Figure 2. ¹³C NMR signals of DCOOD in the hydrogenation reactions of CO₂ into formic acid in D₂O.

[RuCl₂(PTA)₄] (2.76 mM) was dissolved in D₂O (2 ml) under N₂ atmosphere in a medium pressure sapphire NMR tube. This solution was pressurized at room temperature to 50 bar with CO₂ and completed to 100 bar with H₂. The system was heated to 60 °C and the reaction was followed by ¹³C NMR (100 MHz) spectroscopy. The figure shows the evolution of the ¹³C NMR signals of DCOOD at 166.3 p.p.m. (time difference between spectra Δt=189 min). The triplet signal of the formic acid is due to the exchange of the hydrogen to deuterium in HCOOH (as D₂O was used as solvent). Reaction time: 148 h.