Alternative solvent to aqua regia to activate Au/AC catalysts for the hydrochlorination of acetylene

In this paper, we demonstrate that the less toxic, relatively safe, and recyclable organic aqua regia (OAR) can be employed as a greener alternative solvent to conventional aqua regia to activate Au/AC catalysts for the hydrochlorination of acetylene. We show that Au-based catalysts prepared with HAuCl4 as precursor can be prepared initially in water (Au(H2O)/AC). Although catalysts prepared from aqueous HAuCl4 showed poor activity, it can be significantly enhanced by catalyst activation in OAR (Au(H2O)/AC(OAR)). In contrast to the catalyst activation procedure using aqua regia (Au(aq)/AC), we demonstrate that the new activation procedure leads to both improved activity and stability of the resulting Au(H2O)/AC(OAR) catalyst. Further analyses of X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) show that the variations of Au particle size and chemical state caused by OAR treatment promote Au oxidation and high dispersion. In addition, temperature-programmed reduction (TPR) and temperature-programmed desorption (TPD) indicated that the presence of residual sulfur and nitrogen species may help stabilize the cationic Au3+ species and generate a catalyst less prone to deactivation by increasing the reduction temperature of the Au3+ species and enhancing the adsorption of hydrogen chloride over the Au(H2O)/AC(OAR) catalyst. These results suggest that OAR can be substituted for conventional solvents to activate Au/AC catalysts for the hydrochlorination of acetylene.