Abstract: Water-soluble homogeneous catalysts for formic acid dehydrogenation exhibit high efficiency and rapid response. However, such catalysts are relatively sensitive to variations in reaction parameters. In this study, the commercially promising water-soluble ruthenium/triphenylphosphine-3,3',3''-trisulfonic acid trisodium salt (Ru/m-TPPTS) catalyst was employed to systematically investigate the influence of reaction parameters—including catalyst concentration, molar ratio of formic acid to sodium formate (FA/SF), and type of formate cation—on the performance of formic acid dehydrogenation. The results reveal that the activity of the Ru/m-TPPTS catalyst follows a distinct volcano-shaped trend with respect to both FA concentration and the FA/SF ratio. Under optimal conditions of 2.4 M FA and an FA/SF ratio of 6/4, a turnover frequency (TOF) of 2291 h-1 was achieved—five times higher than that of the commercial Ru/m-TPPTS catalyst. Through varying the cationic species of formate, it was discovered that solutions containing Na+ or K+ exhibit a higher dehydrogenation rate compared to those containing NH4+. This difference is attributed to the fact that NH4+ maintains the system at a lower pH, thereby inhibiting the dehydrogenation reaction. Furthermore, the dehydrogenation rate did not increase linearly with catalyst concentration. A double-logarithmic fitting of TOF versus catalyst concentration yielded a slope of n=0.76, suggesting that the reaction is not governed by a single active species. Owing to the high sensitivity of the catalyst to reaction conditions, the hydrogen release process in the water-soluble homogeneous catalytic system was successfully regulated by alternately adding sodium hydroxide (NaOH) and FA. This study provides a theoretical foundation for the reaction control and industrial application of water-soluble homogeneous catalysts.

Key words: Homogeneous catalysts, Formic acid, Formate, pH, Reaction control