Regulating protonation paths for enhanced photocatalytic CO2 methanation by coupling Pt sites on WO2.9/TiO2

Abstract

CO₂ methanation via photocatalysis with water vapor is a sustainable technique for reducing CO₂ emission but is challenged by the high energy barrier associated with the initial adsorption, activation and protonation of CO₂ molecules. In this work, a substoichiometric WO_2.9 thin film with strong Lewis acidity was coated on TiO₂ microspheres, followed by the deposition of Pt cocatalysts on WO_2.9 with controlled Pt single atoms and clusters (Pt–WO_2.9/TiO₂). The methane production rate reached 10.74 μmol h⁻¹ g⁻¹ with a selectivity of 99.8%, which was ∼40 times higher than that of bare TiO₂ (0.27 μmol h⁻¹ g⁻¹). The high methane production rate was attributed to the synergy of Pt sites on the WO_2.9/TiO₂ heterojunction, where the Pt clusters facilitated water dissociation, thereby providing H* through hydrogen spillover on the surface, and the presence of a substoichiometric WO_2.9 surface further enhanced the spillover process. The high density of active H* promoted the protonation pathway for CO₂ activation (CO₂ → COOH⁺ → *COOH), which improved the adsorption of the essential intermediate *CO on Pt single atoms and displayed a significantly reduced energy barrier for the protonation reaction of C1 intermediates, resulting in a mixed reaction pathway. This work provides new insights into a mechanism to regulate the reaction path to facilitate efficient photocatalytic CO₂ methanation.