Magnesium oxide nanosheets as effective catalysts for the synthesis of diethyl carbonate from ethyl carbamate and ethanol
Magnesium oxide nanosheets as effective catalysts for the synthesis of diethyl carbonate from ethyl carbamate and ethanol
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氧化镁纳米片作为氨基甲酸乙酯和乙醇合成碳酸二乙酯的有效催化剂
DOI：
10.1039/c4cy01109k
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发表时间：
2015-01-01
影响因子：
5
通讯作者：
Cao, Yan
中科院分区：
文献类型：
--
作者：
Li, Fengjiao;Li, Huiquan;Cao, Yan
采用热分解法和沉淀法制备了一系列MgO催化剂。以氨基甲酸乙酯（EC）和乙醇为原料合成碳酸二乙酯（DEC），考察了它们的催化性能。其中，以碳酸钠为沉淀剂，经450 ℃焙烧制得的MgO（MgO-SC-450）具有更高的催化活性。在MgO-SC-450催化剂上，当反应温度为210 ℃，乙醇/EC摩尔比为10，反应时间为3 h时，DEC的收率为58.0%，选择性为92.1%。此外，催化活性可以基本上保留在回收实验。采用XRD、Mastersizer 2000、N-2吸附、场发射扫描电镜（FE-SEM）和CO2程序升温脱附（CO2-TPD）等手段对MgO催化剂的结构和表面碱性进行了表征。结果表明，MgO-SC-450具有纳米片状形貌。此外，MgO-SC-450的具有位于225 ℃和275 ℃之间的峰的较大量的适当中等碱性β位有利于获得更优异的上级催化活性。通过准原位红外光谱实验研究了反应物的吸附行为。结果表明，MgO能有效地活化EC，并使乙醇解离成强亲核性的乙氧基。此外，理论计算证实了EC和乙醇在MgO表面的共吸附。根据准原位红外光谱实验和理论计算结果，提出了催化反应的可能机理。
A series of MgO catalysts were prepared by thermal decomposition and precipitation methods. Their catalytic performance was evaluated in the synthesis of diethyl carbonate (DEC) from ethyl carbamate (EC) and ethanol. Among them, MgO prepared using sodium carbonate as the precipitant and calcined at 450 degrees C (MgO-SC-450) exhibited much higher catalytic activity. An excellent DEC yield of 58.0% with a high DEC selectivity of 92.1% could be achieved over the MgO-SC-450 catalyst under optimized reaction conditions: 210 degrees C, ethanol/EC molar ratio of 10, and 3 h. Moreover, the catalytic activity could be essentially retained during recycling experiments. The structure and surface basicity of the MgO catalysts were characterized by X-ray diffraction (XRD), Mastersizer 2000, N-2 adsorption, field-emission scanning electron microscopy (FE-SEM), and temperature-programmed desorption of CO2 (CO2-TPD). It was found that MgO-SC-450 possessed nanosheet morphology. Furthermore, a larger amount of appropriate medium basic beta sites of MgO-SC-450 with the peak located between 225 degrees C and 275 degrees C was favourable for obtaining much superior catalytic activity. Quasi in situ FT-IR experiments were carried out to elucidate the adsorption behaviours of reactants. It was found that EC could be effectively activated and ethanol could be dissociated to a strong nucleophilic ethoxy group by MgO. In addition, theoretical calculation proved the co-adsorption of EC and ethanol on the MgO surface. Based on the results of quasi in situ FT-IR experiments and theoretical calculation, a plausible reaction mechanism has been proposed for the catalytic reaction.