Zeolite-encapsulated transition metal oxo species as selective catalysts

For the purpose of finding novel catalyst systems combining the advantages of traditional homogeneous and heterogeneous catalysts, transition metal vanadium, molybdenum and rhenium oxo complexes such as \rm VO(OC\sb3H\sb7)\sb3,\ MoO\sb2Cl\sb2\ and\ CH\sb3ReO\sb3 were introduced into the pores of different zeolite hosts via a solution impregnation method. Physicochemical characterization by XRF, XRD, EXAFS, UV-VIS, IR, Raman, EPR, solid state NMR, TPD-MS, nitrogen sorption and other methods shows that the vanadium, molybdenum and rhenium oxo species are attached to the zeolite framework through interactions between the metal precursors and the hydroxyl groups inside the supercages of zeolite hosts. The influence of the precursor to host stoichiometry, impregnation conditions and heat treatment on the speciation of the zeolite encapsulated metal oxo species are discussed, and the intrazeolite chemistry of each system is described. The catalytic reactivity and selectivity of the intrazeolite metal oxo species have been studied in alcohol oxidation, olefin epoxidation and alkene metathesis reactions, respectively. Several of the intrazeolite catalyst systems show competitive catalytic reactivity and superior selectivity to the major product compared with their respective homogeneous and/or oxide supported counterparts. In several cases, shape-selective passivation experiments indicate that a major fraction of the catalytic activity is located in the intrazeolite pore system