Effects of reducibility on propane oxidative dehydrogenation over γ-Al2O3-supported chromium oxide-based catalysts

Alumina-supported chromium oxide and binary mixed oxide catalysts of the form Cr-M oxide/gamma- Al2O3 (where M is Ni, Co, Mo, W, Ho, La, Li, Cs or Bi) were found to catalyze the oxidative dehydrogenation of propane at 300 - 450degreesC. The basic characters of the metals were found to determine partly the selectivity to propylene. Cr-Mo/gamma-Al2O3 proved to be the most promising. It exhibited a propylene yield of 10.3% at 450degreesC. The connections between the selectivity and reducibility of the catalyst were explored. TPR results showed that addition of molybdenum to chromium increased the temperature of reduction maxima. Thus the selectivity to propylene was improved by a decrease in the tendency of the catalyst to undergo a redox cycle. Further, an X-ray photoelectron spectroscopy study conducted on a sample of the catalysts showed that the basicity of the catalysts increased with increase in molybdenum. Catalysts with appropriate Cr/Mo ratios exhibited lower selectivity to over-oxidation product than those containing either chromium or molybdenum alone.