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Molecules 2015, 20(2), 2529-2535; doi:10.3390/molecules20022529

Propane Dehydrogenation Catalyzed by ZSM-5 Zeolites. A Mechanistic Study Based on the Selective Energy Transfer (SET) Theory

Chemical Engineering II, University of Lund, P.O. Box 124, SE-22100 Lund, Sweden
Academic Editor: Geoffrey Price
Received: 18 November 2014 / Revised: 4 January 2015 / Accepted: 27 January 2015 / Published: 2 February 2015
(This article belongs to the Special Issue Zeolite Chemistry)
View Full-Text   |   Download PDF [759 KB, uploaded 2 February 2015]   |  

Abstract

Experimentally determined activation energies of propane dehydrogenation catalyzed by ZSM-5 zeolites have been used to test the SET theory. The basis of this theory is that the catalyst system transfers vibrational energy via a resonance process to a specific vibration mode of the reacting molecule. Being excited up to a certain number of vibrational quanta the molecule is brought to reaction. By analyzing the above-mentioned activation energies we found the wave number of this “specific mode” to be 1065 cm−1. This is very close to the rocking vibration of propane (1053 cm−1). We suggest that the propane molecule reacts when excited so that the CH3 group has been forced towards a flat structure with a carbon atom hybridization that is more sp2 than sp3. Consequently there is no way for three H-atoms to bind to the carbon and one of them must leave. This is the starting point of the reaction. The isokinetic temperature of the system was found as Tiso = 727 ± 4 K. From the SET formula for Tiso when both energy-donating (ω) and energy-accepting (ν) vibrations have the same frequency, viz., Tiso = Nhcν/2R, we obtain ν = ω = 1011 ± 6 cm−1. This agrees rather well with the CH3 rocking mode (1053 cm−1) and also with asymmetric “TO4” stretching vibrations of the zeolite structure (ω). View Full-Text
Keywords: propane dehydrogenation; zeolite catalysis; SET; selective energy transfer; activation energies; molecular vibrations; resonance; vibrational quantum numbers; isokinetic temperature propane dehydrogenation; zeolite catalysis; SET; selective energy transfer; activation energies; molecular vibrations; resonance; vibrational quantum numbers; isokinetic temperature
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Larsson, R. Propane Dehydrogenation Catalyzed by ZSM-5 Zeolites. A Mechanistic Study Based on the Selective Energy Transfer (SET) Theory. Molecules 2015, 20, 2529-2535.

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