Formic Acid As a Hydrogen Storage Medium: Ruthenium-Catalyzed Generation of Hydrogen from Formic Acid in Emulsions

Formic
acid is decomposed to H2 and CO2 in
the presence of RuCl3 and triphenylphosphines in an emulsion.
In situ formed ruthenium carbonyls, such as [Ru­(HCO2)2(CO)2(PPh3)2] (1), [Ru­(CO)3(PPh3)2] (2), and [Ru2(HCO2)2(CO)4(PPh3)2] (3), and a large cluster,
involving a Ru12 core, were identified and structurally
characterized from the reaction mixtures. The catalytic activity of
the mono and binuclear complexes was also investigated and it was
found that [Ru2(HCO2)2(CO)4(PPh3)2] (3) shows high stability
even at elevated temperatures and pressures and its activity is 1
order of magnitude lower than those measured for the mononuclear complexes.
It was also attempted to use [Ru­(HCO2)2(CO)2(PPh3)2] (1) as a catalyst
for the hydrogenation of CO2 to formic acid under neutral
conditions. Although the reduction of CO2 did not take
place, the conversion of [Ru­(HCO2)2(CO)2(PPh3)2] (1) to an unexpected
carbonate, [Ru­(CO3)­(CO)2(PPh3)2]·H2O was observed.