Zeolite-encapsulated vanadium picolinate peroxo complexes active for catalytic hydrocarbon oxidations

Zeolite-encapsulated vanadium (IV) picolinate complexes were prepared by tr eatment of dehydrated VO(2+)-NaY zeolite with molten picolinic acids. Treat ment of the NaY-encapsulated VO(pic)(2) complex with urea hydrogen peroxide adduct in acetonitrile allowed to generate peroxovanadium species. The str ucture of vanadium peroxo species was studied by UV-vis, Raman and XAFS spe ctroscopies which suggested the formation of monoperoxo monopicolinate comp lex which could be active intermediate for various oxidation reactions with the catalysts. To elucidate effect of the encapsulation on catalytic perfo rmance, the catalytic properties of the encapsulated complexes were compare d with that of corresponding homogeneous catalyst H[VO(O-2)(pic)(2)]. H2O. The novel 'ship-in-a-bottle' catalysts retain solution-like activities in a liphatic and aromatic hydrocarbon oxidations as well as in alcohol oxidatio n. In addition, the encapsulated vanadium picolinate catalysts showed a num ber of distinct features such as preferable oxidation of smaller substrates in competitive oxidations, increased selectivity of the oxidation of termi nal CH3- group in isomeric octanes and preferable (sometimes exclusive) for mation of alkyl hydroperoxides in alkane oxidations. The distinct features were explained in terms of intrazeolitic location of the active complexes t hat imposed transport discrimination and substrate orientation. On the basi s of the experimental data, a possible mechanism was discussed. Stability o f the vanadium complexes during the liquid phase oxidations and leaching fr om the NaY zeolite matrix were also examined. (C) 1999 Elsevier Science B.V . All rights reserved.