MoOx, species dispersed as small domains on Al2O3, ZrO2, and SnO2 catalyze the oxidative conversion of dimethylether to formaldehyde with high primary selectivity (80-98% HCHO, CH3OH-free basis) at low temperatures (500-550 K). The reaction appears to proceed via redox cycles using lattice oxygen and turnover rates increase with the size and reducibility of MoOx domains. Dimethylether conversion rates (per g) and formaldehyde selectivities at 513 K are significantly higher than those reported previously on various catalysts at significantly higher temperatures (620480 K).