氧化物担载Ni(C_5H_5)_2衍生催化剂的EXAFS表征

EXAFS Characterization of Supported Nickel Catalysts Derived from Ni(C5H5)2

本文以二茂镍为母体化合物,以氧化铝和氧化硅为担体制备了担载镍催化剂。为了表征其结构特点,对这些催化剂热分解处理前后的样品在日本筑波高能物理研究所(Photon-Factory)的同步辐射加速器BL—10B EXAFS实验站进行了外延x-光精细结构谱测定(透射法)。以单散射球面波理论对实验结果进行了多参数拟合,同时对母体化合物也进行了平行测定和拟合,以验证数据及拟合方法的可靠性。研究结果表明,母体化合物的EXAFS结果与文献XRD相一致;母体化合物与担体表面发生了强烈的化学作用;镍组分在催化剂表面高度分散,氧化铝与Ni(C_5H_5)_2有更强的相互作用形成。Ni[(O)_s]_n(n≈4),近一半的镍原子周围有0.30 nm处的镍原子散射;氧化硅上除Ni[(CO)_s]_n(n≈3)外,在0.30 nm处有配位数为2的非成键Ni原子。

Supported nickel catalysts were prepared from NiCp2 (Cp = C5H5) as precursor compound and alumina, silica as supports. The EXAFS (Extended X-ray Absorption Fine Structure) spectra of the precursor compound and the catalysts were measured on synchrotron radiation apparatus (BL-10B Station) of Photon Factory of Japan. The EXAFS data analysis was done on SUN 386/P9 micro-computer with the Program Library for EXAFS Data Processing in which the spherical wave theory was used. Correlation between the EXAFS parameters and error bars of the fitted results were also calculated. The result of EXAFS characterization of NiCp2 was the same as the reported XRD data exactly. The EXAFS results of the catalysts indicated that the precursor compound strongly interacted with the oxide supports. On the surface of alumina, nickel atom was coordinated by surface oxygen atoms (Ni[(O)3]4) and only half of the nickel atoms were surrounded by another nickel atom (Ni-·Ni distance 0. 30 nm), the nickel atoms were coordinated by surface oxygen atoms (Ni[(O)5]3on surface of silica, and each nickel atom was surrounded by two other nickel atoms (Ni -Ni distances 0. 30 nm). These differences were originated from the different surface properties of the supports. Alumina intereacted more strongly with the nickel atoms than silica. The nickel component was highly dispersed on the surface of both alumina and silica.