Photo-Thermo Catalytic Oxidation of C3H8 and C3H6 over the WO3-TiO2 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 (Pt_NP/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 Pt_NP/WO₃-TiO₂ can be accelerated in photo-thermo catalytic C₃H₈ oxidation by overcoming oxygen poisoning. Upon the light irradiation, the apparent active energy (E_a) of the Pt₁/WO₃-TiO₂ and Pt_NP/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∙g_Pt⁻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 Pt_NP/WO₃-TiO₂ is prohibited due to the strong adsorption-induced C₃H₆ poisoning on the Pt nanoparticles, for which the E_a of the Pt_NP/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 E_a 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.

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