth Mn2P2O7 and MnCO3 parent single crystals were used to grow PSC Mn2O3 and Mn3O4 monoliths using a lattice reconstruction strategy.23 We grew the Mn2P2O7 single crystals using a flux method. The porous Mn3O4 single crystal was grown from the Mn2P2O7 parent single crystals in an atmosphere of 50 Torr with Ar (flow rate of 500 sccm) at 650–750 °C. The porous Mn2O3 single crystal was grown from Mn2P2O7 parent single crystals in an atmosphere of 100 Torr with 5% O2/Ar (flow rate of 600 sccm) at 700–800 °C. We also used MnCO3 parent single crystals to grow porous Mn3O4 and Mn2O3 single crystals. The growth of Mn3O4 requires an atmosphere of 300 Torr with Ar (flow rate of 500 sccm) at 500–600 °C. The growth of Mn2O3 was conducted in an atmosphere of 200 Torr with 5% O2/Ar (flow rate of 600 sccm) at 550–650 °C. Construction of isolated Pt1 sites We loaded the isolated Pt to the surface of PSC monoliths using the atomic layer deposition (ALD) approach at ∼1 Torr in a stainless-steel cylinder reactor system (D100-4882; YAONA, Chongqing, China). Argon (99.999%) was used as carrier gas and continuously passed through the reactor at the flow rate of 50 sccm. We used platinum 2,4-pentanedionate [Pt(acac)2, Sigma-Aldrich, Shanghai, China, >99%] as the precursor for the loading of isolated Pt sites at the surface. The PSC monoliths were treated with one cycle of ALD at 200 °C. The duration of first Ar purge, Pt(acac)2 exposure, ozone exposure, and the second Ar purge were 0.5, 1, 1.5, and 2 min, respectively. The characterization method, X-ray absorption fine structure (XAFS) measurements, and calculation method are available in the Supporting Information. Catalytic oxidation reaction We performed the catalytic reaction of CO oxidation at atmospheric pressure in a tubular quartz microreactor with inner diameter of 5 mm. PSC monoliths with the diameter of 5 mm and the thickness of 0.5 mm were loaded. For the CO oxidation reaction, the temperature was increased from 25 to 250 °C with a heating rate of 2 °C min−1. The reaction gas, consisting of 1% CO and 16% O2 balanced with Ar, was fed to the reactor at a total flow rate of 25 sccm. The reaction products were analyzed using on-line gas chromatography (GC) equipped with both flame ionization detector (FID) and thermal conductivity detector (TCD) (GC-2014; Shimadzu, Kyoto, Japan), and a 30 m packed column of CP-poraplot Q. Results and Discussion Growth of PSC Mn3O4 and Mn2O3 monoliths We grew the porous Mn3O4 and Mn2O3 single crystals from the (001) Mn2P2O7 and (014) MnCO3 parent single crystals using a lattice reconstruction strategy, respectively. Supporting Information Figure S1 shows the lattice structures of parent single crystals with atomic evaporation channels, where the (001) Mn2P2O7 shows a vertical channel for the removal of P/O atoms and the (014) MnCO3 shows a vertical channel for the removal of C/O atoms. Under vacuum condition, the removal of P/O and C/O through the lattice channels creates defects at atomic scale leading to a metastable state of the ordered lattice structures. At high temperatures, the reconstruction of lattice structures in a crystallization process would lead to the formation of interconnected pores, and the lattice shrinking from parent carbonate and phosphate single crystals to oxide single crystals mainly contributes to porosity and the formation of pore structure. In this case, other parent single crystals with proper lattice channels and lattice parameters are suitable for the growth of porous single crystals using the lattice reconstruction strategy. The parent single crystals were polished to reduce the mean surface roughness at the surface to <0.2 nm, which is sufficient to eliminate the surface instability for the growth of porous single crystals using the lattice reconstruction strategy ( Supporting Information Figure