PHOTOINDUCED METHANOL FORMATION FROM METHANE AND NO AT 275-K ON HIGHLY DISPERSED VANADIUM-OXIDE SUPPORTED ON VYCOR GLASS AND ITS REACTION INTERMEDIATE SPECIES

UV irradiation at 275 K of the highly dispersed V/Vycor oxide catalyst in the presence of NO leads to the formation of N2 and O2. The decomposition reaction of NO proceeds photocatalytically. In the presence of CH4, UV-irradiation of the catalyst at 275 K leads to the formation of C2H6 and C2H4, but this reaction is found to accompany the reduction of the catalyst as well as the formation of CH3 radicals. A dynamic photoluminescence study of the catalyst in the absence and presence of the reactants indicates that the charge transfer excited triplet state of the surface vanadyl-species (V = O) plays a significant role in these photoinduced reactions of NO and CH4. On the other hand, UV-irradiation of the catalyst at 275 K in the presence of a mixture of NO and CH4 leads to the formation of CH3OH in addition to the above products. The higher the ratio of NO/CH4 in the mixture is, the larger the yield of CH3OH becomes and the smaller the yields of C2H6 and C2H4 become, the reaction proceeding catalytically. Thus, the present results not only imply that the highly dispersed supported vanadium oxide catalysts can be utilized as a potential photocatalyst for de-NOx-ing and/or methane activation at normal temperature but also suggest that the photo-formed oxygen species from NO molecules plays a significant role in the photoinduced CH3OH formation from CH4 and NO on V/Vycor oxide catalysts at 275 K.