CO2 capture by amines in aqueous media and its subsequent conversion to formate with reusable ruthenium and iron catalysts

Abstract

Conversion of carbon dioxide (CO₂) captured from industrial sources (e.g. flue gas of power plants) or even from ambient air to value-added chemicals/fuels through CO₂ capture and utilization (CCU) as a possible strategy to mitigate anthropogenic CO₂ emissions to the atmosphere is proposed. In this context, combining the CO₂ capture and utilization steps to generate fuels instead of going through the intermediate desorption and compression of captured CO₂ has started to attract considerable interest as a way to lower the energy demand for the CO₂ recovery processes involved in usual carbon capture and storage/sequestration approach. The main focus of this study is CO₂ capture in aqueous amine solutions and conversion of the in situ formed ammonium carbamate/bicarbonate/carbonate to ammonium formate. The amines selected for this process served the dual purpose of capturing CO₂ and stabilizing the formate product. The captured CO₂ was selectively converted to formate (up to 95% yield) using, among others, superbases, in the presence of Ru- and Fe-based pincer complexes under moderate reaction conditions (50 bar H₂ at 55 °C). By performing a biphasic reaction (water/Me-THF), the catalyst was recycled for five consecutive cycles and a TON > 7000 was obtained for the formation of ammonium formate from captured CO₂. Overall, a green and straightforward approach to produce formate from captured CO₂ is presented here.