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EnglishWe report here about the results of a study on the oxidation of cyclohexanone to adipic acid with air, catalysed by Keggin-type polyoxometalates of composition H3+xPMo12-xVxO40 (x=1 and 2), which was carried out in a semi-continuous stirred-tank reactor. It was found that when conducted in the presence of a water-only solvent, the reaction proceeds with a redox mechanism, in which the step of reoxidation of the reduced POM by oxygen is rate-limiting. When, however, the reaction was carried out with an acetic acid co-solvent, a radical-chain autoxidation mechanism prevailed, especially when very low amounts of catalyst were used. Autoxidation overlapped with the redox mechanism when the catalyst-to-cyclohexanone ratio was increased. Moreover, the composition of the polyoxometalate, that is, the number of V atoms per Keggin unit, affected the relative importance of the two mechanisms. The selectivity to adipic acid achieved was a function of the reaction mechanism, but also was affected by cyclohexanone conversion, due to the presence of a complex reaction network.
| Titolo: | Evidence for the presence of alternative mechanisms in the oxidation of cyclohexanone to adipic acid with oxygen, catalysed by Keggin polyoxometalates | |
| Autore/i: | CAVANI, FABRIZIO; FRATTINI, ALESSANDRA; MAZZINI, ANDREA; RAABOVÁ, KATERINA; S. Alini; P. Accorinti; P. Babini | |
| Autore/i Unibo: | ||
| Anno: | 2010 | |
| Titolo del libro: | XVI Congresso nazionale di catalisi GIC 2010 "Catalysis between Innovation and atrdition: new challenges and new opportunities for University and Industry" | |
| Pagina iniziale: | O16 | |
| Pagina finale: | O16 | |
| Abstract: | We report here about the results of a study on the oxidation of cyclohexanone to adipic acid with air, catalysed by Keggin-type polyoxometalates of composition H3+xPMo12-xVxO40 (x=1 and 2), which was carried out in a semi-continuous stirred-tank reactor. It was found that when conducted in the presence of a water-only solvent, the reaction proceeds with a redox mechanism, in which the step of reoxidation of the reduced POM by oxygen is rate-limiting. When, however, the reaction was carried out with an acetic acid co-solvent, a radical-chain autoxidation mechanism prevailed, especially when very low amounts of catalyst were used. Autoxidation overlapped with the redox mechanism when the catalyst-to-cyclohexanone ratio was increased. Moreover, the composition of the polyoxometalate, that is, the number of V atoms per Keggin unit, affected the relative importance of the two mechanisms. The selectivity to adipic acid achieved was a function of the reaction mechanism, but also was affected by cyclohexanone conversion, due to the presence of a complex reaction network. | |
| Data prodotto definitivo in UGOV: | 25-feb-2011 | |
| Appare nelle tipologie: | 4.02 Riassunto (Abstract) |
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