S2). Figure 1a shows the X-ray diffraction (XRD) pattern of the PSC (100) Mn3O4 grown on (001) Mn2P2O7 and (014) MnCO3 parent single crystals, which confirms the single-crystalline feature of long-range ordering of the crystal lattice. The atomic force microscopy (AFM) image of the porous microstructure (Figure 1b) indicates uniform pores with an average diameter of ∼30 nm, consistent with the pore size in the Brunauer–Emmett–Teller (BET) test presented ( Supporting Information Figure S3). Figure 1c shows the cross-sectional scanning transmission electron microscopy (STEM) and selected area electron diffraction (SAED) images, in which the slice with porous ultrathin microstructure with the facet of (100) is made by focused ion beam (FIB) milling. The pores are distributed homogeneously, and the pore size of ∼30 nm matches the results of AFM and BET tests as discussed above. The SAED in the inset again validates the single-crystalline features of the interconnected skeletons in the porous architectures. Figure 1 | Lattice structure, microstructure, and chemical states of porous Mn3O4 single crystal. (a) XRD pattern; digital inset. (b) AFM images of a single crystal (Φ10 mm × 0.5 mm). (c) Cross-sectional STEM image of pore structure; SAED inset. (d) HRTEM image of the pore structure. (e and f) Cs-HRTEM with atom stacking. (g) HAADF-STEM image and elemental mapping. The red, white, and green balls represent oxygen, Mn3+, and Mn2+ atoms, respectively. (h) XPS and HS-LEIS spectra. (i) Differential charge density graph of top layer of porous Mn3O4 single crystal. Download figure Download PowerPoint The high-resolution TEM (HRTEM) image (Figure 1d) shows identical lattice orientations around the pores when viewed from a fixed direction, in which the long-range ordering of the crystal lattice further proves the single-crystalline property. The ordered lattice around the pores therefore creates twisted surfaces that are kinetically trapped. In Figure 1e, the spherical aberration correction TEM (Cs-TEM) image shows the lattice spacing of 0.288 and 0.288 nm, which refer to the (200) and (020) planes, respectively. The mole ratio between the metal and O in porous Mn3O4 single crystal is calculated as ∼0.75 by elemental analysis ( Supporting Information Figure S3). The atomic stacking in the skeleton around the pores presents the periodical and ordered atom stacking in the lattice (Figure 1f). Figure 1g shows the elemental mapping in the skeleton, which indicates significant distribution of Mn and O elements. The high-sensitive low-energy ion scattering (HS-LEIS) spectra in Figure 1h confirms the presence of Mn together with O at the top layer of the porous Mn3O4 single crystal. The X-ray photoelectron spectroscopy (XPS) image in the inset shows the typical ionic Mn–O bonding in the bulk. In the HS-LEIS spectrum with Ne+ scattering, no metal signal other than Mn is detected on the top layer of the porous Mn3O4 single crystal. In contrast, the Mn occupies most of the atoms at the top layer in the HS-LEIS with He+ scattering. Figure 1i shows the differential charge diagram of the periodical Mn–O coordination structures at (100) Mn3O4, which indicates the obvious charge transfer from Mn to O in the local structures. The growth, microstructures, and coordination structures of porous Mn2O3 single crystals will be briefly discussed later. Identification of isolated active sites We confined the isolated Pt at the site of Mn in the lattice at the top layer of porous Mn3O4 and Mn2O3 single crystals using an ALD strategy. The HS-LEIS spectra in Figure 2a show the successful deposition of Pt at the top layer of porous single crystals. The Fourier transform (FT) of k3-weight of extended XAFS (EXAFS) spectrum for the isolated Pt1/PSC-Mn3O4 shows a radial distribution at ∼1.62 Å for the Pt–O coordination, whereas the