Characterization techniques EXAFS

Nowadays there is a general consensus that the Ti(IV) atoms are incorporated as isolated centers into the framework and are substituting Si atoms in the tetrahedral positions forming [Ti04] units. The model of isomorphous substitution has been put forward on the basis of several independent characterization techniques, namely X-ray [21-23] or neutron [24-26] diffraction studies, IR (Raman) [52-57], UV-Vis [38,54,58], EXAFS, and XANES [52, 58-62] spectroscopies. 

Fig. 4 Osmium clusters supported on MgO(OOl) a OssC/MgisOs and b OS5C at a surface point Vs defect site [33] these were represented by density functional theory, and the samples were characterized by EXAFS spectroscopy, transmission electron microscopy, and other techniques [15]...

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. 

Deposition of NbOx species of different sizes on a silica support has been performed starting from organo metallic complexes as Nb(T] -C3Hs)4 for a monomer, [Nb(t -C5H5)H-p-(t) , ii C5H4)]2 for a dimer and Nb(OC2H5)s for a monolayer. All species were characterized by EXAFS, XANES, FT-ER, Raman, XPS and ESR techniques. Catalytic performances for conversion of ethanol are summarized in table 3. 

Different characterization techniques, for example X-ray diffraction,EXAFS, SEELFS, electron diffraction (LEED, RHEED, i SAED, and CBED ), and electron microscopy (HRTEM, WBDF ) give information about crystal structure, lattice distances, or morphology. All these techniques give average information about the shapes and the lattice distances of particle collections and of isolated particles. To obtain information about the particles at the atomic level, HRTEM is necessary. Other information about the surface structure of small particles can be obtained by Most HRTEM studies have been devoted to... 

As is evident from the various results discussed above, there is no general consensus regarding the location of titanium inside the MFI structure, notwithstanding more than a decade of research on this question. To characterize TS-1 and determine the titanium location, UV—vis, Raman, and Fourier transform infrared (FTIR) spectroscopy, EXAFS analysis. X-ray and neutron diffraction, and ah initio DFT calculations have aU been used. Some of the analytical difficulties encountered are associated with properties inherent to titanium, and the situation is better when the heteroatom has a higher atomic number such as tin. In this case, characterization techniques that depend strongly on the atomic number such as EXAFS analysis can be used to precisely define the site in the framework that is occupied by the heteroatom (see Section 2.4). 

This review will give a short introduction to the EXAFS and Ap XANES techniques and then focus on various investigations in PEM fuel cells. The advantages and limitations of XAS in fuel cell research will be compared to other characterization techniques, and then investigations of specific Pt-Ru anode catalysts presented. In the light of these recent results, the suitability of the XAS approach to reveal fundamental steps in the reaction mechanisms will be discussed. 

Different characterization techniques are used to get an insight into the location of transition metal ions in an aluminophosphate framework. Generally, the data on the cation location are collected with difficulty since the metal concentration is low. In this regard, it is necessary to use more than one method if a reliable conclusion is to be reached (ie, the simultaneous application of several physical techniques is recommended). The following characterization methods are commonly applied diffuse reflectance UV-vis spectroscopy (DRS), electron spin resonance (ESR), electron spin echo modulation (ESEM), infrared (IR), and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopies, as well as the nuclear magnetic resonance spectroscopy (NMR), Mossbauer spectroscopy and the X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption spectroscopy for fine structure (EXAFS) (167,168) and references therein). 

Despite the presence of organic counterparts and therefore higher phonon energies, Er emission may be observed in OIH as well. As an example, Er -doped diureasils were obtained from different carboxylic acid solvolysis routes [44]. Characterization techniques included X-ray absorption (EXAFS) at the Er Lm-edge, FTIR, and photoluminescence. Judd-Ofelt intensity parameters (Q ) were evaluated from absorption measurements together with the Er Iis/2 radiative lifetime (trad) and the peak emission cross section (cem)- Values so... 

It is no exaggCTation to say that the development of structure characterization techniques for molecular solids has revolutionized the study of organic solid state chemistry. It has allowed for the first time a rationalization of observed properties and transformations (including reactivity) which were previously unexplained by simple chemical means. The principal method used has been diffraction, particularly of X-rays, but also, more recently, of electrons and neutrons. This chapter will first give a basic introduction to crystal symmetry and then describe the use of X-ray, neutron, and electron diffraction, as well as of EXAFS and of vibrational spectroscopy in the study of molecular crystals. 

Eqiupment and techniques for NMR, FITR, Raman, EXAFS and HRTEM characterization are described in [5,6]. Equipment and XPS characterization technique and the methods for textural properties study are given in [7]. 

Elaborate synthetic approaches have been developed that enable significant control over the size and shape of palladium nanostructures. In order to understand the properties of the materials formed based on the preparation method, several characterization techniques have been used. These include electron microscopy, scanning probe microscopy (SPM), nuclear magnetic resonance (NMR) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, infrared (IR) spectroscopy, electrochemistry, X-ray diffraction (XRD), thermogravimetric analysis (TGA), electron diffraction, photoelectron spectroscopy, dynamic light scattering (DLS), extended X-ray absorption fine structure (EXAFS), BET surface area analysis andX-ray reflectivity (XRR). In the following section we will describe the information provided by each of these characterization techniques. 

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