Modified ZnZrOx coupled with ZSM-5 as the catalyst for the hydrogenation of CO2 to aromatics

Direct hydrogenation of CO₂ to aromatics via the methanol-mediated route over an oxide-zeolite bifunctional catalyst has received considerable attention in recent years. However, the activation of CO₂ at mild condition remains a great challenge, as it needs to conquer a high activation energy barrier due to the chemical inertness of CO₂. Herein, ZnZrO_x oxides were modified by a series of transition metals (M = Fe, Cu, Co, Ni) and the modified M-ZnZrO_x oxides were further used together with the commercial ZSM-5 zeolite to comprise the bifunctional M-ZnZrO_x/ZSM-5 composite catalysts for the direct hydrogenation of CO₂ to aromatics. The results indicate that the iron-modified Fe-ZnZrO_x/ZSM-5 catalysts have abundant oxygen vacancies which are active for the transformation CO₂ to aromatics; under 275 °C, H₂/CO₂ = 3, and a space velocity of 600 mL/(g·h), the Fe(4)-ZnZrO_x/ZSM-5 catalyst with an Fe mass fraction of 4% achieves a selectivity of 80.4% to aromatics, where tetramethylbenzene accounts for more than 70.4%, with a single-pass CO₂ conversion of 5.6%. A further increase of the Fe content to 8% can even improve the selectivity to aromatics (85.0%). Such observation should be useful for the design of industrial catalysts efficient for the direct conversion of CO₂ to aromatics.