Nanostructured gold-ceria catalysts are among the most active materials for the low temperature water-gas shift reaction. Different techniques can be used to prepare highly dispersed gold in cerium oxide with or without dopants. We have recently reported that a strong interaction between gold and ceria is responsible for the WGS reaction activity [1,2]. Gold is stabilized in oxidized form in ceria; the amount of stabilized gold correlates with the number of surface oxygen defects of nanoscale ceria.
In highly reducing environments, the gold-ceria interaction can be lost, zerovalent gold is formed, ceria defects are annealed, and deactivation follows. This happens readily above 300 oC, but much less at lower temperatures. The most serious stability issue with ceria-based catalysts is formation of cerium(III) hydroxycarbonate in shutdown to room temperature [2]. However, we have found that addition of a small amount of oxygen (0.5 mole%) in the feed gas can fully stabilize the WGS activity of Au-nano ceria in realistic reformate gas streams at temperature up to 300oC. It can also prevent the formation of cerium(III)hydroxycarbonate at low temperatures. Shutdown to room temperature with water condensation is now possible without any activity loss for the gold-ceria catalysts. The key is the CO oxidation reaction by oxygen that is very fast and not quenched at room temperature. On the other hand, gaseous oxygen addition can not stabilize platinum-ceria catalysts after shutdown to room temperature in the full WGS gas mixture since the light off temperature of CO oxidation over platinum-ceria is much higher than that for gold-ceria.
In this presentation, we will show evidence of the dynamic response of gold-ceria catalysts to different gas environments accompanied by structural characterization by various techniques, including in situ XANES and EXAFS.
References
1. Q. Fu, H. Saltsburg and M. Flytzani-Stephanopoulos, Science 301 (2003) 935.
2. Q.Fu, W.Deng, H. Saltsburg, M. Flytzani-Stephanopoulos, Appl. Catal. B, 56 (2005) 57-68.
3. W. Deng, M. Flytzani-Stephanopoulos, 19th NAM paper # O-305, Philadelphia, PA, May 22-27, 2005.
See more of #571 - Fundamentals of Supported Catalysis I (20004)
See more of Catalysis and Reaction Engineering Division
See more of The 2005 Annual Meeting (Cincinnati, OH)