The variation of the involved base (Fig. ), which is crucial to turn the thermodynamics of the CO2 hydrogenation to formic acid exergonic, reveals the significant role of the chosen base for the catalytic activity. Experiments with ammonia as base show a minor catalytic performance, while the activity increases from NaOH to Na2CO3 to NaHCO3. The promoting effect of NaHCO3 suggests that the reaction mechanism proceeds via the hydrogenation of bicarbonates, which for the other bases originates from the deprotonation of CO2 in aqueous solutions, which has already been discussed in the literature. enhanced catalytic performance, when bicarbonates were used. In addition, other works have emphasized an increased activity for alkali metal bicarbonates compared to their corresponding carbonates or hydroxides. Alkylamines are also capable of generating bicarbonates in aqueous solutions and promoting the CO2 hydrogenation to formate. While the experiments with NEt3 exhibit the second highest activity of the screened bases, the poor miscibility of NPr3 with water presumably inhibits the formation of bicarbonate and the stabilization of the formate. Moderate activities were obtained with the scrubbing amines monoethanolamine (MEA), diethanolamine (DEA) and triethanolamine (TEA). Moreover, the influence of the amount of base is examined, with NaHCO3 as the promoting base (Fig. ). The catalytic activities increase with an enhanced NaHCO3 concentration up to 1 mol L -1 and decrease again with higher NaHCO3 concentrations.