Insight into selectivity of photocatalytic methane oxidation to formaldehyde on tungsten trioxide

Tungsten trioxide (WO₃) has been recognized as the most promising photocatalyst for highly selective oxidation of methane (CH₄) to formaldehyde (HCHO), but the origin of catalytic activity and the reaction manner remain controversial. Here, we take {001} and {110} facets dominated WO₃ as the model photocatalysts. Distinctly, {001} facet can readily achieve 100% selectivity of HCHO via the active site mechanism whereas {110} facet hardly guarantees a high selectivity of HCHO along with many intermediate products via the radical way. In situ diffuse reflectance infrared Fourier transform spectroscopy, electron paramagnetic resonance and theoretical calculations confirm that the competitive chemical adsorption between CH₄ and H₂O and the different CH₄ activation routes on WO₃ surface are responsible for diverse CH₄ oxidation pathways. The microscopic mechanism elucidation provides the guidance for designing high performance photocatalysts for selective CH₄ oxidation.