From Understanding of Catalyst Functioning toward Controlling Selectivity in CO2 Hydrogenation to Higher Hydrocarbons over Fe-Based Catalysts

The conversion of carbon dioxide (CO₂) with hydrogen (H₂), generated by renewable energy sources, into value-added products is a promising approach to meet future demands for sustainable development. In this context, the hydrogenation of CO₂ (CO₂-FTS) to higher hydrocarbons (C₂₊), lower olefins, and fuels should be mentioned in particular. These products are used in our daily lives but are currently produced by energy-intensive and CO₂-emitting oil-based cracking processes. The environmental compatibility and abundance of iron (Fe) used in CO₂-FTS catalysts are also relevant to sustainable development. The CO₂-FTS reaction was inspired by the experience accumulated in long-term research on Fischer–Tropsch synthesis with CO (CO-FTS). A simple grafting of catalyst formulations and reaction mechanisms from CO-FTS to CO₂-FTS has, however, been proven unsatisfactory, likely due to differences in surface adsorbates, chemical potentials of CO and CO₂, and H₂O partial pressure. These characteristics affect both the catalyst structure and the reaction pathways. Consequently, CO₂-FTS provides higher CH₄ selectivity but lower C₂₊-selectivity than does CO-FTS, which appeals to fundamental research to hinder CH₄ formation.