Effect of porous structure on the formation of active sites in manganese hosted in ordered mesoporous silica catalysts for environmental protection

Abstract

Recently ordered mesoporous silicas have been considered as suitable catalyst supports due to their high surface area, well developed porous volume and tuned size, shape and topology of mesopores. Among them SBA-15 and KIT-6 are most promising and studied materials as host matrix of metal/metal oxide nanoparticles. Both structures are characterized with cylindrical mesopores which are 2D- and 3D-packed in the SBA-15 and KIT-6 silicas, respectively. The flexibility of the oxidation state of manganese ensures high oxygen storage capacity of its oxides and provokes their wide application as catalysts in various redox processes. The aim of the current investigation is to clear the effect of pore topology in SBA-15 and KIT-6 mesoporous silicas on the state of the hosted in them manganese oxide nanoparticles. The samples were obtained by incipient wetness impregnation of silicas with manganese nitrate and conventional SiO2 was also used as a reference support. A complex of physicochemical techniques, such as nitrogen physisorption, X-ray diffraction, UV–Vis, XPS, FTIR and temperature-programmed reduction with hydrogen was used for samples characterization. The obtained modifications were tested as potential catalysts for environmental protection via total oxidation of VOCs (ethyl acetate) or hydrogen production from methanol as clean and effective alternative fuel. It was established that the porous structure of mesoporous silica supports influences in a complex way the catalytic behaviour of their manganese modifications, which is determined by the specificity of the reaction medium.