Influence of chlorine coordination number on the catalytic mechanism of ruthenium chloride catalysts in the acetylene hydrochlorination reaction: a DFT study

The catalytic mechanism of Ru-based catalysts in the acetylene hydrochlorination reaction has been investigated via the density functional theory (DFT) method. To study the effect of the chlorine coordination number on the catalytic mechanism, Ru 3 Cl 9 , Ru 3 Cl 7 , Ru 5 Cl 7 , Ru 3 Cl 3 and Ru 3 clusters were chosen as the catalytic models. Our results show that the energy barrier for acetylene hydrochlorination on Ru 3 Cl 9 was as high as 1.51 eV at 458 K. When the chlorine coordination number decreased, the energy barriers on Ru 3 Cl 7 , Ru 5 Cl 7 , Ru 3 Cl 3 and Ru 3 were 1.29, 0.89, 1.01 and 1.42 eV, respectively. On Ru 3 Cl 9 , the H and Cl atoms of HCl were simultaneously added to C 2 H 2 to form C 2 H 3 Cl, while the reaction was divided into two steps on Ru 3 Cl 7 , Ru 3 Cl 3 and Ru 3 clusters. The first step was the addition of H atom of HCl to C 2 H 2 to form C 2 H 3 &z.rad;, and the second step was the addition of Cl atom to C 2 H 3 &z.rad; to form C 2 H 3 Cl. The step involving the addition of Cl was the rate-controlling step during the whole reaction. On Ru 5 Cl 7 cluster, there was an additional step before the steps involving the addition of H and Cl: the transfer of H atom from HCl to Ru atom. This step was the rate-controlling step during the reaction of acetylene hydrochlorination on Ru 5 Cl 7 and its energy barrier was the lowest among all the above-mentioned catalytic models. Therefore, the Ru 5 Cl 7 cluster played the most predominant role in acetylene hydrochlorination with the largest reaction rate constant k TST of 10 3 . Among Ru 3 Cl 9 , Ru 3 Cl 7 , Ru 5 Cl 7 , Ru 3 Cl 3 and Ru 3 catalytic models, Ru 5 Cl 7 performs best. In Ru 5 Cl 7 , the low chloride-coordinated Ru is responsible for activating reactants and adding H to C 2 H 2 , while the high coordinated is responsible for providing Cl to C 2 H 3 &z.rad;.