Support effect in dehydrogenation of propane in the presence of CO2 over supported gallium oxide catalysts

Dehydrogenation of propane to propene in the absence or presence of CO2 over different supported gallium oxide catalysts was investigated. Ga2O3/TiO2, Ga2O3/Al2O3, and Ga2O3/ZrO2 catalysts exhibited high activity, and Ga2O3/SiO2 and Ga2O3/MgO were ineffective catalysts for the dehydrogenation of propane. The conversions of propane over Ga2O3/TiO2, Ga2O3/Al2O3, and Ga2O3/ZrO2 catalysts at 600 °C reached 23, 33, and 39%, respectively. The high dehydrogenation activities are connected with the abundant medium-strong acid sites on the catalyst surface. Carbon dioxide can promote the catalytic dehydrogenation activity of Ga2O3/TiO2 but suppress those of Ga2O3/ZrO2 and Ga2O3/Al2O3. The conversion of propane becomes 32, 26, and 30% in the presence of CO2 over Ga2O3/TiO2, Ga2O3/Al2O3, and Ga2O3/ZrO2 catalysts, respectively. Results of pulse reaction and the H2 and propane chemisorptions indicate that two contrary roles of CO2 exist in the reaction: the positive role of removing dissociatively adsorbed H2 on catalyst surface through the reverse water–gas shift reaction and the negative role of displacing the propane adsorbed on basic sites of catalyst. XPS studies show that the different behavior of the five supported Ga2O3 catalysts may be attributed to the different interactions between the support and the Ga2O3 species. The dehydrogenation reaction is suggested to proceed through a heterolytic dissociation reaction pathway.