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.在三氯化钌（RuCl₃）与三苯基膦（triphenylphosphine）存在的乳液体系中，甲酸可分解为氢气（H₂）与二氧化碳（CO₂）。从反应混合物中鉴定并完成结构表征的原位生成钌羰基配合物包括：[Ru(HCO₂)₂(CO)₂(PPh₃)₂]（1）、[Ru(CO)₃(PPh₃)₂]（2）、[Ru₂(HCO₂)₂(CO)₄(PPh₃)₂]（3）以及一个含Ru₁₂核的大型团簇。本研究考察了单核与双核配合物的催化活性，结果表明配合物(3)即便在升高的温度与压力下仍具备高稳定性，但其催化活性较单核配合物低一个数量级。此外，尝试以配合物(1)作为催化剂，在中性条件下催化二氧化碳加氢制备甲酸，但未发生二氧化碳还原反应，仅观察到配合物(1)转化为一种意外生成的碳酸盐[Ru(CO₃)(CO)₂(PPh₃)₂]·H₂O。