Preparation of Photocatalysts in Micro-pores of Zeolite and Their Reaction Dynamics

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It is of special interest to design the ion and/or cluster size catalysts within the zeolites because these fascinating supports offer unique nano-scaled pore systems, unusual internal surface tipology, and ion-exchange capacities. The pore structure of the zeolite not only allows for reactant molecules to diffuse into the ppre where in can access the catalyst anchored within the zeolite cavities, but also can remain intact during subsequent ion and/or cluster growth. The modification of the space required for a specific photocatalytic reactions is important. Unique photocatalytic properties which cannot be realized in normal catalytic systems can be expected in modified reaction spaces. Zeolites with well-defined nano-pore structure provide one of the most promising modified spaces for photocatalytic reactions.In the present study, it was found that UV-irradiation of the active titanium oxide catalysts in the presence of CO_2 and H_2O at 275 K led to the photocatalytic reduction of CO … More _2. The characteristic features of the photocatalytic reduction of CO_2 with H_2O on the active titanium oxide catalysts were investigated by in situ photoluminescence, UV-Vis, XAFS,ESR,FT-IR and XPS spectroscopic techniques.The reactions on TiO_2 powders produced methane as the major product, while, on the highly dispersed titanium oxide anchored on a porous glass and zeolites the formation of CH_4, CH_3OH,C_2-compounds and CO was observed as the major products. The yields of the phptpcatalytic reactions strongly depended on the type of catalysts, the values of CO_2/H_2O and the reaction temperatures. In situ spectroscopic studies of the system indicated that the photocatalytic reduction of CO_2 with H_2O is linked to the much higher reactivity of the charge transfer excited state, i.e., (Ti^<3+>-O^-)^<3*> of the tetrahedral coordinated titanium oxides species formed on the surfaces. Based on the detection of reaction intermediate species such as Ti^<3+>, H atoms, and C radicals, reaction mechanism for the photocatalytic reduction of CO_2 with H_2O has been proposed on a molecular scale. Less