MnOx/ZrO2 gel-derived materials for hydrogen peroxidedecomposition

Manganese-yttrium-zirconium mixed oxide nanocomposites with three different Mn loadings (5, 15 and 30 wt%) were prepared by sol–gel synthesis. Amorphous xerogels were obtained for each composition. Their structural evolution with the temperature and textural properties were examined by thermogravimetry/differential thermal analysis, X-ray diffraction, diffuse reflectance UV– vis spectroscopy and N2 adsorption isotherms. Mesoporous materials with high surface area values (70–100 m2 g-1) were obtained by annealing in air at 550 C. They are amorphous or contain nanocrystals of the tetragonal ZrO2 phase (T-ZrO2) depending on the Mn amount and exhibit Mn species with oxidation state higher than 2 as confirmed by temperature programmed reduction experiments. T-ZrO2 is the only crystallizing phase at 700 C while the monoclinic polymorph and Mn3O4 start to appear only after a prolonged annealing at 1,000 C. The samples annealed at 550 C were studied as catalysts for H2O2 decomposition in liquid phase. Their catalytic activity was higher than that of previously studied Mn/Zr oxide systems prepared by impregnation. Catalytic data were described by a rate equation of Langmuir type. The decrease of catalytic activity with time was related to dissolution of a limited fraction (up to 15%) of Mn into the H2O2/H2O solution