Quantitative Basicity-Activity Correlation in Ru-Imidazolium Ionic Liquid-Catalyzed Acetylene Hydrochlorination

Abstract

Ionic liquids (ILs), as liquid-phase media in acetylene hydrochlorination, not only optimize the mixing environment of reactants but also stabilize the active sites of metal catalysts. Nevertheless, research in this field is still in its early stages, and systematic analysis and in-depth study of liquid-phase media-ionic liquids are still insufficient. In this study, imidazolium-based ILs ([Bmim]X) with different hydrogen bond basicity (β) values were used to fine-tune the Ru-based liquid-phase catalytic system (Ru-[Bmim]X). It was found that as the β value of [Bmim]X increased, its solubility in HCl and C₂H₂ also increased, resulting in a volcanic trend in the activity of the Ru-[Bmim]X catalysts. Through systematic characterization and theoretical calculations, we identified the active site of the Ru-[Bmim]Cl catalyst as the [RuCl4]⁻ anion and confirmed that the reaction is a two-step mechanism. Various anions of [Bmim]X influence the adsorption of reactants and reactive energy barriers by modulating the electronic and steric effects at the active sites. In particular, the Ru-[Bmim]Cl catalyst showed a remarkable conversion rate of 86.8% and high stability even at a low temperature of 110 °C. These results provide the scientific basis for the development of novel and efficient liquid-phase catalytic systems.