Effect of the catalytic oxidation of ethylene, carbon monoxide and hydrogen on the chemisorption behavior of silver powder

Abstract

A study of the effect of the catalytic oxidation of mixtures of oxygen and hydrogen, ethylene, and carbon monoxide on a silver surface, reproducible to chemisorption behavior, has been carried out using a vacuum ultramicrobalance. Silver powder was subjected to OAOR 2 2 OAOR cycling is repeated exposure of the sample to outgassing, oxygen adsorption, outgassing, and chemical reduction at a constant elevated temperature using the same ambient pressure in each adsorption and reduction step. cycling in situ until reproducible chemisorption behavior was obtained. The powder was then used to catalyze the oxidation of hydrogen, ethylene, and carbon monoxide by allowing oxygen and the reducing gas to mix by diffusion. Measurements of the surface area and chemisorption behavior of the sample after each reaction indicate that surface disorder is increased by the reactions in the order H 2 > C 2H 4 ⪢ CO. The disordered silver surface could be restored to a state of reproducible chemisorption behavior by extended OAOR cycling. It is concluded from this work that during a vigorous catalytic reaction, new surface is being continually exposed and old surface buried in a churning fashion. This action tends to disorder the surface but is compensated by an increased rate of ordering of the high-energy surface formed and an increase in the surface temperature from the heat of reaction. The silver surface ultimately reaches a steady state amount of disorder depending on the rate of reaction and the ambient temperature of the material.