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Titanium oxide species anchored within the Y-zeolite cavities by an ion-exchange method exhibit a high and unique photocatalytic reactivity for the reduction of CO2 with H2O at 328 K with a high selectivity for the formation of CH3OH in the gas phase. The in situ photoluminescence, ESR, diffuse reflectance absorption, and XAFS (XANES and FT-EXAFS) investigations indicate that the titanium oxide species are highly dispersed within the zeolite cavities and exist in a tetrahedral coordination. The charge transfer excited state of the anchored titanium oxide species plays a significant role in the reduction of CO2 with H2O with a high selectivity for the formation of CH3OH, while the catalysts involving the aggregated octahedrally coordinated titanium oxide species show a high selectivity to produce CH4, being similar to reactions on the powdered TiO2 catalysts. The addition of Pt to the anchored titanium oxide catalysts promotes the charge separation which leads to an increase in the CH4 yields in place of CH3OH formation.

Highly dispersed titanium oxide photocatalysts anchored onto transparent plates of porous silica glass were successfully prepared by metal ion implantation, and their photocatalytic reactivity for the liquid-phase photocatalytic degradation of an aqueous 2-propanol solution was compared with that in an aqueous TiO2 dispersion. The titanium ions implanted into the porous silica glass are found to be present on the surface layer as isolated tetrahedral titanium oxide moieties by diffuse reflectance absorption, SIMS, XPS, and XAFS analyses. The specific photocatalytic reactivity of the anchored catalyst was much higher than that for TiO2 powder, which may be attributed to the tetrahedrally coordinated titanium oxide moieties. Metal ion implantation is one of the novel and useful techniques to prepare highly efficient photocatalysts on glass plates.

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