Synthesis, characterization and testing of a new V_2O _5/Al_2O_3-MgO catalyst for butane dehydrogenation and limonene oxidation

摘要

We report the synthesis and characterization of new V_2O _5/Al_2O_3-MgO catalysts and their application in oxidative dehydrogenation and epoxidation reactions. The materials were prepared by wet impregnation under excess acid conditions. Anchoring of the desired species on the support occurs via an exchange reaction between the vanadium complex and surface hydroxyl groups. The IR and UV-Vis spectra of these catalysts indicate the presence of monomeric vanadium species at 5 wt% V _2O_5 loading, along with small amounts of polymeric species at 5 and 10 wt% V_2O_5 loadings. Electron paramagnetic resonance (EPR) spectroscopy reveals the presence of ferromagnetic VO ~(2+) dimers following calcination at 773 K. The catalysts were then tested in two reactions, namely the gas phase oxidative dehydrogenation of n-butane under flow conditions at 773 K and the liquid phase epoxidation of limonene with H_2O_2. The dehydrogenation reaction gave butenes and 1,3-butadiene in moderate selectivity at 8-10% conversion. The epoxidation of limonene was less successful, giving 50-70% selectivity to the 1,2-epoxide at 10-20% conversion.