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. (C) 2017 Elsevier Inc. All rights reserved.