Surface dispersion of molybdena supported on silica, alumina and titania
Abstract
Surface species formed upon impregnation of silica, alumina and titania with aqueous solutions of ammonium molybdate and calcination at 770 K have been studied by X-ray diffraction, specific surface area assessment, scanning electron microscopy, laser Raman spectroscopy and temperature-programmed reduction. Dispersion decreases in the order TiO2> Al2O3SiO2. Polymolybdate species are formed for low loadings, that lead to bulk MoO3 for loadings of 0.4 monolayer on SiO2, but persist for higher loadings on titania and alumina. On this last support, isolated molybdate species have been also found.