High-resolution electron microscopy zeolites

In the present study, we synthesized in zeolite cavities Co-Mo binary sulfide clusters by using Co and Mo carbonyls and characterized the clusters by extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and high resolution electron microscopy (HREM). The mechanism of catalytic synergy generation in HDS is discussed. 

STRUCTURES OF ZEOLITES AND MESOPOROUS CRYSTALS DETERMINED BY ELECTRON DIFFRACTION AND HIGH-RESOLUTION ELECTRON MICROSCOPY... 

Structures of zeolites and mesoporous crystals determined by electron diffraction and high-resolution electron microscopy... 

J. M. (1980) Zeolitic strucmres as revealed by high-resolution electron microscopy. Nature, 286,1-13. 

Pan, M. (1995) High resolution electron microscopy of zeolites. Micron, 27, 219-238. 

High resolution electron microscopy (HREM) is also used extensively for structural examination of zeolites, particularly for intergrowths and faults. EXAFS has been used to determine the local coordination geometry of the exchangeable cations and how this changes on reaction or dehydration. 

New Approaches to the Structural Characterization of Zeolites High Resolution Electron Microscopy and Optical Diffractometry... 

We discuss the combined use of high-resolution electron microscopy, electron diffraction, optical diffractometry and computer graphics for investigating zeolitic structure. Particular attention is given to twinned faujasitic materials and to intergrowth structures in ZSM-5 and ZSM-11 catalysts. 

In this paper we shall describe how high resolution electron microscopy (HREM) can be used in conjunction with selected area electron diffraction (SAED) to probe the local structure of zeolitic solids (2, 5 8) which are often microcrystalline, multi-phasic or twinned. We shall also refer to the application of optical diffractometry (4, 9-11) as a supplemental procedure either for interpretation of electron micrographs, or for analogue diffraction studies of model systems. 

Despite many advances in analytical methods in recent years, the structural characterization of materials that only occur as microcrystals less than about 30 l in diameter remains difficult and laborious. High resolution electron microscopy in the lattice imaging mode is by far the most powerful tool in giving the direct evidence of structural details essential for modelling clues, as has been demonstrated in the cases of recent zeolite structure solutions of theta-l/ZSM-23 (26) and beta (27), in addition to ECR-1. X-ray diffraction methods provide the essential confirmatory data, and sorption molecular probing and various well established spectroscopic methods are useful ancillary tools. 

M. Tsapatsis, M. Lovallo, and M.E. Davis, High-resolution Electron Microscopy Study on the Growth of Zeolite L Nanoclusters. Microporous Mater., 1996, 5, 381-388. 

A. Carlsson, T. Oku, J.O. Bovin, G. Karlsson, Y. Okamoto, N. Ohnishi, and O. Terasaki, The Structure of Iron Oxide Implanted Zeolite Y, Determined by High-resolution Electron Microscopy and Refined with Selected Area Electron Diffraction Amplitudes. Chem. Eur. J., 1999, 5, 244-249. 

The effect of grain size is not always observed experimentally. Table V reports some data about the alkylation of toluene with methanol as a function of the grain size of ZSM-5 and ZSM-11 zeolite samples. It clearly appears that, as expected, a higher selectivity to para-xylene is obtained when the grain size of the ZSM-5 zeolite increases. This does not seem to hold true for ZSM-11, samples prepared in our laboratory. However, a detailed high resolution electron microscopy (HREM) study of the morphology of the grains has shown (63) that ... 

Structure Elucidation from Crystal Powders. For many practical materials, such as polymers and zeolite catalysts, it is impossible to synthesize large crystals. Therefore the structure has to be found from powders. Powder XRD (preferably using synchrotron radiation) and neutron diffraction are the most important techniques, but experiments using other analysis methods like High Resolution Electron Microscopy (HREM) and Electron Diffraction (ED), MAS-NMR and EXAFS can add valuable information (8). 

Pan M, Crozier PA (1993) Low-dose high-resolution electron-microscopy of zeolite materials with a slow-scan CCD camera. Ultramicroscopy 48 332-340... 

Zeolites form another class of materials useful for fundamental studies . As mentioned earlier, zeolites are microporous silica-aluminates with micropores of dimensions comparable to organic molecules. The materials are unique, because these micropores are determined by the three-dimensional crystallographic structure of the material and catalytic events occur at the interphase of zeolite micropore and zeolite lattice. As a result the catalytically active sites are well defined. Zeolites are used in practice in the acidic form or promoted with metal or sulfide particles. High Resolution Electron Microscopy, Neutron Diffraction and Solid State NMR are techniques that arc applied for structural characterization and to study the behaviour of chemisorbed molecules. 

By the 1980s most of the aluminosilicate zeolites currently used industrially were known, and the emphasis shifted to the study of these materials using a range of powerful new techniques that came of age at this time. These included, in particular, solid state NMR, X-ray and neutron powder diffraction analysis, high resolution electron microscopy and computational methods. All were ideal for the study of structural details of solids that were rarely available, and never used in industrial applications, other than as microcrystalline powders. All these techniques are applicable to the bulk of the solid - this in turn makes up the (internal) surface, which is accessible to adsorbed molecules. Since the techniques are able to operate under any conditions of gas pressure, they may be used to extract structural details in situ under the operating conditions of ion exchange, adsorption and catalysis. In particular, zeolitic systems have proved ideal for the study, understanding and subsequent improvement of solid acid catalysts. 

High-Resolution scanning electron and atomic force microscopies observation of nanometer features on zeolite Surfaces... 

It is now possible to observe nanometer features on the surfaces of zeolitic materials using high-resolution scanning electron microscopy. By taking ibidem measurements in combination with atomic force microscopy we are able to illustrate the strengths and weaknesses of both techniques and judge respective resolving power. 

Microporous nanoparticles with ordered zeolitic structure such as Ti-Beta are used for incorporation into walls or deposition into pores of mesoporous materials to form the micro/mesoporous composite materials [1-3], Microporous particles need to be small enough to be successfully incorporated in the composite structure. This means that the zeolite synthesis has to be stopped as soon as the particles exhibit ordered zeolitic structure. To study the growth of Ti-Beta particles we used 29Si solid-state and liquid-state NMR spectroscopy combined with x-ray powder diffraction (XRPD) and high-resolution transmission electron microscopy (HRTEM). With these techniques we monitored zeolite formation from the initial precursor gel to the final Ti-Beta product. 

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