Modification of zeolites using in situ generated active species in the gasphase: II. Redox processes over the Mo5+ isolated sites in zeolites ZSM-5 and beta

The redox ability of isolated Mo5+ cations in model MoH beta and MoH-ZSM-5 systems is studied by in situ ESR. The oxidation of reduced samples by nitr ogen monoxide at 20 degreesC proceeds much faster than oxidation by oxygen. The interaction between Mo5+ ions and propene at 20 degreesC results in th e formation of a complex in which the oxidizability of Mo(V) by NO is subst antially enhanced. UV irradiation increases the oxidation rate for Mo5+ ion s in HZSM-5 by nitrogen monoxide at 20 degreesC, indicating the possibility for the photochemical activation of the process. The step of active site r eduction during the interaction of the samples with the H-2 + NO + He gas m ixtures of various compositions at 500 degreesC is fast, and the dynamic eq uilibrium of the redox Mo(V) reversible arrow Mo(VI) reaction is shifted to the left.