Pt–Pt distribution at ∼2–3 Å is not observed in Figure 2b.12 The X-ray absorption near-edge spectroscopy (XANES) measurements ( Supporting Information Figure S4) confirm that the valence states of isolated Pt species at the top layer of PSC-Mn3O4 are between Pt4+ and Pt0. We further obtained the coordination number of Pt–O bonds by fitting the EXAFS data in Figure 2c and Supporting Information Table S1. It was observed that one Pt atom is coordinated by seven oxygen atoms per the simulation results. We therefore propose a Pt–O5(O2) structure in the inset of Figure 2c, which shows a single Pt atom coordinates with five individual lattice oxygen atoms and one oxygen molecule chemically adsorbed from the atmosphere. High-angle annular dark-field (HAADF)-STEM imaging and elemental mapping of the Pt1/PSC-Mn3O4 sample reveals the uniform dispersion of the isolated Pt in the lattice of the Mn3O4 skeleton (Figure 2d). The homogeneous distribution of isolated Pt at the top layer of the PSC Mn3O4 is presented by Cs-HRTEM imaging of Pt1/PSC Mn3O4 (Figures 2e and 2f). Neither diffraction peaks of Pt in XRD patterns nor obvious changes in Raman spectra are observed for the PSC Mn3O4 even after the loading of Pt by the ALD strategy as shown in Supporting Information Figure S5. Figure 2 | Identification of Pt–O active sites at the top layer of PSC Mn3O4. (a) HS-LEIS spectra of Pt1/PSC-Mn3O4. (b) FT of k3-weighted EXAFS spectra of isolated Pt1 on porous single crystal, PtO2, and Pt foil. (c) The FT-EXAFS curves of the proposed Pt–O5(O2) architecture. Inset is the proposed model of Pt–O5(O2) architecture. (d–f) HAADF-STEM image, elemental mapping, and HRTEM image of porous Mn3O4 single crystal with isolated Pt. Inset image is the line scan of selected area. (g–i) Lattice structure, electron density difference diagrams, and differential charge density graph of pristine, PtO1.5, and PtO1.4 active site viewed along the [001] orientation of Pt1/PSC-Mn3O4. Purple, red, and black balls represent Mn, O, and Pt, respectively. Download figure Download PowerPoint Figure 2g and Supporting Information Figure S6 show the top and side view of the lattice structure, electron density difference diagrams, and differential charge density graph of Mn3O4 viewed along the [001] direction. The coordination structures of the PtO1.4 and PtO1.5 active sites are clarified by the comparative analysis of the Cs-HRTEM image and lattice structures (Figures 2h and 2i). The structures of PtOx are calculated per the equation, x = 1/A + 1/B + 1/C + 1/D + 1/E, where A–E is the coordination number of five O atoms bonding with Pt atom, as shown in Supporting Information Figure S7. The coordination structures of PtO1.5 and PtO1.4 active sites dominate the catalytically active structures at the top layer of porous Mn3O4 single crystals. The density of the Pt–O active sites and the average distance between active sites are calculated to be ∼0.8 nm−2 and ∼1.25 nm, respectively. The specific surface area of PSC Mn3O4 is ∼20 m2 g−1. The content of Pt–O active sites is therefore as high as ∼1.6 × 1019 per gram of PSC Mn3O4, which is consistent with the 0.5 wt % loading content of isolated Pt catalysts. High specific areas are advantageous to increasing Pt loading weight and the atomic dispersion of Pt under higher loading weight.32 In future studies we will focus on other parent single crystals with proper lattice parameters to grow porous single crystals with higher specific surface areas using the lattice reconstruction strategy. We further calculated the defect formation energy of lattice oxygen linked to Mn and Pt ions at (001) Mn3O4 ( Supporting Information Figure S8). The defect formation energy is as high as 3.89 eV for the oxygen linked to Mn at the top layer of (001) Mn3O4. In contrast, the lattice oxygen linked Pt in the local structure of PtO1.5 