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Issue 7, 2002
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On the structure and coordination of the oxygen-donating species in Ti↑MCM-41/TBHP oxidation catalysts: a density functional theory and EXAFS study

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Abstract

We present a combined density functional theory and EXAFS investigation into the geometry and coordination of the oxygen-donating species in surface grafted, tert-butyl hydroperoxide (TBHP) exposed Ti↑MCM-41 oxidation catalysts. The formation of a number of different Ti(η2-peroxo) and Ti(η1-peroxo) type species, including radical and anionic complexes, has been examined, arising from the attack of peroxide (where both hydrogen peroxide and TBHP have been studied) on a tetrahedral TiIV site, together with and without one molecule of water. BP86/DZVP calculations show that the Ti(η1-OOtBu) complex is 33 kJ mol−1 lower in energy than the Ti(η2-OOtBu) complex which is contrary to previous estimates in the literature and we propose that 6-coordinate Ti(η1-OOR) complexes, where R is the peroxide substituent (i.e. R = H for H2O2 and R = tBu for TBHP), are the oxygen-donating species in peroxide/titanosilicate mixtures. X-ray absorption analysis is in good agreement with our DFT predictions that Ti–peroxo species in TBHP/Ti↑MCM-41 systems are 6-coordinate. Furthermore, our DFT cluster calculations and X-ray absorption analysis collectively reveal the presence of 6-coordinate ‘Ti(η2-OOtBu)(OHR)’ and ‘Ti(η1-OOtBu)(OHR)·H2O’ complexes in TBHP/Ti↑MCM-41 catalysts.

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Publication details

The article was received on 31 May 2001, accepted on 25 Oct 2001 and first published on 04 Mar 2002


Article type: Paper
DOI: 10.1039/B104735N
Citation: Phys. Chem. Chem. Phys., 2002,4, 1228-1240
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    On the structure and coordination of the oxygen-donating species in Ti↑MCM-41/TBHP oxidation catalysts: a density functional theory and EXAFS study

    C. M. Barker, D. Gleeson, N. Kaltsoyannis, C. R. A. Catlow, G. Sankar and J. M. Thomas, Phys. Chem. Chem. Phys., 2002, 4, 1228
    DOI: 10.1039/B104735N

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