Hydrochlorination of acetylene using carbon-supported gold catalysts: A study of catalyst reactivation

A study of the reactivation of carbon-supported gold catalysts (Au/C) for the acetylene hydrochlorination reaction is described. Au/C catalysts are deactivated by two competing mechanisms: (i) deposition of carbonaceous material, predominantly at low temperature (60–100°C), and (ii) reduction of Au(III), and possibly Au(I), to Au(0), which occures mainly at higher temperatures (120–180°C). A range of gases have been found to be effective for catalyst reactivation. Air is shown to be effective only for removal of carbonaceous deposits and has no marked effect on the gold oxidation state. However, Cl2 is shown to be effective in oxidising Au(0) and only short reactivation (1 h at 100°C) is required to restore complete catalytic activity. In addition to Cl2, NO and N2O have also been found to be effective and these oxidants can be used during the acetylene hydrochlorination reaction as coreactants to decrease the observed rate of catalyst deactivation. Initial experiments concerning optimisation of the Au/C catalyst are described and the overall experimental data presented suggest that a redox mechanism operates for the formation of vinyl chloride using Au/C catalysts.