ChemInform Abstract: The Reversed‐Flow Gas‐Chromatography Technique Applied to the Kinetics of the Methanation of Carbon Monoxide

Abstract

The reversed-flow gas-chromatography technique has been applied to the methanation reaction of carbon monoxide over two Ni/Al2O3 catalysts. A continuous feed by diffusion of carbon monoxide was used, ensuring a continuous change in its concentration with time over the catalyst bed. An integrated rate equation has been derived, permitting the calculation from experimental data of the rate constant and the order of the reaction with respect to carbon monoxide. This was done for a wide range of fractional conversions to methane at each temperature. Arrhenius activation parameters were computed for each reaction order. The latter changes with temperature discontinuously, but does not change with CO concentration at the same temperature. This is explained by the fact that the method is a pulse technique under steady-state conditions. The findings are compared with recent results in the literature, agreeing with some of them but not with others. They are, however, consistent with a conventional reaction mechanism, assuming a non-homogeneous catalytic surface. A rate equation for the formation of methane, based on this mechanism, has been derived and is used to explain the experimental data, especially the change of reaction order with respect to carbon monoxide with temperature. The rate-determining step is the hydrogenation of CH or CH3 groups.