Situ Mossbauer Spectroscopy

A key factor in the design of electrochemical cells for in situ transmission Mossbauer measurements is to decrease the attenuation of the y-ray beam, so as to reduce the time required for spectra acquisition. This may be accomplished by selecting low-absorption materials for windows and electrode supports and by minimizing the amount of electrolyte in the beam path. Radiation in the keV range penetrates rather deeply into matter, and therefore small amounts of rather high-Z elements can be tolerated without seriously comprising the overall cell transmission. As a means of illustration, the half-absorption length for 14.4-keV X-rays in water is about 3.5 mm, which is approximately 

5 times larger than for 6.4-keV X-rays. From an experimental viewpoint, the decrease in intensity of the 14.4-keV y-rays for aqueous electrolytes is compensated to a certain extent by the higher absorbance of the 6.4-keV X-rays as it makes the use of an external filter unnecessary. 

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In Situ Mossbauer Spectroscopy under Reaction Conditions... 

Applications of In Situ Mossbauer Spectroscopy to the Study of Transition Metal Oxides... 

This work summarizes some applications of in situ Mossbauer spectroscopy to the study of certain aspects of the electrochemistry of iron and iron containing transition metal oxides. A number of illustrations of the use of this technique to the investigation of a wide variety of interfacial phenomena may be found in two recent monographs. (2 ... 

In-Situ Mossbauer Spectroscopy Under Reaction Conditions 141... 

Supported non-framework elements, as well as substituted or doped framework atoms, have been important for zeolite catalyst regeneration. By incorporating metal atoms into a microporous crystalline framework, a local transition state selectivity can be built into the active site of a catalytic process that is not readily attainable in homogeneous catalysis. The use of zeolites for carrying out catalysis with supported transition metal atoms as active sites is just beginning. The local environment of transition metal elements as a function of reaction parameters is being defined by in situ Mossbauer spectroscopy, electron spin echo measurements, EXAFS, and other novel spectroscopic techniques. This research is described in the second part of this text. 

Well dispersed iron oxide on silica of a specific surface area of 50 m /g has proven to be a very suitable catalyst for the selective oxidarion of hydrogen sulfide to elemental sulfur. Under reaction conditions the iron oxide is transformed into ironCII sulfate as revealed by X ray diffraction, Mbssbauer spectroscopy, and wet chemical analysis. The presence of an iron(III) component as observed by ex situ Mossbauer spectroscopy can not be excluded. Although the transfomiation of iTon(]Il) oxide into iron(II) sulfate causes initial deactivation, the increase in selectivity (96%) results in high sulfur yields (up to 94%). 

The aim of this chapter is to provide a brief background to Mossbauer spectroscopy within the context of phase transformations. The relevant parameters are summarised and the effect of temperature and pressure are discussed, particularly with reference to identifying phase transformations and characterising the electronic and structural environment of the Mossbauer nuclei. Instrumentation is summarised, particularly as it relates to in situ measurements of phase transformations, and a brief survey of applications is given. The appendix includes a worked example that illustrates the methodology of investigating a phase transformation using in situ Mossbauer spectroscopy. Numerous textbooks and review chapters have been written on Mossbauer spectroscopy, and a selection of the most relevant ones as well as some useful resources are listed in Table 1. 

Liquefaction. Montano et al. [ ] have investigated the transformation of pyrite to pyrrhotite in coal liquefaction environments. They conducted in situ Mossbauer spectroscopy measurements on coals maintained at 1.24 MPa nitrogen pressure and observed changes in the isomer shift at approximately 300°C that signalled the beginning of the transformation of pyrite to pyrrhotite. The transformation accelerated between 300 and 400°C, and from 20 to 80 percent of the pyrite in four different coals was transformed after one hour at 440°C. From examination of both the in situ spectra and the spectra of cooled residues, they concluded that the pyrrhotite underwent covalent bonding to the coal molecules, causing a catalytic effect on coal liquefaction. 

Table 12 Results of in situ Mossbauer spectroscopy on (0-1) type Sn-Pt/Si02 catalyst used in room temperature oxidation of CO (Reproduced from ref. 139 with permission)... 

According to the results of in situ Mossbauer spectroscopy the formation and stabilization of the PtSn (1 1) alloy phase has been shown under condition of room temperature CO oxidation (see results presented in Table 12). One of the most active surfaces of the PtSn (1 1) alloy phase, the (110) phase, was chosen to model the interaction of the CO molecule with the metal surface. The computer modeling and the related calculations were made on density functional level. In this model a small cluster of the (110) surface of the PtSn phase as shown in Figure 25a, was selected in order to calculate and investigate the interaction of the CO molecule with the metal surface. 

Fig. 5.92. Electrochemical cell for in situ Mossbauer spectroscopy in the transmission mode [538]...

Fierro, C.A., M. Mohan, and D.A. Scherson (1990). In situ Mossbauer spectroscopy of a species irreversibly adsorbed on an electrode surface. Langmuir 6,1338-1342... 

Trapp S, Limbach CT, Gonser U et al (1995) Enhanced compressibUity and pressure-induced structural changes of nanocrystaUine iron in situ Mossbauer spectroscopy. Phys Rev Lett 75 3760-3763... 

Feder, R, F. Trolard, G. Klingelhdfer, and G. Bourrie. 2005. In situ Mossbauer spectroscopy Evidence for green rust (fougerite) in a gleysol and its mineralogical transformations with time and depth. Geochimica et Cosmochimica Acta 69, no. 18 4463-4483. doi 10.1016/j.gca.2005.03.042. 

The aim of this chapter is to report on recent advances in the in situ Mossbauer spectroscopy with synchrotron radiation on thin films that became possible due to the instrumentation developments at the nuclear resonance beamline ID 18 of the ESRF. After a detailed description of the beamline and of the UHV system for in situ experiments, a brief introduction into the basic NRS techniques is given. Finally, the application of these techniques to investigate magnetic, diffusion, and lattice dynamics phenomena in ultrathin epitaxial Fe films deposited on a W(l 10) substrate is presented and discussed. 

The furnace for in situ Mossbauer spectroscopy put between 7-rays source and detector of the Mossbauer spectrometer. 

The states of Fe in Ir-Fe/Si02 catalyst have great effects on the catalytic performance in PROX reaction, and the promotional role of Fe is always associated with the presence of H2 in the reaction stream. By employment of quasi in situ Mossbauer spectroscopy, a clear picture, which shows the changes of different Fe species with increasing the H2 concentrations from 0 to 40%, is obtained. 

G. Klingelhofer, G.M. da Costa, A. Prous, B. Bernhardt, Rock paintings from Minas Gerais, Brasil, Investigated by in situ Mossbauer spectroscopy. Hyperfine. Interact. C 5, 423-426 (2002)... 

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