Pyrolysis Mossbauer spectroscopy

The types of macrocycles most studied in which the active metal center is believed to be retained include Co, Fe, Ru porphyrins and related macrocycles. In these studies the optimal pyrolysis temperature is often reported to be between 400-800 °C. Above these temperatures, the active site begins to be destroyed, and activity decreases.49 An array of characterization techniques have been used to support these claims. XPS analysis has demonstrated that at the highest activity of samples, the surface composition of metal and nitrogen is also at its highest.78,96 Above the optimal treatment temperature, nitrogen and metal begin to disappear from the surface. Furthermore, Mossbauer spectroscopy and XAS have been used to... 

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. 

Our early work has demonstrated that MOssbauer spectroscopy is a useful means for detecting changes in oxidation (electronic) states and structures induced by radiolysis, photolysis and pyrolysis in solid iron compounds (1-6). In a more detailed Mt)ssbauer/IR study of the photolysis of potassium tris(oxalato)-ferrate(111), we characterized several products observed in solids under a variety of conditions and proposed a mechanism with the following sequence of photolytic and subsequent reactions in such systems (7) ... 

Another comparison can be made with the Mossbauer spectroscopy results of Williamson et al. (8). For "TOSCO-II shale" with a grade of 40 gal/ton, they report that about 75% of the pyrite is converted to pyrrhotite during Fischer assay. Considering that some of this sulfur may be incorporated into the oil and that some H2S is produced by kerogen pyrolysis, this result agrees with the results shown in Figure 12. 

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... 

During the 1990s, van Veen and collaborators mainly studied the electrochemical kinetics of oxygen reduction. Their results are presented in Sect. 3. These mechanistic studies were, however, always based on the model in which the C0-N4 or Fe-N4 moieties of the respective macrocycles were retained intact at all pyrolysis temperatures. Their last contribution to the molecular structure of the catalytic site was a study in 2002 of catalysts obtained by adsorption of iron tetramethoxyphenyl porphyrin chloride (ClFeTMPP) on Vulcan XC-72, heat treated between 325 and 800°C in inert atmosphere, and characterized by EXAFS and Mossbauer spectroscopy, as well as by cyclic voltammetry". The loading of these catalysts was 7 wt% chelate ( 0.5 wt% Fe). 

As an alternative to wet ehemical routes of analysis, this monograph deals mainly with the direct deformulation of solid polymer/additive compounds. In Chapter 1 in-polymer spectroscopic analysis of additives by means of UV/VIS, FTIR, near-IR, Raman, fluorescence spectroseopy, high-resolution solid-state NMR, ESR, Mossbauer and dielectrie resonance spectroscopy is considered with a wide coverage of experimental data. Chapter 2 deals mainly with thermal extraction (as opposed to solvent extraction) of additives and volatiles from polymerie material by means of (hyphenated) thermal analysis, pyrolysis and thermal desorption techniques. Use and applieations of various laser-based techniques (ablation, spectroscopy, desorption/ionisation and pyrolysis) to polymer/additive analysis are described in Chapter 3 and are critically evaluated. Chapter 4 gives particular emphasis to the determination of additives on polymeric surfaces. The classical methods of... 

---