Mossbauer spectroscopy decomposition

Electrobalances suitable for thermogravimetry are readily adapted for measurements of magnetic susceptibility [333—336] by the Faraday method, with or without variable temperature [337] and data processing facilities [338]. This approach has been particularly valuable in determinations of the changes in oxidation states which occur during the decompositions of iron, cobalt and chromium oxides and hydroxides [339] and during the formation of ferrites [340]. The method requires higher concentrations of ions than those needed in Mossbauer spectroscopy, but the apparatus, techniques and interpretation of observations are often simpler. 

Properties of FeCr,o solid samples have been studied by X-ray diffraction, 57Fe Mossbauer spectroscopy and magnetic measurements to stimulate the interaction of Fe with fullerene. FeCr,o samples have been prepared by decomposition of the 1,3-dipolar cycloadduct of the fullerene and ferrocene nitrile oxide. The components exhibit super paramagnetic properties originating from an interaction between FeCr,o complexes within the nano-particles. Each nano-particle consists of hundreds to thousands complexes (546). 

The present paper focuses on the interactions between iron and titania for samples prepared via the thermal decomposition of iron pentacarbonyl. (The results of ammonia synthesis studies over these samples have been reported elsewhere (4).) Since it has been reported that standard impregnation techniques cannot be used to prepare highly dispersed iron on titania (4), the use of iron carbonyl decomposition provides a potentially important catalyst preparation route. Studies of the decomposition process as a function of temperature are pertinent to the genesis of such Fe/Ti02 catalysts. For example, these studies are necessary to determine the state and dispersion of iron after the various activation or pretreatment steps. Moreover, such studies are required to understand the catalytic and adsorptive properties of these materials after partial decomposition, complete decarbonylation or hydrogen reduction. In short, Mossbauer spectroscopy was used in this study to monitor the state of iron in catalysts prepared by the decomposition of iron carbonyl. Complementary information about the amount of carbon monoxide associated with iron was provided by volumetric measurements. 

The results of Mossbauer spectroscopy investigations of Fe(C0)5 decomposition on Ti02 samples pretreated in three different fashions are given in Table I. These three samples were pretreated in a manner intended to produce different populations of Ti + ions and hydroxyl groups on the surface of the support. This is explained in the discussion section. 

In Table II, it can be seen that decomposition at low temperatures left a CO/Fe ratio on the surface of between 0.8 and 1.3. A reasonable explanation for the high CO to iron ratios on the surfaces, given the fact that Mossbauer spectroscopy studies show that a large fraction of the iron is oxidized, is that iron subcarbonyl species are stable on the surface at 383 K. This is true since CO does not adsorb strongly on iron oxides (35). 

The [TPPFeCl] -NaBITi system in diglyme has been shown to perform remarkably efficiently as a catalyst for the reduction of nitrobenzenes to anilines. Although both TPPCo and TPPMnCl also catalyze the reduction of p-chloronitrobenzene to jo-chloroaniline, their catalytic activities are much lower thanthatofTPPFeCl. Anothertype of reduction catalyst, in this case of dioxygen to water, begins with carbon-supported chloroiron(ni) tetramethoxyphenylporphyrin, which is then heat-treated at 900 °C for one h." This causes decomposition of the porphyrin to produce metallic, carbidic and oxidic iron, as detected by Mossbauer spectroscopy. The active... 

Eu-Y shows essentially no activity for NjO decomposition, and Eu Mossbauer spectroscopy indicates that the Eu does not undergo reduction in 1 atm of flowing Hj at TOOK for 5 h. However, when Fe is present, reduction of Eu does occur. Unfortunately, Eu does not have a large quadrupolar splitting so that no information concerning the location of these cations is available from the Mossbauer spectroscopy. 

Advances using EXAFS coupled with Mossbauer spectroscopy have given better insight into the location, coordination shell, and oxidation states of multimetallic ensembles on supporting oxides. Still, relatively little is known at present about the actual shapes and structures of the mixed metal species resulting from the thermal decomposition of the precursor clusters. In particular, the extent to which the original cluster framework, metal composition, and ligand coordination is maintained is unclear. 

