| Photocatalytic production Methanol and Hydrogen form Methane with Water has a great significance in utilization of natural gas and exploitation of hydrogen resource from water. In this thesis, we extended this study to the gas-solid reaction system by using the photo-stimulated surface catalytic reaction （PSSCR） technology, and designed the supported coupled semiconductors and the fixed bed annular photoreactor to fit for this study. The preparation methodology, surface structure, chemical adsorption, photon absorption property and photocatalytic activity of the supported coupled semiconductors were systematically investigated. 1. TiO2/SiO2（TiSiO） were prepared by the chemical modification reaction on SiO2, then MoO3-TiO2/SiO2（MoTiSiO）, WO3-TiO2/SiO2（WTiSiO）, ZnO-TiO2/SiO2（ZnTiSiO）and MoTiSiO doped Cu2+ （CuMoTiSiO） were prepared by impregnating TiSiO. Based on the characterization of chemical analysis, BET, XRD, Raman, UV-vis DRS, XPS, TPR and IR, the chemical composition and surface structure of TiSiO is founded to be the well-dispersed TiOx units by the Ti-O-Si bonds and the extremely small particle of anatase crystallites; MoTiSiO, WTiSiO, ZnTiSiO and CuMoTiSiO have the high surface area as the silica carrier; the incorporation of TiO2 not only promoted the dispersion of MoO3 and WO3 but also enhanced the interaction MoO3 or WO3 and TiSiO, but decreased the interaction between ZnO and SiO2; MoO3, WO3 and ZnO couple with surface Ti species through （Mo, W, Zn）-O-Ti bonds and form the layer of non-crystalline phase with the surface coordinative unsaturated species including the micro-crystal TiO2; Lewis acid sites （ Mo6+or W6+or Zn2+ and Tin+） and Lewis base sites （Mo=O or W=O and （Mo,W,Zn）-O-Ti） are present on the surface of supported coupled semiconductors; besides of the Mo-O-Cu units, surface structure of CuMoTiSiO is similar to that of MoTiSiO. 2. The chemisorption properties of CH4 and H2O on the supported coupled semiconductors were studied by the chemisorption – infrared and chemisorption – temperature programmed desorption techniques. CH4 can be chemisorbed at the Lewis base sites O2- on the surface to form molecular states associated with C-H bond, and the chemisorption interaction enhanced with temperature increasing. According to the adsorption amount and intensity, MoTiSiO and CuMoTiSiO have the better activation and adsorption capacity of CH4 than WTiSiO and ZnTiSiO, and ZnTiSiO has the poor adsorption capacity of CH4. H2O can be chemisorbed at the Lewis base sites O2- and Lewis acid sites Mn+ to form molecular states and dissociative states, with a adsorption and intensity order of ZnTiSiO>WTiSiO>MoTiSiO. During CH4 adsorption on MoTiSiO together with H2O at 100℃, CH4 can be chemisorbed at Mo=O as molecular state and H2O can be dissociative adsorbed at the Lewis acid site Tin+. 3. The photon adsorption properties of the supported coupled semiconductors were investigated by the UV-vis DRS technique. SiO2 has no photon adsorption property at 250~700nm. Compared with that of TiO2, a significant blue shift in the gap adsorption edge is observed for TiSiO, which is the reflection of quantum size effects and supports interface interaction. The adsorption band of MoTiSiO, WTiSiO and ZnTiSiO at 300~450nm exhibit the adsorption property of the coupled structure, and the coupled effects of （Mo,W,Zn）-O-Ti make the gap adsorption edge red shift, which can improve the photo absorption property of TiSiO. Based on utilization ratio of photo energy of UV lamp, MoTiSiO and WTiSiO have better photo absorption properties than that of TiSiO, but ZnTiSiO has the similar absorption property to TiSiO. The adsorption spectrum of CuMoTiSiO can expand to the visible light because of doped Cu2+. 4. The control tests did not give any products, indicating that photochemical reactions and thermal catalytic reactions can be ruled out. However, it is noteworthy that the products, CH3OH and H2, can be detected besides a small amount of C2H6 on supported coupled semiconductors at 150℃ under UV irradiating for 1h. A... |
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