Kinetics of selective oxidation of dimethyl ether to formaldehyde over Al2O3-supported VOx and MoOx catalysts

The kinetic behaviors of dimethyl ether(DME) selective oxidation to formaldehyde were investigated over Al2O3-supported VOx and MoOx catalysts. It was showed that the reaction is pseudo-zero order with respect to both dimethyl ether and oxygen molecule, suggesting that the reaction of surface intermediate CH3O* is likely to be the rate-determining step. The apparent activation energies for the target reaction were determined to be 122 kJ/mol over the VOx/Al2O3 catalyst and 125 kJ/mol over the MoOx/Al2O3 catalyst, respectively. With the decrease of contact time, the dimethyl ether conversion decreased linearly, while the selectivity of HCHO increased, indicating that formaldehyde is the preliminary product of the selective oxidation of dimethyl ether.