Md. Alba et al., TITANOSILICATE MESOPOROUS MOLECULAR-SIEVE MCM-41 - SYNTHESIS AND CHARACTERIZATION, Journal of physical chemistry, 100(6), 1996, pp. 2178-2182
The location and coordination of titanium in the titanosilicate mesopo
rous molecular sieve MCM-41 prepared from Ti(IV) ethoxide as the sourc
e of titanium was studied by XRD, IR spectroscopy, Si-29 MAS NMR, and
XANES. The results are interpreted on the basis of isomorphous substit
ution of Ti for Si. XANES shows that titanium is 4-coordinate and that
Ti(IV) does not form a regular TiO4 tetrahedron. This is caused by th
e larger size of the Ti(IV) atom in comparison with Si(IV), resulting
in a distortion in the silica matrix, and/or by the presence of H2O in
the coordination sphere of titanium. Such distortion is consistent wi
th the line broadening observed in the Si-29 MAS NMR spectra, brought
about by the wider distribution of the Si-O-Si angles in SiO4 tetrahed
ra as titanium is progressively incorporated in the silica matrix, and
with the changes in the vibrational lattice infrared bands.