The architecture of catalytically active centers in titanosilicate (TS-1) and related selective-oxidation catalysts

Detailed X-ray spectroscopic studies yield the three-dimensional structure of Ti(IV) centered active sites in a series of TS-1 catalysts, in which titanium ions substitutionally replace a small fraction of the silicon sites in the pentasil structure, Silicalite-1. Advantage has been taken of the atomic structure of Ti(OSiPh3)(4), (determined separately by X-ray diffraction). A detailed EXAFS analysis of the X-ray absorption spectra of Ti(OSiPh3)(4) which takes advantage of the full cluster multiple scattering methodology leads to the precise nature of the coordination of the Ti ions in a series of TS-1 samples. It proved possible to distinguish between the tetrapodal [i.e., Ti(OSi)(4)] and tripodal structure [i.e., Ti(OSi)(3)OH] shown (see T. Maschmeyer, F. Rey, G. Sankar and J. M. Thomas, Nature, 1995, 378, 159; ref. 1) to be present in high performance anchored titanosilicate epoxidation catalysts.