CuO(CoO,MnO)/SiO2纳米复合气凝胶催化剂载体的溶胶-凝胶法制备及成胶机理

采用正硅酸乙酯(tetraethyl orthosilicate,TEOS)和Cu,Co,Mn的醋酸盐溶液,通过溶胶-凝胶法、常压干燥制备了过渡金属氧化物含量高达75%(质量分数)的CuO(CoO,MnO)/siO2纳米复合气凝胶,对其成胶机理进行了分析.结果表明:制得的CuO(CoO,MnO)/SiO2纳米复合气凝胶具有SiO2气凝胶的纳米孔隙三维网络结构和高比表面积;当过渡金属醋酸盐与TEOS的比例不同时,Cu,Co和Mn能够与氧在网络结构中形成不同程度的-O-M-O一桥键连接;通过气凝胶的多孔网络分隔作用,可使更多过渡金属氧化物CuO,CoO和Mno的超细粒子均匀分散于CuO(CoO,MaO)/SiO2复合气凝胶或SiO2气凝胶骨架中.这种结构既有利于提高催化剂负载量,又能充分利用CuO,CoO和MaO的助催化作用,因此CuO(CoO,MnO)/SiO2纳米复合气凝胶可作为催化剂载体用于催化合成碳酸二苯酯及其它催化领域.     

CuO(CoO,MnO)/SiO_2纳米复合气凝胶催化剂载体的溶胶-凝胶法制备与表征

以正硅酸乙酯(tetraethyl orthosilicate,TEOS)、乙酸铜、乙酸钴、乙酸锰为原料,采用溶胶-凝胶法、常压干燥制备了CuO(CoO,MnO)/SiO2纳米复合气凝胶.分析了过渡金属氧化物MO与Sio2的质量比、温度和pH值对凝胶形成的影响.采用场致发射扫描电镜(FE-SEM)、BET、傅里叶变换红外分析(FTIR)、热重-差热分析(TG-DTA)、电子散射能谱分析(EDS)和化学分析等对CuO(CoO,MnO)/SiO2纳米复合气凝胶的微观结构和组成进行了研究.结果表明,纳米复合气凝胶的颗粒约在20～100nm,比表面积为344～733m2/g,孔径范围为2～22nm,而且过渡金属Cu、Co和Mn能够与氧形成部分一O-M-O-桥键连接,并与Si通过化学键形成三维网络结构;纳米复合气凝胶试样中的多元过渡金属氧化物含量可控制在3%～75%(质量分数).这种结构和组成既有利于提高催化剂负载量,又可充分发挥过渡金属氧化物的助催化作用.     

Preparation of CuO-CoO-MnO/SiO<Subscript>2</Subscript> nanocomposite aerogels as catalyst carriers and their application in the synthesis of diphenyl carbonate

CuO-CoO-MnO/SiO2 nanocomposite aerogels were prepared by using tetraethyl orthosilicate (TEOS) as Si source, and aqueous solution of Cu, Co and Mn acetates as transition metal sources via sol-gel process and supercritical drying (SCD) technique. The effect of synthesis conditions on gelation was investigated. Moreover, the composition of the CuO-CoO-MnO/SiO2 nanocomposite aerogels was characterized by electron dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS), and the specific surface area of the nanocomposite aerogels was determined by the Brunauer-Emmett-Teller (BET) method. Diphenyl carbonate (DPC) as the product was analyzed by gas chromatography (GC). The experimental results show that the range of optimal temperature for gelation is 30-45 ℃, and the pH is 3.0-4.5. CuO-CoO-MnO/SiO2 nanocomposite aerogels are porous with a specific surface area of 384.9-700.6 m2/g. Compared to CO2 SCD, ethanol SCD is even favorable to the formation of aerogel with high specific surface area. The transition metals content in the nanocomposite aerogels can be controlled to be 0.71at%-13.77at%. With CuO-CoO-MnO/SiO2 nanocomposite aerogels as catalyst carrier, the yield of DPC is in direct proportion to the atomic fraction of transition metals in the nanocomposite aerogels, and it is up to 26.31 mass%, which is much higher than that via other porous carriers.     

CuO(CoO,MnO)/SiO_2纳米复合气凝胶催化剂载体的制备及其在合成碳酸二苯酯中的应用

以正硅酸乙酯为硅源,以乙酸铜、乙酸钴和乙酸锰的水溶液为前驱体,采用溶胶–凝胶法和CO2超临界干燥工艺制备了CuO(CoO,MnO)/SiO2纳米复合气凝胶。采用场发射扫描电镜、透射电镜和电子散射能谱分析等对纳米复合气凝胶的微观结构和组成进行了表征。采用Brunauer–Emmett–Teller法测定了纳米复合气凝胶的比表面积、孔径及孔径分布。以纳米复合气凝胶为载体制备了负载型催化剂,用于催化合成碳酸二苯酯(diphenyl carbonate,DPC),并用气相色谱仪对反应液进行了分析。结果表明:纳米复合气凝胶的粒径为20～100nm,孔径为2～8nm,平均孔径为3.16nm,比表面积为664.4m2/g;过渡金属的摩尔含量为13.77%;催化合成DPC的质量收率达27.14%。