Hydrogenation of CO2 to Aromatics over Fe-K/Alkaline Al2O3 and P/ZSM-5 Tandem Catalysts

A highly efficient tandem catalyst comprising an iron-potassium bimetal-modified alkaline Al2O3 catalyst and a phosphorus-modified ZSM-5 zeolite (denoted as Fe-K/a-Al2O3&P/ZSM-5) for directly hydrogenating CO2 to aromatics reported. The hydrogenation conversion route of CO2 -> olefins -> aromatics on the tandem catalyst is demonstrated. The Fe-K/a-Al2O3 catalyst solely serves as a metal active center to hydrogenate CO2 to lower olefin intermediates with high selectivity, and the P/ZSM-5 zeolite, which provides acid sites, Byproduct can rapidly convert lower olefin intermediates to aromatics by polymerization and dehydrocyclization. Moreover, the addition of alkaline Al2O3 as the support leads to the improved dispersion of the Fe-K bimetal and subsequently promotes CO2 adsorption, thereby inhibiting the adsorption of H-2 and benefitting the formation of lower olefin intermediates. Strong acid sites of HZSM-5 zeolites with low Si/Al ratios are essential for the formation of aromatics. The appropriate proximity of two active components in the tandem catalyst is critical to the highly selective catalytic process for hydrogenating CO2 to aromatics. The granule-mixing catalyst maintains strong acidity and CO2 adsorption capacity, boosting the hydrogenation of CO2 to aromatics. Phosphorus modification changes the acid strength of HZSM-5 zeolites and increases the amount of medium-strength acid sites, further promoting the generation of aromatics, which exhibits a 36.4% CO2 conversion as well as a 35.5% selectivity for aromatics among the carbon products within CO2 and the tandem catalyst is suitable at a low H-2/CO2 ratio with merely a 10.2% byproduct CO selectivity. In addition, HZSM-5 with a low phosphorus loading is conducive to the aromatization of lower olefins, and the phosphorus loading of 0.8 wt % is found to be suitable.