Quantum-dots containing Fe/SBA-15 silica as “green” catalysts for the selective photocatalytic oxidation of alcohol (methanol, under visible light)

Fe/SBA-15 catalysts containing iron oxide nanoparticles confined inside silica pores (replicated, internal, poorly crystalline) and grown outside silica grains (external, mainly crystalline hematite) in different proportions are prepared using a single silica support. Fe-species are deposited by the two-solvent technique with two iron salts precursors (Fe(NO3)3·9H2O, FeCl3·6H2O) and two solvents (cyclohexane, hexane) for 11 wt% of iron. Calcination is performed in reproducible conditions (700 °C, 2 °C/min, thin bed, in air). SAXS measurements are used to show that the 2D hexagonal structure of the used silica is maintained after Fe-loading and calcination. Ar sorption measurements show that the pores are partially plugged. The oxidation of pure methanol is used as a test reaction to compare photocatalytic properties. H2O2 and visible light both activate the reaction. More active catalysts are formed with hexane associated with FeCl3·6H2O than with Fe(NO3)3·9H2O. A reversed situation is observed with cyclohexane. Iron leaching (after 1 h 30 of test, up to 3 mg of Fe by mL) is important. These results are expected to be of interest in the exploration of size and shape “nanocatalysis” and to provide a further understanding for the reactions that take place when porous silicas are used as supports.