Activated carbon-supported mercuric chloride (HgCl2) is used as an industrial catalyst for acetylene hydrochlorination. However, the characteristic of easy sublimation of HgCl2 leads to the deactivation of the catalyst. Here, we showed that the thermal stability of the Hg/AC catalyst can be evidently improved when CsCl is added into the Hg/AC catalyst. Compared with the pure Hg/AC catalyst, the sublimation rate of HgCl2 from the Hg–Cs/AC catalyst decreased significantly and the Hg–Cs/AC catalyst showed better catalytic activity and stability in the reaction. This promoting effect is related to the existence of cesium mercuric chlorides (CsxHgyClx+2y) highlighted by XRD, HR-TEM and EDX analyses. Thus, reacting HgCl2 with alkali chlorides to form alkali-mercuric chlorides may be a key to design highly efficient and thermally stable mercuric chloride catalyst for hydrochlorination reactions.CsCl can interact with HgCl2, forming a new compound, CsxHgyClx+2y. The addition of CsCl changes the existing form of the Hg atoms in the catalyst, resulting in the improvement of the thermal stability and catalytic efficiency of the mercuric chloride catalyst under reaction conditions.

The effect of the amount of precipitant ammonia on the Cu0/Cu+ ratio of Cu/SiO2 prepared by the deposition–precipitation method is investigated. Species at different preparation stages, resulted from the amount of ammonia used, are identified by the XRD and FTIR techniques. Chrysocolla together with either copper nitrate hydroxide or copper hydroxide coexist in the uncalcined catalysts. Upon calcination, the latter two species are converted to CuO particles while chrysocolla remains. Following reduction, CuO is transformed to metallic Cu and chrysocolla is converted to Cu2O. The value of Cu0/Cu+ ratio can be evaluated using the peak areas in their TPR profiles. Hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG) shows that the selectivity of EG depends on the Cu0/Cu+ ratio. Catalyst prepared with the addition of ammonia solution at n(NH3)/n(Cu2+) = 0.9 for precipitation–deposition gains a more suitable Cu0/Cu+ ratio upon reduction and thus has a higher selectivity for EG.The Cu0/Cu+ ratio of Cu/SiO2 synthesized by the deposition–precipitation method using ammonia as a precipitant can be modulated by controlling the amount of ammonia used, and it affects the selectivity of the products of dimethyl oxalate hydrogenation greatly.