Electron microscopy zeolites

Key words microporous materials, zeolites, electron microscopy, structure determination... 

Analytical electron microscopy permits structural and chemical analyses of catalyst areas nearly 1000 times smaller than those studied by conventional bulk analysis techniques. Quantitative x-ray analyses of bismuth molybdates are shown from lOnm diameter regions to better than 5% relative accuracy for the elements 61 and Mo. Digital x-ray images show qualitative 2-dimensional distributions of elements with a lateral spatial resolution of lOnm in supported Pd catalysts and ZSM-5 zeolites. Fine structure in CuLj 2 edges from electron energy loss spectroscopy indicate d>ether the copper is in the form of Cu metal or Cu oxide. These techniques should prove to be of great utility for the analysis of active phases, promoters, and poisons. 

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. 

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. 

Electron crystallography offers an alternative approach in such cases, and here we describe a complete structure determination of the structure of polymorph B of zeolite beta [3] using this technique. The clear advantage of electron microscopy over X-ray powder diffraction for elucidating zeolite structures when they only occur in small domains is demonstrated. In order to test the limit of the structural complexity that can be addressed by electron crystallography, we decided to re-determine the structure of IM-5 using electron crystallography alone. IM-5 was selected for this purpose, because it has one of the most complex framework structures known. Its crystal structure was solved only recently after nine years of unsuccessful attempts [4],... 

For normal zeolite beta samples, the domains of polymorphs A and B are only a few nanometers in size and heavily intergrown. This is not large enough for a full structure determination by electron microscopy. However, in a polymorph B enriched zeolite beta sample [2], we could find areas of sufficient size. 

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. 

Study by Transmission Electron Microscopy Tomography of gold nanoparticles in reduced Au/zeolites... 

Tomography was applied during Transmission Electron Microscopy (TEM) analysis of various reduced Au/zeolite samples. The size and location of the gold nanoparticles as a function of the support characteristics and preparation method are discussed. 

Figure 2. Scanning electron microscopy of (a) zeolite X-chitosan, (b) zeolite Y-chitosan and (c) mordenite-chitosan composites prepared by encapsulation of zeolites during the gelling of chitosan.

Scanning electron microscopy indicated that the zeolites crystals are homogeneously dispersed in the surface and the core of the composites. Figure 2 presents micrographs of cross-sections of the chitosan-zeolite spheres and shows that the morphology of the zeolite crystals has not been affected by the gelling of chitosan. 

After the catalytic runs no modification of mean particle size is observed for this last system. Conversly, Ru CO) deposited on silica-alumina is readily decomposed at 200°C to metallic particles of 1 nm mean size which are also catalysts for the F-T synthesis. The catalytic activity at 200°C is C i one tenth of the Y zeolite supported ones and methane is practically the only hydrocarbon formed. Electron microscopy examination of the catalyst after reaction reveals a drastic sintering of the... 

Transmission electron microscopy pictures were taken using a JE0L 100 CX microscope. For some samples lateral micro-analysis of thin sections of zeolite was carried out using a HB-5 VG microscope equipped with EDX accessory at IFP (11). 

Analytical electron microscopy of individual catalyst particles provides much more information than just particle size and shape. The scanning transmission electron microscope (STEM) with analytical facilities allows chemical analysis and electron diffraction patterns to be obtained from areas on the order of lOnm in diameter. In this paper, examples of high spatial resolution chemical analysis by x-ray emission spectroscopy are drawn from supported Pd, bismuth and ferric molybdates, and ZSM-5 zeolite. 

Figure 1.13. (1) Electron microscopy picture of a zeolite L crystal with a length of 1.5 pm. (2-5) True color fluorescence microscopy pictures of dye loaded zeolite L crystals. (2-4) Fluorescence after excitation of only Py+ (2) after 5-min exchange with Py+, (3) after 2 h exchange with Py+, (4) after additional 2 h exchange with Ox+. (5) The same as 4 but after specific excitation of only Ox+. (See insert for color representation.)...

Figure 1.33. Upper electron microscopy (EM) pictures of the investigated zeolite L samples with different crystal length lz (1) 300 nm (2) 500 nm (3) 850 nm (4) 1400 nm (5) 2400 nm. Lower Fluorescence intensity after specific excitation of only Py+ at 460 nm (scaled to the same height at the maximum of the Py+ emission) of Py+ loaded and Ox+ modified zeolite L crystals with constant Py+ loading (ppy+ = 0.11) as a function of crystal length. The Ox+ modification was two molecules at both ends of the channel, on average.

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... 

Transmission electron microscopy (TEM) can provide detailed stmcture of zeolites. I use the word characterize or characterization for stmctural study on a unit cell scale, such as various kind of stmctural defects and basic stmctural units, and determine or determination for obtaining atomic coordinates within the unit cell for all the atoms of a crystal. A simple text or reviews for stmctural characterization of porous materials can be found in a book or review articles [1-6]. Now, we are in a new era, that is, we can determine new stmctures of micro- and mesoporous materials only by electron microscopy(EM), an area called electron crystallography (EC) [7-11]. 

Application of transmission electron microscopy (TEM) techniques on heterogeneous catalysis covers a wide range of solid catalysts, including supported metal particles, transition metal oxides, zeolites and carbon nanotubes and nanofibers etc. 

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