【作者】 吴玉；

【导师】 徐柏庆；

【作者基本信息】 清华大学 ， 化学， 2008， 博士

【摘要】 负载型纳米Au催化剂是近20年来多相金属催化领域的热点方向,Au/TiO₂是其中的一个典型代表。然而不同形态的TiO₂,特别是一维（1D）TiO₂在充当纳米Au催化剂载体时能否赋予Au/TiO₂更优异的催化作用效果尚少有报道。另一方面,Au/TiO₂在储存过程中的失活已成为阻碍其应用的主要因素。本文在实现了形貌可控合成TiO₂的基础上,研究了Au/TiO₂催化剂结构和性能的关系。探究Au/TiO₂室温存放稳定性的工作首次发现未还原Au3+和吸附H2O对催化剂稳定性有很大影响,据此发展了一种室温保存Au/TiO₂催化剂的方法。提出了利用TiCl4-丙酮混合物合成TiO₂纳米晶的新方法。在TiCl4/丙酮摩尔比（TiCl4/Ac）不大于1/15时,改变TiCl4/Ac和反应温度可以选择合成锐钛矿TiO₂（TiO₂-A）纳米颗粒,并在4-10 nm范围内调控其尺寸;在TiCl4/Ac≥1/10时,生成金红石型TiO₂纳米纤维。提出了形成TiO₂纳米晶的可能机理。还以乙醇-水混合液代替水,对既有的碱液水热处理粉体TiO₂制备钛酸纳米管的方法进行了改进,实现了钛酸纳米线和纳米管的可控合成。在400oC焙烧后分别制得了TiO₂（B）纳米线（NW-TiO₂（B））和TiO₂-A纳米棒（NR-TiO₂-A）。用沉积-沉淀法制备了系列Au/1D-TiO₂催化剂,研究了它们对CO氧化和1,3-丁二烯加氢反应的催化性能。对于CO氧化反应,Au/NR-TiO₂-A的催化活性是Au/P25-TiO₂的1.6倍,是Au/TiO₂-A的4倍,是Au/NW-TiO₂（B）的8倍。对于1,3-丁二烯选择加氢反应,Au/NW-TiO₂（B）和Au/P25-TiO₂表现出相当的催化活性,但Au/NR-TiO₂-A的催化活性不足它们的1/3。表明1D-TiO₂是很有发展潜力的Au催化剂载体,有望为研制高性能Au/TiO₂催化剂创造机会。为提高Au/TiO₂催化剂的存放稳定性,制备了Au3+比例和吸H2O量不同的Au/P25-TiO₂催化剂。发现Au/TiO₂样品中Au3+所占比例越高而吸附H2O量越低,其室温储存稳定性就越高。在此基础上制备了Au3+比例为100%且吸H2O量很低的Au/P25-TiO₂催化剂,它在室温储存150天后的催化活性仍然与新鲜催化剂相当。这些结果表明保持Au物种处于Au3+状态并防止催化剂吸H2O是阻止Au/TiO₂存放失活的关键。更多还原

【Abstract】 Supported gold catalysts have been extensively studied during the past 20 years. Au/TiO₂ is one typical type of supported Au catalysts and has been extensively investigated. However, it is not known well how the catalytic behavior of Au/TiO₂ changes if we use different kinds of TiO₂, especially one-dimensional （1D） TiO₂ as supports. On the other hand, Au/TiO₂ may deteriorate when storing at room temperature, which has hindered the future applications of Au/TiO₂. In this paper, we show two new methods to synthesize 1D-TiO₂. We also compared the catalytic activity of Au supported on 1D-TiO₂, P25-TiO₂ and anatase TiO₂ nanoparticles （TiO₂-A）, for the CO oxidation and selective hydrogenation of 1,3-butadiene. It is shown that the crystal phase and morphology of TiO₂ strongly affect the catalytic activity of Au/TiO₂ catalysts. The investigation on storage of Au/TiO₂ showed the first time that the influence of Au3+ percentage and water amount on the deactivation behavior of catalysts stored at room temperature.A novel method to synthesize single-phase titania nanomaterials was shown by autoclaving titanium tetrachloride in acetone at 80-140 oC. Depending on the molar ratio of TiCl4 to acetone （TiCl4/Ac）, TiO₂ materials with different phases and morphologies were obtained. When the TiCl4 concentration was no higher than TiCl4/Ac = 1/15, single-phase anatase TiO₂ nanocrystals in sizes ranging from 4 nm to 10 nm were prepared by tuning TiCl4/Ac ratios from 1/90 to 1/15. On the other hand, when the TiCl4 concentration was high enough （e.g., TiCl4/Ac≥1/10）, single-phase rutile TiO₂ nanofibres were obtained selectively. With the aid of GC-MS analysis of organic products in the liquid phase, it is shown that the controlled hydrolysis of TiCl4 with water, which was in-situ generated from the TiCl4 catalyzed aldol-condensation reactions of acetones, played an important role in the formation of the titania nanomaterials. This mechanism was also supported by our success in using other ketones as the alternatives of acetone in the synthesis. We also autoclaved anatase titania in NaOH-containing ethanol-water solutions to make controlling-synthesis of titanate nanotubes and nanowires. Nanotubes turned to be anatase nanorobs （NR-TiO₂-A） with calcination at 400 oC, while nanowires changed to TiO₂（B） nanowires （NW-TiO₂（B））.The synthesized 1D-TiO₂ was then used to prepare supported Au catalysts with deposition-precipitation method. CO oxidation data show that the activity of Au/NR-TiO₂-A is 1.6 times that of Au/P25-TiO₂, 4 time that of Au/TiO₂-A, and 8 times that of Au/NW-TiO₂（B）. While conversion of 1,3-butadiene on Au/NW-TiO₂（B） is comparable to that on Au/P25-TiO₂, and 3 times that on Au/NR-TiO₂-A. These data suggest that 1D-TiO₂ is a kind of promising support of Au catalysts, which may provide opportunities for discovering and inventing high-performance Au/TiO₂ catalysts.In order to improve the stability of Au/TiO₂ during storage at ambient temperature, we controlled the syntheses of Au/P25-TiO₂ catalyst with different percentage of Au3+ and water amount. It was found that maximizing the percentage of Au3+ and minimizing the phy-sisorbed water on Au/TiO₂ surface could slowdown the deactivation during storage. Basing on the above results, A Au/P25-TiO₂ containing 100% Au3+ and less amount of physi-sorbed water could effectively preserve its activity for CO oxidation after storing at room temperature for 150 days. These data show that the main point to preserve activity of Au/TiO₂ during storage is to keep more percentage of Au3+ and less amount of physic-sorbed water.更多还原