【作者】 张晨曦；

【导师】 徐华龙； 唐颐；

【作者基本信息】 复旦大学 ， 物理化学， 2010， 博士

【摘要】 目前,催化反应过程在化学工业中起着主导的作用,催化剂研究已成为核心的技术渗透到经济、社会发展和人类生活的各个领域,在节约资源和能源、缩短与简化生产流程、转换原料路线以及环境保护等方面发挥着越来越重要的作用。以绿色化学为主导思想,从原子经济学角度思考,从化学反应机理出发,开发出高性能的新型催化剂已成为一个非常值得深入研究的课题。为了得到更加高效的催化剂,对于催化材料的研究开发可通过对现有催化剂合成路线加以改进或是采用新的合成技术。更进一步,则可以通过合理的设计开发出具有独特新型结构的催化材料。材料科学技术的进步为我们设计新型高性能催化剂提供了新的思路和方向。因此,结合特定反应的机理、特性和实际需求,利用材料科学的研究手段和成果,开发出具有高活性和高稳定性的各类催化材料,对于催化科学和材料科学都具有非常重要的学术价值和实用意义。醇选择性催化氧化是制取醛酮化合物最具有竞争力的工艺路线之一,其目标产物醛酮化合物是一类重要的精细化学品和有机合成中间体。脂肪醇气固相氧化过程具有无添加有机溶剂、产物分离容易和催化剂便于回收再利用等优点。现有的醇气固相选择性氧化反应以银基催化剂为主体,其中以电解银催化剂的应用最为广泛。电解银催化剂需要在500℃以上的温度条件下才能表现出理想的催化活性,对于高碳醇的氧化通常表现为选择性较低,产物中伴有较多的过度氧化和裂解副产物。在低温范围则催化活性明显不足。而对于负载型银基催化剂,如沸石银催化剂,其热传导性能差和不易再生的缺点都限制了它的工业化高效应用。尤其对于各类长链醇氧化,现有的催化剂都无法给出理想的解决方案。因此,本论文从醇的选择性氧化反应机理出发,设计合成具有新型结构的高效银基催化剂,并以此催化剂合成方法指导研制甲醇制氢催化剂。甲醇制氢是燃料电池车研究中的一个重要课题,研究应用较多的催化剂包括贵金属催化剂和铜基催化剂,其中贵金属催化剂低温活性好,但存在资源稀缺,极易CO中毒的特点；而铜基催化剂则存在着在高于300℃的条件下容易烧结,迅速失活的问题。针对这些问题,本论文从催化剂设计角度,研究了具有新型结构的双金属催化剂和类贵金属碳化物材料,以寻求制备简便的高性能甲醇制氢催化剂。本论文主要开展了以下几个方面的工作：(1)利用硝酸银和硅粉之间自发的氧化还原反应,采用化学沉积方法,制备具有树枝形貌的微米树枝银催化剂,并考察其在醇氧化反应中的催化性能,并研究了催化剂的晶面择优取向性与其催化活性之间的关系；(2)以硅粉为基底,制备新型硅纳米线阵列镶嵌银催化剂,并对其在长链醇催化氧化反应中的催化性能进行考察；(3)将化学沉积方法应用到制备双金属甲醇制氢催化剂,合成了新型硅纳米线阵列镶嵌铜铂双金属催化剂,并将其应用到甲醇重整制氢反应中；(4)以有机无机复合物为前驱体制备的多孔碳化钼纳米线,并将其性能特点与传统程序升温还原方法制备的碳化铝进行比较；(5)以有机无机复合物为前驱体制备负载型碳化钼催化剂,并考察其甲醇分解制氢反应性能。在醇氧化的机理研究中认为,银(111)晶面对于醇选择性氧化过程具有高效活性。本文从此机理出发,采用化学沉积方法(Electroless Metal Deposition,简称EMD法),即利用硝酸银和硅之间自发的氧化还原反应,以硅片为载体,设计制备了具有银(111)晶面择优取向的新结构树枝银催化剂。在制备过程中,通过调节反应液中硝酸银浓度,制备出具有不同程度银(111)晶面择优取向性的树枝银催化剂,在正辛醇催化氧化反应中表现出晶面择优取向性和醛选择性之间的密切关联。用作为脂肪二元醇1,2-丙二醇的催化剂,则可以通过降低过度氧化产物来提高适度氧化产物丙酮醛的选择性。此种微米树枝银催化剂对于一系列脂肪伯醇和脂肪二元醇底物都显示出选择性氧化的优越性能。设计高分散且具有高温稳定性的银基催化剂一直是醇选择性氧化催化剂研究的热点和难点。本文结合结晶电解银和负载银基催化剂的特点,设计制备了具有新型结构以硅纳米线阵列为载体的镶嵌银催化剂。采用化学沉积方法,首次以硅粉为载体,通过简单的焙烧过程完成催化剂的制备。此种催化材料特殊的结构所具有的开放的硅阵列载体可以有效地降低反应过程扩散限制；硅纳米线阵列载体中镶嵌的分立的金属颗粒则具有很好的高温抗烧结性能。在脂肪伯醇的催化氧化中,可以有效地提高低温反应条件下醇的转化率和产物醛的选择性。并且在一系列脂肪伯醇的氧化中都体现出此种性能,具有很好的普适通用性。采用化学沉积方法,以硅粉为载体,制备了硅纳米线阵列镶嵌铜铂双金属催化剂。Cu-Pt@SiNW催化剂通过Cu和Pt的相互作用,在甲醇重整制氢反应中相较于单金属铂催化剂表现出较高的二氧化碳选择性和稳定性；相比单金属铜催化剂则表现出更好的氢气选择性,是一种新型的甲醇重整制氢催化剂。以有机无机复合物为前驱体制备的多孔碳化钼材料,具有独特的一维多孔形貌,其独特的形貌使它较传统程序升温还原方法(TPR)制备的碳化铝具有更大的比表面积和更好的抗表面积碳能力。将此种碳化钼纳米线应用到甲醇分解制氢反应中,较TPR法制备的碳化钼体现出更佳的制氢效率和稳定性。以有机无机复合物为前驱体制备的负载型碳化钼是一类制备简便、安全且高效的甲醇制氢催化剂。氢气生成速率可高达3780μmol·min-1·gcat-1。金属钻对此碳化钼催化剂起到了十分重要的的促进作用。它作为一种碳纳米管生成催化剂,及时将碳化钼表面积碳转化为碳纳米管,释放活性位,使得催化剂稳定性得以很大地提高。但与此同时过高的钴的比例又会使反应趋向C-O键断裂,使得副产物甲烷增多,氢气选择性下降,因此在一定的Mo/Co摩尔比条件下,才能得到最佳的制氢效率和催化剂稳定性。更多还原

【Abstract】 Catalysis is now playing a leading role in chemical industry. Research on catalysis has become a key technology, which is in almost every part of people’s life and development of economy and society. It is playing an important part in saving energy, simplifying production procedures and protecting environment. It’s been a significant subject of how to design effective new catalysts with the purpose of protecting environment and satisfying the requirement of atomic economy. In order to synthesize more effective catalysts, we can work on the present preparation methods or explore new synthesis techniques to develop functional materials with better performance in catalysis. Further, researchers can work on developing unique novel catalysts with special structures. Material science has offered us new thoughts and directions in designing effective advanced catalytic materials. It is significant for