Titanosilicalites (MFI-type): Composition, statistical and local structure, catalytic properties

This article presents the results of a study of three commercial titanosilicalites (TS-1, TS-1N, TS-1G) with general formula [(Ti x Si 12-x )O 24 ] × w H 2 O (MFI-type) using the X-ray study (XRPD), IR spectroscopy (FT-IR), X-ray absorption spectroscopy (EXAFS/XANES), differential scanning calorimetry (DSC), Brunauer–Emmett–Teller method (BET), UV-VIS spectroscopy. It was established that the samples contain amorphous oxygenous titanium-containing formations, which does not allow the use of quantitative elemental methods of analysis to determine the content of titanium ions in the framework. The full-profile Rietveld method was used to determine the silicate modules (Si/Ti = 53 for TS-1, Si/Ti~47 for TS-1N and TS-1G) and the coordination numbers of titanium: CNTi~5.0, CNTi = 4.5, CNTi>5.0, respectively in the structures of TS-1, TS-1N, TS-1G. The distribution of Ti 4+ ions over the sites of the MFI-type structure with the orthorhombic symmetry (space group Pnma, z = 8) were found: T2, T6, T10 for TS-1, T8, T10 , T5 (unlikely) for TS-1N ( Т10 double positions in sinusoidal channels) and Т2, Т10, Т12, Т9 (unlikely) for TS-1G ( Т10 and Т12 double positions in sinusoidal channels). The best indicators of the allyl chloride epoxidation in the epichlorohydrin process at 30 °C were achieved for TS-1N and TS-1G. A higher yield of acetaldehyde was found on the TS-1(75) sample (TS-1 sample annealed at 75 °C for 2 h) at 290 °C (non-oxidative ethanol conversion), and ethylene - on the TS-1G(500) sample (TS-1G annealed at 500 °C for 2 h) at 700 °C (propane conversion). The revealed correlations between the catalytic parameters and the characteristics of the samples studied were discussed. • The three commercial TS-1 zeolites were studied by a complex of methods. • Samples differ in the volume and surface compositions and in the coordination of Ti. • TS -1 with identical or different Si/Ti have different distribution of Ti over Si sites. • Si/Ti, Ti coordination, acidity and donor acceptor sites affect the catalytic properties.