【作者】 国洁；

【导师】 王亚权；

【作者基本信息】 天津大学 ， 化学工艺， 2013， 博士

【摘要】 如何有效控制剧烈放热的化学反应速率，是解决化学还原法制备的Ni-B非晶态合金纳米颗粒易团聚、催化剂活性和热稳定性差等问题的关键。本文分别制备四种镍有机配合物，即镍与水合肼形成的[Ni(N2H4)2]Cl2、[Ni(N2H4)3]Cl2和镍与乙二胺形成的[Ni(en)2]Cl2、[Ni(en)3]Cl2来调控Ni-B非晶态合金催化剂的制备过程。通过XRD, TEM, BET和DSC等对制备的催化剂进行表征，发现配合物稳定性越大，对化学还原制备Ni-B非晶态合金催化剂的调控能力越强。有机配体调控制备的催化剂呈均一的纳米颗粒，与传统化学还原法相比分散度更好、热稳定性更高。根据XPS和H2-TPD结果分析证明配体在还原过程中可以增加催化活性中心Ni的富电子程度同时弱化Ni–H的强度，可使活性中心的转化频率TOF提高。催化葡萄糖加氢反应和硼氢化钠水解制氢反应中，配体调控制备的催化剂活性高于直接化学还原制备的催化剂，其中[Ni(en)3]Cl2配合物制得的催化剂催化葡萄糖加氢转化率最高，达到98.6%，且催化硼氢化钠水解反应活性也最高，仅1min达到100%产氢量。催化剂活性高是结构效应和电子效应协同作用的结果。连续原位升温处理Ni-B非晶态合金进行XRD表征，结果表明晶化过程开始Ni3B微晶占主要成分，随着温度的升高，Ni3B微晶不断解体含量下降同时Ni微晶生成、长大，含量升高。有机配体可以影响制得催化剂的热稳定性，使其晶化开始温度提高，晶化过程减缓。其中，[Ni(en)2]Cl2配体调控制备的Ni-B非晶态合金Ni3B微晶向Ni晶体转变的过程最缓慢，在673K时仍有一定部分的Ni3B微晶存在。用[Ni(en)2]Cl2配合物化学镀制备的Ni-B-e电极在NaOH溶液中电催化氧化乙醇反应的速率常数k2=8.19×103Lmol-1s-1比直接化学还原生成Ni-B-n电极的k2值1.09×105Lmol-1s-1高将近3个数量级，对碱性溶液中的乙醇有更高的电化学催化活性。用[Ni(en)2]Cl2制备的Ni-B/C电极在573K热处理后，对碱性溶液中的甲醇有较高的电化学催化活性。推测机理为适当的热处理使得晶化生成Ni3B-Ni纳米微晶混合物高度分散产生的结构效应和Ni3B原子簇中Ni和B的电子效应。研究柠檬酸钠和H2O2协同作用调控生成形貌均一、稳定的Ni-B纳米颗粒。结果表明，H2O2氧化新生的、结构不稳定的Ni-B纳米颗粒，而柠檬酸根离子与某一晶面的金属镍生成配合物，使Ni-B纳米颗粒被配合物覆盖生长相对稳定。更多还原

【Abstract】 The key point to directly solve the problem of Ni-B amorphous alloys particleaggregation, low activity and thermal stability should be effectively controlling therate of strongly exothermic chemical reduction. In this thesis, we reported using fournickel organic complexes to control the preparation of Ni-B amorphous alloy catalyst,including [Ni(N2H4)2]Cl2，[Ni(N2H4)3]Cl2synthesized by nickel and hydrazine and[Ni(en)2]Cl2,[Ni(en)3]Cl2synthesized by nickel and ethylenediamine, respectively.The catalysts were characterized by XRD, TEM, BET and DSC techniques. The resultillustrated the greater stability of the nickel organic complexes, the stronger control ofthe preparation of Ni-B amorphous alloy catalyst from the chemical reduction. Theas-prepared Ni-B amorphous alloys were uniform spherical nanoparticles and hadhighly dispersed and more thermal stability than Ni-B amorphous alloys obtained viadirect reduction of Ni2+byBH4. The analysis of XPS and H2-TPD spectras confirmednickel organic complexes in reduction could increase electron-rich of Ni center andweaken bond strength of Ni–H, which could enhance the TOF value. When used inthe hydrogenation of glucose and hydrolysis of sodium borohydride, the as-preparedNi-B catalyst exhibited much higher activity than the conventional Ni-B catalystsobtained via direct reduction of Ni2+by BH4. The highest conversion of glucose inNi-B sample, which produced by reducing [Ni(en)3]Cl2was98.6%. And it also hasthe highest activity of sodium borohydride hydrolysis reaction, only1min hydrogenyield was100%. The higher activity could be attributed to both structure effect andelectronic effects.Temperature rising processing of Ni-B amorphous alloys was continuously in situ.XRD patterns showed when the crystallization process starts Ni3B microcrystallinesaccounted for the main component. With temperature increasing, the Ni3Bmicrocrystallines decreased while Ni microcrystallines constantly grew up. The nickelorganic ligand might affect the thermal stability of as-prepared catalysts, so that thethreshold temperature of the crystallization is increased and the crystallization processis slowed. Obviously, the process of transforming Ni3B microcrystallines to Nicrystals of Ni-B amorphous alloys prepared by [Ni(en)2]Cl2is the most slowly. Whentemperature up to673K, there is still a certain part of the Ni3B microcrystallines exist.Ni-B-e electrode prepared by the electroless deposition technique of chemicalreduction of [Ni(en)2]Cl2withBH4exhibited much higher electrocatalytic activity than the Ni-B-n electrode obtained via direct reduction of nickel metallic ions. Therate constant of ethanol electrocatalytic oxidation on Ni-B-e electrode, which is8.19×103Lmol-1s-1inereased a proximately by the3orders on Ni-B-e electrode,which is1.09×105Lmol-1s-1. The Ni-B/C electrode, prepared by the electrolessdeposition technique of chemical reduction of [Ni(en)2]Cl2withBH4washeat-treated at573K. It showed the best activity in methanol oxidation. The effects ofthe heat treatment can be attributed to both the formation of a highly dispersedmicrocrystalline Ni3B-Ni nanocomposites and the electronic interaction between Niand B in Ni3B clusters.Synergy of Citrate ions and H2O2can generate uniform and stable Ni-Bnanoparticles. Due to oxidation of H2O2, the nascent structural of Ni-B nano-particlesis instability. The nickel citrate complexes covered one crystal surface of the nickel.The Ni-B nano-particles, which have particular morphology, are growth relativelystable.更多还原