Chloride-Induced Highly Active Au Catalyst for Methyl Esterification of Alcohols

of main observation and conclusion Chloride is generally regarded as a harmful species for the heterogeneous catalysts, especially Au catalysts. In this work, a series of active Au/NiOx catalysts were successfully prepared with co-precipitation method by tracking the concentrations of chloride in the re-dispersed aqueous solutions. For methyl esterification of alcohols, the highest active Au/NiOx catalysts could be prepared from aqueous solutions containing 8-13 ppm chloride, the yield of methyl benzoate of catalyst Au/NiOx-9 was 99%. The catalyst structures and the role of chloride in catalysts were explored by ICP, BET, XPS, TEM and EXAFS characterizations. It was found that the appropriate amount of residual chloride in Au catalysts was beneficial to their catalytic activities. Especially for Au/NiOx-9, the appropriate amount of residual chloride had positive effects on the physicochemical properties of Au/NiOx catalyst, the position of Au nanoparticles (NPs) located on NiOx crystallites and the ratio of Au delta+/Au-0 in catalyst, which together resulted in its high reactivity.