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

The gold-catalysed oxidation of carbon monoxide was studied by Mössbauer 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. Mössbauer spectroscopy analysis of this sample showed that the fresh/as-received catalyst contained mostly Au3+ in the form of AuOOH⋅xH2O. Based on earlier studies, the support was proposed to be predominantly ferrihydrite, Fe5HO8 ⋅ 4H2O. In situ FTIR in the presence of CO and CO + O2 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 OH. 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.