Catalytic properties and structures of nano-amorphous Ni–B alloys affected by annealing temperatures Original Research Article

The catalytic activities of nano-amorphous Ni–B alloy catalysts prepared by chemical reduction and then annealed at various temperatures were investigated by using the benzene hydrogenation as a probe reaction. The results indicated that the benzene conversion (63%) and turnover frequency (0.67 s−1) reached a maximum for the nano-amorphous Ni–B alloy catalyst annealed at an optimized temperature of 623 K. Such values were about 110 and 70% higher than those of the as-prepared one. A high annealing temperature of 773 K led to a dramatic decrease in the catalytic activity of Ni–B alloy. From the XAFS and XRD results, we confirmed that the nano-amorphous Ni–B alloy annealed at 573 or 623 K was composed of nano-crystalline Ni and crystalline Ni3B. After being annealed at the higher temperature of 773 K, the Ni–B alloy may result in the decomposition of crystalline Ni3B into crystalline Ni and aggregation of nano-crystalline Ni into crystalline Ni with a large size. Our results indicated that the nano-crystalline Ni showed higher activity and turnover frequency than nano-amorphous Ni–B alloy did. We propose that the order of catalytic activity of benzene hydrogenation for various phases in the amorphous Ni–B alloy is as follows: nano-crystalline Ni > nano-amorphous Ni–B alloy > crystalline Ni ≈ crystalline Ni3B.