VANADIUM-CONTAINING ZSM5 ZEOLITES - REACTION BETWEEN VANADYL TRICHLORIDE AND ZSM5/SILICALITE

Treatment with VOCl3 vapor (593-793 K) results in removal of silanol groups from silicalite and H-ZSM5 and formation of (= SiO)3 = VO species that are relatively resistant to hydrolytic regeneration of silanols. With H-ZSM5, VOCl3 treatment also removes most Bronsted acid sites associated with framework aluminum. This removal is only partly reversible on treatment with H2O: the irreversible and reversible parts are associated respectively with dealumination and with proton removal via binding of vanadium species at framework aluminum. There is no X-ray diffraction evidence for structural change as a result of these treatments. ESR revealed small amounts of paramagnetic vanadyl species in hydrated V/silicalite and V/ZSM5, attributed to reduction from V5+ by HCl, possibly augmented with V/ZSM5 by reaction with zeolite acidity. At 293 K the paramagnetic vanadyl is mobile in hydrated V/silicalite and immobile in hydrated V/ZSM5.