Alkylation of benzene using CO2 and H2 over ZnZrOx/ZSM-5: the effect of Y doping

Abstract

The increase in the CO₂ concentration in the atmosphere has caused a serious global climate problem. Aromatics are important intermediates in chemical production, and by utilizing CO₂ in aromatic synthesis not only the effective utilization of CO₂ can be realized, but also carbon emission reduction can be effectively achieved. Herein, a bifunctional catalyst prepared by physically mixing Y-doped ZnZrOx metal oxide with the zeolite ZSM-5 was applied to the synthesis of toluene and xylene by the alkylation of benzene using CO₂ and H₂. The bifunctional catalyst Y0.1/ZSM-5 showed the best reaction performance. 17.3% conversion of CO₂, 30.8% conversion of benzene, and 71.6% selectivity of toluene and xylene were achieved. And 96.8% of the liquid-phase products were toluene and xylene. Based on the CO₂-TPD, H₂–D₂ exchange, H₂-TPR, EPR, XPS, and in situ DRIFTS results, a small amount of Y doping can effectively increase more oxygen vacancies on the surface of ZnZrOx to promote CO₂ adsorption and activation. The activation of hydrogen was enhanced resulting from Y–Zn interactions. In the reaction pathway, Y doping accelerated the conversion of CO₂ to HCOO* species to promote the reaction process, allowing more methanol to participate in the benzene alkylation reaction and further improving the CO₂ and benzene conversion.