Oxidative dehydrogenation of ethane to ethylene with CO2 via Mg-Al spinel catalysts: Insight into dehydrogenation mechanism

This study compares the CO₂-assisted oxidative dehydrogenation of ethane (CO₂-ODHE) performance of Mg-Al spinel catalysts doped with various metals (Cr, Fe, Co, Ga) that possess dehydrogenation activity. Both experimental and theoretical analyses were conducted to explore the reaction mechanism of CO₂-ODHE on the spinel catalyst. The findings indicate that the MgFeAlO₄ spinel catalyst exhibited CO₂-ODHE activity at 600 °C, achieving a CO₂ conversion rate of 20.3 %, an ethane conversion rate of 27.9 %, and an ethylene selectivity of 87.9 %. Mechanistic studies revealed that CO₂ activation primarily occurs through the reverse water-gas shift reaction, and density functional theory calculations identified the doped metal ions as the principal active sites for ethane activation. These results suggest that CO₂-ODHE on the spinel surface follows a mechanism of catalytic dehydrogenation coupled with the reverse water-gas shift reaction. Additionally, the effects of Fe doping contents and reaction temperature were investigated. When the ratio of Fe³⁺ to Al³⁺ was 1, corresponding to the MgFeAlO₄ spinel catalyst, the CO₂-ODHE performance was optimal, yielding 23.3 % ethylene. Increasing the reaction temperature enhanced ethane conversion but reduced ethylene selectivity, with both ethane conversion and ethylene selectivity reaching approximately 49 % at 700 °C.