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.

三氧化钨 （WO₃） 被认为是最有前途的光催化剂，用于将甲烷 （CH₄） 高度选择性氧化为甲醛 （HCHO），但催化活性的来源和反应方式仍然存在争议。在这里，我们以 {001} 和 {110} 个方面为主的 WO₃ 作为模型光催化剂。显然，{001} 面可以通过活性位点机制轻松实现 HCHO 的 100% 选择性，而{110}面几乎不能保证通过自由基方式对 HCHO 以及许多中间产物的高选择性。原位漫反射红外傅里叶变换光谱、电子顺磁共振和理论计算证实，CH₄ 和 H₂O 之间的竞争性化学吸附以及 WO₃ 表面不同的 CH₄ 活化途径是导致 CH₄ 氧化途径不同的原因。微观机理阐明为设计用于选择性 CH₄ 氧化的高性能光催化剂提供了指导。