Catalysis by Transition-Metal Carbides. VII. Kinetic and XPS Studies of the Decomposition of Methanol on TiC, TaC, Mo2C, WC, and W2C

The catalytic decomposition of methanol was investigated on a series of powdered transition-metal carbides, such as TiC, TaC, Mo2C, WC, and W2C, which had been catalytically activated by evacuation at high temperatures. WC was found to produce methyl formate (HCOOCH3) with a high selectivity (above 80%), whereas CO and H2 were mainly produced on clean TaC, Mo2C, and W2C surfaces. XPS measurements combined with an analysis of the peak intensities revealed that the catalytic activation of WC and TaC was attributable to the removal of surface oxygen and the subsequent formation of monocarbide surfaces. On the other hand, the minor activities leading to the formation of methyl formate on W2C and Mo2C were concluded to be due to the formation of oxycarbide surfaces. The deuterium distributions in the products during the reaction of CH3OD suggest that the methyl formate is produced via the dimerization of the intermediate adspecies, CH2O.