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Design of a Bimetallic Au/Ag System for Dechlorination of Organochlorides: Experimental and Theoretical Evidence for the Role of the Cluster Effect

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posted on 10.11.2014, 00:00 by Leonid V. Romashov, Levon L. Khemchyan, Evgeniy G. Gordeev, Igor O. Koshevoy, Sergey P. Tunik, Valentine P. Ananikov
The experimental study of dechlorination activity of a Au/Ag bimetallic system has shown formation of a variety of chlorinated bimetallic Au/Ag clusters with well-defined Au:Ag ratios from 1:1 to 4:1. It is the formation of the Au/Ag cluster species that mediated C–Cl bond breakage, since neither Au nor Ag species alone exhibited a comparable activity. The nature of the products and the mechanism of dechlorination were investigated by ESI-MS, GC-MS, NMR, and quantum chemical calculations at the M06/6-311G­(d)&SDD level of theory. It was revealed that formation of bimetallic clusters facilitated dechlorination activity due to the thermodynamic factor: C–Cl bond breakage by metal clusters was thermodynamically favored and resulted in the formation of chlorinated bimetallic species. An appropriate Au:Ag ratio for an efficient hydrodechlorination process was determined in a joint experimental and theoretical study carried out in the present work. This mechanistic finding was followed by synthesis of molecular bimetallic clusters, which were successfully involved in the hydrodechlorination of CCl4 as a low molecular weight environment pollutant and in the dechlorination of dichlorodiphenyl­trichloroethane (DDT) as an eco-toxic insecticide. High activity of the designed bimetallic system made it possible to carry out a dechlorination process under mild conditions at room temperature.