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

Formic acid is decomposed to H 2 and CO 2 in the presence of RuCl 3 and triphenylphosphines in an emulsion. In situ formed ruthenium carbonyls, such as [Ru(HCO 2 ) 2 (CO) 2 (PPh 3 ) 2 ] ( 1 ), [Ru(CO) 3 (PPh 3 ) 2 ] ( 2 ), and [Ru 2 (HCO 2 ) 2 (CO) 4 (PPh 3 ) 2 ] ( 3 ), and a large cluster, involving a Ru 12 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 [Ru 2 (HCO 2 ) 2 (CO) 4 (PPh 3 ) 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(HCO 2 ) 2 (CO) 2 (PPh 3 ) 2 ] ( 1 ) as a catalyst for the hydrogenation of CO 2 to formic acid under neutral conditions. Although the reduction of CO 2 did not take place, the conversion of [Ru(HCO 2 ) 2 (CO) 2 (PPh 3 ) 2 ] ( 1 ) to an unexpected carbonate, [Ru(CO 3 )(CO) 2 (PPh 3 ) 2 ]·H 2 O was observed.