【作者】 江玲超；

【导师】 严新焕；

【作者基本信息】 浙江工业大学 ， 应用化学， 2009， 硕士

【摘要】 负载金属催化剂由于其原子利用率高、催化性能优异等特性广泛应用于石油化工、精细化工和环境催化等领域。负载金属催化剂通常由浸渍法和离子交换法等传统方法制得,并已应用于工业化生产。但这些方法都存在制备过程复杂、影响因素较多和重复性差等缺点,严重影响催化剂的催化性能。本论文的目的是采用新方法制备负载金属催化剂,以期获得高性能的负载金属催化剂,具有重要意义。本论文采用了两种负载金属催化剂制备新方法,第一种是脉冲激光沉积法,目前只有法国Rousset课题组和美国Brenner课题组从事这方面的研究,而我们是第三个从事脉冲激光沉积法制备负载纳米金属催化剂的课题组。脉冲激光沉积法是采用脉冲激光激发金属使之生成等离子体,等离子体再定向沉积到载体表面制得负载金属催化剂。该方法是物理制备法,由金属原子直接负载到载体表面,中间无化学反应,具有一步完成、操作简便和过程绿色化等特点。第二种是载体直接吸附可溶性纳米颗粒制备负载金属催化剂,该方法是目前国际上负载催化剂制备的研究新热点,可以制得金属颗粒小于5nm,高度分散的负载金属催化剂,从而大幅度提高催化剂的催化性能。载体直接吸附可溶性纳米颗粒是采用金属有机化合物（如Pd₂（dba）₃）在还原剂（如氢气）下分解,制得溶剂稳定的可溶性纳米金属颗粒,再通过载体直接吸附,将其吸附负载到载体表面制得负载金属催化剂。该制备方法制备工艺简单,容易操作,制各过程中影响催化剂性质及催化性能的因素少,催化剂制备重复性好,制备过程很少有污染,溶剂可重复利用。本论文采用脉冲激光沉积法制备Pt/Al₂O₃催化剂和一系列不同载体负载的Pt,Pd催化剂;采用载体直接吸附可溶性纳米颗粒制备Pd/Al₂O₃和Pd/C催化剂;采用XRD、TEM、ICP和XPS等表征手段表征了这两种新方法制得的负载金属催化剂的晶态结构、表面形态、金属负载量及电子状态等物理化学性质。以邻氯硝基苯催化加氢合成邻氯苯胺反应为探针反应测试脉冲激光沉积法制备的负载Pt,Pd催化剂的催化性能;分别以Suzuki反应和Heck反应为探针反应测试载体直接吸附可溶性纳米颗粒制备的Pd/Al₂O₃和Pd/C催化剂的催化性能。研究结果如下:1.催化剂表征结果表明,脉冲激光沉积法制备条件载体温度、沉积池压力和激光电压对Pt/Al₂O₃催化剂的Pt颗粒度、分散度及负载量有很大影响。邻氯硝基苯催化加氢结果表明,激光制备条件对Pt/Al₂O₃催化剂催化邻氯硝基苯加氢性能也有很大的影响。Pt/Al₂O₃催化剂催化活性随着载体温度升高而降低,随沉积池压力和激光电压增大而降低;邻氯苯胺选择性随载体温度升高而增大,随沉积池压力增大而增大,但随激光电压增大而降低。较佳的激光制备条件为:激光电压260V,沉积池压力300Pa,载体温度600℃。在此条件下制得的Pt/Al₂O₃催化剂催化邻氯硝基苯加氢反应,邻氯硝基苯的转化率达到99.8%,邻氯苯胺的选择性达到99.4%,表现出较高的加氢性能和抑制脱卤性能。2.脉冲激光沉积法制备了一系列不同载体负载的Pt,Pd催化剂。催化剂表征结果表明,金属颗粒按CNTs＜γ-Al₂O₃＜SiO₂依次增大,金属分散度越来越差。负载Pt催化剂活性组分Pt与载体之间的电子作用可以忽略,而负载Pd催化剂活性组分Pd与载体之间有较强的电子作用,并且按Pd/CNTs＞Pd/Al₂O₃＞Pd/SiO₂依次降低。邻氯硝基苯催化加氢结果表明,CNTs负载的金属催化剂相比γ-Al₂O₃和SiO₂负载的金属催化剂在催化活性与选择性方面都表现出了很好的优越性。对于负载Pt催化剂,载体对其催化性能的影响可以从几何效应和载体结构及性质两方面得到解释。对于负载Pd催化剂,载体对其催化性能的影响可以从几何效应、电子效应和载体结构及性质三方面得到解释。由于脉冲激光沉积法制备的负载Pt,Pd催化剂的活性组分主要负载在载体的外表面,故这一系列催化剂可以很好地抑制加氢产物邻氯苯胺的深度加氢脱氯,提高邻氯苯胺的选择性。3.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P&Al₂O₃催化剂Pd金属颗粒以零价态均匀地负载在载体表面,且分散度高,粒径在3-8 nm之间;活性组分Pd与载体γ-Al₂O₃存在电子作用,电子由γ-Al₂O₃的O向Pd转移。SuZuki反应结果表明,载体直接吸附可溶性纳米颗粒制得的Pd/Al₂O₃催化剂能较好地催化溴苯与苯硼酸的Suzuki反应;最优反应条件为:碱K₂CO₃、DMF/H₂O溶剂的体积比例7/3、DMF/H₂O溶剂回流（110℃）和Pd负载量2.0 wt%;在此反应条件下,30min内溴苯完全转化,偶联产物联苯的产率达到99%;Pd/Al₂O₃催化剂也能较好地催化溴代芳烃与苯硼酸的Suzuki反应,对位吸电子基加快反应速率,对位供电子基减慢反应速率。4.催化剂表征结果表明,载体直接吸附可溶性纳米颗制得的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3-8nm之间;Pd/C催化剂Pd 3d_5/2和Pd 3d_3/2电子结合能都增大,电子从Pd向活性炭转移。Heck反应结果表明,载体直接吸附可溶性纳米颗粒制备的Pd/C催化剂可以较好地催化碘苯及对位有吸电子基的溴代芳烃与丙烯酸甲酯的Heck反应;最优反应条件为:碱K₂CO₃、溶剂DMF和反应温度120℃;在此反应条件下,120min内碘苯完全转化,偶联产物的产率达到99%;Pd/C催化剂对对位有供电子基的溴代芳烃和氯代芳烃与丙烯酸甲酯的Heck反应催化效果较差;载体直接吸附可溶性纳米颗粒制备的Pd/C催化剂具有较好的重复使用性能,反应3次,催化剂活性没有明显下降,偶联产物产率仍在98%以上,比传统的商用Pd/C催化剂具有更好的稳定性。总之,通过本项目研究表明,脉冲激光沉积法制备的负载Pt,Pd催化剂具有很高的催化邻氯硝基苯加氢性能和抑制脱卤性能;载体直接吸附可溶性纳米颗粒制备的Pd/Al₂O₃催化剂对溴苯的Suzuki反应具有很高的催化性能;载体直接吸附可溶性纳米颗粒制备的Pd/C催化剂对碘苯与有吸电子基的溴代芳烃的Heck反应具有很高的催化性能。脉冲激光沉积法和载体直接吸附可溶性纳米颗粒都是制备负载金属催化剂的新型方法,制备过程简单,影响因素少,并且非常绿色化;选择恰当的工艺参数可获得定量负载及颗粒粒径可控的负载金属催化剂;采用这两种新方法可制备金属颗粒小、高分散度、高催化性能的其他单组分或多组分负载金属催化剂;采用这两种方法制备的负载金属催化剂,可应用到其他多相催化反应,获得高转化率、高选择性的目标产物。同时,这两种制备负载金属催化剂的新方法也具有一定的工业化应用前景。更多还原

【Abstract】 Supported metal catalysts are extensively applied in petrochemical industry,fine chemistry and environmental catalysis owing to its high metal utilization ratio and good catalytic properties.Supported metal catalysts are usually prepared by impregnation and chemical reduction,and have been found wide application in industry.However,these preparation methods have the drawbacks of complicated procedure,too many influence factors,poor reproducibility,which affecting the catalytic properties,companying with