Chlorocuprate(I) ionic liquid as an efficient and stable Cu-based catalyst for hydrochlorination of acetylene
The gas–liquid reaction process for acetylene hydrochlorination, especially using ionic liquids (ILs) as homogeneous reaction media, has gained much attention because it can effectively avoid the deactivation caused by hot spots and carbon deposition. However, the relatively low activity and high price of the currently used ILs limit their practical applications. Herein, we synthesize a series of chlorocuprate(I) ILs to explore an efficient and stable Cu-based catalyst for acetylene hydrochlorination. The N-methylpyrrolidonium hydrochloride–0.60CuCl ([Hnmpo]Cl–0.60CuCl) IL exhibits the best catalytic performance, showing an acetylene conversion of 86% over 150 h under the conditions of 180 °C and 50 h−1 GHSV. It is confirmed that the Cu(I) species is the major active component and extremely stable under the reaction conditions via characterization of TGA-DSC-FTIR, ICP-OES, XPS, UV-vis, ESI-MS, and Raman. In addition, the [Hnmpo]Cl–0.60CuCl IL has the capacity to effectively activate HCl, which is directly observed by in situ FTIR. By combining the experimental results and theoretical calculations, we propose the reaction mechanism and find that the catalytic performance of chlorocuprate(I) ILs is positively correlated with the adsorption of HCl. The strong interaction with HCl is identified as the key characteristic of the [Hnmpo]Cl–CuCl IL, which endows it with excellent catalytic performance. Briefly, this study shows that the cost-effective [Hnmpo]Cl–CuCl IL can be a viable alternative to the commercial heterogeneous HgCl2/AC catalyst for acetylene hydrochlorination.