Multi-step pyrolysis

Wu L, Nabae Y, Mraiya S, Matsubayashi K, Islam NM, Kurold S, Kakimoto M, Ozaki J, Miyata S (2010) Pt-liee cathode catalysts prepared via multi-step pyrolysis of Fe phthalocya-nine and phenolic resin for fuel cells. Chem Commun (Camb) 46(34) 6377-6379... 

Mechanism [5] was based on the results obtained from multi-step sequential pyrolysis experiments in an inert atmosphere (23). This mechanism [5] differs from [3], primarily in that [5] was proposed to be surface catalytic in nature, and that the reaction between the oxide particle surface and the organohalogen was considered only as the first step, initiating the process leading to the eventual formation of volatile antimony species. 

The pyrolysis of water washed beech wood can only be described by multi-step formal models. The most successful approach is a mechanism with three parallel reactions, as commonly used throughout the literature ... 

The pyrolytic process is commonly performed In an inert atmosphere or even at low pressure. However, it is not always possible to perform the process in gas phase (such as for polymers). Even in gas phase, but mainly in condensed phase, a series of chemical interactions may occur between different pyrolysis products. This, in addition to the multi-step characteristics, makes the result of the pyrolytic process extremely complex. The individual reaction types taking place during pyrolysis can, however, be studied independently. 

Concentration techniques in GC are used mainly for trace analysis. Pyrolysis commonly generates enough material for a GC analysis even when a very small amount of sample is taken for analysis. For this reason, concentration techniques are not frequently associated with Py-GC. However, in some instances it is necessary to analyze both the volatile compounds that are generated at mild heating of the polymer (sometimes below 100° C) and also the typical pyrolysis products. Several two-step (or multi-step) experiments were reported [40c] that allow this type of analysis. 

In solution, [Os5C(CO)i4] is obtained in low yields (ca 37%) from [Os3(CO)i2] by a multi-step process involving pyrolysis of the latter cluster to give [Os5C(CO)i5] followed by reaction with Na2C03 in methanol. ... 

Therefore we attempted to simulate advanced pyrolysis using a multi-step model (MSM). This model was developed using TGA- and DSC-derived kinetic coefficients, determined for chemically and thermally treated oil shale samples by modelling particular reaction steps. The MSM is based on the reaction scheme shown in Fig. 4-116 which displays a series of parallel and consecutive first order reactions. K and B denote the kerogen and bitumen originally present in the oil shale B, B, and to /Jj are non-volatilized intermediates and products (solids and liquids) to are volatilized products (gases and vapors) and/j to/jg are the stoichiometric coefficients that fulfil the condition ... 

These differences in pyrolysis behavior of the oil shales can be explained by structural differences in the corresponding kerogen types. The kerogens of oil shales Aleksinac, Estonia, and Korea are associated with type I, which is of predominantly paraffinic nature. Oil shale Knjazevac is associated with kerogen type HI, which is of predominantly aromatic nature. Thus the multi-step model appears to be suitable for simulating the pyrolysis of oil shales with kerogen type I, but cannot be properly adjusted for the other kerogen types. 

Complex, Multi-step, or Non-concerted Pericyclic Processes.—Pyrolysis of labelled tricyclo[8,2,2,0 ]tetradeca-3(8),ll,13-triene (264 -n = D) at 180°C led to the formation of unlabelled 1,2-dimethylenecyclohexane, [ H jbenzene, 2,3-dideuterio-butadiene, and tetralin labelled at the four aromatic ring positions. The labelling pattern suggests that the 1,2-dimethylenecyclohexane and benzene derive from a common precursor, as do the butadiene and tetralin. The suggested reaction pathway is shown in Scheme 3 and involves preliminary [1,3] sigmatropic or biradical rearrangement of (264) into (265), which in turn is transformed into (266) by intramolecular [4 +2] cycloaddition retro-[4 +2] addition is considered to convert... 

The molecular square 12.1b - i.e., [l.l.l.ljparacyclophane - has been synthesized using an adventurous multi-step procedure, which involves flash vacuum pyrolysis at 550 °C and a Diels-Alder cycloaddition to form the... 

Despite the fact that direct analysis methods exclude a cost-intensive separation step overall analysis cost may still be high, namely by the need for more sophisticated instrumentation (allowing for a physical rather than chemical separation of components) or extensive application of chemometric techniques. The wide variety of additives that are commercially available and employed complicate spectroscopic data analysis. For multicomponent analysis some kind of physical separation of additive signals is often quite helpful, e.g. based on mobility (as in LR-NMR or NMRI), diffusion coefficient (as in DOSY NMR), thermal behaviour (as in a thermal analysis and pyrolysis techniques) or mass (as in tandem mass spectrometry). The power of signal processing techniques (such as multi-wavelength techniques, derivative spectrophotometry) is also used to the fullest extent. 

Maia et al. [332] eliminated interferences in the direct determination of Hg in powdered coal samples by means of analyte transfer during the pyrolysis step from the platform to a graphite tube wall. This graphite tube was permanently modified with Pd, and detection limits in the range of 0.025-0.05 pg/g were obtained. In simultaneous multi-element determinations of Cu, Cr, Al, and Mn in urine, Pd was also very successfully used as a matrix modifier [333]. The use of Pd as a modifier, and also in combination with dynamic background correction techniques such as the Smith-Hieftje technique (see Section 4.6.3), enables a considerable enhancement of the analytical accuracy of AAS, as shown in the case of As determinations [334]. 

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