Characterization of copper and vanadium containing heteropolyacid catalysts for oxidative dehydrogenation of propane

Multicomponent Keggin-type heteropolyacid catalysts were prepared by refluxing MoO3, V2O5 and CuO in aqueous solutions of phosphoric acid. Characterization of the recovered solids by elemental analysis, thermal gravimetric analysis, infra-red spectroscopy, W-Vis reflectance spectroscopy, and X-ray absorption spectroscopy at the K edges of Mo and Cu, indicated V ions substituted for Mo ions in phosphomolybdic acid, whereas Cu ions did not substitute into the Keggin units. The Cu ions apparently functioned as charge-balancing counter ions in the neutral solid since formation of a Cs salt lowered the Cu content. The activity of Cu,V-containing heteropolyacid for oxidative dehydrogenation of propane to propene at 573 K was greater than that of H3PMo12O40 and H4PMo11VO40, but was similar to that of a physical mixture of CuO and H4PMo11VO40 Substitution of Cu into a Keggin unit does not appear to be necessary for promotion of the oxidative dehydrogenation reaction. (C) 1999 Elsevier Science B.V. All rights reserved.