【作者】 沈江；

【导师】 范康年；

【作者基本信息】 复旦大学 ， 物理化学， 2006， 博士

【摘要】 复合银催化剂的制备及其在多碳醇选择性氧化反应中的催化性能羰基化合物是一种重要的有机化合物，包括醛和酮两大类，广泛应用于医药、农药、香料等诸多领域。目前，随着现代石油化工和精细化工的发展，一些结构比甲醛更复杂的多碳羰基化合物越来越受到人们的重视。例如，丙酮醛作为一种医药工业的中间体，有着非常广泛的应用前景；一些碳链结构复杂的醛类，如3，5，5-三甲基己醛在精细化工中需求较大。合成多碳醛酮的一种非常重要的反应途径就是多碳醇类的选择性氧化，即将醇上的羟基脱氢氧化形成羰基，主要包括单元醇的选择性氧化和多元醇的选择性氧化两个过程。目前，多碳醇的气相选择性氧化是一种原子收率高且环境友好的合成路线；在这一过程中，银基催化剂有着非常广泛的应用。在乙二醇气相氧化制乙二醛以及1，2-丙二醇气相氧化制1，2-丙二醛等反应中，银基催化剂部成功实现了工业化。从目前的研究现状来看，银基催化剂主要可以分为两大类：电解银催化剂和负载银催化剂。这两种不同的银催化剂在各自的领域都有着重要的应用。但是，对于电解银催化剂来说，低温活性较差，高温选择性和稳定性不足成为限制其应用的主要问题；而对于负载银催化剂来说，热传导性和再生性的不足也限制它的工业化应用。因此，探寻两种催化剂的结构性能与催化反应规律、研究在不同反应体系中的催化行为，并在此基础上开发出性能优越的新型复合银催化剂，进一步提高催化反应的转化率和选择性，成为本论文主要的研究方向。本论文主要开展了以下几个方面的工作：1)研究电解银催化剂在多碳醇（包括单元醇和多元醇）中的选择性催化氧化行为；2)采用电化学镶嵌法，将第二相微粒La₂O₃嵌入到电解银催化剂中去，形成物理间隔，制备出La₂O₃/Ag复合催化剂，从而提高电解银催化剂的高温活性和抗烧结性能，提高催化剂的稳定性；3)考虑到负载银催化剂的高分散所带来的较高的低温活性，利用合适的载体SiO₂，ZrO₂以及SBA-15，制备出负载型的Ag/SiO₂，Ag/ZrO₂和Ag/SBA-15催化剂，并研究了载体对于催化活性位的影响；4)在前面工作的基础上，开创性地联用Seed-film方法和原位电解法，合成具有三层结构的纳米电解银—沸石膜复合催化剂，并研究了催化剂的构效关系。一、电解银催化剂在醇选择性氧化反应中的催化表现首先采用传统的电解法，制备了电解银催化剂，应用的反应体系有：多元醇1，2—丙二醇选择性氧化制丙酮醛，单元醇3，5，5—三甲基己醇制3，5，5—三甲基己醛。实验结果表明，对于多元醇的反应来说，电解银催化剂在大于400℃情况下可以获得较好的反应活性，在400℃时，电解银催化剂可以获得96％的1，2—丙二醇转化率和45％的丙酮醛选择性。但是，电解银催化剂的低温活性较差，同时其高温选择性（＞500℃）也不理想。对于大分子单元醇3，5，5—三甲基己醇来说，因为受到催化活性的限制，反应过程中为了获得较好的活性，必须将反应温度提升，由于其分子结构中支链较多，这样会相应地引起断链反应的发生，副反应将会明显增加。XRD和SEM的结果说明电解银催化剂在高温条件下，易于发生团聚，使得活性下降，而正是这一因素，导致了电解银催化剂不能够被更广泛地应用于包括单元醇和多元醇在内的多碳醇选择性氧化反应中。二、复合电解银催化剂La₂O₃/Ag的制备及催化性能研究采用超声波诱导的电化学镶嵌法制备了掺杂La₂O₃微粒的复合电解银催化剂。XRD和SEM结果表明了第二相微粒La₂O₃成功地均匀嵌入电解银微粒之间，形成了物理间隔。应用Scherrer公式计算发现，在同一焙烧温度下，随着La₂O₃含量的增加，银颗粒的平均半径呈下降趋势。同时，对电解银催化剂和复合La₂O₃/Ag催化剂在不同温度下进行焙烧后发现：随着焙烧温度的提升，两种催化剂中银颗粒的平均半径均逐渐增大，但是增加的幅度后者明显缓于前者。由此表明：第二相微粒的加入，有利于提高电解银的高温抗烧结性能。通过对1，2—丙二醇催化氧化制丙酮醛的反应过程的研究，发现La₂O₃的加入会抑制银的催化活性，这一现象在低温条件下较为显著；但是，La₂O₃的加入极大地改善了催化剂的高温抗烧结性能，当反应温度大于550℃时，复合结晶银催化剂的产率高于电解银催化剂。在400℃时，镶嵌了0.8％的La₂O₃复合结晶银催化剂的1，2—丙二醇转化率为85.3％，丙酮醛选择性为37.2％；当温度升高到600℃时，镶嵌了0.8％的La₂O₃复合结晶银催化剂的1，2—丙二醇转化率为93.3％，选择性为28.7％，而此时电解银催化剂的1，2—丙二醇转化率为99.1％，丙酮醛选择性仅为8.6％。三、Ag/SiO₂、Ag/ZrO₂和Ag/SBA-15催化剂的制备、表征及反应过程研究以SiO₂、ZrO₂和SBA-15为载体分别制备负载型银催化剂Ag/SiO₂、Ag/ZrO₂和Ag/SBA-15。通过对1，2—丙二醇选择性催化氧化制丙酮醛反应研究，发现Ag/ZrO₂以及Ag/SBA-15催化剂都具有较为优良的低温活性，而Ag/SiO₂催化剂的催化性能则不如前二者。在此基础上，进一步研究载体与活性组分之间的相互关系。XRD的表征结果表明：ZrO₂载体随着焙烧温度的提高，分别呈现出四方、混相以及单斜三种不同的晶相，其中以单斜晶相对银颗粒的分散最为有利。UV-vis的研究表明，以ZrO₂为载体，有利于形成游离态的银离子以及银团簇这样的反应活性位，其中以单斜的ZrO₂为载体最易于形成反应活性位。XPS研究表明：以单斜ZrO₂为载体的Ag/ZrO₂催化剂其Ag3d结合能发生最大的正向位移，体现出大量游离态的银正离子的存在。对于Ag/SBA-15的XRD研究表明，银的加入，并没有破坏SBA-15的特有结构，同时金属银在载体上的分散情况非常好。UV-vis的研究发现，随着银载量的增加，250和280mm处的特征吸收峰相应增强，体现了活性位的增加。同时，对比Ag/ZrO₂和Ag/SAB-15两种催化剂的催化活性发现，虽然后者的比表面远远大于前者，并且Ag/SAB-15催化剂中银的分散情况也更加好，但是，Ag/ZrO₂催化剂的活性却高于Ag/SAB-15催化剂，由此说明：ZrO₂的吸电子效应对于活性位的产生有着非常显著的正效应。四、纳米银—沸石膜催化剂（SZF）的制备、表征及催化反应采用Seed-film方法制备先在铜网上生长出一层超薄的沸石膜，再通过原位电解技术，将纳米电解银颗粒生长在沸石膜表面，经焙烧后形成纳米银—沸石膜催化剂SZF（Silver Zeolite Film Catalyst）。SEM测试发现，SZF催化剂具有精细的三层结构，基底铜网、超薄沸石膜以及纳米银颗粒。TEM结果显示，大量的银颗粒尺寸在10nm以下，且分散均匀。在XRD图谱中没有沸石膜特征衍射峰，进一步说明了沸石膜的超薄结构。采用UV-vis方法检测SZF催化剂的表面活性位，发现有大量的游离态银正离子的存在；通过XPS方法从另一个侧面发现，Ag3d结合能的正向位移体现了游离态银离子在SZF催化剂表面的富集。纳米电解银颗粒产生的大量反应活性位使得SZF催化剂在多碳醇选择性氧化领域表现出良好的催化性能。在活性测试中，选取了有代表性的九种不同的醇，包括了脂肪单元醇，脂肪多元醇，芳香醇以及碳环醇，对比传统的电解银催化剂，纳米银—沸石膜催化剂SZF体现出了非常明显的低温活性优势。与此同时，发现多碳醇的分子结构以及羟基的位置变化对于反应结果有一定的影响。对于单元醇而言，反应的核心问题在于提高原料醇的转化率，进而提高反应活性；而对于多元醇而言，如何提高对于目标产物的选择性是最终提升反应活性的一个关键性问题。更多还原

