The oxidation of methanol on a silver (110) catalyst

Abstract

The oxidation of methanol was studied on a Ag(110) single-crystal by temperature programmed reaction spectroscopy. The Ag(110) surface was preoxidized with oxygen-18, and deuterated methanol, CH 3OD, was used to distinguish the hydroxyl hydrogen from the methyl hydrogens. Very little methanol chemisorbed on the oxygen-free Ag(110) surface, and the ability of the silver surface to dissociatively chemisorb methanol was greatly enhanced by surface oxygen. CH 3OD was selectively oxidized upon adsorption at 180 K to adsorbed CH 3O and D 2 18O, and at high coverages the D 2 18O was displaced from the Ag(110) surface. The methoxide species was the most abundant surface intermediate and decomposed via reaction channels at 250, 300 and 340 K to H 2CO and hydrogen. Adsorbed H 2CO also reacted with adsorbed CH 3O to form H 2COOCH 3which subsequently yielded HCOOCH 3 and hydrogen. The first-order rate constant for the dehydrogenation of D 2COOCH 3 to DCOOCH 3 and deuterium was found to be (2.4 ± 2.0) × 10 11 exp(−14.0 ± 0.5 kcal mole · RT)sec −1. This reaction is analogous to alkoxide transfer from metal alkoxides to aldehydes in the liquid phase. Excess surface oxygen atoms on the silver substrate resulted in the further oxidation of adsorbed H 2CO to carbon dioxide and water. The oxidation of methanol on Ag(110) is compared to the previous study on Cu(110).