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Theoretical calculation using density functional B3LYP correlation-exchange is employed to study the structure of different sizes of the VAPO-5 clusters. The results indicate that the substitution of either the phosphorus site or the aluminum site of the aluminophosphate-5 framework with vanadium is generally not feasible. The calculated structures are comparable with those from the in-situ X-ray absorption (XANES and EXAFS) of the V K-edge. The isolated vanadium was found to exist as a mono-oxo (V 4+ ) O)(O f ) 4 species for reduced, dehydrated VAPO-5 and as a di-oxo V 5+ O 4 species for calcined, dehydrated VAPO-5. The coordination geometry of the mono-oxo V 4+ species is sensitive to the presence of water molecules, and the water molecules may exchange with the framework oxygens that are coordinated to the V 4+ center.

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Isomorphous and non‐isomorphous substitutions of transition metal and IIIA elements for framework atoms of molecular sieves are very interesting in order to modify their acidic and redox catalytic properties. In this paper, we review the interaction between metal cations other than Al+3 with zeolitic frameworks in Ti, Co, V and Ga‐containing silicate and aluminophosphate zeolites detected by spectroscopic investigations. During synthesis and redox treatments, solvent, oxidant and surface silanol groups sometimes were found to attach to the framework metal ion sites, perhaps involved in the variation from tetrahedral to non‐tetrahedral coordinations.

Based on the density functional theory calculation using B3LYP hybrid method, a distorted square pyramidal (V 4+ dO)(O f ) 4 unit in a reduced and dehydrated VAPO-5 is formed by the vanadium (IV) oxide ion anchored to two neighboring 12-membered TO 4 rings of the aluminophosphate-5 lattice. By breaking two V-O-T bonds on one twelve-membered-ring to form another VdO bond, V 4+ can be oxidized to a tetrahedral di-oxo V 5+ O 4 unit. The computed structures of vanadium oxide species have been confirmed by Raman spectroscopy.

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