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.