【作者】 刘铮；

【导师】 王峰；

【作者基本信息】 北京化工大学 ， 材料科学与工程， 2012， 博士

【摘要】 由于人类对大自然的过度开发和利用，资源、能源缺乏和环境污染等问题越来越突出的摆在人们面前。因此，二十一世纪对现有资源和能源的合理利用以及对环境的保护越来越受到人们的重视，同时对新能源的开发也已成为亟待解决的难题，“高效，节能，环保”的概念受到日益剧增的关注。工业加氢是工业中一个关键的反应，如何提高工业加氢的效率对于高效和节能有重要的意义；同时，发展对于环境更友好，自身更高效的电源，也具有十分重大的战略意义，燃料电池被广泛认为是一种能实现这个目标的新技术。以上两个领域的发展和进步的都非常依赖于催化剂的开发。目前，工业加氢反应催化剂和燃料电池的电极催化剂都主要采用贵金属类。但是，贵金属铂钯资源稀少，价格昂贵，不利于控制成本和长期利用。因此非贵金属类催化剂，尤其是镍系催化剂在这两个领域的应用逐渐受到人们的关注。但是，目前的镍系催化剂存在稳定性，活性不足等缺陷，急需人们解决。基于上述背景，本文主要研究了镍及镍基二元合金/多壁碳纳米管复合催化剂的制备及其催化加氢和电催化性能的研究。采用了化学镀和改良的液相还原法两种制备方法，制备得到了三种镍系催化剂，分别是非晶态镍基二元合金MWCNT/Ni-B和MWCNT/Ni-P催化剂，以及晶态MWCNT/Ni催化剂，系统研究了催化剂制备方法对于催化剂制备的影响，并采用XRD，SEM，HRTEM，XPS，ICP，TG-DTA等测试手段对得到的不同催化剂的物理性能进行了详细的表征，得到了最优化的制备手段。最后，将两种非晶态镍基二元合金催化剂应用在苯乙烯和苯的催化加氢反应中并研究了其动力学过程；将三种镍系催化剂应用在碱性乙醇燃料电池领域，研究了不同催化剂对于乙醇电催化氧化的性能，机理与动力学过程，得到了优化催化剂的方案。取得的主要创新性成果如下：（1）开发出通过化学镀法制备两种镍基非晶态二元合金MWCNT/Ni-B催化剂化学镀体系，以NiCl₂·6H₂O为主盐，乙二胺为络合剂，氢氧化钠为pH调节剂， NaBH₄为还原剂，通过控制反应时间在敏化-活化的多壁碳纳米管的表面上成功负载上了平均粒径约为60nm的Ni-B非晶态二元合金纳米粒子，其分布均匀，呈现棉花状孔道结构，为典型的非晶态结构。随着化学镀反应时间的增加，Ni的负载量逐渐增加，B在Ni-B粒子中的含量也逐渐增加，导致晶化温度也最终增加到326°C。通过XPS测试可以得知硼元素给镍元素提供电子使得镍表面呈现电子富集状态。（2）开发出通过化学镀法制备两种镍基非晶态二元合金MWCNT/Ni-P催化剂的化学镀液体系，以NiSO₄·6H₂O为主盐，C₆H₅Na₃O₇为络合剂，（NH4）₂SO₄为添加剂，氢氧化钠为pH调节剂，NaH₂PO₂·H₂O为还原剂，通过对反应镀液浓度，反应时间，NaOH添加量，反应温度的优化，在敏化-活化完的多壁碳纳米管表面上成功负载上了平均粒径约为100nm的Ni-P非晶态二元合金纳米粒子，其分布均匀，为均匀的实心结构。对最优催化剂的测试表明Ni-P纳米粒子为典型的非晶态结构，晶化温度大约为360°C，在高温退火后Ni-P粒子会发生团聚并变大，呈现出Ni和Ni3P的混合相。（3）通过对两种非晶态镍基二元合金催化剂催化加氢性能及反应动力学研究发现，两种非晶态MWCNT/Ni-B和MWCNT/Ni-P均对苯乙烯加氢反应有着优异的催化能力，在较容易达到的条件下均能实现苯乙烯100%选择加氢转化成乙苯。研究两种非晶态催化剂的动力学参数可知，苯乙烯具有相同的反应级数一级，MWCNT/Ni-P催化剂具有更小的氢气反应级数，并且可以在较低的温度范围实现苯乙烯的100%转化，同时拥有比MWCNT/Ni-B催化剂更高的动力学反应速率常数k=35122.2·e（-4914.7/T）；并且，也具有比MWCNT/Ni-B催化剂相对更小的反应活化能E=40.86kJ/mol，表明MWCNT/Ni-P催化剂具有相对更好的催化活性。进一步研究MWCNT/Ni-P催化剂对苯的催化加氢发现其对苯也具有良好的催化活性，可以将苯选择加氢转化为环己烷，苯的转化率随着时间的增加呈线性增长，说明苯在反应中的反应级数为零级。此外，苯的转化率在180°C左右存在一个大约为60%的最大值，分析原因可能是：第一，温度上升后，催化剂表面的芳烃覆盖率会随着温度上升而下降，导致在某一个温度点有最大值；第二，最大温度点可能是由苯和其反应还原分子竞争吸附导致。（4）开发出改良的液相化学还原法，通过引入经过酸化-敏化活化预处理的多壁碳纳米管，控制添加表面活性剂CTAB量和溶液体系pH值为10左右，采用水合肼在为还原剂80°C反应1小时，最终得到了在多壁碳纳米管表面分布均匀的细小多晶镍纳米粒子，粒径大约为20nm。添加剂十二烷基二甲基溴化铵（CTAB）的可以同镍离子和在适当的pH值范围进行络合，当含有低浓度CTAB（<120mM）的溶液时，在Pd金属周围会由CTAB表面活性剂形成一种双分子层结构，它可以控制还原剂水合肼和镍/水合肼络合物在其金属表面的浓度，进而控制反应速率；当CTAB的浓度增加到一定程度（>120mM）时候，溶液倾向于油性，在Pd纳米粒子表面将会形成胶束，它会阻止水合肼和镍/水合肼络合物分子从溶液中扩散到金属粒子表面，进而无法得到还原催化剂。（5）通过对三种镍系催化剂电催化性能及反应动力学研究发现，三种镍系催化剂在碱性介质中均表现出对乙醇良好的电催化氧化能力，电极过程受到乙醇扩散的控制。MWCNT/Ni催化剂具有最高的对于乙醇氧化的峰值电流，其原因可能是由其更加细小的晶粒尺寸，进而拥有更大的活性反应表面积所引起。比较三种催化剂的动力学过程可发现，MWCNT/Ni-B催化剂跟MWCNT/Ni有着相近的乙醇氧化速率，但是都远远高于MWCNT/Ni-P催化剂。其原因归结于MWCNT/Ni-B催化剂中B跟Ni之间的电子转移和MWCNT/Ni中Ni纳米粒子细小的粒径和良好的分散效果。因此，如果制备出粒径<20nm的非晶态Ni-B纳米粒子负载在多壁碳纳米管上的催化剂，预计会具有很高的乙醇催化氧化电流，同时又拥有快速的氧化速率。更多还原

【Abstract】 Due to the over-exploitation and utilization of nature by human,resources, energy shortages and environmental pollution problems arebecoming more and more serious eventually. Therefore, in the21thcentury, therational use of existing resources and energy, as well as protection of theenvironment has been paid more and more attention by human beings,meanwhile, the development and utilization of new energy has become apressing problem. The concept of “efficiency, energy saving, environmentalprotection” has been paid increasingly attention. Hydrogenation is a keyreaction in the industrial production, the way of improving the efficiency ofindustrial hydrogenation is of significance importance for the efficient andenergy-saving. Meanwhile, the development of more friendly for environmentand more efficient power supply is of great strategy, and fuel cell is widelyregarded as the new technologies to achieve this goal, and the developmentand progress of the above two fields dependent on the development ofcatalysts. At present, the catalysts for industrial