Chemistry Department Colloquium

The use of CO2 as raw material can be a significant contribution to closing the carbon cycle, which is also called CCU (Carbon Capture and Utilization). One possible route is the conversion of CO2 with green hydrogen to certain hydrocarbons such as methanol or mixtures of hydrocarbons such as Fischer-Tropsch products. This route is pursued by so-called e-refineries which need huge capacities of renewable electricity and water electrolysis. CHEMampere, which is a Stuttgart Research Initiative (see: www.chemampere.com, [1]), follows the concept of decentralized and distributed CO2-neutral chemical production, given that renewable electricity production is itself decentralized and that the largest renewable electricity power plants are capable of producing electricity only in the order of several Gigawatts (GW).
Formic acid is a suitable intermediate for such a decentralized chemical production, because it is an intermediate for various future downstream processes such as fermentation [2], C-C coupling, transfer hydrogenations or carbonylation. Furthermore, it can be directly produced from CO2 and renewable electricity by electrocatalytic reduction. Sn, Bi, and In are the preferred active sites for this reaction which need to be present in a large amount and simultaneously supplied through a large three phase boundary (TPB) by electrons, CO2, and electrolyte. This results in a complex optimization problem of the catalyst (structure, morphology) [3], the electrode (wetting, local concentrations) [4], and reaction conditions (temperature, residence time) [5] which will be exemplarily shown in this presentation. Last but not least, a CO2 neutral production of formic acid comprises the avoidance of side products (e.g. bicarbonate/carbonate) as well as the separation and recirculation of the electrolyte and CO2, that has not been converted. Finally, formic acid must meet the desired target concentration, e.g. 80 wt.%. The process energy required for this must not be of fossil origin, but should also come from renewable sources. Thus, an „all-electric" process based on renewable electricity is preferred and will be demonstrated.