Efficient conversion of carbon dioxide to methanol is a key process to reach a methanol economy, based on a closed carbon cycle. Such goal could be achieved by the 6-electron reduction of carbon dioxide or its hydrogenation to methanol. However the electro reduction of carbon dioxide currently suffers from low faradaic efficiency and selectivity, whereas its hydrogenation is limited by the high hydrogen pressure required.
An interesting alternative would consist in utilizing formic acid (FA) as a C–H bond shuttle in the reduction of CO2 to methanol. This strategy relies on the 2–electron reduction of CO2 to FA, in an electrochemical cell, and this methodology is now technically and economically available, thanks to efficient electrocatalysts. Disproportionation of FA is then required to produce methanol. Although decomposition of FA usually leads to dehydrogenation or dehydration to form CO2 and CO, respectively  Miller, Goldberg et al. showed, for the first time in 2013, that a molecular complex could promote the disproportionation of FA to methanol. Using [(C5Me5)Ir(bpy)(H2O)][OTf]2 (bpy=2,2’–bipyridine) as a catalyst, aqueous solutions of FA could be converted to MeOH, at 80 °C. Though promising, this strategy currently suffers from the use of expensive iridium catalysts and the yields of methanol do not exceed 1.9 %.
Catalysts with improved activity and selectivity are highly desirable to reach the potential of this approach. In this presentation, we will report the efficient disproportionation of FA to methanol, with methanol yields of up to 50.2 %, using ruthenium molecular catalysts. Different pathways involving transient ruthenium–hydride species have been unveiled, based on mechanistic experimental and DFT investigations.
Solène Savourey, Guillaume Lefèvre, Jean–Claude Berthet, Pierre Thuéry, Caroline Genre and Thibault Cantat.
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