New strategy of creation of local catalytic sites in definite electronic and coordination states

Atomic-scale engineering of catalytic functions of isolated redox sites in confined environments of zeolitic channels is proposed as a new approach to the investigation of structure-properties relationship in heterogeneous ‘biomimetic’ catalysis. It is shown that the design of such catalysts, on the base of high-silica zeolites, containing isolated transition-metal cations as active redox sites, may present promising opportunities for creation of new types of contacts from a practical point of view. A detailed analysis of transition-metal cation incorporation into high-silica zeolites by either conventional or solid-state exchange is given. Stabilization of one or several transition-metal ions by matrices of high-silica zeolites (mainly H-ZSM-5) is discussed. The influence of different factors on the processes of cationic-species stabilization is analyzed. These data are correlated with the results of catalytic testing in reactions of total oxidation of hydrocarbons (HC), direct decomposition of NO_x and SCR of NO_x by HC. The relationship between catalytic activity and selectivity of cationic sites and their coordination and electronic state, regulated by either thermal treatment or introduction of different anionic ligands, is analyzed.