Mechanism of deactivation of Au/Fe2O3 catalysts under water-gas shift conditions

摘要

The stability of Au supported catalysts for the water-gas shift reaction was studied. Two types of continuous flow experiments were performed, i.e. temperature-programmed and long-term isothermal stability test. The highest initial rate was obtained for catalysts used without any calcination or other high-temperature treatment. The continuous flow experiments showed that all Au/ Fe2O3 catalysts deactivated under water-gas shift conditions. The deactivation trend occurred independently on the Au loading, the method of preparation, calcination or high-temperature treatment.The various causes on the deactivation, i.e. the formation of carbon-containing species, the change of Au particles or changes of the support were investigated in terms of DRIFTS coupled with MS, TGA, TEM, N_2 physisorption, ICP, and XRD. Even though stable carbonate and carbonyl surface species were found on the spent catalysts, the quantity of these species indicated that they are not the main cause of the deactivation. Furthermore, the agglomeration of the Au particles was not severe and was not observed for all Au catalysts. The deactivation of Au/Fe2O3 was mainly caused by the change of the support. A significant reduction of the surface area of the support is taking place during the water-gas shift reaction as a function of time on stream. This decrease of the surface area can almost solely explain the decrease on the catalytic activity.