Redox and photo-redox properties of isolated Mo5+ ions in MoH-ZSM-5 and MoH-beta zeolites: in situ ESR study

Redox and photo-redox properties of isolated Mo5+ ions stabilized in H-ZSM- 5 and H-beta zeolites are studied by in situ ESR in flowing O-2, NO, H-2, a nd C3H6. Upon oxidation of pre-reduced samples at 20(degrees)C, NO demonstr ates a higher oxidative ability, as compared with O-2. Interaction of Mo5ions with propene at 20(degrees)C results in formation of a chemisorption c omplex with enhanced reactivity of Mo(V) toward NO. Illumination of the Mo5 +/HZSM-5 sample with UV-visible light causes measurable acceleration of Mo( V) oxidation by NO at 20(degrees)C. Therefore, photochemical activation of the oxidation step could be realized, in principle, for Mo/zeolite catalyst s. At 500(degrees)C in the reaction mixture NO + H-2, the step of the catal ytic site reduction is fast, and the dynamic equilibrium of the redox react ion Mo(VI) <-> Mo(V) for MoH-ZSM-5 and MoH-beta seems to be strongly shifte d to Mo5+.