and PtO1.4 at the top layer of (001) Mn3O4 demonstrates significantly reduced defect formation energies of 1.50 and 1.81 eV, respectively. It means that the homogeneously distributed Pt–O active sites highly contribute to the dynamic formation of oxygen vacancy in the Pt–O–Mn local structures at the top layer of porous Mn3O4 single crystals. We grew PSC Mn2O3 and prepared Pt1/PSC-Mn2O3 using the ALD strategy. Figure 3a shows the XRD pattern of PSC Mn2O3 with the preferential growth of [110] orientation from Mn2P2O7 and MnCO3 single crystals. The STEM image of PSC Mn2O3 indicates an ∼30 nm pore size in the porous architectures (Figure 3b). The SAED image in the inset shows the single-crystalline property of the skeleton with [110] lattice orientation, which is consistent with the preferential growth of the (110) facet of PSC Mn2O3 in the XRD results. The porous architectures and average pore size of PSC Mn2O3 are similar to those of the PSC Mn3O4. Figure 3c shows the Cs-HRTEM image with the lattice spacing of 0.384 and 0.166 nm, which refer to the (112) and (440) planes, respectively. The atomic stacking in the inset shows the ordered distribution of Mn and O atoms, which again validates the single-crystalline features of the skeletons. The mole ratio between Mn and O in the porous Mn2O3 single crystal is calculated to be ∼0.67 from the elemental analysis ( Supporting Information Figure S3). HS-LEIS spectroscopy confirms the presence of Mn together with O at the top layer of PSC Mn2O3, whereas the XPS shows a typical ionic Mn–O bond ( Supporting Information Figures S9a and S9b, respectively). Figure 3 | Identification of Pt–O active sites at the top layer of PSC Mn2O3. (a) XRD pattern and digital image of PSC Mn2O3 (Φ10 mm × 0.5 mm). (b) Cross-sectional STEM and SAED of the porous architectures. (c) Cs-HRTEM image of the skeleton. Inset shows the atomic stacking. Red and blue balls represent O and Mn atoms, respectively. (d) HS-LEIS spectra of PSC Mn2O3 with and without isolated Pt sites. (e) HAADF-STEM image and elemental mapping of PSC Mn2O3 with isolated Pt sites. (f) HRTEM image of PSC Mn2O3 with isolated Pt sites. Lattice structure, electron density difference diagrams, and differential charge density graph of (g) Mn2O3 single crystal, (h) PtO1.4, and (i) PtO1.5 active sites at top layer viewed along [111] direction. Purple, red, and black balls represent Mn, O, and Pt atoms, respectively. Download figure Download PowerPoint The differential charge diagram of the Mn–O coordination structure shows obvious charge transfer from Mn to O atoms on the top layer as shown in Supporting Information Figure S9c. In the Pt1/PSC-Mn2O3, the isolated Pt ions are atomically dispersed at the site of Mn in the lattice at the top layer of PSC Mn2O3 per the elemental mapping and Cs-HRTEM image in Figures 3d–3f. An absence of Pt–Pt first- and second-shell interactions in the EXAFS results further confirms atomically dispersed Pt ions in the lattice at the top layer ( Supporting Information Figure S9d). The coordination number of Pt–O active sites is generally similar to that of the Pt1/PSC-Mn3O4. The active sites of PtO1.4 and PtO1.5 dominate the isolated Pt sites in the lattice at the top layer of Pt1/PSC-Mn2O3, as shown in Figures 3g–3i. Obvious charge transfer from Pt to O is observed, leading to the electron-deficient states of isolated Pt ions in the lattice at the surface. Supporting Information Figure S10 shows that the defect formation of lattice oxygen linked to Mn at (111) Mn2O3 is as high as In contrast, the calculated formation energy of oxygen vacancy linked to Pt ions in the local structures of PtO1.5 and PtO1.4 active sites are reduced to and eV, respectively. It that the lattice oxygen linked to isolated Pt ions is much more active than that linked to Mn in the lattice at the top layer of the