【作者】 黄钟斌；

【导师】 严新焕；

【作者基本信息】 浙江工业大学 ， 应用化学， 2010， 硕士

【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更多还原

【Abstract】 Supported noble metal catalysts were usually prepared by impregnation, ion-exchange process, coprecipitation, Sol-gel method and have been widely applied in the field of petrochemicals, fine chemicals and environmental catalysis for their high activity, easy separation and recyclable, etc.However, these methods often have the drawbacks of complicated procedures, non-green to environment and many influencing factors. It is well known these problems not only affect the overall performance of the catalyst, but also might caused the environmental pollution.In this thesis, a new method was proposed that the carrier was utilized to adsorb metal nanoparticles directly, which were obtained from the decomposition of Pt2(dba)3 (dba = dibenzalacetone) for the preparation of catalysts. This adsorption type method is able to prepare uniform particle size, narrow distribution range and structure controlable of high-performance catalysts. The adsorption Pt/C catalysts were characterized by transmission electron microscopy (TEM), inductive coupled plasma emission spectrometer (ICP) and X-ray photoelectron spectroscopy (XPS). The liquid phase hydrogenation of o-chloronitrobenzene (o-CNB) was used to test the catalytic properties of the catalysts and the corresponding hydrogenation dynamics was also first carried out. The adsorption Pd/C catalyst was also characterized by TEM、XRD and XPS, and showed extraordinary properties in Suzuki coupling reaction. The results are listed as follows:1、The characterization results showed that active constituent Pt on the Pt/C catalyst additives was in more electron-deficient state after the AC modified by Fe, and Pt nanoparticles distributed on the surface of the catalyst (10 times higher than average levels), forming an egg-shell structure. The results of catalytic hydrogenation of o-chloronitrobenzene showed that the best performance could be obtained when the dosage of Fe additive was doubles that of Pt. The conversion of o-CNB reached to 100% with the activity defined by TOF of 78 S-1 combined with the selectivity of 99.5% to corresponding aniline. Moreover, the selectivity can increased to 99.9% by adjusting the reaction conditions. In addition, macroeconomic factors (such as temperature, pressure,stirring rate) which could affect the dehalogenation were studied in detail. On the basis of low dehalogenation over the certain catalyst, a broad rule is proposed that the TOF whatever factors caused by decide dehalogenation rate essentially. In stability, the TTO of the catalyst can reach to 625,000 and the the main reason for the decreased activity was the aggregation of Pt nanoparticles. Meanwhile, the loss of active Pt was only 7%, which indicate the internal bonding strength between Pt nanoparticles and support is strong.2、A new reaction path was found that the hydroxylamine could be obtained directly from the hydrogenation of nitro-compound. Further kinetic studies demonstrated that the reaction rate is zero-order in o-chloronitrobenzene concentration and first-order with respect to hydrogen pressure,and the activation energy is 58.8 kJ/mol. The rate limiting step was adsorption of H2.3、The characterization results of Pd/C showed that the Pd with zero valent state loadad evenly in the carrier surface, of which particle size was in the range of 3-6 nm. This adsorption Pd/C catalyst showed extraordinary properties in Suzuki reaction. Under the conditions of 80 oC, and 0.5 h, the catalyst can catalyze Suzuki reactions of aryl bromide with coupling product yield of 98%. The coupling reactions of aryl bromides containing electron-withdrawing groups proceeded more efficiently than that of bromobenzene, while aryl bromides containing electron-donating groups needed a longer reaction time for completion. It can also catalyze o-chloronitrobenzene with yield of 64% in 1 h when the reaction temperature was 110 oC, and the yield can be higher than 90% with extending the reaction time.In conclusion, the adsorption method for preparing supported catalyst is simple and green, and tractable. Especially, the addition of Fe for the the Pt/C catalyst could significantly improve its catalytic performance for the selective hydrogenation of o-chloronitrobenzene which have showed the prospect of industrial application. Meanwhile,the Pd/C catalyst also exhibited very excellent catalytic effect for the Suzuki reaction of bromobenzene. It is believed this preparation method could be further extended to other supported metal catalysts preparation and corresponding reaction system.更多还原