【作者】 陈建；

【导师】 林海强； 袁友珠； 姚元根；

【作者基本信息】 厦门大学 ， 化学工程， 2022， 硕士

【摘要】 α,β-不饱和醛选择性加氢是一类重要的精细化学品转化过程,其加氢产物广泛用于香精香料、医药等高附加值精细化工品的生产。α,β-不饱和醛包括肉桂醛、巴豆醛和丙烯醛等,通常希望选择加氢的目标产物为不饱和醇,即在保留C=C键的前提下进行C=O键加氢。然而从热力学上看,C=O键的键能为715 kJ/mol,大于C=C的键能615 kJ/mol。此外,C=O键的加氢自由焓变比C=C键大35 kJ/mol,C=O键加氢的难度大于C=C键,因此高选择性地得到不饱和醇十分困难。开发高性能不饱和醛选择加氢催化剂,提高C=O键加氢活性与选择性,具有重要的工业应用价值与学术研究价值。本学位论文将巴豆醛作为底物分子,以气相巴豆醛选择加氢制备巴豆醇为目标反应,研究Ir基催化剂改良策略和构效关联。已有的研究显示,Ir基催化剂对巴豆醛选择加氢具有较高的C=O键选择性,但反应活性相对较低。然而,采用共浸渍方法制备的负载型Ir-Ru双金属催化剂表现出较高的催化活性与巴豆醇选择性。通过系统地研究不同Ir/Ru摩尔比、催化剂载体、反应温度和预处理温度等对负载型Ir-Ru双金属催化剂的巴豆醛选择加氢性能的影响。结果表明,以SiO₂为载体,在373 K、常压、氢醛比为80和Ir/Ru摩尔比为1:1时,巴豆醇收率最高达到70.5%,此时,巴豆醇选择性为86.1%,巴豆醛转化率为81.9%。而单金属Ir/SiO₂和Ru/SiO₂催化剂在相同条件下的收率分别为18.6%和12.7%,仅为Ir1-Ru1/SiO₂催化剂的1/3。进一步的实验结果表明,引入Ru还有助于提高Ir-Ru双金属催化剂的性能稳定性。在上述结果基础上,对Ir-Ru双金属进行一系列表征以将催化剂结构与催化性能关联。XRD与HR-TEM表征结果表明,Ir-Ru双金属催化剂在还原过程中形成Ir-Ru合金（fcc）结构,Ru可以促进Ir的分散,催化剂反应前后粒径未明显增大;H₂-TPD与NH₃-TPD实验结果表明,Ir-Ru合金化能够提高氢气的吸附活化效率,表面酸性也得到一定程度的增强;H₂-TPR与XPS结果表明,Ru在一定程度上促进了 Ir物种的还原,Ir-Ru双金属催化剂中表面Ir0物种增多,来自Ru的电子转移到Ir上,使得Ir上的电子云密度增大,很可能在一定程度上抑制了 C=C键加氢;CO-DRIFT表征结果表明,Ir-Ru双金属催化剂中CO在Ir金属上的线式吸附增强,桥式吸附减弱,Ir的分散度也有一定程度的增加。以上表征结果表明,在Ir中引入Ru后,改变了单一金属Ir和Ru的理化性质,Ir-Ru在几何结构上形成了合金,通过电子效应,使Ir表面电荷富集,更好的活化C=O键,表现出双金属协同效应,使Ir-Ru合金催化剂表现出优异的常压巴豆醛选择性加氢制备巴豆醇的催化性能。更多还原

【Abstract】 Selective hydrogenation of α,β-unsaturated aldehydes is an important class of fine chemical conversion processes,and its hydrogenation products are widely used in the production of high value-added fine chemicals such as flavors and fragrances and pharmaceuticals.α,β-unsaturated aldehydes include cinnamaldehyde,crotonaldehyde and acrolein,and the target product of hydrogenation is usually unsaturated alcohol.Thermodynamically,the bond energy of C=O is 715 kJ/mol,which is greater than the bond energy of C=C of 615 kJ/mol.In addition,the free enthalpy changes of hydrogenation of the C=O bond is 35 kJ/mol larger than that of the C=C bond,and the difficulty of hydrogenation of the C=O bond is greater than that of the C=C bond,so it is very difficult to obtain unsaturated alcohols with high selectivity.The study and development of high effective and selective catalysts to enhance C=O bond hydrogenation activity and selectivity is of great industrial application and academic research value.This dissertation prepares Ir-based catalysts for the synthesis of crotonol from crotonaldehyde in the gas phase as a typical example for the selective hydrogenation ofα,β-unsaturated aldehydes,and studies the structure-activity relationship of the catalyst and the reaction performances.It has been proven that Ir-based catalysts have high C=O bond selectivity for the selective hydrogenation of crotonaldehyde but with low reactivity.Alternatively,the loaded Ir-Ru bimetallic catalysts prepared by coimpregnation method exhibited enhanced catalytic activity and selectivity of target product.On basis of this,the effects of different Ir/Ru molar ratios,catalyst carriers,reaction temperatures and pretreatment temperatures on the performance of crotonaldehyde hydrogenation over loaded Ir-Ru bimetallic catalysts were systematically investigated in this dissertation.The results show one of that the best carrier was SiO₂,and a high crotonol yield of 70.5%was achieved at 373 K,atmospheric pressure,hydrogen to aldehyde ratio of 80 and Ir/Ru molar ratio of 1:1,when the conversion of crotonaldehyde was 81.9%and the selectivity of crotonol was 86.1%.The yield of the monometallic Ir/SiO₂ and Ru/SiO₂ catalyst was 18.6%and 12.7%under the same conditions,which was only 1/3 of that of the Ir1-Ru1/SiO₂ catalyst.Further experimental results show that the introduction of Ru also helped to improve the performance stability of the Ir-Ru bimetallic catalyst.Based on above results,a series of characterizations over Ir-Ru bimetallic catalysts were performed in order to study the relationship between catalyst structure and catalytic performance.The XRD and HR-TEM characterization results indicate that the Ir-Ru bimetallic catalyst forms an Ir-Ru alloy（fcc）structure during the reduction process,Ru can promote the dispersion of Ir,and the particle size does not increase significantly after reaction;The experimental results of H₂-TPD and NH₃-TPD show that alloying of Ir-Ru can improve the hydrogen adsorption,as well as enhance the surface acidity to some extent;The H₂-TPR and XPS results show that Ru promoted the reduction of Ir species,and the surface Ir0 species increased in the Ir-Ru bimetallic catalyst,and the electron transfer from Ru to Ir increased the electron cloud density on Ir,which probably inhibited the C=C bond hydrogenation to some extent;The CODRIFT characterization results show that the linear adsorption of CO on Ir metal in IrRu bimetallic catalysts is enhanced and the bridge adsorption is weakened,and the dispersion of Ir is increased.The above characterization results show that the introduction of Ru into Ir resulted in the formation of Ir-Ru alloy nanoparticles,which changed the physical and chemical properties of the counterpart metals of Ir and Ru,and exhibited excellent catalytic performance for the selective hydrogenation of crotonaldehyde to crotonol at atmospheric pressure.更多还原