Kinetics of the Selective Low-Temperature Oxidation of CO in H2-Rich Gas over Au/α-Fe2O3

The selective CO oxidation (also referred to as PROX) on a Au/α-Fe2O3catalyst in simulated reformer gas (low concentrations of CO and O2, 75 kPa H2, balance N2) at atmospheric pressure was investigated over almost two orders of magnitude in CO partial pressure (0.025–1.5 kPa) and over a large range ofpO2/pCOratios (0.25–10). Quantitative evaluation of CO oxidation rates as a function of CO and O2partial pressure at 80°C yields reaction orders with respect to CO and O2of 0.55 and 0.27, respectively. The apparent activation energy for this reaction evaluated in the temperature range of 40–100°C is 31 kJ/mol. At 80°C, the selectivity, defined as the ratio of oxygen consumption for CO oxidation to the total oxygen consumption, reaches 75% at large CO partial pressures (1.5 kPa), but decreases significantly with diminishingpCO. This is related to the fact that the H2oxidation rate is independent of the CO partial pressure, consistent with a reaction mechanism where oxygen adsorbed at the metal/metal oxide interface reacts with H and CO adsorbed at low coverages on the supported Au nanoclusters. The selectivity increases with decreasing temperature, reflecting a higher apparent activation energy for H2oxidation than for CO oxidation. A comparison with Pt/γ-Al2O3, a commonly used PROX catalyst with an optimum operating temperature of ca. 200°C, demonstrates that Au/α-Fe2O3already offers comparable activity and selectivity at 80°C.