chemists to take advantage of research technologies and results of material science to develop various kinds of catalysts according to actual requirements in production based on mechanism and characteristics of catalytic reactions.It is a competitive process route of making carbonyl compounds, including aldehydes and ketones, from selective oxidation of alcohols. The target products are one basic kind of fine chemicals and organic intermediates. Gas phase oxidation of aliphatic alchohols has the advantages of zero use of solvent, easy separation of products and facile recovery of catalysts. Major present catalysts for gas phase oxidation of alcohols are silver-based catalysts, among which, bulk electrolytic silver catalyst is the most widely applied one. It is essential for electrolytic silver catalysts to work above 500℃to achieve satisfying performance. It is hard to present good selectivity at higher temperatures, while at lower temperatures it shows deficient catalytic activity for oxidation of alcohols. As for supported silver catalyst, its properties of low thermal conductivity and difficulty to recovery limit its industrial application. Especially, for various kinds of long chain alcohols, none of the present catalysts can show satisfying performance. Our work focuses on developping novel effective catalysts with new structure on foundations of mechanism of catalytic oxidation of alcohols from the point of view of catalyst design.The process of producing hydrogen from methanol is an important subject in research on fuel cell vehicles. The most applied catalysts are noble metal based catalysts and copper based catalysts. Noble-metal based catalysts have good activity under low temperatures but their limited resource and CO-poisoning features have limited their industrial application, while Cu-based catalysts suffer from poor thermal stability above 300℃due to the sintering of metals. Aiming at these problems, we work on preparing new bimetallic catalyst and noble metal-like catalysts adopting new fabricating techniques to develop effective methanol to hydrogen catalysts.In this work, our research concentrates on the following fields:1) the preparation of micro-dendritic silver catalyst via electroless metal deposition method and their application in alcohol oxidation with satisfying selectivity of the corresponding aldehydes; 2) the preparation of Ag@SiNW catalyst via electroless metal deposition method and their catalytic performance in oxidation of long chain alcohols; 3) the preparation of bimetallic Cu-Pt@SiNW catalyst via electroless metal deposition method and their catalytic application in methanol steam reforming reaction; 4) the preparation of nanoporous Mo2C NWs catalyst with organic-inorganic hybrid as the precursor and their performance compared with bulky Mo2C catalyst synthesized via TPR method in methanol decomposition; 5) the preparation of supported Mo2C catalyst and their performance in methanol decomposition.In mechanism research of alcohol oxidation reactions, it is found that (111) crystal plane of silver catalyst favers selective oxidation pathway of alcohols. Therefore, we conducted our research based on the present mechanism and fabricated novel micro-dendritic silver catalyst with selective orientation of (111) crystal plane via electroless