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

Oxygen adsorption on gamma-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 --> infinity was the same for all the studied catalysts, the rate of the adsorption was, however, different, increasing in the order: CrOx/Al2O3 < CrOx/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.