Ionic Liquids Promoted Transformation of Carbon Dioxide

The unique physicochemical properties of ionic liquids (ILs) make them be widely applied in many areas. Especially, in chemical reaction processes ILs are capable of serving as solvents, catalysts, additives, electrolytes, and display high performances. In the past few decades, the carbon dioxide (CO₂) emission issue has caused worldwide attention, and various strategies has been developed to solve the problems caused by CO₂ emission. As an accessible, renewable, and environmentally friendly C1 feedstock, CO₂ has been intensively investigated for synthesis of value-added chemicals, fuels, and materials via thermocatalysis, electrocatalysis, and photocatalysis. As a kind of efficient catalysts or promoters, various ILs have been employed in the chemical transformation of CO₂. Especially, the CO₂-reactive ILs can chemically capture and activate CO₂, and further catalyze the CO₂ transformation under metal-free and mild conditions, which provide novel protocols to produce value-added chemicals. The catalytic systems comprising IL and metal catalysts combine the advantages of ILs and metal catalysts, and can achieve the reductive transformation of CO₂ coupled with hydrogenation, providing green routes to access fuel and chemicals. Besides, the IL-based electrolytes have been applied in electrocatalytic reduction of CO₂, which cooperate with electrodes to achieve electrocatalytic transformation of CO₂ into different products. In this review article various CO₂-reactive ILs are first introduced focusing on activation mechanism of CO₂. Then, the IL-catalyzed CO₂ transformation under metal-free conditions, reductive transformation of CO₂ over IL-metal catalytic systems, and electrocatalytic transformation of CO₂ in IL-based electrolytes are summarized concentrating on the roles of ILs in chemical reactions. The final section extends the scope of this review to prospects and challenges in IL-catalyzed or promoted CO₂ transformation.