Kinetics of the water-gas shift reaction over a rhodium-promoted iron-chromium oxide catalyst

The addition of a small amount of rhodium to a high temperature iron-chromia water-gas shift catalyst has been found to accelerate significantly the approach to equilibrium. The kinetics of the reaction have been studied in terms of the separate forward and backward reactions, and using a feed composition typical of those produced by steam reforming. It was found impossible to avoid the influence of mass transfer under relevant high-temperature operating conditions. A power rate law incorporating thermodynamic limitations best described the kinetic data for the reforming mixture. An equation based on forward and backward expressions was less satisfactory. Comparison of the observed kinetics with those reported in the literature for undoped catalysts indicates that the promoter has the greatest effect on the reactivity of carbon monoxide and hydrogen.