Redox and catalytic chemistry of Ti in titanosilicate molecular sieves: an EPR investigation

Bal, Rajaram ; Chaudhari, Karuna ; Srinivas, D. ; Sivasanker, S. ; Ratnasamy, Paul (2000) Redox and catalytic chemistry of Ti in titanosilicate molecular sieves: an EPR investigation Journal of Molecular Catalysis A: Chemical, 162 (1-2). pp. 199-207. ISSN 1381-1169

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An EPR study of Ti3+ in titanosilicate molecular sieves, TS-1, TiMCM-41, ETS-10 and ETS-4 is reported. Ti4+ is reduced to Ti3+ by dry hydrogen above 673 K. Ti ions in TS-1 and TiMCM-41 are located in tetragonally elongated Td and those of ETS-10 and ETS-4 in a tetragonally compressed Oh geometric positions. Reduction at 873 K revealed the presence of two non-equivalent Ti3+ sites in TS-1 and TiMCM-41. Ti4+ ions in a tetrahedral geometry are more difficult to reduce than in an octahedral symmetry. The effects of cation exchange and Pt impregnation, on the geometry and reducibility of titanium in ETS-10, are also examined. Interaction of a tetrahedrally coordinated Ti3+ with O2 or H2O2 results in a diamagnetic titanium(IV) hydroperoxo species. Under the same conditions, an octahedrally coordinated Ti3+ forms a paramagnetic titanium(IV) superoxo species. The higher catalytic activity of TS-1 and TiMCM-41 in selective oxidation reactions is probably a consequence of the formation of the hydroperoxy species on their surface during the catalytic reaction. The presence of Pt in the vicinity of Ti enables the use of H2 and O2 (instead of H2O2) to generate the active hydroperoxy site. The absence of formation of titanium hydroperoxy species in ETS-4 and ETS-10 is the cause of their inactivity in selective oxidation reactions.

Item Type:Article
Source:Copyright of this article belongs to Elsevier Science.
Keywords:Titanosilicates; Porous Materials; EPR of Ti3+; Catalytic Oxidation; Structure-reactivity; Redox Behaviour of Titanium
ID Code:41387
Deposited On:28 May 2011 09:34
Last Modified:17 May 2016 23:08

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