Relationship between the local structures of titanium oxide photocatalysts and their reactivities in the decomposition of NO

Photocatalysts involving titanium oxides were prepared by an ion-exchange and impregnation method in which zeolites with different Si/Al ratios were used as supports. Those photocatalysts with low Si/Al ratios exhibited high and unique photocatalytic reactivity for the direct decomposition of NO into N-2, O-2, and N2O at 275 K. In situ photoluminescence, diffuse reflectance absorption, and XAFS investigations indicated that the titanium oxide species are highly dispersed within the zeolite and exist in tetrahedral coordination. The charge transfer excited state of these highly dispersed titanium oxide species plays a significant role in the decomposition of NO with a high selectivity for the formation of N-2 and O-2, while the catalysts involving the aggregated octahedrally coordinated titanium oxide species show a high selectivity to produce N2O, being similar to the reactions observed on the powdered bulk TiO2 photocatalysts.