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 CeO 2 and SiO 2 supports. The materials were characterized by XRD and EXAFS at the Mn K and Au L III 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-MnO 2 along with some amorphous Mn 3 O 4 upon treatment of the precursor oxide with sulphuric acid. The CO treatment induces the formation of reduced phases, Mn 3 O 4 (Hausmannite) and Mn 2 O 3 (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.