6. Use of CO₂ as Source of Carbon for Energy-Rich C_n Products

Catalytic CO₂ conversion to clean fuels and chemicals is crucial for mitigating the climate change and reducing the dependence on nonrenewable energy resources. Converting CO₂ by hydrogenation using heterogeneous catalysts has been extensively studied in the past decades, and the products distribution can be manipulated by selecting catalysts and reaction conditions. Generally, CO₂ conversion to hydrocarbons and to alcohols are the two routes that have been explored the most, and significant advances have been made in developing efficient catalysts and understanding the thermodynamics and kinetics of the two paths. However, effective catalysts and processes are required to selectively maximize CO₂ conversion to either C₂–C₄ olefins, C₅+ hydrocarbons, or aromatics and to minimize CH₄ and CO. Catalysis for higher alcohols synthesis from CO₂ is still in the very early stage and requires more fundamental research due to the lack of understanding the possible reaction pathways and of controlling the key intermediates. This review summarizes the progresses in CO₂ conversion via heterogeneous catalysis for the two pathways in the past five years and discusses the origin of the activity and plausible reaction mechanism through a combination of computational, experimental, and analytical studies, along with suggestions for designing improved catalysts in the future.