Efficient and stable N-heterocyclic ketone-Cu complex catalysts for acetylene hydrochlorination: the promotion effect of ligands revealed from DFT calculations

Cu-based catalysts are a promising alternative to toxic mercury catalysts for acetylene hydrochlorination, but their effectiveness is limited due to the poor dispersion and deactivation caused by reduction, agglomeration, and carbon deposition. In this study, the activity and stability of carbon-supported CuCl2 catalysts were largely improved by introducing N-heterocyclic ketones. Remarkably, N-methyl-2-pyridone (NM2P) coordinated Cu-based catalysts exhibited over 95% acetylene conversion with better stability under the reaction conditions of T = 180 °C, GHSV (C2H2) of 80 h-1, and VHCl/VC2H2 = 1.2. The combined results of characterization and exhaustive density functional theory (DFT) calculations revealed that the O-Cu coordination between the NM2P ligand and Cu cation strengthened the combination of reactants and Cu active sites, lowering the key reaction energy barrier, thereby leading to high activity. Meanwhile, the addition of the NM2P ligand significantly inhibited the reduction of Cu2+ to Cu+/Cu0, avoiding the formation of CuCl aggregates and the coking caused by Cu0, enhancing the catalytic stability. Overall, our study provides important insights into the design and optimization of Cu-based catalysts for acetylene hydrochlorination.

Active centre and reactivity descriptor of a green single component imidazole catalyst for acetylene hydrochlorination

A green catalyst for acetylene hydrochlorination yielding a VCM is presented using imidazole as a single component metal-free catalyst. The mechanisms and reactivities of imidazole-catalyzed acetylene hydrochlorination have been investigated by combined computational and experimental studies. The electronic effects of ortho-substituents on the reactivities have also been investigated. Through theoretical calculations and experimental studies, the nitrogen-atom including a lone pair active site of single component imidazole for metal-free acetylene hydrochlorination is proposed. It is suggested that the nitrogen-atom including a lone pair of imidazole adsorbs an HCl molecule to form an imidazole-HCl complex, which serves as the active catalyst to participate in the reaction process of acetylene hydrochlorination. Besides, the results show that C₂H₂ assists in the electrophilic addition of HCl, undergoing an almost planar six-membered ring transition state. Computational studies on the ortho-substitution of the active sites will have an important impact on the catalytic efficiency.

Demystifying the mechanism of NMP ligands in promoting Cu-catalyzed acetylene hydrochlorination: insights from a density functional theory study

Experimental results and DFT calculations revealed the promoting effect of NMP on catalytic reactivity and the inhibiting effect of NMP on the reduction of Cu²⁺ to Cu⁺ and Cu⁰, respectively.