Tunable Redox Cycle and Enhanced π-Complexation in Acetylene Hydrochlorination over RuCu Catalysts
Yurui Fan, Haomiao Xu, Zhisong Liu, Songyuan Sun, Wenjun Huang, Zan Qu, Naiqiang Yan
Abstract
Acetylene hydrochlorination is the core reaction in vinyl chloride monomer (VCM) production. Ruthenium chloride (RuClx) has emerged as a promising nonmercury alternative to replace the supported mercuric chloride (HgCl2) catalysts. However, it has some obstacles such as low activity, coke deposition, and over-reduction of active ruthenium (Ru) species. In this study, we found that the cooperation of Cu(X) (X = 0, I, and II) enhanced both the acetylene (C2H2) conversion efficiency (>96%) and VCM selectivity (>97%). Notably, the anchored Cu(I) ions can promote the rapid C2H2 molecule adsorption through Cu(I)-alkynyl π-complexation with the side-on mode. Furthermore, the one-electron complementary redox cycle of Cu(I)/Cu(II) pairs contributed to the Ru(III)/Ru(IV) cycle in the catalytic process. Density functional theory calculation results indicated that the Ru–O–Cu coordination sites played a crucial role in the catalytic activity of the hydrochlorination reaction, and the migration of Cl* was identified as the rate-limiting step of the entire catalytic pathway. The bimetallic RuCu/AC catalyst guaranteed the continuity and high efficiency of the reaction. Moreover, for the long-term catalytic reaction over 100 h, the C2H2 conversion efficiency was only decreased by 1.46% due to the restriction of in situ coke formation. These findings provide guidance for designing efficient Ru-based catalysts and solutions for engineering applications to replace existing mercury-contained catalysts.