Chloride-Induced Highly Active Catalyst for Methyl Esterification of Alcohols
Journal Title: Archives of Organic and Inorganic Chemical Sciences - Year 2018, Vol 3, Issue 1
Abstract
In recent decades, Au catalysts have received growing attentions and been widely applied in many important research fields [1], since good performance of Au catalysts was discovered [2]. However, the controllable preparation of highly active heterogeneous catalysts is still a longstanding challenge till now, especially Au catalysts. Many efforts have been devoted to this problem. The active site, structure and the quantum size effect of Au catalyst [3], active oxygen species of the support [4], suitable reducible oxide supports [5],and so on, have been extensively studied. Additionally, catalyst precursors, bases, pH value, aging time, and calcinations temperature are also crucial conditions [2,6]. Nevertheless, the controllable preparation of highly active Au catalyst is still difficult to realize even strictly following all above conditions. Chloride (usually as Cl-) is generally regarded as a poison for Au catalyst, Because of strong interaction of chloride and Au. We realized the reproducible preparation of Au/Fe2O3 catalyst for CO oxidation [7]. It is meaningful to explore whether this method can be applied to other catalysts and reactions or not. In this work, Methyl esterification of alcohols was chosen as model reaction. The controllable preparation of highly active Au/ NiOx catalyst was realized by tracing the concentrations of chloride in the re-dispersed aqueous solutions. 20ml Ni(NO3)36H2O (0.011 M) and 1.05 ml HAuCl4 (0.24M) were mixed together and were drop wise added into 60 ml Na2CO3 solution (0.31M) under vigorous stirring in 3h. The turbid liquid was divided into four sections and separation by centrifugation. Each section of the recovered precipitate was re-dispersed in different amount of deionised water and ultrasonically washed for 1h. The chloride concentration in the re-dispersed aqueous solution of each section was determined by CHI660D electrochemical workstation. Then, the solid was separated by centrifugation, dried at 80o C for 3h and calcined at 350 oC for 0.5 h to produce the catalyst sample, which was denoted as Au/NiOx-X, in which X suggested the chloride concentration in ppm. The catalytic activities of 15 Au/NiOx samples, which were prepared from the re-dispersed aqueous solutions with chloride concentrations in the range of 2 to 108 ppm, for esterification of benzyl alcohol were studied. According to the results shown in Figure 1, catalytic activity of Au/NiOx varied with the changing of chloride concentration. The yields of methyl benzoate were lower than 21% if the catalysts were prepared from aqueous solutions containing >22ppm chloride. More active catalysts were produced when the chloride concentrations were going down. The Au/ NiOx catalysts with the highest catalytic activity were prepared from aqueous solutions containing 8-13ppm chloride, the yield of methyl benzoate of catalyst Au/NiOx-9 was >99%. Surprisingly, the catalysts turned less active again when the chloride concentrations were < 8ppm. Typically, the yield of methyl benzoate was 20% with catalyst Au/NiOx-3.
Authors and Affiliations
Chengming Zhang, Yongzhao Wang, Yongxiang Zhao
Keywords
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- EP ID EP603527
- DOI 10.32474/AOICS.2018.03.000154
- Views 80
- Downloads 0
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