Catalysts thermal behavior

Besides the prediction of calcination temperatures during catalyst preparation, thermal analysis is also used to determine the composition of catalysts based on weight changes and thermal behavior during thermal decomposition and reduction, to characterize the aging and deactivation mechanisms of catalysts, and to investigate the acid-base properties of solid catalysts using probe molecules. However, these techniques lack chemical specificity, and require corroboration by other characterization methods. 

Figure 11.24 Simulation of the thermal behavior of a catalyst in a multitube test reactor. (AH > 100 kJ/mol, Tiri et 523 K, Treactor 523 K, porosity 80%, /.bed 3.0W/mK, GHSV 10000 h-1, reactor tube geometry 0.11 x 0.007 m).

Fig. 2.12 Simulation of the thermal behavior of a catalyst in a multitube test reactor. Though the reaction is highly exothermic, no thermal contamination of neighboring reactor sites is experienced. DH >100 kj mol-1 inlet 523 K, reactor 523 K. Porosity 80% bed 3.0Wmf GHSV 10000 h" 0.11x0.007 m.

The first array-based technique was designed specifically to study reactions on solid phase catalysts as IR thermography.9,19 This approach utilizes IR sensitive FPA detectors to measure the temperature of catalysts under reaction conditions. This approach has the advantages of a theoretical high thermal sensitivity, typically several tens of millikelvin, and the ability to study both endothermic and exothermic reactions. The main disadvantage of this approach, however, is the lack of chemical information. It must be assumed that the temperature change is associated entirely with the desired reaction pathway. The presence of unexpected side reactions will not be detected in this approach, as long as they have similar thermal behavior as the reaction under study. 

The Michael addition of methyl a-acetamidoacrylate (196) with pyrrole (1) under silica-supported Lewis acid (Si(M) Si(Zn), Si(Al) and Si(Ti)) assisted by microwave irradiation (MW) afforded the alanine derivatives 395 and 396 dependent on the reaction conditions (Scheme 81) [153]. Both MW and thermal activation for pyrrole gave only Michael product 396, whereas alanine derivatives 395, which are the a-Michael addition product, and 396 were observed with A1 and Ti-catalyst. This behavior shows that aluminium and titanium Lewis acids can form a new acceptor in an irreversible way. The Si(M) or p-TsOH catalyzed reactions of N-benzylpyrrolc 397 with the acrylate 196 under MW gave the product 398 as sole product. The reaction yield has been increased by using a catalytic amount of p-TsOH (Scheme 82). 

Thermal Behavior of Catalyst Particles and Pellet Runaway... 

Techniques such as DTA, TG or DSG study the thermal behavior of a catalyst as it undergoes heating at a constant rate. For example, DTA relies on the measurement, as function of time, of the difference between the temperature of the sample (Tj) and that of a reference material (rj, upon heahng both materials in a furnace. AT = T — is related to the heat evolved (or absorbed) by the sample at a time when the sample undergoes an endothermic or exothermic reaction. In the TG and DTG methods, the variation with time of the sample mass (dm or dm/dt) is measured as a function of temperature while the sample is heated at a constant rate [7]. 

Balbontin, G. Dainelli, D. Galimberti, M. Paganetto, G. Thermal behavior of highly stereoregular syndiotactic polypropylene from homogeneous catalysts. Makromol. Chem. 1992, 193, 693. 

Thermal behavior of the films and film catalysts are shown in Fig. 5. Tg of PES-MC was 236°C whereas that of PMo-PES-MC was 219°C. Tg of PMo-PSF-MC was not detected from a room temperature to 350°C. However, considering that the physical state of PMo-PSF-MC was changed after the reaction over 170°C and became fragile, Tg of PSF was supposed to be lowered after blending with PMo. The decreased Tg of PSF and PES after blending with PMo means that there is no... 

The first metallocene -and the first catalyst in general- able to produce highly syndiotactic polypropene (s-PP), was the Q-symmetric Me2C (Cp) (9-Flu)-ZrCp (Cs-1 in Chart 18)." The behavior of this catalyst and the characterization of 5 pp397-407 have been extensively reviewed. A number of studies on the thermal behavior, crystal structures, and morphology of 5-PP have appeared in the litera-... 

Rocchiccioli-Deltcheff, C., Amirouche, M., Herve, G., Fournier, M., Che, M., Tatibouet, J.M. 1990. Structure and catalytic properties of silica-supported polyoxomolybdates. 2. Thermal behavior of unsupported and silica-supported 12-molybdosilic acid catalysts from IR and catalytic reactivity studies. Journal of Catalysis 126(2) 591-599. 

A. Bolognesi, W. Poizio, G. Zhuo and T. Ezquerra. The thermal behavior of poly(3-octylthienylene) synthesized by an Ni-based catalyst DSC, optical microscopy and XRD analyses. Ear. Polym. J. 32(9), 1097-1103 (1996). 

During the last two decades, the DTA-EGD-GC on-line coupled simultaneous apparatus has been applied in the following fields solid catalysts [77-79], anti-oxidation additives in petroleum [80], thermal characteristics of coal [81-83], mineralogy [60, 84-87], organometallic chemistry [88-90], polymer chemistry [91], pharmaceutical chemistry [92], environmental protection chemistry and the thermal behavior of all kinds of chemical compounds [62, 63]. Numerous DTA-EGD-GC curves are shown in Chapter 13. 

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