【作者】 胡玉；

【导师】 侯震山；

【作者基本信息】 华东理工大学 ， 工业催化， 2010， 博士

【摘要】 本文以液相还原的方法,分别以2,3-二甲基-1-(3-N,N’-二(2-吡啶)-丙酰胺)咪唑六氟磷酸盐([BMMDPA]PF6)和1-(3-氨丙基)-2,3-二甲基咪唑盐([AMMIM]X) (X=Br-, OAc-)功能化离子液体为稳定剂,分别制备出在离子液体相和水相中稳定存在的纳米钯和纳米镍催化剂。利用UV-vis, XRD, TG, TEM, XPS和活性评价等多种研究方法,系统考察了催化剂的制备条件、物理化学性质(金属纳米颗粒的尺寸以及表面电荷性质)和催化反应性能之间的相互关系。通过研究主要得出以下结论：(1)合适的还原条件以及反应条件对催化反应活性和选择性有着非常重要的影响。作为稳定剂的功能化离子液体可以经过特殊分子设计：一方面保证其在对应反应溶剂中有良好的溶解性,保证反应物与纳米催化剂的良好的互溶性和传质速率；另一方面通过引入特殊官能团可以在还原过程中控制纳米颗粒的大小,增加其稳定性,防止聚集失活,同时也有可能改善纳米颗粒表面的电荷性质,提高反应活性和选择性。但过多的稳定剂会堵塞催化剂活性中心,不利于加氢反应的进行。通过对比实验发现：催化剂制备过程中剩余的稳定剂和添加剂在反应时会严重抑制催化活性,但可以通过多次离心分离洗涤等后处理步骤除去。此外,合适的还原条件有助于制备出粒径小,分散性好的过渡金属纳米颗粒,能使其保持高的反应活性和选择性；而温和的反应条件有利于提高纳米催化剂的稳定性和增加使用寿命。(2)通过UV-vis、XRD、TG、TEM、XPS和元素分析等多种表征手段证明：制备的Pd(0)或Ni(0)晶相均属于典型的面心立方晶系；即使通过多次离心分离洗涤后处理步骤,仍有重量含量约为24%的离子液体吸附在催化剂表面；并且功能化离子液体与纳米催化剂表面明显发生了电荷转移以及配位稳定作用。(3)通过对含不同阴离子的功能化离子液体[AMMIM]X稳定的镍纳米催化剂加氢活性研究发现：阴离子对加氢反应活性有重要影响。BF4-和[N(CN)2]-在反应条件下容易发生水解,引起Ni(0)被氧化成没有活性的Ni(Ⅱ)物种；含有多-OH或-COOH官能团的阴离子由于其较强的配位作用,毒害催化中心,导致催化剂前驱体很难被还原；以醋酸根,p-丙氨酸根和乳酸根为阴离子的三种功能化离子液体稳定的镍纳米催化剂在合适的反应条件下对柠檬醛C=C双键的选择性加氢可以得到相近的产率。通过对以OAc-和Br-为阴离子的功能化离子液体进一步研究发现：以前者为稳定剂时制备的镍纳米催化剂虽然粒径较大,但由于OAc-亲核能力相对较弱,因而能在更加温和的反应条件下表现出更高的加氢活性和选择性,通过循环实验发现该催化剂稳定性也相对较好。(4)本文另一新颖之处在于：将功能化离子液体稳定的Pd、Ni纳米催化剂分别分散在离子液体或水相当中,采用环境友好的两相催化体系(有机／离子液体相、有机／水相)对催化加氢反应进行研究。结果发现这两种催化体系对多种底物的选择性加氢反应都得到很高的转化率和选择性,优于商业催化剂,并在催化剂循环实验中发现纳米催化剂即使使用多次仍能保持较好的稳定性,活性和选择性也仍维持较高水平。更多还原

【Abstract】 In this work, two kinds of functionalized ionic liquids-[2,3-dimethyl-1-(3-N, N-bis(2-pyridyl)-propylamido) imidazolium hexafluorophosphate ([BMMDPA]PF6) and 1-(3-aminopropyl)-2,3-dimethyl-imidazolium salts [AMMIM]X (X=Br-, OAc-)] were first synthesized and utilized for stabilizing palladium and nickel nanoparticles. The nanoparticles have been applied to selective hydrogenation in ionic liquids and aqueous phase, respectively. The relationships of the preparation conditions, physico-chemical characteristics (especially the particle size, surface electronic character) with the performance of the catalyst were discussed and analyzed by UV-vis, XRD, TG, TEM, XPS methods.(1) Suitable preparation and mild reaction conditions were favorable to enhancing the activity and selectivity of the catalyst.As stabilizers, the functionalized ionic liquids could be specially designed to increase the nanocatalysts solubility in reaction media (avoiding the mass transfer limitations), to control the nanoparticles size and enhance the stability of nanocatalysts from being aggregated. They could also alter the surface electronic characteristics of the nanocatalysts, and thus leading to the higher activity and selectivity. In the control experiments, it was found that the excess stabilizer would block and deactivate the active centre of the catalysts and seriously suppressed the activity of the hydrogenation. However, the purification steps seemed to be an effective way to remove the excess ligands adsorbed on the surface of the catalyst and the activity could be recovered. Besides, suitable pre-reduction conditions were critical to obtaining small, well-dispersed and stabilized nanoparticles and thus kept their high activity and selectivity.(2) XRD analysis had confirmed that both of the Pd(0) and Ni(0) crystallites were indexed as face-centered cubic (fcc) structure. UV-vis, TG, ICP-AES, TEM and XPS analyses showed that even if the nanocatalysts had been underwent the purification steps, there was still ca.24 wt.% of ionic liquid remaining on their surface.(3) The different anions in functionalized ionic liquids-[AMMIM]X utilized for stabilizing Ni(0) nanocatalysts significantly affected their activity towards selective hydrogenation of C=C double bonds of citral:BF4- and [N(CN)2]- were easy to hydrolyze under reaction conditions, which would induce the highly active Ni(0) nanocatalysts to be oxidized into unreactive Ni(II) species; the anions containing more -OH or -COOH groups with strong coordination ability would lead the precursor hard to be reduced to active metal nanocatalysts; Ni(0) nanocatalysts stabilized by [AMMIM]X (X=OAc-,NH2CH2CH2COO-and CH3CH(OH)COO-) had showed comparable performance under optimized reaction conditions. The activity difference of OAc- and Br- anions was unexpected:although the size of Ni(0) nanoparticles stabilized by [AMMIM]OAc was much bigger, they owned higher activity and stability. This could be ascribed to stronger hydrophility of Br- anion and thus some of the active centers were blocked by Br- and became inaccessible to substrates.(4) The strategy in this work was to utilize biphasic catalytic system (organic/ionic liquid, organic/aqueous phase), which was convenient for the recycling of the catalysts. The present catalytic systems had showed higher activity and selectivity towards many substrates than commercial catalysts.更多还原