Synthesis and Spectroscopic Characterization of Vanadium incorporated V-AlMCM-41 Molecular Sieves

Abstract

A solid-state reaction of V2O5 with AlMCM-41 followed by calcinations generated V5+ species in the mesoporous materials. Dehydration results in the formation of a vanadyl species, VO2+, that can be characterized by electron spin resonance (ESR). The chemical environment of the vanadium centers in V-AlMCM-41 was investigated by XRD, EDX, diffuse reflectance UV-VIS, ESR, 29Si, 27Al, and 51V NMR. It was found that the vanadium species on the wall surface and inside the wall of the hexagonal tubular wall of the V-AlMCM-41 were completely oxidized to tetrahedral V5+ and transformed to square pyramidal by additional coordination to water molecules upon hydration. The oxidized V5+ species on the wall surfaces and inside the wall were also reversibly reduced to VO2+ species or lower valences by thermal process.