Steering CO2 hydrogenation coupled with benzene alkylation toward ethylbenzene and propylbenzene using a dual-bed catalyst system

Utilization of CO2 as a C-1 resource for the synthesis of aromatics is of great significance and is also related to carbon recycling. However, forming an ethylated or propylated side chain at the benzene ring by this strategy is difficult, and the products reported are methylated aromatics. Here, we show the first CO2 hydrogenation in tandem coupling with benzene alkylation to synthesize ethylbenzene and propylbenzene over a dual-bed system containing ZnZrOx, SAPO-34, and phosphorus-modified ZSM- 5 catalysts. Controlled experiments and density functional theory studies reveal that the intermediate reactive species CHxO* (x = 1- 3) of CO2 hydrogenation are preferentially alkylated with benzene to give methylated aromatics, rather than to form ethylated and propylated aromatics, when the three catalysts are simply mixed. By contrast, the three catalysts with rationally spatial distribution in the dual-bed system can afford 83.5% selectivity to ethylbenzene or 64.7% to propylbenzene in total aromatics without deactivation after 100 h.

Automated summary

Utilizing CO2 as a C-1 resource for synthesizing aromatics is significant, but forming an ethylated or propylated side chain at the benzene ring is challenging. In this study, a dual-bed system with rationally distributed catalysts was used for the first time to achieve CO2 hydrogenation in tandem coupling with benzene alkylation, enabling the synthesis of ethylbenzene and propylbenzene with high selectivity.