EVIDENCE OF THE PRESENCE OF TWO DIFFERENT FRAMEWORK TI(IV) SPECIES IN TI-SILICALITE-1 IN VACUO CONDITIONS : AN EXAFS AND A PHOTOLUMINESCENCE STUDY

In a previous contribution (J. Phys. Chem. 1994, 98, 4125) we reported EXAFS data collected at ADONE on a high quality Ti−silicalite (TS-1) sample (Ti = 1.47 wt %) dehydrated in a carefully controlled atmosphere at 400 K. The importance of that paper was to definitively clarify that Titanium atoms occupy silicon substitutional framework positions. However, due to the large incertitude associated with the estimated first shell Ti-coordination number (N = 4.4 ± 0.6), it was not possible to clarify if only perfect “closed” Ti(OSi)4 sites are present or if a considerable fraction of defective “open” Ti(OSi)3 (OH) sites must also be considered (in an ideal EXAFS measurement N is expected to be five if only open sites are present, due to the insertion of a fifth oxygen of the silanol formed in the adjacent Si center when the Ti−O−Si bridge is broken). We report more recent EXAFS data collected at LURE DCI on a high quality TS-1 (Ti = 2.03 wt %) sample:  the higher photon flux of that facility and the higher Ti ...