Effect of Doped Cu~(2+) on Photo-Stimulated Surface Reaction between Methane and Water over MoO_3-TiO_2/SiO_2

MoO 3-TiO 2/SiO 2 and Cu 2+-doped MoO 3-TiO 2/SiO 2 were prepared by impregnating 5.3%TiO 2/SiO 2 that was prepared by the chemical modification method, and they were used for gas-phase photo-catalytic production of CH 3OH and H 2 from CH 4 and H 2O in a fixed-bed annular photo reactor under UV irradiation. The selective formation of CH 3OH may be attributed to the coupled effect of MoO 3 and TiO 2, and the photo quantum yield of CH 3OH is markedly enhanced after Cu 2+ introduction. Results of XRD, UVDRS, IR and TPD showed that the well-dispersed surface coupled species comprising Mo-O-Ti and Mo-O-Cu bonds are formed on the catalyst surface, and they make the photo absorption threshold blue shift due to the quantum size effect. Compared with TiO 2/SiO 2 and MoO 3/SiO 2, the photo absorption capacity, adsorption and activation ability for CH 4 and H 2O of MoO 3-TiO 2/SiO 2 and Cu/MoO 3-TiO 2/SiO 2 are effectively enhanced. During the photo-stimulated surface catalytic reaction, the O- hole centers created by the charge-transfer excitation can enhance the activation of CH 4, and the active species O- can be stabilized when the photoelectron is transferred by reduction of Cu 2+ to Cu+. The possible reaction mechanism was discussed.