severe environmental pollution.This thesis tries to produce supported metal catalyst with better catalytic properties by novel preparation methods.In this thesis,two novel methods were used for preparation of supported metal catalysts,laser vaporization deposition（LVD） and soluble metal nanoparticles direct-adsorption.At present,only three research goups around the world,Rousset’s,Brenne’s and ours’,are to be employed in Laser vaporization deposition.A pulsed laser was focused on the bulk metal and a plasma was formed;Afterward,the plasma was oriented and deposited onto the surface of the support and nucleated to form metallic clusters.Laser vaporization deposition is a physical method,which is a simple and green approach for preparation of supported metal catalysts with few affecting factors on the catalytic properties.Soluble metal nanoparticles direct-adsorption is also a simple and green approach for preparation of supported metal catalysts.Soluble metal nanoparticles were extensively studied around the world,currently.Supported metal catalyst with small particles（＜5 nm） and high metal dispersion can be obtained by soluble metal nanoparticles direct-adsorption,exhibits good catalytic properties.The soluble metal nanoparticles were obtained by the decomposition of organometallic precursors such as Pd₂（dba）₃ using a reducing gas such as hydrogen gas in a solvent and stabilized by the solvent; Afterwards,the stable metal nanoparticles were adsorbed on the surface of support to produce the supported metal catalyst.There were few factors affecting the catalytic properties during the preparation process.In this thesis,Pt/Al₂O₃ catalyst and a series supported Pt,Pd catalyst were produced by laser vaporization deposition of bulk metals;Pd/Al₂O₃ and Pd/C catalysts were prepared by soluble metal nanoparticles direct-adsorption. The catalysts were characterized by X-ray diffraction（XRD）,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 obtained by laser vaporization deposition;Suzuki reaction and Heck reaction were used to test the catalytic properties of Pd/Al₂O₃ and Pd/C catalysts obtained by soluble metal nanoparticles direct-adsorption,respectively.The results are listed as follows:1.The characterization results show,the support temperature,the pressure of chamber and the voltage of laser have an impact on the properties of the Pt/Al₂O₃ catalyst obtained by laser vaporization deposition.The hydrogenation results show,the catalytic activity decreases with the support temperature,the pressure of chamber and the voltage of laser.The selectivity to o-chloroaniline（o-CAN） increases with the support temperature,the pressure of chamber,but decrease with the voltage of laser.The catalyst prepared under 300 Pa,600℃and 260 V exhibits the best catalytic properties, obtaining o-CAN with 99.4%selectivity at a conversion level of 99.8%.2.The characterization results show,the supports have a significant influence on the metal dispersion,the particles size and the electronic state of metal.The metal particles on CNTs are smaller than that onγ-Al₂O₃ and SiO₂; The metal-support interaction for the Pt-based catalysts is negligible,but the metal-support interaction for the Pd-based interaction is in order Pd/CNTs＞Pd/γ-Al₂O₃＞Pd/SiO₂.The hydrogenation results show the superiority of CNTs versus the high surface areaγ-Al₂O₃ and SiO₂ in terms of