Annealing crystallization and catalytic activity of ultrafine NiB amorphous alloy

Annealing crystallization of ultrafine NIB amorphous alloy prepared by the chemical reduction method. was studied by DTA, XRD and XAFS techniques. The XRD and XAFS results have revealed that the crystallization process of ult rafine NiB amorphous alloy proceeds in two steps. First, ultrafine NiB amor phous alloy is crystallized to form metastable nanocrystalline Ni3B at an a nnealing temperature of 325 degreesC, Second, the nanocrystalline Ni3B is f urther decomposed into crystalline Ni at 380 degreesC or higher temperature , the local structure around Ni atoms in resultant product is similar to th at in Ni foil. It was found that the catalytic activity of nanocrystalline Ni3B for benzene hydrogenation is much higher than that of ultrafine NiB am orphous alloy or crystalline Ni, The result indicates that the active sites of nanocrystalline Ni3B for benzene hydrogenation are composed of both Ni and B with proper geometry configuration.