Catalytic of CO oxidation We conducted in FT spectroscopy of CO adsorption for both Pt1/PSC-Mn3O4 and Pt1/PSC-Mn2O3, which shows the typical at for the of CO to isolated Pt ions at surfaces, to the isolated sites ( Supporting Information Figure We used the conductivity method to the surface oxygen exchange that is mainly by the defect reaction during the reversible between oxygen vacancy and lattice oxygen at surfaces. In Figure both Pt1/PSC-Mn3O4 and Pt1/PSC-Mn2O3 show surface oxygen exchange coefficients significantly enhanced to approximately seven- and eightfold in to the PSC Mn3O4 and PSC Mn2O3, respectively. The effective activation of lattice oxygen linked to isolated Pt ions in the lattice the formation energy of oxygen vacancy as by density ( Supporting Information Figures and The loading of isolated Pt sites at the surface of deliver enhanced surface oxygen exchange coefficients in to Figures and show the conductivity of and Pt1/PSC-Mn2O3, which indicates that the loading of isolated Pt sites at the top layer of PSC oxides on the The loading of isolated Pt to the of the and of the ( Supporting Information Table S2). The enhancement of surface oxygen exchange coefficients of Pt1/PSC-Mn3O4 and Pt1/PSC-Mn2O3 is mainly by the effective activation of lattice oxygen linked to isolated Pt ions at the top layer of PSC Figure | of Pt1/PSC-Mn3O4 and (a) Surface oxygen exchange characterization with oxygen pressure from 1 × to 1 × (b) of conductivity of with and without isolated Pt sites. (c) of conductivity of with and without isolated Pt sites. and pressure X-ray photoelectron spectrum of Pt and Mn of the Pt1/PSC-Mn3O4 with from ∼1 × to 1 × (f) The differential charge of Pt–O active sites at surface. Download figure Download PowerPoint We used pressure XPS to study the valence state of the metal ions at the surface of in with oxygen The Pt spectra of the Pt1/PSC-Mn3O4 confirms the of Pt4+ and species at the isolated Pt sites at the top layer of PSC-Mn3O4 at ∼1 × (Figure In contrast, the Pt4+ ions are reduced to as the oxygen pressure to ∼1 × that the activity of Pt ions is even in such a of oxygen Figure shows that the valence states of Mn ions generally which confirms that the activity of Mn ions is much than that of Pt ions in lattice with the of oxygen The electronic structures of the surface of PSC oxide are with the of Pt to Mn and O at the top that the electronic structures of manganese oxide are similar to that of Pt after the loading of isolated Pt ( Supporting Information Figure The activation of lattice oxygen in the local structure of the PtO1.5 and PtO1.4 active sites (Figure contributes to the enhanced surface oxygen exchange Mn3O4 and Mn2O3 demonstrate chemical but the local structures and of the Pt–O active sites are generally similar to other at the top layer of the Mn3O4 and Mn2O3. The similar structure of active sites be to the of activity of Pt ions in the lattice even at the top layer of Mn2O3 and Mn3O4. active sites are the of the catalytic activity oxidation reaction. Figures show the of CO PSC Mn2O3, PSC Mn3O4, and Pt1/PSC-Mn2O3 at °C. oxidation of CO with air is observed at °C for both PSC Mn2O3 and PSC Mn3O4. The loading content of 0.5 wt % of isolated Pt at the top layer of PSC oxides the operation temperatures to as as 65 °C. In this case, the activation of lattice oxygen linked to isolated Pt ions in lattice at the top layer of PSC oxides contributes to the enhanced catalytic activity and the operation temperature for CO oxidation. Figures and shows the of CO oxidation with Pt1/PSC-Mn3O4 and Pt1/PSC-Mn3O4 wt % of which demonstrates the high stability of CO oxidation even after 50 In Figure both Pt1/PSC-Mn3O4 and Pt1/PSC-Mn2O3 show stability without degradation of even after operation for 300 h. For the Pt-loaded

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