Rate expression for water-gas shift over a gold/ferrochrome catalyst

The kinetics of low-temperature water-gas shift over gold/ferrochrome catalysts were studied at atmospheric pressure and temperatures between 160 and 180 °C. During two extended kinetic experiments lasting 903 and 1313 h, the activity of the catalyst decreased by 52% and 78%, respectively. The corresponding changes in the Brunauer-Emmett-Teller surface areas were 16% and 12%, respectively, suggesting that changes in the support surface area are not the primary cause for deactivation. The use of a bracketing technique, wherein the system was regularly returned to a standard set of reaction conditions, allowed the rate expression to be written as the product of an activity factor, which accounted for catalyst deactivation, and a power-law rate expression, which accounted for the dependence of the reaction rate upon temperature and composition. The power-law kinetic expression, including a term to account for the approach to equilibrium, was found to describe the kinetics of the reaction reasonably well. The resulting reaction orders were 0.39 for CO, 0.99 for H ₂O, -0.28 for CO₂, and -0.25 for H₂, and the apparent activation energy was equal to 88.2 kJ/mol.