metal deposition by making use of the spontaneous redox reaction between AgNO3 and Si with silicon wafer as the substrate. In preparation process, samples with different selective orientation degrees could be fabricated by regulating AgNO3 concentration in reaction solvent. These samples show distinguishing selectivity of 1-octanal in probe reaction of oxidation of 1-octanol. This result demonstrates the close association between catalytic selectivity of the objective product and selective orientation property of the as-prepared catalysts. When applied to oxidation of 1,2-proplyene glycol, micro-dendritic silver catalyst can effectively improve selectivity of methylglyoxal by reducing over-oxidation products. Moreover, micro-dendritic silver catalyst shows better performance than electrolytic silver catalyst in oxidation of both aliphatic primary alcohols and aliphatic diols.It has always been a hotspot and difficulty of fabricating silver-based catalysts with high dispersion degree and good stability for selective oxidation of alcohols. We designed novel silver catalyst with special morphology of silver particles embedded in silicon nanowire arrays combining the specialties of electrolytic silver and supported silver catalysts. Ag@SiNW catalyst is easily prepared by eletroless metal deposition method with cheap silicon powder as the substrate, followed by calcination process. The special structure of Ag@SiNW catalyst offers open microenvironment, which can effectively reduce diffusion limitation effect in catalytic reactions. Separate Silver particles embedded in silicon nanowire arrays have excellent anti-sintering property. When applied in selective oxidation of aliphatic primary alcohols, Ag@SiNW catalyst shows good catalytic activity and selectivity of corresponding aldehydes under lower temperatures.Bimetallic Cu-Pt catalyst with particles embedded in silicon nanowire arrays support (Cu-Pt@SiNW) is fabricated via eletroless metal deposition method with silicon powders as the substrate. When applied to steam reforming of methanol, it shows better catalytic stability and CO2 selectivity than one component Pt counterpart, while shows better hydrogen selectivity than one component Cu counterpart through interaction between Cu and Pt. Mo2C nanowires catalyst is synthesized with organic-inorganic hybrid as precursor. Its unique nanoporous one dimensional morphology provides larger specific area and better anti-sintering property than Mo2C catalyst prepared by TPR method. When applied to methanol decomposition reaction, it shows better catalytic stability and hydrogen production rate.Supported Mo2C catalyst fabricated with organic-inorganic hybrid as precursor is one easily-made and effective catalyst for producing hydrogen from methanol. The highest hydrogen production rate achieved in our experiment is as high as 3780μmol·min-1·gcat-1·Cobalt works as an important promoter for the as-prepared supported Mo2C catalyst. Co working as a CNT-formation catalyst effectively transforms carbon deposition on Mo2C nanoparticles and exposes the active sites. But the existence of Co also increases the by-product selectivity as a result of C-O bond scission of methoxy intermediate. Thus, only under appropriate Mo/Co molar ration, can best performance of Co-Mo2C/CNT catalyst be achieved.更多还原