Abstract
Previously, we reported a strong Fe-Cu synergy in CO2 hydrogenation to olefin-rich C2+ hydrocarbons over the γ-Al2O3 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. H2-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 H2 and CO2 species, consequently enhanced CO2 conversion and C2+ selectivity. Adding K increased the adsorbed-CO2/adsorbed-H2 ratio by greatly enhancing the moderately and strongly adsorbed CO2 and slightly suppressing the moderately and strongly adsorbed H2, resulting in a significantly increased O/P ratio in the produced hydrocarbons. The product distribution analysis and in situ DRIFTS suggested that CO2 hydrogenation over the Fe-Cu catalyst involved both an indirect route with CO as the primary product and a direct route to higher hydrocarbons.
Highlights
Waste CO2 can be utilized as a carbon source to synthesize valuable chemicals and transportation fuels
In combination with the catalytic reaction data, we systematically examined the mechanistic roles of Fe-Cu bimetallic composition and K promoter, and their influences on CO2 conversion and the formation of olefin-rich C2+ hydrocarbons
When we compared the Fe-Cu catalyst with relevant studies of Fe-based catalyst, we found that this CO2/H2 adsorption behavior is the key to light olefin formation
Summary
Waste CO2 can be utilized as a carbon source to synthesize valuable chemicals and transportation fuels. A high energy input is normally required for CO2 conversion, especially when CO2 is the solo reactant. Characterization of CO2 Hydrogenation Fe-Cu Catalysts demand could be much reduced and CO2 conversion would become thermodynamically easier when one or more molecules with high Gibbs free energy such as hydrogen (ΔG° 0 kJ/mol) could co-react with CO2 (Song, 2006). Developing effective catalysts for selective conversion of CO2 to light olefins is highly desired (Riedel et al, 1999; Song, 2002; Song, 2006; Centi and Perathoner, 2009; Wang et al, 2011)
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