Preparation And Photo-catalysis Reaction Behavior For Methane And Carbon Dioxide Of Coupled-semiconductors Cu/MoO₃-CdS/SiO₂

Direct photosynthesis of hydrocarbon oxygenates from methane and carbondioxide is of great significance for economic value and environmental protection. Inthis paper, Photo-Stimulated Surface Catalytic Reaction (PSSCR) was applied to thereaction system, and a series of supported oxide-sulfide coupled-semiconductors andCu-modified oxide-sulfide coupled-semiconductors were designed and prepared. Thephase configuration, energy band structure, optical absorption property, and photocatalyticperformance of the materials from methane and carbon dioxide tohydrocarbon oxygenates were systematically investigated.Supported oxide-sulfide coupled-semiconductors of MoO₃-MS/SiO₂ andCu/MoO₃-MS/SiO₂(M=Zn, Cd) were prepared successfully by the stepwiseimpregnationmethod. The phase composition of catalysts were tested by XRD, IR,Raman, TPR techniques. The results showed that the main species of MoO₃-MS/SiO₂series semiconductors were MoO₃, MMoO₄, MS(M=Zn, Cd). The band of Mo-OM(M=Zn, Cd) was formed between Mo and M(Zn, Cd) on the surface of SiO₂. Theloading of active components, calcining temperature had great effects on the phasecomposition, structure and dispersion of active components on the semiconductormaterials.The optical absorption properties and energy gap (Eg) of the coupledsemiconductorswere investigated by the UV-Vis DRS experiments and Kubella-Munk function F(R_∞). The calcining temperature, loading of active components ofsupported oxide-sulfide coupled-semiconductors had great impacts on absorptionproperty and the band structure. The addition of Cu modified the photo absorptionproperty of the coupled-semiconductors and produced a Schottky barrier effect whichcan enhance the ability to capture photogenerated electronic, prevent recombination ofphotogenerated electron-hole pairs and enhance the activity of photo-catalyticmaterials in some ways. According to the energy band structureof semiconductorcompounds, its E_g and the matching relation with its the band level(E_V, E_C), thedifferent migration patterns and the related redox abilities of the photogeneratedelectrons and holes were also discussed. The photo-catalytic reaction evaluating results of supported oxide-sulfidecoupled-semiconductors showed that the photosynthesis of ethyl formate frommethane and carbon dioxide could be carried out over both MoO₃-MS/SiO₂ andCu/MoO₃-MS/SiO₂(M=Zn, Cd) under UV irradiation (intensity 0.65 mW/cm²,wavelength 365 nm). With the reaction conditions of temperature 80¹50℃, spacevelocity 90 h^-1, CH₄/CO₂= 1/1.2 and the irradiation of UV light, the conversion ofmethane reached 2.15%, while the selectivity of ethyl formate was 98.21% onCu/MoO₃-ZnS/SiO₂, and the conversion of methane reached 1.91%, while theselectivity of ethyl formate was 100% on Cu/MoO₃-CdS/SiO₂.