Conditions: the catalyst was dissolved in 2 ml H2O ([RuCl2(PTA)4]=2.76 mM) under N2 atmosphere. This solution was pressurized at room temperature with CO2 (50 bar) and completed with H2 to the desired pressure. The system was heated at 60 °C and stirred until the equilibrium of the reaction was reached (72–96 h). The final yield of formic acid was determined by 1H NMR spectroscopy with DSS as an internal standard. The values are averaged from three to six measurements with a reproducibility of ±15%. The trend line is shown as a guide and is not a mathematical fit of the data.