Generalized and high temperature synthesis of a series of crystalline mesoporous metal oxides based nanocomposites with enhanced catalytic activities for benzene combustion

Abstract

We report here a generalized synthesis of various crystalline mesoporous metal oxides including CeO₂, Cr₂O₃, Fe₂O₃, SnO₂, Ce_0.5Zr_0.5O₂, TiO₂, Al₂O₃ and ZrO₂ from the self-assembly of a basic poly 4-vinylpyridine (P4VP) template with various metal precursors based on their strong acid–base interaction under high temperature (180 °C) hydrothermal conditions. Using the typically crystalline mesoporous metal oxide of CeO₂, after removing the template by calcination at 550 °C and loading with various transition metal oxides such as MnO_x, various transition metal oxide functionalized crystalline mesoporous CeO₂ (MnO_x/P4VP–CeO₂) were obtained. X-ray diffraction (XRD) patterns show that the resulting mesoporous metal oxides exhibit a high degree of crystallinity, and the transition metal oxides active sites have been successfully loaded into these samples. N₂ sorption–desorption isotherms, SEM images show that the resulting crystalline mesoporous metal oxides, such as CeO₂, have a large BET surface area (94 m² g⁻¹) and abundant mesopores, which exhibit monolithic morphology with crystal sizes ranging from 5 to 15 μm, giving a uniform pore size centered at 5 nm. XPS spectra show that the active sites such as MnO_x exhibit the phases of MnO₂ and Mn₂O₃ in P4VP–CeO₂. H₂-TPR curves show that MnO_x/P4VP–CeO₂ exhibits decreased reductive temperatures of both active sites of the MnO_x and P4VP–CeO₂ supporter when compared with the samples reported previously. More importantly, MnO_x/P4VP–CeO₂ exhibits much better catalytic activities and good recyclability for catalyzing the oxidation of benzene than that of MnO_x loaded commercially crystalline CeO₂, which will be very important for their wide applications for VOCs removal in industry.