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Chromium sites in zeolite framework: Chromyl or chromium hydroxyl groups?

Abstract : A combined experimental and ab initio periodic DFT calculation on the structure and stability of different chromium-substituted zeolite models are presented. Experimental investigation by XRD, FT-IR and UV-vis show the presence of chromium in SiBEA zeolite. The favorable chromium sites are characterized by their calculated geometrical parameters, energetics, vibrational frequencies and protonation/deprotonation energies. The theoretical vibrational frequencies are compared with experimental FT-IR measurements. A phase diagram was constructed on the basis of calculated total energies of the optimized structures. Cr(III) is stabilized in the zeolite framework as a tri-coordinated site. Cr sites are predicted to be more acidic than group V containing zeolites. Dehydration of the site leads to the formation of a Cr(VI) containing a Crdouble bond; length as m-dashO group. These results are fully consistent with experimental data and allow the identification of the molecular structure of chromium sites in a zeolite framework.
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Submitted on : Monday, October 22, 2012 - 4:02:48 PM
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Frederik Tielens, Mazharul M. Islam, Gabriella Skara, F. de Proft, Tetsuya Shishido, et al.. Chromium sites in zeolite framework: Chromyl or chromium hydroxyl groups?. Microporous and Mesoporous Materials, Elsevier, 2012, 159, pp.66-73. ⟨10.1016/j.micromeso.2012.02.046⟩. ⟨hal-00744253⟩



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