【作者】 石建东；

【导师】 刘自力；

【作者基本信息】 广西大学 ， 化学工艺， 2004， 硕士

【摘要】 α，β不饱和醛的选择加氢还原在有机合成、精细化工、化学医药等领域有着广泛的应用。反应涉及C=O和C=C双键的竞争加氢而生成不同的加氢产物，因此，寻找和开发高效价廉的加氢催化剂，深入研究其加氢反应机理，具有重要的学术价值和现实意义。 本文采用浸渍法制备了Co／Al₂O₃、Co-Ce／Al₂O₃和Pd／Al₂O₃催化剂，并在肉桂醛的加氢反应中对其进行了活性评价。借助于一系列近代物理测试方法对催化剂进行了表征，将催化剂的活性与选择性和金属催化剂还原前后及反应过程中的变化进行了关联。重点以原位红外光谱技术为手段，对比考察了肉桂醛、巴豆醛分子在氧化铝负载的金属催化剂上的反应行为，阐述了不同催化剂上可能的α，β不饱和醛加氢机理。特别是针对Pd催化下的原位红外的结果，结合量子化学计算软件（Gaussian98）的使用，对巴豆醛C=C键的加氢作了简单的理论探讨。 Co／Al₂O₃催化剂对肉桂醛的加氢反应表现出了低的反应活性和较高的不饱和醇选择性。XRD和XPS结果表明，Co₃O₄与载体之间存在着SMSI效应，Co对C=O的加氢遵循Horiuti-Polanyi机理。Ce对Co组分的调变作用不明显，根据原位红外光谱的实验结果，我们提出了Co-Ce／Al₂O₃催化剂上肉桂醛选择加氢的可能的电子效应，第二种金属组分的促进作用可用“亲电C=O活化”机理解释。Pd对C=C键加氢给出了几乎接近100％的饱和醛收率，我们认为在α，β不饱和醛分子中，除了存在C=C和C=O之间的加氢竞争以形成饱和醛和α，β不饱和醇外，对于饱和醛的形成也存在着不同加氢途径的竞争，即饱和醛的形成除了通常的3，4-位吸附加氢产生外，也可以由C=C=O和C=C=C两种吸附结构的转变生成的烯醇结构形成。 为此，本文在B3LYP／6-311G（d）的理论水平下，优化了反应体系的反应物、产物和中间体的几何构型，计算了他们的振动频率并与实验振动频率进行了对比。对于巴豆醛加氢的两个反应通道，以烯醇结构的转变为例进行了振动分析，找到并证实了反应过程的过渡态。在此基础上计算了反应物、过渡态和产物的能量并进行了零点能的修正，得到了考虑零点能后的反应能垒。巴豆醛C=C键加氢的三个反应能垒分别为648.99、684.71和194.73kJ／mol，整个反应为放热反应，反应热为92.3kJ／mol。于是我们认定反应（1）是主要反应，反应（2）和反应（1）的能垒比较接近，使巴豆醛生成丁醛的反应也存在着3，4-和1，4-加氢的竞争，而第二个反应通道中反应（3）的能垒可解释原位反应中观察到的烯醇结构。更多还原

【Abstract】 The synthesis of a large number of fine chemicals, particularly in the field of chemistry, medicine and pharmaceuticals, involves the selective hydrogenation of a, -unsaturated aldehyde. The competitive hydrogenation between the C=G and C=C double bonds is the key to determine the different hydrogenation products. Saturated carbonyls are comparatively easy to achieve because thermodynamic favors the hydrogenation of the C=C bond. Therefore, research efforts were directed at looking for efficient but cheap hydrogenation catalyst and developing its responding hydrogenation mechanism to improve the selectivity to unsaturated alcohols.In the first part of our dissertation, three kinds of catalysts Co/Al2O3, Co-Ce/Al2O3 and Pd/Al2O3 were prepared by impregnancy method. Subsequently, catalyst activity evaluation was proceeded in the hydrogenation reaction of cinnamaldehyde. A series of modern physical tests were also carried out to establish relations between selectivity and activity and changes during the course of reduce and reaction of abvoe catalysts. The reaction behaviors of cinnamaldehyde and crotonaldehyde moleculars on the alumina-supported metal catalysts were investigateded mainly by in-situ FT-IR spectroscopy. Although the reaction mechanism was quite varified over different catalysts, the progressive experiments were proceeded to discover the completed reaction mechanism. Especially, the quantum chemistry calculation software (Gaussian98) was used to help discuss the C=C hydrogenation of crotonaldehyde.The low reaction activity and higher saturated alcohol selectivity in the reaction of cinnamaldehyde on Co/Al2O3 catalyst was attributed to the SMSI effect between Co3O4 and carrier. It is assumed that hydrogenation of carbonyls on Co surfaces occurs via the Horiuti-Polanyi mechanism. In order to explain the little promoting effect of Ce to Co, the possible electronics effect which referred to as "electrophilic C=O activation" was brought up to account for the promoting effect of the second metal according to the experiment results of in-situ FT-IR. Palladium catalyst is very active for C=C bond hydrogenation and gives almost a 100% yield to saturated aldehyde. It is thought there also exsits competition in the formation of saturated aldehyde besides the usual competition betweenC=C and C=O to formate saturated aldehyde and a, p-unsaturated alcohol respectively, namely, except the 3,4-addition of hydrogen gives the saturated aldehyde, two kinds of adsorbed structures C=C=O and C=C=C can also formate the enol, which isomerizes into a saturated aldehyde.For this, in the next part of the thesis, we use transition state theory to investigate the reaction of crotonaldehyde hydrogenation. Using density functional theory, the geometric parameters and vibration frequencies were calculated at B3LYP/6-311G(d) level. The theoretical frequencies are well in agreement with the experimental data. The geometries of reactants, transition states and products have been optimized and verified by frequency analysis. The relative single-point energies of the above structures have been calculated at the same level. The zero-point-energy ( ZPE ) corrections were obtained. The three reaction barriers are 648.99 kJ/mol and 684.71 kJ/mol and 194.73 kJ/mol respectively. By comparing the calculated barriers, it is found that reaction (1) is the main reaction path and the approach of the reaction barriers between reaction (1) and reaction (2) results in the competition of 3,4-addition and 1,4-addition of hydrogen. The whole reaction is exothermic reaction with the energy of 92.3 kJ/mol. The barrier of reaction (3) is responsible for the enol structure observed in the in-situ FT-IR.更多还原