【Abstract】 Carbonyl compounds are important in fine chemical industries, Pharmaceuticals, agrochemicals, perfumes and flavors, which include the aldehyde and the ketone. With the development of petrochemical industry and the modern fine chemical industry, those carbonyls that possess more than one carbon atom have attracted many concerns. Nowadays, the focus is on two types of reactions. One is the selective oxidation of mono-alcohols, where the desired products are often those of moderate oxidation, i.e., aldehydes and ketones. The other is the selective oxidation of polyhydric alcohols, where the target products are often moderately oxidized compounds while the products of lean oxidation （a-hydroxyketone）, and where over oxidation （carboxyl acid, CO2） or cracking should be avoided. Up to now several silver-based catalysts including bulk silver and supported silver catalysts have been developed for the oxidation of alcohols. However, some serious problems are still encountered in the application of such catalysts. For example, in the case of conventional bulk silver （e.g., industrial electrolytic silver）, the low catalytic activity at low temperatures often leads to the formation of the byproducts of lean oxidation, such as a-hydroxyketone. On the other hand, at a higher reaction temperature （>500 °C）, the products of cracking and/or over oxidation are mainly obtained. To improve the catalytic performance of silver-based catalysts, great efforts have been made by either adding additives to bulk silver catalysts, or dispersing the silver particles on suitable supports. Supported silver is expected to enhance the dispersion and stability （anti-sintering ability） of silver, and thus its catalytic activity at relatively lowtemperatures. However, compared with bulk silver catalysts, supported silver catalysts usually have a low heat conductivity, which has greatly restricted their practical application, especially in some strongly-exothermic oxidation reactions. Hence the design of a catalyst with the elaborate structure and better performance is still a challenge for the research in alcohol catalytic oxidations, especially for those with relatively complex molecular structures （e. g., polyhydric alcohols） where the current catalysts are inapplicable because of the complexity in selectivity and/or low activity at low temperatures.In this work, our research is concentrated on the following fields: 1) the study of the catalytic performance of electrolytic silver in the selective oxidation of alcohols; 2) the preparation of the complex La₂O₃/Ag catalyst via the electrolytic inlay method by enchasing the La₂O₃ particles into the interface of the electrolytic particles to improve its anti-sintering ability; 3) the preparation of different types of supported silver catalysts: Ag/SiO₂, Ag/ZrO₂, Ag/SBA-15 and their catalytic performance in the alcohol oxidation: 4) the fabrication of nano-silver/zeolite film/copper grid catalyst via the combination of seed-film method and the electrolytic process and its great catalytic performance for the selective oxidation of alcohols with different structures.1. The electrolytic silver catalyst was prepared through the electrolytic process and was adopted in the selective oxidation of 1,2-propylene glycol and 3,5,5-trimethyl hexanol. It is shown that the electrolytic silver catalyst exhibits good activity when reaction temperatures are above 400°C. However the activity in low temperatures and high temperatures is poor. In the case of 3,5,5-trimethyl hexanol, the catalytic performance of electrolytic silver is not ideal because the complicated molecular structure of 3,5,5-trimethyl hexanol restrains the enhancement of reaction temperature. According