Vrålstad Torbjørn, Glomm Wilhelm R, Rønning Magnus, Dathe Hendrik, Jentys Andreas, Lercher Johannes A, Oye Gisle, Stöcker Michael, Sjöblom Johan
Ugelstad Laboratory, Department of Chemical Engineering, Norwegian University of Science and Technology (NTNU), N-7491 Trondheim, Norway.
J Phys Chem B. 2006 Mar 23;110(11):5386-94. doi: 10.1021/jp056900p.
Cobalt-containing mesoporous materials that have been prepared using different procedures have been comparatively characterized by transmission electron microscopy/energy-dispersive X-ray spectroscopy (TEM/EDS), extended X-ray absorption fine structure spectroscopy (EXAFS), X-ray absorption near edge spectroscopy (XANES), and ultraviolet-visible (UV-vis), near-infrared (NIR), and mid-infrared (mid-IR) spectroscopies, and the results provide new insights into the local environment and properties of cobalt in this type of material. TEM/EDS analyses have shown that tetraethyl orthosilicate (TEOS) may be less appropriate as a silicon source during the syntheses of cobalt-containing mesoporous materials, because the distribution of cobalt throughout the framework may become uneven. EXAFS has been determined to be the most suitable method for direct verification of framework incorporation, by identifying silicon as the backscatterer in the second shell. Such a direct verification may not be obtained using UV-vis spectroscopy. From EXAFS analyses, it is also possible to distinguish between surface-bound and framework-incorporated cobalt. There is a good agreement between the results obtained from XANES and UV-vis regarding the coordination symmetry of cobalt in the samples. The presence of cobalt in the silica framework has been determined to create Lewis acid sites, and these acid sites are suggested to be located at tetrahedral cobalt sites at the surface.
采用不同方法制备的含钴介孔材料已通过透射电子显微镜/能量色散X射线光谱（TEM/EDS）、扩展X射线吸收精细结构光谱（EXAFS）、X射线吸收近边光谱（XANES）以及紫外可见（UV-vis）、近红外（NIR）和中红外（mid-IR）光谱进行了比较表征，结果为这类材料中钴的局部环境和性质提供了新的见解。TEM/EDS分析表明，在含钴介孔材料的合成过程中，正硅酸四乙酯（TEOS）作为硅源可能不太合适，因为钴在整个骨架中的分布可能会变得不均匀。EXAFS已被确定为直接验证骨架掺入的最合适方法，通过将硅识别为第二壳层中的背散射体。使用UV-vis光谱可能无法获得这种直接验证。通过EXAFS分析，还可以区分表面结合的钴和掺入骨架的钴。在样品中钴的配位对称性方面，XANES和UV-vis获得的结果之间有很好的一致性。已确定二氧化硅骨架中钴的存在会产生路易斯酸位点，并且这些酸位点被认为位于表面的四面体钴位点处。
