Mechanism of Low-Temperature CO Oxidation on Pt/Fe-Containing Alumina Catalysts Pretreated with Water

In a previous article (Catal. Commun. 2012, 17, 194), we reported that Pt/Fe-containing alumina catalysts pretreated with water could catalyze CO oxidation even below room temperature. To clarify the effect of the water pretreatment and the reaction mechanism of the novel catalytic system, in situ Fourier transform infrared (FT-IR), and X-ray absorption fine structure (XAFS) measurements during CO oxidation were conducted. From FT-IR measurements, it was revealed that the Pt surface of the catalyst was covered with CO and that the adsorbed CO molecules did not desorb easily, as in the case of conventional Pt/Al2O3 catalyst. Pt L-III XAFS results also suggested the presence of CO on the Pt surface during CO oxidation. Thresholds of Fe K X-ray absorption near-edge structure shifted with the change between oxidative (0.5% O-2/He) and reductive (1% CO/He) atmospheres, indicating that the Fe redox change Fe2+ <-> Fe3+ can participate in the reaction. From the degree of the shifts and average Pt diameters derived from high-angle annular dark-field scanning transmission electron microscopy and metal dispersion measurements, it was concluded that PtNP/FeOx boundaries were efficiently formed upon the water pretreatment. The enhanced reactivity of the water-pretreated catalyst can be attributed to the increased number of boundaries and Pt diameter.