Deactivation mechanism of AuCl3 catalyst in acetylene hydrochlorination reaction: a DFT study

Abstract

The deactivation mechanism of AuCl₃ catalyst in the reaction of acetylene hydrochlorination was studied by using AuCl₃ dimer model and the density functional theory (DFT) method. Four possible paths for the acetylene hydrochlorination reaction catalyzed by AuCl₃ were illustrated with corresponding transition states. The activation free energies and reaction rate constants of the four paths were also analyzed. It is apparent that when HCl and C₂H₂ coadsorbed on the AuCl₃ dimer, the C₂H₂ was co-catalyzed by HCl and the AuCl₃ dimer to produce C₂H₃Cl and the reaction energy barrier was as low as 23.35 kcal mol⁻¹. If the HCl in the gas phase could not adsorb on the Au site within the set time, the intermediate chlorovinyl was difficult to desorb from the AuCl₃ catalyst as its desorption energy was as high as 41.336 kcal mol⁻¹. As the reaction temperature increased, C₂H₂ became easier to be adsorbed on the AuCl₃ catalyst prior to HCl, which resulted in the side reaction and the rapid deactivation of the AuCl₃ dimer due to the loss of Cl atoms. Our calculations are necessary for us to clearly understand the experimental results, which indicate a great dependence of activity and stability of AuCl₃ catalysts on the HCl : C₂H₂ ratio as well as the temperature.