Selective photo-assisted oxidation of methane into formaldehyde on mesoporous VOx/SBA-15 catalysts

Mesoporous VOx/SBA-15 samples have been prepared by different impregnation methods, characterized by N-2 adsorption and diffuse reflectance UV-visible spectroscopy, and their photocatalytic reactivity evaluated for the selective oxidation of methane with oxygen at 220degreesC under UV irradiation. Vanadium in dehydrated VOx/SBA-15 samples was found to be predominantly as isolated four-coordinated V5+ species, especially at V loading below 2.5wt%. VOx/SBA-15 catalysts prepared by impregnation with an aqueous solution of ammonium metavanadate (AMV) showed a maximum rate of formation of formaldehyde of 525 mumol g(-1) h(-1) (selectivity of 93.8 mol%) at a vanadium content of 2.65 wt%. Both the rate of formation and selectivity of formaldehyde were improved when vanadium was impregnated on the SBA-15 support from a vanadyl sulfate methanolic solution (rate of formation of HCHO = 733 mumol g(-1) h(-1), selectivity = 95.4 mol%). VOx/SBA-15 catalysts were seen to be more effective for the selective photo-assisted oxidation of methane than VOx/SiO2 catalysts.