The effect of water on the selective gas phase oxidation of acrolein to acrylic acid on a Mo/V/W mixed oxide catalyst was studied by performing steady‐state isotopic transient kinetic analysis experiments with H218O. Experiments were performed in the temperature range of 90–345 °C at ambient pressure. It could be shown that acrolein exchanges its carbonylic oxygen with oxygen from water even at low temperatures (<200 °C), at which no acrolein oxidation occurs. At higher temperatures (>200 °C), the oxygen atoms of the water molecules incorporate into all oxidation products such as acrylic acid, carbon monoxide, and carbon dioxide.
Oxidation of acrolein to acrylic acid on Mo/V/W-mixed oxide catalysts has been studied by means of the isotopic exchange method steady-state isotopic transient kinetic analysis (SSITKA). As a result of these isotopic exchanges performed with 16 O 2 and 18 O 2 , some new mechanistic details could be obtained. Acrolein exchanges its oxygen with oxygen of the mixed oxide catalyst. Additionally, the kinetics of the different isotopologues is significantly influenced by oxygen exchange reactions between the surface and the bulk sites. From the SSITKA results, an extended reaction model has been deduced. Thus, the experimentally gained data of the individual isotopologue kinetics could be verified by modeling.
Nitriles act as important intermediates for the chemical industry and are accessible on a large scale through hydrocyanation or ammonoxidation. Nitrile hydrolysis yields amides and acids used in various applications. The conventional nitrile hydrolysis process relies on stoichiometric amounts of mineral acid or base which inherently deliver great amounts of waste brine. Improving this process towards green chemistry would require reaction conditions which can provide technically significant results without the use of catalysts. Under these conditions, the hydrolysis of valeronitrile in pure supercritical water was investigated. The experiments were performed in a continuous high pressure laboratory-scale apparatus at a temperature between 400 and 500 degrees C, 30 MPa pressure and maximal residence time of 100 s. Nitrile conversion and valeric acid selectivity greater than 90% were achieved.
Mittels der Isotopenaustauschmethode SSITKA (steady‐state isotopic‐transient kinetic analysis) ergaben sich Rückschlüsse zum Mechanismus der Partialoxidation von Acrolein zu Acrylsäure an Mo/V/W‐Mischoxidkatalysatoren. Der Isotopenaustausch erfolgte mit den beiden Sauerstoffisotopen 16O2 und 18O2. Dabei findet am Katalysator ein Austausch des Carbonylsauerstoffs im Acrolein mit Festkörpersauerstoff statt. Zusätzlich wird die Kinetik der unterschiedlichen Isotopologenspezies durch eine Austauschreaktion von Sauerstoff zwischen belegten und unbelegten Zentren an der Oberfläche und in der Volumenphase des Katalysators signifikant beeinflusst. Gestützt durch einen erweiterten Modellvorschlag zum Mechanismus konnten über Simulationen die experimentell gewonnenen Isotopologenkinetiken verifiziert werden.
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