Effect of Ga2O3 Content on the Activity of Al2O3-Supported Catalysts for the CO2-Assisted Oxidative Dehydrogenation of Propane

Propylene production through the CO2-assisted oxidative dehydrogenation of propane (CO2-ODP) is an effective route able to address the ever-increasing demand for propylene and simultaneously utilize CO2. In this study, a series of alumina-supported gallium oxide catalysts of variable Ga2O3 loading was synthesized, characterized, and evaluated with respect to their activity for the CO2-ODP reaction. It was found that both the catalysts’ physicochemical characteristics and performance were strongly affected by the amount of Ga2O3 dispersed on Al2O3. Surface basicity was maximized for the sample containing 20 wt.% Ga2O3, whereas surface acidity was monotonically increased with increasing Ga2O3 loading. A volcano-type correlation was found between catalytic performance and acid/base properties, according to which propane conversion and propylene yield exhibited optimum values for intermediate surface basicity and acidity, which both correspond to the sample containing 30 wt.% Ga2O3. The dispersion of a suitable amount of Ga2O3 on the Al2O3 surface not only enhances the conversion of propane to propylene but also suppresses the formation of side products (C2H4, CH4, and C2H6) at temperatures of practical interest. The 30%Ga2O3-Al2O3 catalyst exhibited very good stability at 550 °C, where byproduct formation and carbon deposition were limited. Mechanistic studies indicated that the reaction proceeds through a two-step oxidative route with the participation of CO2 in the abstraction of H2, originating from propane dehydrogenation, through the reverse water–gas reaction (RWGS) reaction, shifting the thermodynamic equilibrium towards propylene generation.