Comparative Study on the Catalytic Performance of Single-Phase Mo-V-O-Based Metal Oxide Catalysts in Propane Ammoxidation to Acrylonitrile

Five single-phase Mo-V-O-based mixed metal oxides, Mo-V-O, Mo-V-Te-O, Mo-V-Sb-O, Mo-V-Te-Nb-O, and Mo-V-Sb-Nb-O, all of which assume the same orthorhombic structure, were prepared by hydrothermal method, and propane ammoxidation to acrylonitrile (AN) using these mixed oxides as catalysts was performed in order to clarify roles of the constituent elements. All of the catalysts were found to be active for propane ammoxidation. The AN selectivity was increased by approximately a factor of 2 by the introduction of Te or Sb to the Mo-V-O oxide catalyst and further increased by the introduction of Nb to the Mo-V-Te-O and Mo-V-Sb-O catalyst. At the same time, the oxidative decomposition of ammonia to nitrogen was retarded by the introduction of Te, Sb, and Nb. Reaction network analyses for each catalyst revealed that Mo and V in a framework structure are responsible for oxidative activation of propane to propene, which is the rate-determining step, and that Te or Sb clearly promotes the conversion of the formed propene to AN, whereas catalysts without Te or Sb clearly promote the destructive conversion of propene to COx. The data also revealed that Nb suppresses the further reaction of AN to undesired products. Active sites for the selective ammoxidation of propane to AN are discussed on the basis of the catalyst crystal structure.