Study On The Preparation And The Surface Properties Of Nano-size Ni-based Amorphous Alloy Catalysts

Nowadays, Ni-B amorphous alloy with short-range ordering, long-range disordering and metastable state of thermodynamic strueture have widely used in hydrogenation and became a focus in research. The most common preparation method of Ni-B amorphous alloy is chemical reduction. This method is an environmental friendly process because of the mild condition, water by-product and the boron oxide or boric acid that could be used for other processes. But the catalysts activity were effected to a certain extent for the gathering of activity atom clusters, the lower atom utilization, the higher inactivation of oxidate, and easier crystallization under high-temperature. Therefore, enhancing the catalytic hydrogenation activity from the preparation of the catalyst is very important, such as manipulation the surface properties, reducing the particle size of active component; increasing the dispersion of the activity atom clusters and improving the thermal stability.The nickel-based catalyst were prepared by chemical reduction of Ni²⁺ with BH₄^- in aqueous solution, and the cost was more cheaper, the catalytic activity was higher, and the preparationof process was environmental friendly. Then the external field and the nickel-based complexes were inducted in this preparation. The surface properties of the catalysts were studied by Transmission Electron Microscope(TEM), Differential Scanning Calorimetry(DSC), X-ray Diffraction(XRD), X-ray Photoelectron Spectroscopy(XPS) and Temperature Programmed Desorption(TPD), and the catalytic activity was studied by the liquid phase glucose hydrogenation.The Ni-B amorphous alloy catalysts were all have the amorphous structure, which prepared under the external electromagnetic and ultrasound field. But the catalysts of Ni-B amorphous alloy prepared under the external electromagnetic exhibited fewer hydrogenation activities than the regular Ni-B obtained via direct reduction of Ni2+ with BH4-. Moreover the external ultrasound field has greatly improved hydrogenation activity. So the external ultrasonic field has greater positive effects on the catalyst activity than the external electromagnetic field. Prepared Ni-B catalysts under the external ultrasound were found out that: The ultrasound cavitation has changed the surface properties: the particle size was much smaller, the thermal stability was enhanced, the larger desorption peak of hydrogen, and the stronger powerful ability of hydrogen. And when the ultrasonic power is 90 W, the glucose hydrogenation has the highest (70.0%) conversion rate. So the ultrasonic power has great influence on the hydrogenation activity, the bigger the ultrasonic power, the smaller the catalyst activity.The Ni-B amorphous alloy catalysts were prepared by reduction of nickel-hydrazine complexes with BH4- under the ultrasonic power of 105 W, which exhibited the best catalytic activity, the higher dispersion and thermal stability, the uniform particle size (15 nm). But the particle size of Ni-B amorphous alloy catalysts which prepared by reduction of nickel-ethylenediamine complex with BH4- under the ultrasonic power of 105 W was about 10 nm, the temperature of crystalline was enhanced and the thermal stability was better; and the surface properties has remarkably improved than the pure the external ultrasound field and the direct reduction of nickel with BH₄^-. However, the higher ultrasonic power, the reunioner catalysts, and the active center of catalysts could be covered, and then obtained the lower conversion rate of glucose hydrogenation.When reduction of Ni-based complexes with BH4-, the first step was broken the steric hindrance formed by Ni2+ and ligand, and then opened the bond energy of the complex, so the reduction could happen. Therefore the reduction rate of Ni-based complexes was slowed and avoided the unreacted metal ions that mixturing in the catalysts. The kind and the number of the ligand are the both important factors to affect the catalysts forming. Moreover, the cavitation of ultrasonic have the important effect for the surface properties control of catalysts, and the catalysts of Ni-B amorphous alloy have the higher dispersion degree with surface activity center and the smaller particle size. But the effects of the complexes with the surface properties were not to be neglected; only the combined action of the ultrasonic and the complexes can obtained the perfect Ni-B amorphous alloy.