Role of CO2 in dehydrogenation of propane over Cr-based catalysts

The effect of CO2 on the activity for the dehydrogenation of C3H8 over Cr/SiO2 and Cr/Al2O3 prepared by impregnation method was investigated. The activity of Cr/SiO2 was enhanced with increasing the partial pressure of CO2, while the activity of Cr/Al2O3 was remarkably reduced by the addition of a small amount of CO2. Kinetic analysis suggested that CO2 adsorbed on Al2O3 inhibited the adsorption of C3H8, and that CO2 reduced the activity of Cr/Al2O3. Cr K-edge XAFS spectra and TPR profiles indicated that the redox cycle between Cr(III)O6 and Cr(VI)O4 had an important role in the dehydrogenation of C3H6 over both Cr/SiO2 and Cr/Al2O3 regardless of the support. CO2 could oxidize a part of Cr(III) species to Cr(VI) species under the reaction condition. As a result, in the case of Cr/SiO2, the oxidative dehydrogenation of C3H8 over Cr(VI) species took place in addition to the simple dehydrogenation over Cr(III) species.