The oxidation of methanol on electrolytic silver catalyst

Abstract

The oxidation of methanol on the surface of electrolytic silver catalyst has been investigated with Temperature-Programmed Reaction Spectroscopy (TPRS). It has been found that on a clean surface of electrolytic silver no adsorption of CH 3OH or H 2 occurred except the adsorption of small amounts of H 2O or CO 2, but the ability of silver to chemisorb the gases mentioned above was greatly enhanced by oxygen preadsorbed on the surface. In the reaction of methanol with preadsorbed oxygen-18, three distinct groups of product were observed at 400, 500 ± 20, and 620 K, respectively. At room temperature, the selective oxidation of methanol led to adsorbed surface species CH 3O(a). During desorption, CH 3O(a) decomposed and HCHO, CO 18O, and H 2 18O were evolved simultaneously at 400 K as the first group of products. At high oxygen coverage, surface oxygen interacted with the carbon atom of CH 3O(a) to form another type of stable surface intermediate H 3CO 18O(a), which decomposed with a pseudo-second-order kinetics at 600 K, yielding only HCHO and H 2 18O with a stoichiometric ratio of 2:1. The evolution of the second group of products CH 3OH, CO 18O, and H 2 18O at 500 K was rate-limited by desorption of the products.