to the XRD and SEM investigation, the silver particles in the electrolytic silver are easy to sinter at high temperatures, which is the hurdle for it to be used in the selective oxidation of alcohols with lame molecular sizes.2. La₂O₃/Ag complex silver catalyst was prepared by ultrasonic electrolytic method. The catalysts with different loading weight of La₂O₃ were investigated by SEM, XRD and ICP. The crystal structure of silver was not destroyed after mixing with small amount of La₂O₃ in electrolytic process, but thermo-stability was improved obviously. The activity and stability of complex silver catalysts were compared in selective oxidation of 1,2-propylene glycol reaction system between 1%La₂O₃/Ag and pure electrolytic silver catalyst. The results revealed that at high temperature e.g. 600°C, the conversion of 1,2-propylene glycol over La₂O₃/Ag catalyst was 93.3% and the selectivity to methyl glyoxal was 28.7%; while those two values over the electrolytic silver catalysts are 99.1 % and 8.6%, respectively.3. Three types of supported silver catalysts were prepared: Ag/SiO₂, Ag/ZrO₂, Ag/SBA-15. According to the activity test, the selective oxidation of 1,2-propylene glycol, both Ag/ZrO₂ and Ag/SBA-15 exhibited good catalytic performance in low reaction temperatures, however the improvement of the activity of Ag/SiO₂ is slight. The investigation of the support effect shows that the crystal state of ZrO₂ has great influence over the catalytic behaviors of Ag/ZrO₂ catalysts. The monoclinic ZrO₂ will do most favor to the activity improvements. The UV-vis investigation revealed that in the Ag/m-ZrO₂ catalyst, there lived much more isolated silver ions than that in the other types of Ag/ZrO₂ catalysts. The XRD investigation over the Ag/SBA-15 showed that the introduction of silver would never destroy the specific ordered structure of SBA-15 molecular sieves. The large specific surface of Ag/SBA-15 catalysts provide the silver particles with better dispersion level, which will benefit the formation of active sites in the catalyst surface according to the characterization of UV-vis and XPS.4. The selective oxidation of a series of alcohols to their corresponding carbonyl products was carried out over a rationally designed in situ electrolytic nano-silver/zeolite film/copper grid （SZF） catalyst, which was prepared by a combination of the seed-film method for the fabrication of an ultrathin zeolite filmand the in situ electrolytic process for the formation of highly dispersed silver nanoparticles. At a relatively low reaction temperature （ca. 320°C）, the SZF catalyst with highly dispersed in situ electrolytic silver nanoparticles exhibited a much higher activity for the oxidation of mono-alcohols and a higher selectivity for ketonic aldehyde in the oxidation of di-alcohols than the conventional bulk electrolytic silver catalyst. On the basis of the combination of diffuse reflectance ultraviolet visible spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction and thermoanalysis, the remarkably high activity and selectivity of the SZF catalyst was attributed to the highly dispersed silver nanopartieles which were stabilized by the zeolite film against sintering and accordingly the large amount of Ag⁺ ions and Ag_n^δ+ clusters existed in the silver nanopartieles. The improvements of the catalytic performance of the SZF catalyst in a wide application extension will bring new concerns in both theoretical and applied fields.更多还原