负载型金催化剂催化乙醇选择氧化反应

Selective Oxidation of Ethanol over Supported Gold Catalysts

选择不同氧化物(Al2O3,SiO2,TiO2,MgO)和H-ZSM-5分子筛作为载体,以尿素为沉淀剂,采用沉积-沉淀法制备了一系列负载型金催化剂.采用X射线衍射、电感耦合等离子体发射光谱、程序升温还原、NH3程序升温脱附和透射电镜等技术对催化剂样品进行了表征,并测定了催化剂对乙醇选择氧化反应的催化性能.选择Au/Al2O3催化剂,考察了金负载量、反应条件(温度、压力、时间)和添加剂对乙醇选择氧化反应的影响.结果表明,所制备的Au/Al2O3催化剂的金负载率较高,金粒子较小(3～4nm)且分布均匀.载体对金催化剂催化乙醇氧化反应有显著影响,主要产物为乙醛、乙酸乙酯和缩醛.以TiO2为载体时,乙醇转化率较高.以Al2O3为载体时,乙酸乙酯选择性较高;少量碱性添加剂可抑制缩醛的生成,并可提高乙醇转化率和乙酸乙酯选择性.在优化的条件下,乙醇转化率可达4.7%,乙酸乙酯选择性可达93.5%.

Some oxides （Al2O3, SiO2, TiO2, MgO） and H-ZSM-5 zeolite were used as supports to prepare Au catalysts by depositionprecipitation （DP） with urea as a precipitator. The catalysts were characterized using X-ray diffraction, inductively coupled plasma emission spectroscopy, temperature-programmed desorption, temperature-programmed reduction, and transmission electron microscopy and used to catalyze the oxidation of ethanol. The results indicated that Au/Al2O3 prepared using urea-DP could obtain high Au loading, and the Au particles were well distributed with the average size of 3-4 nm. The supports, reaction temperature, oxygen pressure, and the additive had some effects on the selective oxidation. The Au/TiO2 catalyst presented the highest catalytic activity. However, the highest selectivity for acetic ester was obtained over Au/Al2O3. An appropriate quantity of basic additive in the reaction system could evidently increase the ethanol conversion and the selectivity for acetic ester. The ethanol conversion was about 4.7 % with about 93.5 % selectivity for acetic ester under the optimal conditions.