UV-VISIBLE DIFFUSE-REFLECTANCE SPECTROSCOPY OF ZEOLITE-HOSTED MONONUCLEAR TITANIUM-OXIDE SPECIES

Mononuclear titanium oxide species in faujasites of different Si/Al ra tios are prepared by reaction of dehydrated zeolites with TiCl4 at 100 degrees C. The analysis of UV-vis diffuse reflectance spectra in comb ination with Raman spectroscopy and X-ray diffraction reveals the pres ence of three different types of titanium oxide species in the faujasi te structure exhibiting excitation energies for the charge transfer fr om the 2p orbitals of oxygen ligands to the 3d orbitals of Ti of aroun d 36 000, 45 000 and 49 000 cm(-1). A reliable evaluation of diffuse r eflectance spectra requires the calculation of the Kubelka-Munk spectr a from the absolute reflectance of the sample. The different titanium oxide types are proposed to result from monofunctional, bifunctional, and multifunctional bonding of TiCl4 to isolated or neighboring OH gro ups or to hydroxyl nests with coordination numbers ranging from four t o six. The blue shifts in the UV-vis spectra of mononuclear titanium o xide species can be discriminated from those of quantum-sized titania particles.