Catalytic and multinuclear MAS NMR studies of a thermally treated zeolite ZSM-5 |
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| Affiliation: | 1. Fakultät für Physik und Geowissenschaften, Universität Leipzig, 04103 Leipzig, Germany;2. Institute of Chemical Reaction Engineering, University of Erlangen-Nuremberg, 91058 Erlangen, Germany;1. Department of Chemical Engineering, Ferdowsi University of Mashhad, P.O. Box 9177948944, Mashhad, Iran;2. Department of Chemistry, Ferdowsi University of Mashhad, P.O. Box 9177948974, Mashhad, Iran;3. Department of Engineering, Senior Process Engineer, South Pars Gas Complex, P. O. Box 311/75391, Assalouyeh, Iran;4. Research Institute of Petroleum Industry (RIPI), Azadi Sport Complex, P.O. Box 14665-1998, Tehran, Iran;1. Charles D. Davidson School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, West Lafayette, IN 47907, USA;2. Department of Chemical Engineering, University of Florida, 1030 Center Drive, Gainesville, FL 32611, USA;1. State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China;2. Wuhan Institute of Physics and Mathematics, The Chinese Academy of Sciences, Wuhan 430071, China;3. Hubei Key Laboratory of Fuel Cells, Wuhan University of Technology, Wuhan 430070, China |
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| Abstract: | Catalysts of ZSM-5 type were obtained by synthesis with tetrapropyl-ammonium-bromide (TPABr) as a template and subsequent hydrothermal treatment up to 1173 K. 1H-, 27Al-, and 29Si-NMR spectroscopy and the direct oxidation of benzene with N2O as a catalytic test were applied to characterize the products. 27Al MAS NMR and 27Al 3QMAS NMR studies of the samples give evidence that fivefold-coordinated extra-framework aluminum species exist if the product is treated at 1173 K and then rehydrated. The values of all characteristic catalytic key data are highest when the catalysts are precalcined at 1173 K. This is a clue that species giving rise to fivefold-coordinated aluminum species in the hydrated products are responsible for the high catalytic key data. The nature of these species is not yet clear. Two models for the species are in agreement with our experimental findings. |
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