Application of thermal analysis to the investigation of catalysts

A short review of the possibilities of application of thermal analysis to the investigation of catalysts is given: analysis of catalysts, investigation of the processes during the preparation of catalysts, desactivation of catalysts, and interaction of reactants or catalytic poisons with the catalysts. Several examples are mentioned.

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Zusammenfassung Eine kurze Übersicht über die Möglichkeiten des Einsatzes der Thermoanalyse zur Prüfung von Katalysatoren wird gegeben: Analyse der Katalysatoren, Prüfung der Vorgänge während der Herstellung von Katalysatoren, Inaktivierung von Katalysatoren, Wechselwirkungen zwischen Reagenzien oder Katalysatorengiften und den Katalysatoren. Eine Anzahl von Beispielen wird erwähnt.

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Résumé On piésente une rapide vue d'ensemble sur les possibilités d'application de l'analyse thermique à l'étude des catalyseurs: l'analyse des catalyseurs, l'étude des processus ayant lieu lors de la préparation des catalyseurs, la désactivation des catalyseurs, l'interaction de réactifs ou de poisons sur les catalyseurs. Plusieurs exemples sont mentionnés.

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The discretized flow on domains of attraction: a structural stability result

It is well known that, for stepsize sufficiently small, compactattractors of ordinary differential equations persist underdiscretization. The present paper describes the structure ofthe discrete-time dynamical system obtained via discretizationon A(M_h)\M_h where M_h is the approximate attractor and A(M_h)is its domain of attraction. The existence of a smooth embeddinginto a continuous-time parallelizable flow is proved. The constructioncan be used to define sections for discretizations and can beinterpreted as a justification of the method of modified equations.     

Measurement and modeling of peroxides half-life: A thermo-kinetic approach

Half-life values of organic peroxides at elevated temperature conditions are important in characterizing the reactivity and are often available in literature or through vendors. However, there is often lack of details/accuracy on methods used to obtain these values, as well as differences in methods across vendors and publications, thus resulting in discrepant reactivity profile. To address this, a method involving calorimetric experiment and thermo-kinetic modeling was developed. The current approach was applied on five peroxides samples to obtain kinetic parameters and estimate their half-life in the temperature range of interest. The measurements were performed by DSC under non-isothermal conditions on the dilute peroxide solutions (∼0.12 M in mineral oil) and the data were kinetically treated according to three model-based and one model-free kinetic equations. A very good agreement was found between the half-life calculated by all kinetic methods, but significant differences were noticed with the kinetic parameters reported in literature. Additionally, the obtained half-life results, based on non-isothermal measurements developed kinetic models, were validated through isothermal calorimetric testing. Given the accuracy and robustness of our results, the current method can be applied to estimate half-life of organic peroxides at elevated temperature conditions.     

Selectivity of bifunctional zeolite catalysts for the transformation of methanol to acetaldehyde and benzaldehyde

Methanol may be in the temperature range 350–500°C catalytically oxidized in one step to acetaldehyde and benzaldehyde over bifunctional catalysts containing the redox active component bi–Mo–O together with the HZSM-5 zeolite. In comparison with HZSM-5 zeolite alone (without the redox active component Bi–Mo–O) a 15 times higher selectivity to C₂+ aldehydes was attained. The analysis of the infrared spectra of the surface complexes of methanol formed in its interaction with the proton donor sites of the bifunctional catalyst at 400°C led to the suggestion of the probable mechanism of the oxidative transformation of methanol to higher aldehydes.

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350–500°C , , - Bi–Mo–O HZSM-5.

     

pH-responsive copolymer films by surface-catalyzed growth

We have engineered a new class of pH-responsive polymer films on gold surfaces by first developing a controlled, surface-catalyzed polymerization to prepare a copolymer film consistent with poly(methylene-co-ethyl acetate) and subsequently hydrolyzing the ester side chains to varying extents to yield carboxylic acids (denoted as PM-CO2H). When pH is increased, the acid groups become deprotonated or charged, dramatically increasing their water solubility and greatly altering the film properties. The carboxylic acid content within the copolymer film can be adjusted by changing the monomer concentration ratio used in the polymerization process or the length of time for the hydrolysis. We have designed PM-CO2H films to consist predominately (>95%) of polymethylene (PM) so that the film is hydrophobic in the uncharged state and, thereby, exhibits an extremely large pH-induced response in barrier properties once ionized. The effect of polymer composition on pH response was investigated by electrochemical impedance spectroscopy (EIS), reflectance-absorption infrared spectroscopy (RAIRS), and contact angle measurements. At a 1%-4% molar acid content, the copolymer film exhibits a 5 orders of magnitude change in its resistance to ion transport over 2-3 pH units. The pH at which this response begins can be tailored from pH 5 to pH 10 by decreasing the acid content in the film from 4% to 1%.