The mechanism of low-temperature CO oxidation with Au/Fe2O3 catalysts:: a combined Mossbauer, FT-IR, and TAP reactor study

The gold-catalysed oxidation of carbon monoxide was studied by Mossbauer spectroscopy, in situ FTIR, and multiple time-resolved analysis of catalytic kinetics (MultiTRACK), an advanced TAP reactor system. The active catalyst studied was 3.4% Au/Fe2O3, which was used without drying and/or pretreatment. Mossbauer spectroscopy analysis of this sample showed that the fresh/as-received catalyst contained mostly Au3+ in the form of AuOOH (.) xH(2)O. Based on earlier studies, the support was proposed to be predominantly ferrihydrite, Fe5HO8 (.) 4H(2)O. In situ FTIR in the presence of CO and CO + O-2 showed an initial increase in the bicarbonate regions, a decrease in carbonates, and a signal at 1640 cm(-1), attributed to consumption of OH/H2O during the reaction. MultiTRACK analysis showed that with pulsing of CO onto a fresh catalyst sample, initially only a limited, irreversible amount of CO adsorbed. Adsorption of CO increased with increasing number of pulses, and CO2 production and, to a lesser extent, H2O were observed after significant surface coverage by CO. A mechanism is proposed that involves a carbonate/bicarbonate intermediate and enhancement of the rate with the presence of surface OR The activity of the sample seems to be a function of the presence of -OH species on the support, gold, or interface sites, the rate of desorption Of CO2, or decomposition of surface carbonates. (C) 2004 Elsevier Inc. All rights reserved.