In situ XAS with high-energy resolution: The changing structure of platinum during the oxidation of carbon monoxide

The catalytically active species during the oxidation of carbon monoxide over a real alumina-supported platinum catalyst under atmospheric pressure are determined by combining in situ high-energy resolution fluorescence detection X-ray absorption spectroscopy (HERFD XAS) at the Pt L3 edge and kinetic measurements. Catalysts were prepared by incipient wetness impregnation. The oxidation of carbon monoxide occurred in two distinctive regimes, a high-activity regime and a low-activity regime, which have high and low rates of reaction respectively. In the low-activity region, the catalyst is poisoned by carbon monoxide, limiting the dissociative adsorption of oxygen. In the high-activity regime, all CO is desorbed from the surface, increasing the rate of reaction. The low carbon monoxide concentration enables oxygen to react to the surface in this reaction regime generating a more reactive surface. HERFD showed that different phases are active depending on the reaction conditions in nano-sized catalyst particles.