Investigating the role of promoters (Ga, Nb, La, and Mg) on In2O3-based catalysts: Advancing on CO2 hydrogenation to C5+ hydrocarbons

Abstract

Utilizing carbon dioxide (CO2) as a sustainable feedstock for producing chemicals and renewable fuels is of paramount importance, particularly in the face of intricate climate changes. However, despite significant CO2 hydrogenation advancements to different C1 chemicals, synthesizing value-added products with more carbons remains challenging due to the extreme inertness of CO2 and the high C–C coupling barrier. Thus, herein, we introduce a series of In2O3-promoted catalysts with different basicities (Ga/In2O3, Nb/In2O3, La/In2O3, and Mg/In2O3) to evaluate their role in the production of methanol that was used as an intermediate for the production of gasoline-range hydrocarbons after going through an HZSM-5 zeolite bed. While oxygen vacancies on the catalysts' surfaces are undoubtedly crucial, we have observed that the basicity of the promoters plays a significant role in their effectiveness. Interestingly, there seems to be a threshold regarding this matter, meaning that the promoter must possess an intermediate level of basicity. However, CO2 adsorption becomes excessively strong when the promoter is too basic, favoring the undesired reverse-water gas shift (RWGS) reaction and CH4 formation with acid counterparts. Our findings showed that the Ga-promoted In2O3 catalyst with intermediate basicity balances activity and selectivity, resulting in a higher yield of hydrocarbons. The observed outcome highlights the significant role of catalyst component interactions in suppressing undesirable reactions and improving overall performance. The Ga-promoted catalyst exhibited higher selectivity for hydrocarbons, averaging 61%, compared to In2O3, which achieved a selectivity of 54%.