MAS NMR study of the layered host α-vanadyl phosphate dihydrate: potential as a shape-selective catalyst

Abstract

Two magnetic resonance methods, magic-angle spinning (MAS) NMR and EPR, were used in the characterisation of the layered phase α-VOPO₄·2H₂O, and its n-butylammonium and n-butylamine intercalates. These revealed that intercalating molecules could replace water molecules in the coordination sphere of vanadium and that this influences the relative stability of the different oxidation states of the transition metal. Based on these findings, α-VOPO₄·2H₂O was tested for catalytic activity in the Diels–Alder cycloaddition of methyl vinyl ketone to cyclopentadiene. The layered phase displayed some catalytic activity with the ratio of products indicating a degree of shape selectivity. This catalysis was shown by EPR to involve electron donation to the layered host, with methyl vinyl ketone being intercalated (and activated) as a radical cation.