Photocatalytic Reduction of CO₂ with H₂O on Titanium Oxides Anchored within Micropores of Zeolites:  Effects of the Structure of the Active Sites and the Addition of Pt

Abstract

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 CO 2 with H 2 O at 328 K with a high selectivity for the formation of CH 3 OH 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 CO 2 with H 2 O with a high selectivity for the formation of CH 3 OH, while the catalysts involving the aggregated octahedrally coordinated titanium oxide species show a high selectivity to produce CH 4, being similar to reactions on the powdered TiO 2 catalysts. The addition of Pt to the anchored titanium oxide catalysts promotes the charge separation which leads to an increase in the CH 4 yields in place of CH 3 OH formation.