SELECTIVE T-SITE SUBSTITUTION AS A CAUSE OF THE ANISOTROPY OF LATTICE EXPANSION IN TITANOSILICATE-1 INVESTIGATED BY MOLECULAR-DYNAMICS AND COMPUTER-GRAPHICS

The selective substitution of a silicon by titanium in MFI lattice was investigated by molecular dynamics (MD) and computer graphics (CG). It was demonstrated that the MD method, using a simple two-body interatomic potential, is effective to reproduce the framework structure. The lattice expansion as a function of the location and concentration of Ti in the titanosilicate with the MFI structure (titanosilicate-1, TS-) was calculated, and the results were consistent with experimental data. The anisotropic lattice expansion due to Ti substitution in various crystallographic sites of MFI lattice was studied. The favorable site for Ti substitution was discussed by comparing the expansions of lattice parameters reported by X-ray diffraction(XRD) studies. MD and CG are effective methods for explaining the anisotropic lattice expansion and for determining the substituted sites of isomorphous substitution in TS-1.