The kinetics and mechanism of the methanation of carbon monoxide on a nickel-silica catalyst

Abstract

The kinetics of the methanation of carbon monoxide were measured on a 5% nickel on silica catalyst in a differential flow micro-reactor at temperatures from 460 up to 840 K, carbon monoxide pressures from 1 to 650 Torr and hydrogen pressures from 55 to 700 Torr. The rates observed covered 5 orders of magnitude. With increasing temperature from low to higher temperatures, the reaction order for carbon monoxide increased from −1 to almost +1 and the reaction order for hydrogen decreased from +1 to almost zero. Both reactants have an influence on the order of reaction for the other. A maximum was found in the reaction rate as a function of the carbon monoxide partial pressure. These facts indicate a competitive adsorption of hydrogen and carbon monoxide and suggest that a Langmuir-Hishelwood type of rate equation might describe the data. A number of mechanisms was tried. Those mechanisms which described the experimental data best, were based on dissociative adsorption of carbon monoxide and addition of a hydrogen atom to adsorbed CH X as the rate determining step. With x = 1 , an excellent description of the data is obtained.