the catalytic activity and the selectivity to o-CAN.The effect of the supports may be interpreted by geometric effect and the textures and properties of the supports for the Pt-based catalysts.However,the effect of the supports may be interpreted by geometric effect,electronic effect and the textures and properties of the supports for the Pd-based catalysts.In addition, hydrogenolysis of the C-C1 bond in o-CAN is well inhibited over supported Pt, Pd catalysts obtained by laser vaporization deposition due to the metal particles deposited on the outer surface of the supports.3.The characterization results of the Pd/Al₂O₃ catalyst obtained by soluble metal nanoparticles direct-adsorption show,the Pd particles are evenly distributed over the surface ofγ-Al₂O₃,and the size range is 3-8 nm;The Pd particles size is invariant between pre-supported and Pd/Al₂O₃ catalyst.The electron is transferred fromγ-Al₂O₃ to Pd.The best Suzuki reaction results was obtained with K₂CO₃ as base,DMF/H₂O volume ratio 7/3 as solvent, reflux,and Pd loading 2.0 wt%,which provided the highest brornobenzene conversion of 100%and the highest biphenyl yield of 99%in 30 min.The substrates with electron-withdrawing groups or electron-donating groups were all achieved in good yields.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.4.The characterization results of the Pd/C catalyst obtained by soluble metal nanoparticles direct-adsorption show,the Pd particles are evenly distributed over the surface of active carbon,and the size range is 3-8 nm;The Pd 3d_5/2 and Pd 3d_3/2 level binding energies of Pd/C catalyst are higher than that of bulk Pd metal.The electron is transferred from Pd to active carbon. The best Heck reaction results was obtained with K₂CO₃ as base,DMF as solvent and reaction temperature 120℃,which provided the highest iodobenzene conversion of 100%and the highest coupling yield of 99%in 120 min.The coupling reactions of iodobenzene and aryl bromides containing electron-withdrawing groups proceeded efficiently,while aryl bromides containing electron-donating groups and aryl chlorides hardly proceeded.The catalyst can be reused for 3 times,exhibiting better stability than commercial Pd/C catalyst.In conclusion,it is clear that supported Pt,Pd catalysts obtained laser vaporization deposition exhibit good catalytic properties on the hydrogenation of o-CAN;Pd/Al₂O₃ catalyst obtained by soluble metal nanoparticles direct-adsorption exhibits good catalytic properties on Suzuki reaction of aryl bromides;Pd/C catalyst obtained by soluble metal particles supported method exhibits good catalytic properties on Heck reaction of iodobenzene and aryl bromides containing electron-withdrawing groups.Laser vaporization deposition and soluble metal particles supported method are novel,simple and green approaches for preparation of supported metal catalyst;Under suitable conditions,supported metal catalysts with metal particles and loading controllable can be produced;Other single component or multicomponents supported metal catalysts also can be produced by the two novel methods; These supported metal catalysts obtained by the two novel methods can be potentially applied in several mutil-phase reactions to produce the target products with high conversion and selectivity.In addition,the two novel methods can be potentially applied at the industrial scale.更多还原