Effective Suppression of CO Selectivity for CO2 Hydrogenation to High-Quality Gasoline

Abstract

CO2 hydrogenation to gasoline fuels remains a sticky problem of CO selectivity from reverse water-gas shift reactions over a metal oxide and zeolite bifunctional catalyst. Herein, we report an efficient catalyst combining a Fe–Zn–Zr–T oxide hydrothermally treated with TPABr solution and HZSM-5 zeolite for CO2 hydrogenation into high-quality gasoline. The hydrothermal treatment contributes to the obvious enrichment of the Zn component and the residual Br on the surface of Fe–Zn–Zr–T oxide, as compared to Fe–Zn–Zr oxide, as well as the increased number of oxygen vacancies. These surface properties not only induce the increase of the H2 adsorption and CO2 adsorption ratio but also enhance the adsorption strength of the HCOO* species and the desorption rate of CH3O* species (close intermediate of methanol) over Fe–Zn–Zr–T oxide, which are responsible for higher methanol selectivity and lower CO selectivity. Furthermore, the presence of the adsorbed CO* species and higher C2+ hydrocarbon selectivity on Fe–Zn–Zr oxide affirm the F–T route of CO2 hydrogenation except for the methanol route, while the F–T route is effectively restrained after the TPABr hydrothermal treatment of Fe–Zn–Zr–T oxide. As the Fe and Zn–Zr molar ratio decreases, more HCOO* and CH3O* species on Fe–Zn–Zr (0.1:1:1)–T–24 h can form, which is in good agreement with the much higher methanol selectivity on Fe–Zn–Zr (0.1:1:1)–T–24 h oxide and hydrocarbon selectivity on the Fe–Zn–Zr(0.1:1:1)–T–24 h@HZSM-5 core–shell catalyst. The CO selectivity and C5+ isoalkane selectivity in gasoline on Fe–Zn–Zr(0.1:1:1)–T–24 h@HZSM-5 are up to 24% and 93%, respectively, with a CO2 conversion of 18%. The good matching of the Fe–Zn–Zr–T oxide and HZSM-5 zeolite plays the crucial role in the C5+ isoalkanes selectivity in gasoline over the Fe–Zn–Zr–T@HZSM-5 core–shell catalyst.