High-resolution electron microscopy general discussion

The aspects of catalyst characterization have been discussed in detail elsewhere, for example, see references [2-6], and the numerous methods, some of which are restricted to specific elements and isotopes, that can supply the above knowledge have been tabulated. However, a review should be useful here of only the methods that are most readily available to the general catalytic researcher, such as TEM (Transmission Electron Microscopy) including SEM (Scanning Electron Microscopy) and HREM (High Resolution Electron Microscopy), XRD (X-ray Diffraction), physisorption and chemisorption. Because of the unique information it can provide, EXAFS (Extended X-ray Absorption Fine Structure) is also discussed briefly. 

The use of EPR as a key tool to characterize electronic structure and to reveal the nature of the active sites has been recently considered by Fittipaldi et al. [40], The power of the EPR technique to investigate the local properties is exemplified with C , N , B , and F , as weU as some anion codoped Ti02 and has been summarized, and the limitations and challenges are critically discussed. In particular, complementary techniques in addition to the EPR characterization, such as high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), XRD, Raman spectroscopy, and computational calculations, can improve the general understanding. 

Transmission electron microscopy (TEM) is a powerful method for imaging ultrafine structures of materials. In principle, TEM apparatus provides high resolution enough to observe molecules in subnanometer scale. However, it is not so easy, in practice, to apply TEM for imaging supermolecules on an atomic level owing to their thermal oscillation under the measurement conditions. Thus, TEM analysis of supermolecules has been generally discussed on a nanometer scale up to the present time. 

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