吸附法制备蛋壳型Pt、Pd纳米催化剂及催化性能研究

发布时间：2018-02-02 14:29

本文关键词： 蛋壳型催化剂液相催化加氢加氢动力学 Suzuki反应　出处：《浙江工业大学》2010年硕士论文　论文类型：学位论文

【摘要】： 负载型金属催化剂由于其活性高、易分离、金属可回收等特点被广泛应用于石油化工、精细化工和环境催化等领域。无论在实验室研究还是在工业化生产,都是极为重要的一类催化剂。目前,常用负载金属催化剂的制备方法有:浸渍法、离子交换法、共沉淀法、溶胶-凝胶法等。但是这些方法往往存在以下缺点:如制备过程复杂、非绿色化、影响因素较多、金属纳米颗粒可控性较差等。这些都会影响到催化剂的整体性能。本论文提出一类新的负载金属纳米催化剂制备方法,即采用载体直接吸附金属纳米颗粒的方法制备负载型金属催化剂,我们称之为吸附法。先将有机金属化合物在还原气氛下分解得到稳定的纳米溶胶,再用载体直接吸附金属纳米颗粒以制备负载型金属纳米催化剂。该方法可以制备粒径小、分布均匀、分散度好、结构可控的高性能催化剂。而且由于其制备纳米溶胶的方法的简单、绿色化使得制备得到的催化剂性能重复性高,污染较少。采用吸附法制备得到Pt/C纳米催化剂,并对载体进行了金属助剂的改性处理。通过TEM、ICP和XPS等手段的研究详细表征了催化剂的表面形态、金属负载量、金属电子状态及Pt纳米颗粒的分布情况等。以邻氯硝基苯催化加氢合成氯代苯胺反应为探针反应测试其催化性能,并进一步研究了该反应的加氢动力学。采用吸附法制备得到Pd/C催化剂,通过TEM、XRD及XPS详细表征了其表面形态、Pd的分布情况等。以溴代苯及氯代苯为底物的Suzuki偶联反应为探针测试其催化性能。具体内容如下: 1.催化剂表征结果表明,对活性炭载体的Fe助剂处理可以使制备得到的Pt/C(Fe)催化剂中的Pt处于更为强烈的缺电子状态,XPS宽扫表征结果表明,催化剂表面分布的Pt纳米颗粒是平均值的10倍,形成了蛋壳型的结构。邻氯硝基苯催化加氢结果表明, Fe助剂的添加量为Pt含量的2倍时,达到了催化的最佳性能:在1 MPa、60 oC的条件下,转化率100%,活性(TOF)达到了78 S-1,邻氯苯胺的选择性高于99.5%,TTO大于625000。该催化剂对邻氯硝基苯液相加氢活性、选择性和稳定性达到了高度的统一,其中活性和稳定性是目前文献报道中的最佳值。通过研究发现,Fe助剂的引入有利于改善活性组分的电子状态和分布结构,导致了其对邻氯硝基苯加氢性能的提高。此外,基于该催化剂对反应选择性的特点,我们详细讨论了不同宏观因素对脱卤的影响,总结并发现了在高活性条件下,这些宏观因素(如温度、压力)的影响本质上是通过TOF决定了脱卤率的规律。并从碰撞动力学角度加以阐明。而且通过表征发现活性下降的主要原因是载体结构的坍塌以及纳米颗粒的迁移导致了团聚失活。而活性组分流失量仅为7%,表明了Pt的负载程度相当牢固。 2.研究吸附型催化剂对邻氯硝基苯的加氢机理。并通过对其动力学研究,我们发现了一条新的反应路径,即从硝基基团直接加氢制的相应羟胺的路径。并且结合文献详细的论证了这条新补充路径,结合动力学研究数据,研究了吸附型催化剂对邻氯硝基苯及爱情那个具有高选择性的原因。进一步的动力学研究表明:对反应物浓度为零级反应,对氢压为一级反应,活化能为58.8 kJ/mol,催化剂对氢气的吸附为反应的速率控制步骤。 3. Pd/C催化剂表征结果表明,载体直接吸附可溶性纳米颗粒制得的Pd/C催化剂Pd金属颗粒以零价态均匀地负载在载体表面,且分散度好,粒径在3-6 nm之间。Suzuki反应结果表明,吸附法制得的Pd/C由于其结构上的优势,能很好地催化溴代苯与苯硼酸的Suzuki反应。在80 oC下,0.5 h后偶联产物收率可达98%以上。其中对位吸电子基可加快反应速率,而对位供电子基可减慢反应速率。以邻氯硝基苯为底物时,在110 oC下1 h后偶联产物收率可达64%;延长反应时间,产物收率可达90%以上。总之,用吸附法制备得到负载型金属催化剂,制备过程简单绿色化,影响因素少,且催化剂的结构可控、重复性好。将Fe助剂改性过的Pt/C催化剂用于邻氯硝基苯催化加氢反应,取得非常好的效果,具有工业化应用前景。将吸附型Pd/C催化剂用于Suzuki反应的研究也获得了很好的催化效果。同时,这种制备方法也具有一定的普适性,可进一步研究推广至其他负载型金属催化剂的制备
[Abstract]:The supported metal catalysts are widely used in petrochemical , fine chemical industry and environmental catalysis because of their high activity , easy separation and recoverable metals . The preparation methods of commonly used metal catalysts are as follows : dipping , ion exchange , co - precipitation , sol - gel method , etc . However , these methods often have the following disadvantages : the preparation process is complicated , non - green , the influencing factors are more , the controllability of metal nanoparticles is poor , etc . These can affect the overall performance of the catalyst . The invention provides a preparation method of a novel supported metal nano catalyst , which comprises the following steps of : preparing a supported metal catalyst by adopting a method for directly adsorbing metal nanoparticles by using a carrier ; and then decomposing the organic metal compound in a reducing atmosphere to obtain stable nano sol , and then directly adsorbing the metal nanoparticles with a carrier to prepare a supported metal nano catalyst . The Pt / C nano - catalyst was prepared by adsorption method . The surface morphology , metal loading , metal electron state and distribution of Pt nanoparticles were characterized by TEM , ICP and XPS . The catalytic properties of the catalyst were investigated by means of TEM , XRD and XPS . The catalytic properties of Pd / C catalyst were characterized by TEM , XRD and XPS . 1 . The catalyst characterization results show that the Pt / C ( Fe ) catalyst can be prepared by the Fe assistant treatment . The catalytic hydrogenation activity , selectivity and stability of the catalyst are more than 99.5 % . The catalytic hydrogenation activity , selectivity and stability of the catalyst are higher than 99.5 % and 625000 . 2 . The hydrogenation mechanism of o - chloronitrobenzene by adsorption catalyst was studied . Through the study of its kinetics , we found a new reaction path , that is , the path of the corresponding hydroxylamine from the direct hydrogenation of nitro group . 3 . Pd / C catalyst characterization results show that the Pd / C catalyst Pd / C catalyst directly adsorbed by the carrier is uniformly distributed on the surface of the carrier in a zero - valent state , and the dispersity is good , the particle size is between 3 and 6 nm . The results of the Suzuki reaction show that Pd / C prepared by the adsorption method can catalyze the Suzuki reaction of bromobenzene and phenylboronic acid . The yield of the coupling product can reach 64 % after 1 h at 110 oC . The yield of the product can reach over 90 % . in general , that supported metal catalyst is prepare by the adsorption method , the preparation process is simple and green , the influence factor is small , the structure of the catalyst is controllable , and the repeatability is good .

【学位授予单位】：浙江工业大学
【学位级别】：硕士
【学位授予年份】：2010
【分类号】：O643.36

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