An efficient way to use CO2 as chemical feedstock by coupling with alkanes

The most promising method to eliminate CO2 is to find large-scale and value-added applications of CO2 as a carbon resource. However, the utilization of CO2 as feedstock for basic chemicals has long been a great challenge owing to its high thermodynamic stability. Herein, we report the coupling conversion of CO2 with light alkanes over the HZSM-5 zeolite with much higher aromatic selectivity than light alkanes as the only reactant. A CO2 conversion of 17.5% and n-butane conversion of 100% with aromatic selectivity of 80% could be achieved by the coupling reaction at the CO2 to n-butane ratio of 0.475, in which CO2 not only acted as an agent for balancing hydrogen in the reaction but also partly (-25%) incorporated into the aromatic products. Methyl-substituted lactones (MLTOs) and methyl-substituted cycloalkenones (MCEOs) were identified as key intermediates during the coupling reaction. 13C isotope labeling experiments, 13C solid-state NMR, in-situ diffuse reflectance infrared Fourier transform spectroscopy, and density functional theory (DFT)calculations revealed that CO2 could react with carbonium ions generated from alkane cracking to form MLTOs, which could further get converted into MCEOs, thus generating aromatic compounds. This coupling reac-tion provides guidance for the direct utilization of CO2 to produce value-added chemicals with the simultaneous transformation of light alkanes.(c) 2023, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Automated summary

The challenging utilization of CO2 as feedstock for basic chemicals has been addressed by coupling conversion of CO2 with light alkanes over HZSM-5 zeolite, leading to higher aromatic selectivity. The coupling reaction achieved a CO2 conversion of 17.5%, n-butane conversion of 100%, and aromatic selectivity of 80% at a CO2 to n-butane ratio of 0.475. Key intermediates were identified, and the catalytic mechanism was explored, providing guidance for the direct utilization of CO2 to produce value-added chemicals with the transformation of light alkanes.