Titanosilicate Mesoporous Molecular Sieve MCM-41: Synthesis and Characterization

Abstract

The location and coordination of titanium in the titanosilicate mesoporous molecular sieve MCM-41 prepared from Ti(IV) ethoxide as the source of titanium was studied by XRD, IR spectroscopy, 29Si MAS NMR, and XANES. The results are interpreted on the basis of isomorphous substitution 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 the 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 with the line broadening observed in the 29Si MAS NMR spectra, brought about by the wider distribution of the Si−O−Si angles in SiO4 tetrahedra as titanium is progressively incorporated in the silica matrix, and with the changes in the vibrational lattice infrared bands.