Tunable Redox Cycle and Enhanced π-Complexation in Acetylene Hydrochlorination over RuCu Catalysts

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.