CO2 Hydrogenation to Olefin-Rich Hydrocarbons Over Fe-Cu Bimetallic Catalysts: An Investigation of Fe-Cu Interaction and Surface Species

Abstract

Previously, we reported a strong Fe-Cu synergy in CO 2 hydrogenation to olefin-rich C 2 + hydrocarbons over the γ-Al 2 O 3 supported bimetallic Fe-Cu catalysts. In this work, we aimed to clarify such a synergy by investigating the catalyst structure, Fe-Cu interaction, and catalyst surface properties through a series of characterizations. H 2 -TPR results showed that the addition of Cu made both Fe and Cu easier to reduce via the strong interaction between Fe and Cu. It was further confirmed by X-ray absorption spectroscopy (XAS) and TEM, which showed the presence of metallic Fe and Fe-Cu alloy phases in the reduced Fe-Cu(0.17) catalyst induced by Cu addition. By correlating TPD results with the reaction performance, we found that the addition of Cu enhanced both the moderately and strongly adsorbed H 2 and CO 2 species, consequently enhanced CO 2 conversion and C 2 + selectivity. Adding K increased the adsorbed-CO 2 /adsorbed-H 2 ratio by greatly enhancing the moderately and strongly adsorbed CO 2 and slightly suppressing the moderately and strongly adsorbed H 2 , resulting in a significantly increased O/P ratio in the produced hydrocarbons. The product distribution analysis and in situ DRIFTS suggested that CO 2 hydrogenation over the Fe-Cu catalyst involved both an indirect route with CO as the primary product and a direct route to higher hydrocarbons.