Deactivation Mechanisms for Pd/Ceria During the Water-Gas Shift Reaction

The mechanism responsible for the irreversible deactivation of ceria-supported precious metals for the watergas-shift reaction has been investigated through accelerated aging tests. It is shown that deactivation of Pd/ ceria occurs more rapidly at 673 K compared to 523 K when operating with an integral reactor in 25 torr each of CO and H2O. By heating a fresh catalyst in H2, H2O, CO, or CO2, it was shown that deactivation occurs due to the presence of CO. Measurements of metal dispersion by CO adsorption and by x-ray diffraction show that deactivation on Pt/ceria and Pd/ceria catalysts in our studies was due to a loss of metal surface area. Finally, water-gas-shift rates on a series Pd/ceria catalysts with ceria crystallite sizes ranging from 7.2 to 40 nm and Pd loadings of either 1 wt% or 6 wt% demonstrated that rates were strictly proportional to the Pd surface area. Based on these observations, ceria-supported precious metals could be active and stable for the watergas-shift reaction if steps are taken to avoid metal particle-size growth. Comments Postprint version. Published in Journal of Catalysis, Volume 212, Issue 2, 10 December 2002, pages 225-230. Publisher URL: http://dx.doi.org/10.1006/jcat.2002.3789 This journal article is available at ScholarlyCommons: http://repository.upenn.edu/cbe_papers/53