超细NiB非晶态合金的结构及催化性能

采用XAFS、XRD和DTA技术研究了化学还原法制备的超细NiB非晶态合金的结构及退火晶化行为.结果表明，NiB非晶态合金的退火晶化分两步进行在598K形成晶态的Ni3B和纳米晶的Ni；652K退火导致Ni3B分解以及纳米晶Ni聚集.在623K退火处理后的NiB样品的苯加氢活性最高.活性组分的苯加氢催化性能高低顺序为纳米晶Ni＞超细Ni-B非晶态合金＞晶态Ni.超细Ni-B非晶态合金的活性中心主要为纳米晶的Ni和Ni富集的NiB非晶态.超细NiB非晶态合金催化剂在反应过程中失活的原因主要是纳米晶Ni的聚集和积碳而所导致活性表面降低.

Local Structure and Catalytic Performance of Ultrafine NiB Amorphous Alloy

Ultrafine NiB amorphous alloy prepared by chemical reduction wascharacterized by X-ray absorption fine structure (XAFS), X-ray diffraction (XRD), and Differential thermal analysis (DTA). The DTA result indicated that the crystallization of ultrafine NiB amorphous alloy was carried out in two steps, as indicated by two strongly exothermic peaks located at 598 and 652 K, respectively. Two metastable intermediate states, i.e., crystalline Ni3B and a nanocrystalline Ni phase, were formed in the first exothermic process of ultrafine NiB amorphous alloy. Annealing at the temperature higher than 652 K may result in the decomposition of crystalline Ni3B into crystalline Ni and aggregation of nanocrystalline Ni. The activities of benzene hydrogenation for NiB samples showed a maximum at the optimized annealing temperature of 623 K and a minimum at the higher annealing temperature. The results showed the catalytic activity for the benzene hydrogenation of the NiB alloy sample was in this order: nanocrystalline Ni＞ultrafine NiB amorphous alloy＞crystalline Nicrystalline Ni3B. It is considered that the active sites are nanocrystalline Ni and amorphous NiB with fcc Ni-like structure for ultrafine NiB amorphous alloy.