Study of mixed-oxide catalysts containing bismuth, vanadium and antimony. Preparation, phase composition, spectroscopic characterization and catalytic oxidation of propene
The structural and catalytic properties of oxides in the Bi–V–Sb–O system, which are propene oxidation catalysts, have been studied. Two domains of solid solutions exist for the compounds BiV1–xSbxO4, with the scheelite structure for 0 ⩽x < 0.04 and a monoclinic structure for 0.876 ⩽x⩽ 1. Characterization by X-ray photoelectron spectroscopy (X.p.s.) shows that for a given MO (M = Bi, V or Sb) environment, the higher the average interatomic distance, the higher the cation binding energy, corresponding to an effective decrease in electronic density. From a semi-quantitative X.p.s. analysis of the surface composition of the BiV1–xSbxO4 system it is shown that for low values of x(x⩽ 0.10) the surface concentrations of vanadium and oxygen decrease sharply compared with those of the other elements. Activities and selectivities for acrolein, determined in a stirred gas–solid reactor, are measured as a function of x. Oxides having the scheelite structure exhibit a sharp increase in activity with increasing x. The larger performance found for x= 0.035 is connected with a high oxygen mobility.