Unravelling the mechanism of benzene-enhanced hydrogenation of CO₂ to propane

Herein, a straightforward method is proposed for the selective conversion of CO₂ and H₂ into propane. This is achieved in a 50 mL batch reactor (45 bar and 230–270 °C) by combining a RhIn/MgO_x catalyst with highly acidic ZSM-5 and co-feeding benzene. The addition of 50 mg of benzene is found to be optimal to skew the hydrocarbon selectivity away from C₂ and C_4–6 towards C₃, while maintaining high conversion (>60%) and low CO selectivity (27%) during the 10-hour reaction. Benzene promotes the formation of propane by enhancing the aromatic hydrocarbon pool cycle at the expense of the olefinic cycle. Benzene achieves this by “grabbing” in-situ produced methanol and preventing the over-methylation of aliphatics. In turn, the generated polymethyl benzene species undergo a paring mechanism to produce propylene, which is converted to propane. The role of benzene is elucidated through comprehensive characterisations and extensive control experiments.