Selective Oxidation Of Dimethyl Ether To Formaldehyde Over Al₂O₃ Supported VOx/MoOx Catalysts

Dimethyl ether (DME) chemistry opens a new approach to the optimal utilization of synthesis gas for its economic and technique advantage of one-step synthesis and the environmental benign features. The present work was focused on catalytic performance of the selective oxidation of DME to formaldehyde (HCHO) over Al₂O₃ supported MoO_x/VO_x catalysts, and its reaction kinetics, as well as the intermediates and mechanism of the reaction.Both Al₂O₃ supported MoO_x/VO_x catalysts are active and the highest DME conversions and HCHO selectivities can be achieved if the content of MoO_x/VO_x species are close to their monolayer dispersion capacities over Al₂O₃ support. The supported VO_x catalysts are more active than the supported MoO_x catalysts and the reaction temperature is lower for about 20°C over the former than over the latter at the same DME conversion and selectivity to HCHO. The DME conversion of 21.3% was achieved with the HCHO selectivity of 75% over VO_x/ Al₂O₃ catalyst at 300°C. The dissociated CH₃O* species, which was formed from dissociative adsorption of DME on the Al₂O₃ supported MoO_x/VO_x catalysts, reacts on the catalyst surface via the following competitive routes: (1) CH₃O* + O→HCHO* + OH* (2) CH₃O* + CH₃O*→HCHO* + CH₃OH*Because of the simultaneous existence of these two competitive reaction routes, we demonstrated that the more the active lattice oxygen, the higher the...