COMPUTER-SIMULATION STUDY ON ISOMORPHOUSLY SUBSTITUTED SILICALITES

The influence of isomorphous substitution on the structure and vibrational spectra of the orthorhombic form of silicalite was studied by means of the molecular dynamics technique. Replacement of silicon by model T atoms with the parameters of germanium points to the T3 position as the most preferable one for T atom siting in the structure. The substitution leads to significant changes in the size and shape of the channels so that for the structure with a Si/T ratio of 11 the distances between the positions of oxygen atoms that determine the dimensions of the straight channels are ca. 7.4 x 9.2 Angstrom as compared with ca. 8.1 x 8.4 Angstrom for pure silicalite. Analysis of the vibrational spectra reveals spectral regions sensitive to the incorporation of non-silicon atoms into the framework.