Synergistic ionic liquid and hydrogenation catalyst for highly efficient and reversible carbon capture and utilization under mild conditions

This study discloses the first system for reversible carbon capture and utilization (CCU) and direct air capture and utilization (DACU) to formic acid (FA) under benign conditions enabled by a synergistic operation between the ionic liquid (IL) EMIM propionate (EMIM: 1-ethyl-3-methylimidazolium) and hydrogenation catalyst iPrRu-MACHO-Cl (carbonylchlorohydrido[bis(2-di-i-propylphosphinoethyl)amine]ruthenium(II)). The IL absorbs CO2 from raw biogas or simulated air under source-integrated conditions, i.e. 30 °C and 1-2 bar of CO2 source. Then, iPrRu-MACHO-Cl catalyzes the hydrogenation of the IL-captured CO2 to FA at 30 °C and 1-20 bar H2. Additionally, the system exhibits high activity for FA dehydrogenation, producing pure CO2 and H2 at temperatures down to just 50 °C, thus providing optimal conditions for the first example of a benign Liquid Organic Hydrogen Carrier (LOHC) system that simultaneously can carry out decarbonization. Using real biogas (41% CO2, 1 bar, 30 °C), the system successfully cycles between converting CO2 to FA to approximately 100 mol% FA/IL and reversing it back to pure CO2/H2, maintaining high activity over multiple cycles. The system is also active under continuous-flow conditions. Under a 1:5 CO2:H2 flow (1 bar), the IL achieves a FA saturation of 67 mol% FA/IL, corresponding to 17 wt% FA/IL. Mass spectrometry (MS) data further indicates that the IL captures CO2 from air. Notably, this work does not involve any additives nor volatile organic solvents. Finally, the superior performance is attributed to the electron donicity and low viscosity of EMIM propionate, which likely enhance CO2 solubility and catalyst interaction.