Carbon Dioxide Hydrogenation to Formic Acid with Self‐Separating Product and Recyclable Catalyst Phase

The homogeneously catalyzed hydrogenation of carbon dioxide to formic acid is a promising route for carbon dioxide utilization and power‐to‐X concepts. Separation of the product and the catalyst under retention of the performance of the catalyst remains a major challenge, however. Herein, we present a Ru‐phosphine catalyzed reaction system comprising only a hydrophobic solvent as the catalyst phase and N‐methyldiethanolamine as a base. The formation of formic acid causes a spontaneous separation of the monophasic reaction mixture into a pure formic acid/amine product and a recyclable catalyst phase. By optimizing the reaction conditions, a turnover number of 1590 in a single reaction and a total turnover number of 5590 after four recycling runs were achieved. Simply separates: An alternative process concept is presented for the homogeneously catalyzed hydrogenation of carbon dioxide to formic acid based on a liquid‐liquid biphasic reaction system. The selection of N‐methyldiethanolamine as a base and of a solvent of low polarity for the catalyst generates a biphasic system without using an additional solvent for extracting the formic acid/amine product – it simply spontaneously separates.