Effect of tetralol and tetralone in the tetralin oxidation with copper and chromium heterogeneous catalysts
Advancing the chemical engineering fundamentals
Catalysis - III (T2-13c)
Keywords: Tetralin oxidation, Cu/PVP, Cr/PVP catalyst, Tetralol
The oxidation of naphteno-aromatics molecules is important in the production of oxygenated diesel to reduce emissions, as well as for the Fine Chemistry Industry to produce ketone type derivatives. In particular the development of a selective catalyst able to perform this oxidation with high stability is an important area of research. In this paper we have studied the conversion of tetralin into tetralone – probe type molecules for the oxidation reactions- using air, Cu/PVP and Cr/PVP catalysts. The kinetics of the reaction was studied in a semi continuous stirred tank reactor in presence of different concentration of products (tetralone and tetralol), time on stream, and temperature to study their effect on catalyst activity, selectivity and stability. The products were analyzed by GC-MS and the solid characterized by chemical analysis, FTIR, CNMR, and ESR. We have found that tetralin is oxidized via adsorption on the metal and then transformed into an on-surface peroxide. That starts the cycle of oxidation which progresses towards ketone, alcohol and polyoxygenated products by reducing the metal. The presence of oxygen regenerates the active species. The work shows that for Cu/PVP (poly(4-vinylpyridine) catalysts, the presence of tetralol at a certain concentration inhibits the reaction (90ºC, atmospheric pressure, and bubbling air for 24 hours). If tetralol was added either at the beginning or after starting the reaction, this was inhibited; however if the selectivity to tetralone was high enough, i.e. tetralol is rapidly oxidized, the level of alcohol in the reaction media is always low, and the oxidation smoothly progresses. When Cr+3 is used instead of Cu+2, the catalytic behavior changes and the inhibiting effect of tetralol is lower. It was also verified that the partial reoxidation of tetralol occurred faster with Cr/PVP and that tetralone did not inhibit the reaction. FTIR characterization of both fresh and used catalysts revealed that the C-N stretching band shifts towards higher wavenumber due to metal coordination. The intensity of the IR band decreases as a result of tetralol adsorption onto the metal site. The preferential adsorption of Tetralol, results in gradual loss of activity since no metal leaching was detected. Catalysts were reused three times without an observable decrease in activity . However, the presence of adsorbed species retarded the start up of the reaction (induction period) when used catalysts were employed and no conversion was detected before 8 hours. The ESR analysis of the spent catalyst provides additional information to this respect. The paper discusses the mechanism of reaction.
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Presented Thursday 20, 16:00 to 16:20, in session Catalysis - III (T2-13c).
