The effects of MoO3 impregnation order on the catalytic activity for propane combustion over Pt/ZrO2 catalysts: the crucial roles of Pt–MoO3 interfacial sites density

MoO3 promoted Pt/ZrO2 catalysts were prepared by co-impregnation (Pt–Mo/ZrO2) or stepwise impregnation (Pt/Mo/ZrO2 and Mo/Pt/ZrO2) for propane combustion. The impregnation order affects the density of active Pt–MoO3 interfacial sites, in the order of: Pt–Mo/ZrO2 (7.60 μmol gcat−1) > Pt/Mo/ZrO2 (3.40 μmol gcat−1) > Mo/Pt/ZrO2 (1.20 μmol gcat−1). The turnover frequency, TOFPt–MoO3, of Pt–MoO3 interfacial sites is much higher than the TOFPt of Pt active sites (at least 50 folds). Thus, the catalytic activity for propane combustion is in the order of: Pt–Mo/ZrO2 > Pt/Mo/ZrO2 > Mo/Pt/ZrO2 > Pt/ZrO2. Kinetic results illustrate that the MoO3 promotion significantly weakens the strong adsorption of oxygen species on the catalyst and enhances the catalytic activity. The activation energy is reduced the most over the Pt–Mo/ZrO2 catalyst (Ea of the Pt/ZrO2 catalyst: 102.8 ± 4.8 kJ mol−1; Ea of the Pt–Mo/ZrO2 catalyst: only 40.3 ± 1.8 kJ mol−1).