Hydrogenation of CO2 into aromatics over ZnZrO–Zn/HZSM-5 composite catalysts derived from ZIF-8

Abstract

The direct conversion of CO₂ to aromatics is of great strategic significance for the realization of carbon capture, utilization, and storage. However, the efficient conversion of CO₂ is still challenging due to its thermodynamic stability and chemical inertness. Herein, we report a ZnZrO solid solution prepared via direct calcination using ZIF-8 and Zr(NO₃)₄·5H₂O as precursors. Zn-Modified nano-hierarchical-pore HZSM-5 zeolite (Zn/Z5) was prepared via steam-assisted crystallization using ZIF-8 as a sacrificial template and Zn source. The ZnZrO–Zn/Z5 composite catalyst was prepared by the physical mixing of the two components, which was used to catalyze the hydrogenation of CO₂ to aromatics. The physical and chemical properties of the catalysts were investigated using XRD, SEM, TEM, N₂ adsorption–desorption, ICP-OES, EDX, NH₃-TPD, Py-IR, H₂-TPR, XPS, CO₂-TPD and other characterization methods. The effects of the ZnZrO calcination temperature, different Zn/Zr ratios, reaction conditions and the spatial distance between the ZnZrO and the Zn/Z5 zeolite on the catalytic performance of the catalytic hydrogenation of CO₂ to aromatics were investigated. The generalized gradient approximation (GGA) of density functional theory (DFT) simulation results showed that the adsorption and activation capacity of ZnZrO for CO₂ can be significantly improved with the increase of oxygen vacancies. Finally, the reaction mechanism was investigated by in situ DRIFTS. Under the optimal reaction conditions, a CO₂ conversion of 15.2% and aromatic selectivity of 63.9% can be achieved over the ZnZr₈O(350)–Zn/Z5 composite catalyst, and excellent catalytic stability was demonstrated.