Structure and the Metal Support Interaction of the Au/Mn Oxide Catalysts

Gold catalysts with loading 1 and 10 wt % were prepared by deposition−precipitation method with urea over mesoporous manganese oxide, obtained through a surfactant-assisted procedure by using cetyltrimethylammonium bromide (CTAB), followed by treatment with sulphuric acid. For comparison, Au(10 wt %) was also deposited over commercial CeO2 and SiO2 supports. The materials were characterized by XRD and EXAFS at the Mn K and Au LIII edges and XPS. Moreover, the analyses were performed on the samples treated under 1%CO/He, at 250 °C for 90 min. The structural and surface results of the as prepared manganese oxide confirmed the formation of γ-MnO2 along with some amorphous Mn3O4 upon treatment of the precursor oxide with sulphuric acid. The CO treatment induces the formation of reduced phases, Mn3O4 (Hausmannite) and Mn2O3 (Bixbyite). Gold particles have a positive effect in promoting the reduction of manganese oxide and this effect is more pronounced in the Au(10 wt %) catalyst, which exhibits an enhanced CO oxidation activity with respect to both the Au(1 wt %) sample and the metal-free manganese oxide. The higher efficiency of Au(10 wt %) catalyst is attributed to a strong metal−support interaction between gold nanoparticles and support, as demonstrated by the presence of a component Au−O at 2.1 Å in the Fourier transform of the EXAFS signal of both the fresh and the CO-treated samples.