Kinetic Study of the Low-Temperature Water-Gas Shift Reaction over a Cu—ZnO Catalyst

The water—gas shift reaction on industrial copper-based catalyst ICI 52—1 was investigated by the transient kinetic, chemisorption, thermogravimetric and photoelectron spectroscopic methods. A significant reduction of the catalyst and an increase in the surface area were observed during the initial activation at 250°C. The presence of reduced surface copper was confirmed by photo-electron spectroscopy. The studies of stationary water-gas shift kinetics at 200-250°C revealed that the reaction orders with respect to carbon monoxide and water are below 1. The transient experiments started after exposure to nitrogen showed that the carbon dioxide response was faster than the hydrogen response at 250 and 235°C, whereas at 150 and 200°C the carbon dioxide and hydrogen liberation rates were almost equal. The carbon dioxide and hydrogen formation rates were enhanced by water and water-hydrogen pretreatments of the catalyst. The pretreatment procedure affected the shift reaction dynamics but not the stationary reaction rate. A reaction mechanism based on the kinetic studies and the catalyst properties is discussed. The mechanism includes both catalyst oxidation-reduction and bimolecular surface reaction steps.