Oxygen adsorption and catalytic performance in oxidative dehydrogenation of isobutane on chromium oxide-based catalysts

Abstract

Oxygen adsorption on γ-Al₂O₃-, TiO₂ (anatase)-supported chromium oxide and on unsupported chromia in amorphic and crystalline form, has been studied with a gravimetric method in the temperature range 523–623 K. The equilibrium oxygen uptake at p→∞ was the same for all the studied catalysts, the rate of the adsorption was, however, different, increasing in the order: CrO_x/Al₂O₃<CrO_x/TiO₂<Cr₂O₃ amorph.<Cr₂O₃ cryst. Measurements of oxidative dehyrogenation of isobutane on the catalysts given above have shown that the selectivity to isobutene decreases in the same sequence. The higher selectivity values and the change in the rate constant of the isobutane oxidative dehydrogenation with conversion, observed for the Al₂O₃- and TiO₂-supported chromium oxide catalysts, have been ascribed to the lower coverage of the surface of the catalyst with oxygen in the stationary state of the isobutane oxidative dehydrogenation, as compared with unsupported chromia.