Abstract
The two-dimensional morphology of molybdenum oxycarbide (2D-Mo(2)CO(x)) nanosheets dispersed on silica is found vital for imparting high stability and catalytic activity in the dry reforming of methane. Here we report that owing to the maximized metal utilization, the specific activity of 2D-Mo(2)CO(x)/SiO(2) exceeds that of other Mo(2)C catalysts by ca. 3 orders of magnitude. 2D-Mo(2)CO(x) is activated by CO(2), yielding a surface oxygen coverage that is optimal for its catalytic performance and a Mo oxidation state of ca. +4. According to ab initio calculations, the DRM proceeds on Mo sites of the oxycarbide nanosheet with an oxygen coverage of 0.67 monolayer. Methane activation is the rate-limiting step, while the activation of CO(2) and the C-O coupling to form CO are low energy steps. The deactivation of 2D-Mo(2)CO(x)/SiO(2) under DRM conditions can be avoided by tuning the contact time, thereby preventing unfavourable oxygen surface coverages.