hydrogenation and fuel cellelectrode are mainly noble metals. However, the noble metals such asplatinum and palladium have the disadvantages of lacking of resources,expensive, difficult in controlling the cost and long-term utilization. Therefore,the application of non-noble metal catalysts, especially nickel series in thesetwo fields has been paid more and more attention gradually. However, thenickel catalysts have the advantages of lacking of catalytic activity, stabilityand so on, leading to the difficulties of the applications in actual utilization.Based on the background above, this thesis has mainly focused on thestudies of preparation of nickel and nickel-based binary alloy supported onmulti-walled carbon nanotubes and their applications as hydrogenationcatalysts and electrocatalyts. We applied two synthesis methods, electrolessdeposition and optimized liquid phase reduction for the preparation of threenickel-series catalysts, which are amorphous MWCNT/Ni-B, MWCNT/Ni-Pcatalysts and crystalline state MWCNT/Ni catalysts, and systematical studiedthe effect of preparing methods on the behavior of catalysts. The detailphysical properties of the catalysts are characterized by XRD, SEM, HRTEM,XPS, ICP and TG-DTA and obtained the most optimized preparationparameters. Then, we studied the applications of the two amorphous Ni-basedbinary alloys for catalytic hydrogenation of styrene and benzene and their kinetic processes. Finally, we exploited the applications of the three Ni-seriescatalysts in the field of alkaline ethanol fuel cell by researching their catalyticperformances, mechanisms and kinetic processes for ethanol electrocatalyticoxidation. The main creative achievements are exhibited as follows:（1） A novel electroless bath containing NiCl2·6H₂O as predominant salt,ethylenediamine as complexing agent, NaOH as pH regulator and NaBH4asreduction agent has been successfully developed to deposit the Ni-Bnanoparticles on the sensitized-activated MWCNT by controlling the reactiontime. The obtained Ni-B binary alloy nanoparticles are fine spheres comprisedof amorphous structure with the morphologically unique fine-structure likeflowers, and homogenously dispersed with a narrow particle size distributioncentered at around60nm diameter. With the increase of electroless platingreaction time, the Ni loading as well as B content in the Ni-B particlesgradually increase, leading to the crystallization temperature eventuallyincreased to326°C, finally. XPS results indicated that there are electronstransferred from boron to nickel making the surface electro-enrich.（2） A novel electroless bath containing NiCl2·6H₂O as predominant salt,C₆H₅Na₃O₇as complexing agent,（NH4）₂SO₄as special additive, NaOH as pHregulator and NaH₂PO₂·H₂O as reduction agent has been successfullydeveloped to deposit the Ni-P binary alloy nanoparticles on thesensitized-activated MWCNT by optimizations of the reaction time,electroless bath concentration, NaOH added amount and the reactiontemperature. The obtained Ni-P nanoparticles are fine spheres of solid state,and homogenously dispersed with a narrow particle size distribution centeredat around100nm diameter. The tests results showed that the Ni-Pnanoparticles of the optimal catalysts are typical amorphous structure and thecrystallization temperature is about360°C. After the high temperatureannealing, the Ni-P nanoparticles agglomerate and become larger comprisedof Ni and Ni3P mixed phases.