Porous scanning transmission electron

For the detailed study of reaction-transport interactions in the porous catalytic layer, the spatially 3D model computer-reconstructed washcoat section can be employed (Koci et al., 2006, 2007a). The structure of porous catalyst support is controlled in the course of washcoat preparation on two levels (i) the level of macropores, influenced by mixing of wet supporting material particles with different sizes followed by specific thermal treatment and (ii) the level of meso-/ micropores, determined by the internal nanostructure of the used materials (e.g. alumina, zeolites) and sizes of noble metal crystallites. Information about the porous structure (pore size distribution, typical sizes of particles, etc.) on the micro- and nanoscale levels can be obtained from scanning electron microscopy (SEM), transmission electron microscopy ( ), or other high-resolution imaging techniques in combination with mercury porosimetry and BET adsorption isotherm data. This information can be used in computer reconstruction of porous catalytic medium. In the reconstructed catalyst, transport (diffusion, permeation, heat conduction) and combined reaction-transport processes can be simulated on detailed level (Kosek et al., 2005). 

In this context, the SPM techniques (and especially STM and AFM) appear, a priori, ideally suited for the direct visualization of the porous structure of materials at scales which are not so readily accessible by other means (e.g., scaiming and transmission electron microscopies). However, the performance of such a task is confronted with two major limitations. The first one arises from the fact that detection with SPM is exclusively restricted to the outermost surface of the sample. Accordingly, this implies that only the most external porosity of the material can be probed, whereas no information on the bulk (inner) porosity, which might not be identical to the former, is revealed. The second drawback is related to the finite dimensions of the probing tip, which limits the size of the voids (pores) physically accessible (and thus detectable) by the tip on the sample surface. Obviously, pores significantly smaller than the tip diameter will pass uimoticed to the instrument when the surface is scanned. As a specific example, the tips normally employed in AFM are not sharp enough to provide access to the whole mesopore range (between 2 and 50 nm). 

The porous structure of active carbons can be characterized by various techniques adsorption of gases (Ni, Ar, Kr, CO ) [5.39] or vapors (benzene, water) [5,39] by static (volumetric or gravimetric) or dynamic methods [39] adsorption from liquid solutions of solutes with a limited solubility and of solutes that are completely miscible with the solvent in all proportions [39] gas chromatography [40] immersion calorimetry [3,41J flow microcalorimetry [42] temperature-programmed desorption [43] mercury porosimetry [36,41] transmission electron microscopy (TEM) [44] and scanning electron microscopy (SEM) [44] small-angle x-ray scattering (SAXS) [44] x-ray diffraction (XRD) [44]. 

Neo M, Kotani S, Fnjita Y, Nakamnra T, Yamamnro T, Bando Y, Ohtsnki C, Kokubo T (1992) Differences in ceramic-bone interface between snrface-active ceramics and resorbable ceramics a study by scanning and transmission electron microscopy. J Biomed Mater Res 26 255-267 Netz DJA, Sepulveda P, PadnoUelli VC, Sparado ACC, Alencastre JB, Bentley MVLB, Marchetti JM (2001) Potential use of gelcasting hydroxylapatite porous ceramic as an implantable drug deliveiy system. Inti J Pharmaceut 213 117-125... 

Microstructure of porous anodic oxide films was investigated with transmission electron microscope JEM-T6 and scanning electron microscopes JSM-840 and JSM-35. 

We have selected ordered porous crystalline transition metal oxides that meet all three of the following criteria. The first criterion is that they are ordered porous materials, and that ordered pores were observed by transmission electron microscopy (TEM) or scanning electron... 

Commonly used spectroscopic or analytical techniques for characterizing surfaces and coating layers on porous silicon are Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy, energy dispersive X-ray spectrometry, fluorescence spectroscopy, UV-Vis absorption/reflectance spectroscopy, thin film optical interference spectroscopy, impedance spectroscopy, optical microscopy, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, ellipsometry, nitrogen adsorption/desorp-tion analysis, and water contact angle. 

Fig. 15 a Scanning and b transmission electron microscopy images of highly porous M-N-C derived from the mixed nitrogen precursor approach, using both cyanamide and polyaniline in tandem... 

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