Hybrid catalysis in carbon dioxide valorization

Carbon dioxide, generally viewed as pollutant, has recently started being considered a building block molecule in green synthesis. In order to produce valuable chemicals from carbon dioxide, strategies based on hybrid catalysis and simulation of biological processes were devised and integrated. A method of immobilization was optimized to support an enzyme, alcohol dehydrogenase, on magnetic nanoparticles, making them easily recoverable and active. The enzymatic cofactor NADH was successfully regenerated from NAD+, with either formate anion or molecular hydrogen as hydride donor, using an organometallic catalyst based on Iridium, [Ir(5-C5Me5)phenNO2Cl]+Cl-. The Turn-Over-Frequency (TOF) of the immobilized enzyme and that of the catalytic regeneration of NADH was similar, with the generation of NADH being slightly faster than its consumption, which is ideal for integrating both on the same system. Using formate anion as the hydride source, TOF for the conversion of NAD+ into NADH was 274 mmol NADH.h-1.g Ir-1, while the conversion of acetaldehyde into ethanol with ADH immobilized in magnetic nanoparticles, consuming NADH, was 45 mmol NADH.h-1.g ADH-1. Efficiency of the integration of both steps was evaluated by the formation of ethanol from acetaldehyde, NAD+, formate anion, immobilized ADH and iridium catalyst. Ethanol was quantified by GC-FID using acetonitrile as internal standard, showing a TOF of 58 mmol Etanol.h-1.g ADH-1. Currently, the enzymatic activity under hydrogen gas as hydride donor, as well as the immobilization of the remaining enzymes of the dehydrogenation cascade: formaldehyde dehydrogenase and formate dehydrogenase, is being studied, in order to convert carbon dioxide into methanol with a reusable, bioinspired catalytic system. In summary, our results suggest the development of a promising biocatalytic system for the conversion of CO2 to methanol.