Difraction and complementary analysis methods for the design of MFI-type titanosilicalites with catalytic properties

Abstract

The article presents the analysis and generalization results of all hierarchy levels of compositions of the framework orthorhombic MFI-type titanosilicalites (TS-1), obtained by X-ray diffraction and X-ray absorption spectroscopy (synchrotron), scanning electron microscopy, scanning/transmission electron microscopy (S/TEM), microanalysis (ICP, EDX, XPS). Impurity phases were found by electron diffraction, which are not detected by the X-ray method that explains the discrepancy between the real compositions of TS-1 and their elemental composition (titanium and silicon content). The phases compositions (framework and framework voids compositions) of TS-1 with the general composition of [Ti4+12-xSi4+xO24] × wA with Si/Ti = 47 and 53 (A is water), 60 and 73.5 (A is organic template TPAOH or without it) as well as Ti4+ ions distribution over the crystallographic sites with the identification of the most favorable sites for Ti4+ incorporation were refined by the Rietveld method. The local environment of Ti4+ ions by oxygen atoms (with or without vacancies; with or without atoms from the organic template) was established and their different coordination numbers were explained. Potassium ions in the particles of synthesized samples, the presence of which is due to the purity of the initial components, and a higher content of titanium ions in shapeless or spherical particles, as a rule, amorphous were found. Orthorhombic MFI-type zeolites with low or without titanium content were found to form faceted crystallites in the form of pseudohexagonal prisms. The relationship between the catalytic properties and the size of crystallites and nanoparticles, Si/Ti ratio and the coordination environment of Ti4+ has been established.