Active Phase of FeOx/Pt Catalysts in Low-Temperature CO Oxidation and Preferential Oxidation of CO Reaction

The interface between metal and reducible oxide has attracted increasing interest in catalysis. The FeOx Pt interface has been a typical example, which showed remarkable activity for the preferential oxidation of CO (PROX) at low temperatures. However, model catalytic studies under vacuum conditions or in high-pressure O-rich environment at 450 K have reported two different active phases with iron in two different valence states, invoking a possible pressure gap. To identify the active phase for low-temperature CO oxidation and PROX, it is necessary to investigate the stability and activity of FeO/Pt(111) under the realistic reaction conditions. We thus conducted an in situ study on FeO/Pt(111) from ultrahigh vacuum to the atmospheric pressure of reactant gases. Our study shows FeO islands were easily, oxidized in 1 Torr O-2 to form the trilayer FeO2 islands. However, the presence of 2 Torr CO could prevent the oxidation of FeO islands and lead to CO oxidation at the FeO/Pt(111) interface. The FeO/Pt(111) surface exhibits an excellent activity for CO, production with an initial reaction rate measured to be similar to X 10(14) molecules-cm(-2)-s(-1) at 300 K. FeO islands supported on Pt(111) were further investigated in the PROX gas, i.e., the mixture of 98.5% H-2, 1% CO, and 0.5% O-2 at elevated pressures up to 1 bar. Our results thus bridged the pressure gap and identified the bilayer FeO islands on Pt(111) as the active phase for PROX under the realistic reaction conditions.