Photo-Thermo Catalytic Oxidation of C<sub>3</sub>H<sub>8</sub> and C<sub>3</sub>H<sub>6</sub> over the WO<sub>3</sub>-TiO<sub>2</sub> Supported Pt Single-Atom Catalyst

Abstract: Catalytic oxidation is a commonly employed technology in the industry for removing volatile organic compounds (VOCs) due to its exceptional efficiency under mild operating conditions. Although supported Pt-based nano-catalysts are recognized widely as one of the most promising and extensively used industrial catalysts for VOC abatement, their practical application, and development are restricted by their exorbitant cost. Single-atom catalyst (SAC) with maximized metal utilization and exclusive electronic character has been explored extensively in various catalytic reactions. However, Pt SAC is usually deemed to be inactive in hydrocarbon oxidation reactions in thermal catalysis, compared with its nanoparticle counterpart. Here, we demonstrate that the WO3-TiO2 supported Pt SAC (Pt1/WO3-TiO2) exhibits much higher activities than the corresponding nanoparticle catalyst (PtNP/WO3-TiO2) in photo-thermo catalytic oxidation of C3H8 and C3H6, which represent different kinds of typical VOCs. A key finding is that the activities of Pt1/WO3-TiO2 and PtNP/WO3-TiO2 can be accelerated in photo-thermo catalytic C3H8 oxidation by overcoming oxygen poisoning. Upon the light irradiation, the apparent active energy (Ea) of the Pt1/WO3-TiO2 and PtNP/WO3-TiO2 decline from 116 to 60 kJ·mol-1 and from 103 to 30 kJ·mol-1, respectively, substantiating their effectiveness in photo-thermo catalysis. Notably, a substantially higher reaction rate of 3792 μmol∙gPt-1∙s-1 on the Pt1/WO3-TiO2 is achieved, which should be a benchmark for C3H8 oxidation. More intriguingly, photo-thermo catalytic C3H6 oxidation on the PtNP/WO3-TiO2 is prohibited due to the strong adsorption-induced C3H6 poisoning on the Pt nanoparticles, for which the Ea of the PtNP/WO3-TiO2 catalyst for C3H6 oxidation is maintained at approximately 55 kJ·mol-1, regardless of the light irradiation. In comparison, the C3H6 poisoning on the Pt1/WO3-TiO2 can be mitigated by light illumination, where the Ea of the Pt1/WO3-TiO2 catalyst for C3H6 oxidation dramatically reduced from 49 to 16 kJ·mol-1, signifying that the high energy barrier of C3H6 oxidation can be mediated by the light. Profiting from the apt affinity between C3H6 and Pt single atoms, the photogenerated electrons accumulated on the Pt single atoms produce repulsive force towards the electron-rich C3H6 molecules, which is conducive to the C3H6 desorption from the Pt1/WO3-TiO2. Therefore, the Pt1/WO3-TiO2 exhibits enhanced activity in photo-thermo catalytic C3H6 oxidation. This study exemplifies that the advantages of SAC are not only saving the consumption of precious metals but also discovering new catalytic reactions on the account of the specific electronic characteristic.