【摘要】 在H2和O2共存条件下,金催化剂催化丙烯气相直接环氧化反应是近年来发展起来的一种新型环氧丙烷(PO)合成技术.本文采用沉积沉淀法制备了一系列Au/TiO2催化剂,考察了反应溶液的pH值、Au负载量、沉淀剂以及焙烧温度等因素对催化剂丙烯环氧化催化性能的影响.结果表明制备条件对催化性能有明显影响:反应溶液的pH值为7.5及Au负载量为2.4%时所得催化剂活性最好;当以Na2CO3、NaOH等含Na+物质作为沉淀剂时,催化性能明显优于Li+、K+等其它碱金属离子;400℃焙烧制得的催化剂活性较好,在50℃低温反应条件下,环氧丙烷得率可达1.3%.HRTEM结果表明,催化剂中Au组分高度分散于载体表面,且随着焙烧温度的增加Au粒因发生聚集而变大,从而影响了催化剂的活性.表面XPS分析证实,活性较好的Au/TiO2催化剂中活性组分Au除部分呈氧化态外,主要是以金属态的形式存在.更多还原

【Abstract】 The gas-phase direct epoxidation of propylene over gold supported catalysts in the mixture of H₂ and O₂ provides a new technology for PO formation. In this paper, a variety of Au/TiO₂ catalysts have been prepared by the DP method. Influences of the pH Value of starting solution, calcination temperature, gold loading and precipitant on the catalytic activity of Au/TiO₂ catalysts for the epoxidation of Propylene have been studied. The results show that the catalysts prepared under the conditions of PH=7.5, Au loading=2.4% and the carbonate or hydroxide of sodium as precipitant exhibit the best epoxidation activity. According to the HRTEM observations, Au species is highly dispersed on the TiO₂ support, and its particle size increases with increasing calcination temperature. It is found that 400 ℃ is the optimum calcination temperature in terms of catalytic activity, and a PO yield of 1.2% can be obtained. In addition, XPS analysis of the highly active catalyst indicates that the catalysts mainly comprise metallic Au species, and only a small amount of oxidized Au exists.更多还原