Mechanism of partial oxidation of methanol over MoO 3

Abstract

The partial oxidation of methanol was carried out over molybdenum oxide at low temperatures, where high-order products (dimethyl ether, dimethoxymethane, and methyl formate) were formed in small amounts. Both the electronic and the geometric states of the catalysts were observed by techniques such as transient experiments, volumetric adsorption, and in situ infrared observation of methoxy group and MoO structural bands. Correlation of activity data with data on the surface state makes it possible to suggest a reaction mechanism for the partial oxidation of methanol over molybdenum oxide. The reaction can be represented by a mechanism involving methoxy intermediates chemisorbed on oxygen vacancy sites. Formaldehyde and CO are mainly produced from methoxy on terminal oxygen (MoO) vacancy sites while bridged oxygen (MoOMo) vacancy sites are responsible for the production of dimethyl ether, dimethoxymethane, and methyl formate. The bond strength of chemisorbed methoxy is greatly affected by the electronic state of the oxygen vacancy. Reduced oxygen vacancy sites weaken the CH bond but strengthen the CO and chemisorption bonds in the methoxy, resulting in the formation of more hydrogen-abstracted products. The decrease in the formation of high-order products (dimethyl ether, dimethoxymethane, and methyl formate) at high reaction temperatures is caused by the decrease in the concentration of bridged oxygen vacancy sites by formation of shear planes in the surface layers.