Characterization of Ca-Bi-Mo oxide catalyst for propane ammoxidation

Abstract

The physicochemical properties of highly active and selective Ca−Bi−Mo oxide for ammoxidation of propane to acrylonitrile were investigated by XRD (powder), IR/Raman, XPS, and TPRX/TPRO (temperature programmed reaction/temperature programmed reoxidation) techniques. It was found that the phases in the Ca−Bi−Mo oxide varied with the composition of the oxide. The modified γ-bismuth molybdate (γ-Bi2MoO6) and defective Ca−Bi−Mo phases produced by addition of Bi oxide played an important role in propane ammoxidation to acrylonitrile. XPS results revealed that the mole ratio of elements on the surface was different from that in the bulk. The concentration of bismuth decreased from the surface to the inner layer of CaxBi12-xMo12 oxide, while the concentration of calcium increased from the surface to the inner layer. The Ca−Bi−Mo oxide showed good catalytic performance when an appropriate amount of calcium oxide was present on the surface along with Bi and Mo oxides. The addition of Ca oxide into Bi−Mo oxide decreased the number of active sites for complete oxidation and increased the ability of reoxidation (O2 consumption) of reduced catalysts.