Zeolites electron microscopy characterization

Inductively coupled plasma-atomic emission spectrometry allows the determination of anionic surfactants (LAS and AS) and inorganic compounds (phosphate, silicate, zeolite, sulfate). Other techniques, such as X-ray fluorescence spectroscopy and X-ray powder diffraction, have been used for the qualitative analysis of inorganic detergents. For surface analysis, optical light microscopy, scanning electron microscopy, and transmission electron microscopy characterize particles, deposition of surfactant, or other detergent ingredients on fabric. 

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. 

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]. 

Infrared spectroscopy has been used to help solve or determine the structure of zeolites. The technique is particularly useful for identifying the presence of double four- and six-rings as well as five-membered pentasil rings. In the structural characterization of beta zeolite, Newsam and coworkers used a variety of techniques including IR, electron microscopy (TEM), X-ray diffraction (XRD) and sorption data to solve the stacked, faulted structure [57]. The presence of IR absorption bands at 1232 and 560cm indicated that the structure contained five-member pentasil building units. 

Many of the characterization techniques described in this chapter require ambient or vacuum conditions, which may or may not be translatable to operational conditions. In situ or in opemndo characterization avoids such issues and can provide insight and information under more realistic conditions. Such approaches are becoming more common in X-ray adsorption spectroscopy (XAS) methods ofXANES and EXAFS, in NMR and in transmission electron microscopy where environmental instruments and cells are becoming common. In situ MAS NMR has been used to characterize reaction intermediates, organic deposits, surface complexes and the nature of transition state and reaction pathways. The formation of alkoxy species on zeolites upon adsorption of olefins or alcohols have been observed by C in situ and ex situ NMR [253]. Sensitivity enhancement techniques play an important role in the progress of this area. In operando infrared and RAMAN is becoming more widely used. In situ RAMAN spectroscopy has been used to online monitor synthesis of zeolites in pressurized reactors [254]. Such techniques will become commonplace. 

Roster, A.J., Ziese, U., Verkleij, A.J., Janssen, A.H., de Graaf J., Geus, J.W., and de Jong, K.P. (2000) Development and application of 3-dimensional transmission electron microscopy (3D-TEM) for the characterization of metal-zeolite catalyst systems. Stud. 

Characterization is the foundahon for the development and commercialization of new zeolites and zeolite-containing catalysts and adsorbents. Chapter 4 provides an overview of the most commonly employed characterization techniques and emphasizes the uhlity and limitations of each of these methods. An example is provided as to how a multi-technique characterization approach is necessary in order to determine the structure of a newly invented zeolite. Techniques covered in this chapter include X-ray powder diffraction, electron microscopy, infrared (IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy and physical/ chemical methods. 

Further characterization of the mechanical properties and structures of such zeolite-reinforced PDMS elastomers by Wen and Mark [139] also utilized small-angle neutron scattering (SANS) [141, 143, 214—220] and transmission electron microscopy (TEM). The neutron-scattering profiles of the pure and zeolite-filled PDMS networks were identical, which indicated negligible penetration of the polymer into the zeolite pores. The TEM pictures showed that the zeolite with the larger pore size had a somewhat smaller particle size, and this is probably the origin of its superior reinforcing properties [62, 139]. 

Characterization of the Ru/KY and Ru/NaY catalysts used in this study by transmission electron microscopy showed that the metal was well-dispersed within the zeolite as particles small enough to fit inside the supercages, less than 1 nm in diameter. 

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

The next stage of characterization focuses upon the different phases present within the catalyst particle and their nature. Bulk, component structural information is determined principally by x-ray powder diffraction (XRD). In FCC catalysts, for example, XRD is used to determine the unit cell size of the zeolite component within the catalyst particle. The zeolite unit cell size is a function of the number of aluminum atoms in the framework and has been related to the coke selectivity and octane performance of the catalyst in commercial operations. Scanning electron microscopy (SEM) can provide information about the distribution of crystalline and chemical phases greater than lOOnm within the catalyst particle. Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) can be used to obtain information on crystal transformations, decomposition, or chemical reactions within the particles. Cotterman, et al describe how the generation of this information can be used to understand an FCC catalyst system. 

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. 

Exchanged zeolites were characterized by N2 adsorption at 77K, X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), immersion calorimetry and NHs-temperature programmed desorption (NH3-TPD). X-ray diffraction patterns (XRD) were obtained with a JSO Debye-Flex 2002 system, from Seifert, fitted with a Cu cathode and a Ni filter, using CuXa radiation (A,=1.5419) and 2°min of scanning rate. X-ray photoelectron spectroscopy (XPS) spectra were acquired with a VG-Microtech Multilab 3000 spectrometer equipped with a hemispherical electron analyzer and Mg Ka (1253.6 eV) 300W X-ray source. 

Powder x-ray diffraction (Siemens D-500 diffractometer) and scanning electron microscopy (JEOL, JSM-840) methods were used for characterization of zeolite products. Infrared spectra (Perkin Elmer 783 infrared spectrophotometer) were used for investigation of nucleation gel. The amount of Si, Al, Na in zeolite products was analysed by conventional analytical method, i.e. gravimetric for Si, gravimetric and volumetric methods (titration by EDTA) for Al and flame photometric method for Na. The WL value in Table 1 was used to estimate the amount of water and organic species in an as-synthesized zeolite product. 

MH zeolites (Si/Al=35 and 480) were prepiared as described elsewhere [14]. The products were calcined at 773 K and exchanged with NH4CL IM. MH(35) was modified by steaming at 673 K for 25 h. All catalysts were characterized using XRD, electron microscopy, FTIR, solid state A1 and Si MAS NMR and sorption of n-hexane. The catalysts used and their properties are listed in Table 1. 

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