Study On The Organic Ligands Control Ni-B Amorphous Alloys NanoParticles Preparation And Their Catalytic Properties

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.