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

Tungsten trioxide (WO 3 ) has been recognized as the most promising photocatalyst for highly selective oxidation of methane (CH 4 ) to formaldehyde (HCHO), but the origin of catalytic activity and the reaction manner remain controversial. Here, we take {001} and {110} facets dominated WO 3 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 CH 4 and H 2 O and the different CH 4 activation routes on WO 3 surface are responsible for diverse CH 4 oxidation pathways. The microscopic mechanism elucidation provides the guidance for designing high performance photocatalysts for selective CH 4 oxidation. Tungsten trioxide (WO 3 ) is considered the most promising photocatalyst for the highly selective oxidation of methane to formaldehyde, though the origins of its catalytic activity and reaction mechanism are still debated. Here, the authors use WO 3 with {001} and {110} facets as model photocatalysts, demonstrating that the photocatalytic oxidation of methane to formaldehyde in WO 3 depends on the surface structure, leading to different formaldehyde selectivity.