（3）The studies of the catalytic hydrogenation performances and reactionkinetics of the two amorphous Ni-based binary alloys MWCNT/Ni-B and theMWCNT/Ni-P catalysts showed that the two amorphous catalysts exhibitedexcellent catalytic activities toward the hydrogenation reaction of styrene,which can be100%selectively hydrogenised transferred into ethylbenzeneunder the condition which can be easily achieved. The kinetic parameters ofthe two amorphous catalysts showed first-order dependence on styreneconcentration for both catalysts. MWCNT/Ni-P catalysts have a smallerreaction order dependence on hydrogen pressure, and styrene can be100%conversed under lower temperature range and showing relatively higher rateconstant k of35122.2·e（-4914.7/T）, smaller activation energy E of40.86kJ/mol,indicating better catalytic activity of MWCNT/Ni-P catalysts. Further study ofthe MWCNT/Ni-P catalysts for catalytic hydrogenation of benzene showed itsexcellent catalytic activity for benzene, which can be selectively conversed to cyclohexane. The conversion of benzene increases linearly with the increasesof time, indicating a zero-order dependence on benzene concentration;meanwhile, there is a maximum value of about60%at the reactiontemperature of180°C, which might be caused by: firstly, the coverage ofaromatics at the surface of catalyst decreases as the temperature rises,resulting in maximum value at a certain temperature point; secondly, themaximum temperature point may be caused by the competitive adsorption ofbenzene and its reduced molecules during the reaction.（4） Developed an optimized liquid phase chemical reduction method bythe introduction of acidificated-sensitized-activated multi-walled carbonnanotubes. After controlled the amount of adding surfactant CTAB, pH valueof the system at about10and used hydrazine as the reducing agent reacted at80°C for1hour, we finally got small polycrystalline nickel nanoparticlesuniformly distributed on multi-walled carbon nanotube surface with particlesize of about20nm. Additive agent CTAB can complex with Ni ion atappropriate pH range. If the aqueous solution had low CTAB concentration（<120mM）, a bilayer could be formed around Pd nanoparticles built by CTABmolecules, which controlled the concentration of both hydrazine andNi/hydrazine close to the Pd surface. In this case, the reduction rate of nickelwas decresed, making the particle size smaller; If the concentration of CTABincreased to high level （>120mM）, the solution inclined to oil state, micellesinstead of bilayers would form on the surface of Pd nanoparticles, which couldinhibit the diffusion of Ni/hydrazine complexes and hydrazine molecules inthe solution, thus prevented the Ni reduction process.（5） The Electrocatalytic behaviors and kinetic studies of three Ni-seriescatalysts showed that all of the three Ni-series catalysts in alkaline mediumexhibited excellent electrocatalytic activities towards ethanol oxidation andthe electrocatalytic process were all controlled by the diffusion of ethanol inthe solution. MWCNT/Ni catalyst had the highest peak current for ethanoloxidation, which possibly caused by the larger reactive surface area fromsmaller particle size. The comparison of kinetic processes on three catalystsshowed that the MWCNT/Ni-B and MWCNT/Ni catalysts had similar valueof ethanol electrooxidation rate, which were both much higher than that ofMWCNT/Ni-P catalysts. The phenomenon could be attributed to the smallparticle size and good dispersion of Ni nanoparticles in MWCNT/Ni catalystsand the electron transfer between B and Ni in MWCNT/Ni-B catalysts.Therefore, if we could successfully synthesize amorphous Ni-B nanoparticlecatalysts with the size less than20nm supported on multi-walled carbonnanotubes, it could be expected to obtain extremely high oxidation current andoxidation rate for ethanol electrooxidation at the same time.更多还原