Abstract
The copper-modified Mg-Al catalyst (Cu/Mg-Al) was synthesized using the incipient wetness impregnation of copper onto the Mg-Al hydrotalcite derived from co-precipitation method. The effects of copper on the characteristics of catalyst were obtained using several characterization techniques. We found that only copper (I) oxide (CuO) species were obtained on the surface after calcination in air by X-ray Diffraction (XRD). However, the basicity of the base decreases slightly, while the density of the base increases due to the decrease in Brunauer-Emmett-Teller (BET) surface area. We carried out the catalytic activity of the Cu/Mg-Al catalyst in the continuous flow reactor through oxidative dehydrogenation of ethanol. We obtained that the copper enhances the catalytic activity in this reaction, and the ethanol conversion increases with increase in temperature, while the acetaldehyde selectivity decreases because of the decomposition of acetaldehyde to carbon dioxide. The highest acetaldehyde yield of 41.8% was at 350 °C. Moreover, we studied the effects of the ethanol concentration by varying the ethanol feed concentrations (99.9%, 75%, and 50%). The ethanol conversion decreases with a decrease in the ethanol concentration due to the high adsorption of water molecules on the catalyst surface. Thus, the negative effect decreases at higher reaction temperature (350–400 °C). Furthermore, we investigated the effect of the reduction condition of catalyst by varying the reduction temperature (300 and 400 °C). The reduction process affects the catalytic activity. The Cu/Mg-Al was comparatively stable for 10 h upon time-on-stream test. It is used as a promising catalyst in oxidative dehydrogenation of ethanol without any reduction step.
概要
目 的
对现有的乙醇氧化脱氢体系中 Mg-Al 催化剂进行改进, 以期获得更高的收率和产物选择性.
创新点
1. 制备Cu 改性的 Mg-Al 催化剂用于乙醇氧化脱氢反应, 获得了更高的乙醛收率和选择性; 2. Cu/Mg-Al 催化剂制备方法简单, 制备价格低廉 (无需贵金属), 制备条件温和 (无需高温高压); 3. Cu/Mg-Al 催化剂在使用前无需预还原.
方 法
1. 采用共沉淀法和浸渍法制备 Cu/Mg-Al 催化剂; 2. 通过乙醇氧化脱氢反应对催化剂进行考评, 以探究Cu 改性、 乙醇浓度和催化剂的还原条件对催化活性的影响.
结 论
1. 与Mg-Al 催化剂相比, 经由Cu 改性的 Mg-Al 催化剂的乙醇氧化脱氢活性显著提高; 在350 °C, 乙醛最大收率为 41.8%. 2. 进料气中水的存在 (乙醇浓度下降) 会对 Cu/Mg-Al 的催化性能产生不利影响, 使得乙醇转化率和乙醛收率下降; 但在高温区间 (350 ∼ 400 °C), 这个不利影响有所减弱. 3. 反应前, 催化剂在氢气气氛下的还原步骤对 Cu/Mg-Al 催化活性的影响不明显.
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Piriya PINTHONG designed the research and performed the experiment. Bunjerd JONGSOMJIT managed and coordinated responsibility for the research activity planning and execution. Piriya PINTHONG wrote the first draft of the manuscript. Piyasan PRASERTHDAM and Bunjerd JONGSOMJIT helped to organize the manuscript. Piriya PINTHONG and Bunjerd JONGSOMJIT revised and edited the final version.
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Piriya PINTHONG, Piyasan PRASERTHDAM, and Bunjerd JONGSOMJIT declare that they have no conflict of interest.
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Project supported by Chulalongkorn University and the Thailand Science Research and Innovation (TSRI) under Catalytic Reaction (CAT-REAC) Industrial Project
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Pinthong, P., Praserthdam, P. & Jongsomjit, B. Oxidative dehydrogenation of ethanol over Cu/Mg-Al catalyst derived from hydrotalcite: effect of ethanol concentration and reduction conditions. J. Zhejiang Univ. Sci. A 21, 218–228 (2020). https://doi.org/10.1631/jzus.A1900451
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DOI: https://doi.org/10.1631/jzus.A1900451