The thermal decomposition reactions of several other layer-lattice clay minerals have also been studied by Al NMR in conjunction with other nuclides. These include a montmorillonite which contained sufficient iron for a complementary study to also be made by Mossbauer spectroscopy (Brown et al. 1987), Fuller s Earth (another... 

Mossbauer spectroscopy was used to examine the chars produced from the pyrolysis reaction. The results, which deal with bulk decomposition compared to the microscopic view obtained from SEM, tended to confirm those obtained above for the initial temperature of decomposition. However, a number of major differences were observed. Pyrite was always a component in the spectra, even those of chars produced at 650°C. In addition the three coals could be classed in two groups Prince and Lingan behaved similarly with the formation of pyrrhotites at around 450-500°C on the other hand No. 26 coal showed little sign of any reaction product even at 650°C (Figs. 2-4), an anomaly considering the fact that selected grains of size 10-20 pm would have been completely reacted. 

Mossbauer spectroscopy. Mossbauer spectroscopy is a unique method for aluminosilicates with relatively high Fe content, giving data on all iron forms present [15,20,21]. There are some concentration limits for low iron containing materials but these could be overcome using Fe isotopic enriched samples. After its decomposition in individual subspectra the observed spectrum provided data on iron oxidation states and different coordinations. 

It is also interesting to note that the decomposition of pseudobinary intermetallic compounds (LaNi4Fe and CeNis-jCo ) leads to the formation of bimetallic transition metal particles which display different selectivities than the catalysts derived from the related binary intermetallic compound (Paul-Boncour et al. 1991, France and Wallace 1988). The characterization of the bimetallic particles by XRD, Mossbauer spectroscopy and magnetism indicated that their composition was close to that of the starting alloy. 

Another experimental probe of BD versus a donation is Mossbauer spectroscopy of a series of iron complexes.54 Plots of isomer shift versus quadrupole splitting for [FeH(PPXL)]+ for L such as H2, N2, CO, MeCN, and Cl show that the H2 complexes fell way off the straight line defined by the a donors, more so than even CO. It was concluded that it bonding in H2 complexes is very significant, more so than in N2 or CO complexes. Theoretical analyses concur that H2 is a much better -acceptor ligand than early calculations showed. More quantitative measures of BD are provided by charge decomposition analysis (CDA) and extended transition state (ETS) analysis.41,55-60... 

The original report of the preparation of [Fe"Cp2l°[TCNE]° described that it exhibited ferromagnetic behavior. A subsequent reinvestigation revealed the presence of Fe(lll) via Fe Mossbauer spectroscopy, and that decomposition induced from the grinding synthesis undoubtedly was the source of the magnetic impurity. " ... 

Zeolites, NaX and NaY, partially exchanged with 5 wL-% Fe were reduced with sodium vapour produced by the thermal decomposition of sodium azide. The metalhc iron particles produced had dimensions of a few nanometers, as revealed by Mossbauer spectroscopy and various other techniques [20]. 

Kuw] Kuwano, H., Nakamura, Y., Ito, K., Yamada, T, Spinodal Decomposition of Fe-Cr-Ni Alloys Studied by Mossbauer Spectroscopy , Nuovo Cimento, 18D, 259-262 (1996) (Calculation, Experimental, Phase Relations, 5)... 

On the other hand, based on pyrolysis mass spectrometry, pyrolysis gas chromatography, microanalysis and mainly Mossbauer spectroscopy ", Yeager and his collaborators who were mainly working at high pyrolysis temperatures (800-850°C) disagreed with the previous school. They concluded that the decomposition of Me-N4 macrocycles starts at about 400-500°C. At 800°C, despite the fact that heat-treated samples retain more than 80% of the nitrogen atom content measured for the untreated... 

IVC] Calorimetry, Mossbauer spectroscopy 5.1-14.3 mass% Co, 4.95-12.92 mass% Cr, Fe = bal. bcc phase spinodal decomposition... 

Alel] Mossbauer spectroscopy, transmission electron microscopy. X-ray diffraction 25-35 mass% Co, 1.5-2 mass% Cr, Fe = bal. 300-525°C spinodal decomposition of bcc phase... 

Bel] X-ray diffraction, Mossbauer spectroscopy 25 mass% Co, 15 mass% Cr, Fe = bal. spinodal decomposition in bcc alloy... 

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