The local structures of transition metal oxides incorporated in zeolites and their unique photocatalytic properties

Abstract

Zeolite catalysts incorporated or encapsulated with transition metal cations such as Mo 6+ , V 5+ , or Ti 4+ into the frameworks or cavities of various microporous and mesoporous molecular sieves were synthesized by a hydrothermal synthesis method. A combination of various spectroscopic techniques and analyses of the photocatalytic reaction products has revealed that these transition metal cations constitute highly dispersed tetrahedrally coordinated oxide species which enable the zeolite catalysts to act as efficient and effective photocatalysts for the various reactions such as the decomposition of NO x into N 2 and O 2 and the reduction of CO 2 with H 2 O into CH 3 OH and CH 4 . Investigations on the photochemical reactivities of these oxide species with reactant molecules such as NO x , hydrocarbonds, CO 2 and H 2 O showed that the charge transfer excited triplet state of the oxides, i.e., (Mo 5+ -O − ) * , (V 4+ -O − ) * , and (Ti 3+ -O − ) * , plays a significant role in the photocatalytic reactions. Thus, the present results have clearly demonstrated the unique and high photocatalytic reactivities of various microporous and mesoporous zeolitic materials incorporated with Mo, V, or Ti oxide species as well as the close relationship between the local structures of these transition metal oxide species and their photocatalytic reactivities.