Hydrochlorination of Acetylene Over the Activated-Carbon-Supported Au Catalysts Modified by N-P-O-Containing Ligand

Etidronic acid (HEDP) and Nitrilotri(methylphosphonic acid) (ATMP) were selected as heteroatoms-containing ligands to modify Au catalysts for acetylene hydrochlorination. Results from several analytical methods reveal an optimal mole ratio of Au/ligand (L) of 1 : 1, with obvious increments over the Au-1-L-1/AC catalyst. The coordination between the Au and the heteroatoms, especially the collocative presence of N, P, and O promoted electron transfer from the heteroatoms to the Aun+ and increased the density of the electron cloud around active centers. This stabilized the Aun+ and increased the difficulty in the reduction of Au species, and re-oxidized the Au-0 to active Aun+ species. Moreover, the coordination inhibited the migration of active components. The increased density of the electron cloud around active centers also weakens the adsorption capacity for C2H2 and strengthens the adsorption ability for HCl of the catalysts, which is conductive for constructing the micro-environment favorable to the reaction. DFT calculations proved the stabilization effect of the heteroatoms-containing ligands, and the energy sequence of the transition states supported the experimental results.