Takahashi R, Sato S, Sodesawa T, Nakamura N, Tomiyama S, Kosugi T, Yoshida S
Department of Materials Technology, Faculty of Engineering, Chiba University, Yayoi, Inage, Chiba 263-8522, Japan.
J Nanosci Nanotechnol. 2001 Jun;1(2):169-76. doi: 10.1166/jnn.2001.018.
A Ni/SiO2 catalyst was prepared by homogeneous precipitation of nickel hydroxide in a sol-gel-derived wet silica gel. The preparation process consists of two successive steps: gelation of silica in the presence of nickel nitrate and urea at 50 degrees C, followed by aging at higher temperature, typically at 80 degrees C, to decompose the urea. The decomposition of urea increases the pH of the solution in the wet gel, leading to the concurrence of structural rearrangement of silica gel and deposition of nickel species. As a result, the structure of the silica changes from a ramified polymeric network into particle aggregates that entrap the nickel cations in the particles. The resulting Ni/SiO2 contains large mesopores that have high thermal stability up to 1000 degrees C and highly dispersed Ni metal particles with typical crystallite size of 4 nm even at high Ni content at 20 wt%.
通过在溶胶 - 凝胶衍生的湿硅胶中均匀沉淀氢氧化镍来制备Ni/SiO₂催化剂。制备过程包括两个连续步骤：在50℃下于硝酸镍和尿素存在的情况下使二氧化硅凝胶化，随后在较高温度（通常为80℃）下老化以分解尿素。尿素的分解提高了湿凝胶中溶液的pH值，导致硅胶结构重排与镍物种沉积同时发生。结果，二氧化硅的结构从分支状聚合物网络转变为颗粒聚集体，这些聚集体将镍阳离子捕获在颗粒中。所得的Ni/SiO₂含有大的中孔，这些中孔在高达1000℃时具有高热稳定性，并且即使在20 wt%的高镍含量下也具有典型微晶尺寸为4 nm的高度分散的镍金属颗粒。
