Characterization Preparation Of Vanadium Substituted Heteropoly Acid Supported Catalysts And Catalytic Properties

Polyoxometalates (POMs) are a class of well-defined transition metal oxygen clusters with composition and structural diversity, showing many applications in materials science, catalysis, etc. However, HPAs still suffer from some shortcomings, such as the low surface area, the high solubility, and the environmental problems. These homogeneous catalytic systems also have difficulties in catalyst separation from the reaction solution and repeated utilization. In order to overcome these disadvantages, the dispersion of them on suitable carriers is full of urgency.In this paper, a series of new hybrid materials composed of the Keggin phosphotungstic acid (H3PW12O40) and vanadium-substituted phosphotungstic acids (H4PVW11O40, H5PV2W10O40and H6PV3W9O40) immobilized on amine-functionalized mesoporous MCM-41, SBA-3molecular sieves and magnetite Fe3O4nanoparticles are respectively prepared and characterized by FT-IR, DRS, XRD, N2sorption measurements, SEM and TEM for their structural integrity and physicochemical properties. It is found that the structure of the heteropolyacids is retained on immobilization over mesoporous materials and magnetite Fe3O4nanoparticles. The catalytic activities of mesoporous supported heteropolyacid are tested in the selective oxidation of alcohols to the carbonyl products with30%aqueous H2O2as oxidant, while the Fe3O4supported heteropolyacid as photocatalysis are tested in the light decolorization of methyl orange (MO) solution. The catalytic activities of different number of vanadium-substituted phosphotungstic acid are investigated. Among the immobilized amine-functionalized SBA-3catalysts, H5[PV2W10O40] immobilized catalyat exhibits the highest activity with75%conversion and99%selectivity in the oxidation of benzyl alcohol to benzaldehyde. Compared with the immobilized amine-functionalized SBA-3catalysts, those of immobilized on amine-functionalized MCM-41exhibit the higher activity and the divanadium-substituted catalyst is proved to be a highly efficient solid catalyst for the selective oxidation of aromatic alcohols to the corresponding aldehydes with H2O2, with97%conversion and99%selectivity. The optimized conditions for the oxidation of benzyl alcohol to benzaldehyde are as follows:0.05g catalyst,5mL toluene as solvent,4mmol alcohol, H2O2/benzyl alcohol=5:1, and80℃for8h. Magnetite Fe3O4nanoparticles supported heteropolyacids exhibit the good photocatalytic activity in the decolorization of MO solution and MO can be degraded within40min with95%decolorization The reaction condition is as follows:50ml solution containing1.5g/L methyl orange and1.5mmol/L H2O2,0.05g catalyst, pH=2.5, under solar light. All the prepared catalysts have the characteristic of easy recovery and quite steady reuse.