Deactivation of a Au/CeO2 catalyst during the low-temperature water-gas shift reaction and its reactivation:: A combined TEM, XRD, XPS, DRIFTS, and activity study

The deactivation of Au/CeO2 catalysts during low-temperature water-gas shift reaction and the underlying physical origin were investigated, comparing the deactivation in different reaction atmospheres and subsequent regeneration of the catalysts by reactive treatment in O-2/N-2 or H2O/N-2 gas mixtures. Based on TEM and XRD measurements, Au and ceria particle sintering (irreversible deactivation) can be excluded as reasons for the deactivation. In addition to the formation of adsorbed monodentate carbonate species, which we recently identified as a major reason for catalyst deactivation under present reaction conditions [Denkwitz et al., J. Catal. 246 (2007) 74], XPS measurements show significant variations in Ce3+ and Aun+ content during reaction in different atmospheres and on regeneration. Reaction generally leads to increasing catalyst reduction (i.e., decreased Aun+ content and increased Ce3+ content); this is reversed during regeneration. The correlation between the relative content of these ionic species and the catalytic activity is not as clear as that between carbonate formation/decomposition and deactivation/regeneration, leaving monodentate carbonate formation as the dominant but not sole reason for catalyst deactivation. (c) 2007 Elsevier Inc. All rights reserved.