The effect of reaction conditions on the stability of Au/CeZrO4 catalysts in the low-temperature water-gas shift reaction

Au/CeZrO₄ catalysts are highly active for the water-gas shift reaction but tend to be unstable and deactivate with time on stream. In this study, in situ DRIFTS-GC was used to investigate the nature of the Au under a range of reaction conditions as the deactivation rate is observed to vary with feed conditions (water concentration, presence of CO₂) and reaction temperature. An analysis of the Au-CO bands during the reaction showed that the rate of change in the Au⁰-CO bands correlated with the deactivation rate under all conditions. Although Au^δ+-CO species may be highly active they are very unstable under the feed and, from a comparison of the behaviour of the Au-CO species under varied feeds and reaction temperatures, it is proposed that metallic gold is the predominant active state in these catalysts for low-temperature WGS reaction. Through varying the feed conditions of the water-gas shift reaction, it was possible to enhance the stability of the catalysts significantly. Following a pre-treatment of the catalyst under the full water-gas shift feed (2% CO, 2% CO₂, 8.1% H₂ and 7.5% H₂O) and removal of CO₂ from this feed, the catalyst was found to be very stable. The extent of deactivation can be altered by varying the feed conditions during a reaction. The discovery of a way to enhance Au catalyst stability for the low-temperature water-gas shift reaction has significant implications for the development and use of these catalysts.