Vanadium(IV) complexes with picolinic acids in NaY zeolite cages Synthesis, characterization and catalytic behaviour

Abstract

Encapsulated vanadium picolinic complexes have been synthesized by treatment of a dehydrated form of VO²⁺-NaY zeolite with molten picolinic acids and characterized by X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES), EPR, FTIR and UV–VIS spectroscopies, and XRD. It was suggested by XRD and XPS that the complexes were located in the zeolite cavities. Differences in the spectroscopic properties of encapsulated and impregnated samples were explained in terms of coordination of vanadium complexes with zeolite –OH groups. The stability of VO(pic)₂ and its adduct with pyridine depended strongly on the complex location. The encapsulated vanadium picolinate complex retained solution-like activity in the liquid-phase oxidation of hydrocarbons and alcohols with hydrogen peroxide.