Studies on crystalline microporous vanadium silicates

Abstract

The synthesis and catalytic properties of V-NCL-1, a novel vanadium silicate, large-pore molecular sieve in various oxidation reactions, are described. The reactions include the oxidation of n-octane, cyclohexane, toluene, trimethylbenzenes, and naphthalene. In the as-synthesized form, most of the vanadium in V-NCL-1 is present as atomically dispersed and isolated V4+ located in framework positions, though not necessarily in tetrahedral coordination. On calcination in air, the vanadium ions are oxidized to the pentavalent state. In addition, part of the vanadium leaves lattice locations and forms nonframework clusters. When the oxidized sample is reduced, V4+ ions are formed again. The three-dimensional silicate structure of the molecular sieve is intact during all these treatments. Due to the presence of large pores. V-NCL-l is able to oxidize bulky molecules such as mesitylene and naphthalene. Unlike their titanium analogs, vanadium silicates are able to oxyfunctionalize the primary carbon atoms in alkanes and the side chains in alkylaromatics