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Oxidative Dehydrogenation of Propane over a VO2-Exchanged MCM-22 Zeolite: A DFT Study

Authors

  • Sippakorn Wannakao,

    1. Laboratory for Computational and Applied Chemistry, Department of Chemistry, Faculty of Science and Center of Nanotechnology, Kasetsart University Research and Development Institute, Kasetsart University, Bangkok 10900 (Thailand), Fax: (+66) 2-562-5555
    2. NANOTEC Center of Excellence, National Nanotechnology Center, Kasetsart University, Bangkok 10900 (Thailand)
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  • Dr. Bundet Boekfa,

    1. NANOTEC Center of Excellence, National Nanotechnology Center, Kasetsart University, Bangkok 10900 (Thailand)
    2. Center for Advanced Studies in Nanotechnology and its Applications in Chemical, Food, and Agricultural Industries, Kasetsart University, Bangkok 10900 (Thailand)
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  • Dr. Pipat Khongpracha,

    1. Laboratory for Computational and Applied Chemistry, Department of Chemistry, Faculty of Science and Center of Nanotechnology, Kasetsart University Research and Development Institute, Kasetsart University, Bangkok 10900 (Thailand), Fax: (+66) 2-562-5555
    2. NANOTEC Center of Excellence, National Nanotechnology Center, Kasetsart University, Bangkok 10900 (Thailand)
    3. Center for Advanced Studies in Nanotechnology and its Applications in Chemical, Food, and Agricultural Industries, Kasetsart University, Bangkok 10900 (Thailand)
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  • Prof. Dr. Michael Probst,

    1. Institute of Ion Physics and Applied Physics, University of Innsbruck, 6020 Innsbruck (Austria)
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  • Prof. Dr. Jumras Limtrakul

    1. Laboratory for Computational and Applied Chemistry, Department of Chemistry, Faculty of Science and Center of Nanotechnology, Kasetsart University Research and Development Institute, Kasetsart University, Bangkok 10900 (Thailand), Fax: (+66) 2-562-5555
    2. NANOTEC Center of Excellence, National Nanotechnology Center, Kasetsart University, Bangkok 10900 (Thailand)
    3. Center for Advanced Studies in Nanotechnology and its Applications in Chemical, Food, and Agricultural Industries, Kasetsart University, Bangkok 10900 (Thailand)
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Abstract

The adsorption and the mechanism of the oxidative dehydrogenation (ODH) of propane over VO2-exchanged MCM-22 are investigated by DFT calculations using the M06-L functional, which takes into account dispersion contributions to the energy. The adsorption energies of propane are in good agreement with those from computationally much more demanding MP2 calculations and with experimental results. In contrast, B3LYP binding energies are too small. The reaction begins with the movement of a methylene hydrogen atom to the oxygen atom of the VO2 group, which leads to an isopropyl radical bound to a HO[BOND]V[BOND]O intermediate. This step is rate determining with the apparent activation energy of 30.9 kcal mol−1, a value within the range of experimental results for ODH over other silica supports. In the propene formation step, the hydroxyl group is the more reactive group requiring an apparent activation energy of 27.7 kcal mol−1 compared to that of the oxy group of 40.8 kcal mol−1. To take the effect of the extended framework into account, single-point calculations on 120T structures at the same level of theory are performed. The apparent activation energy is reduced to 28.5 kcal mol−1 by a stabilizing effect caused by the framework. Reoxidation of the catalyst is found to be important for the product release at the end of the reaction.

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