Catalysis Database

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

Rajaram , Bal and K., Chaudhari and D. , Srinivas and S., Sivasanker and P. , Ratnasamy (2000) Redox and catalytic chemistry of Ti in titanosilicate molecular sieves: an EPR investigation. Journal of Molecular Catalysis A: Chemical , 162 . pp. 199-207.

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Abstract

An EPR study of Ti3q in titanosilicate molecular sieves, TS-1, TiMCM-41, ETS-10 and ETS-4 is reported. Ti4q is reduced to Ti3q 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 Ti3q sites in TS-1 and TiMCM-41. Ti4q 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 Ti3q with O2 or H2O2 results in a diamagnetic titaniumIV. hydroperoxo species. Under the same conditions, an octahedrally coordinated Ti3q forms a paramagnetic titaniumIV. 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 H2and O2instead 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
Subjects:Science > Chemistry
ID Code:137
Deposited By: Dr S Navaladian
Deposited On:28 Feb 2007 13:33
Last Modified:18 Mar 2007 19:56

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