Rationalization of TS-1 synthesis through the design of experiments

Titanium Silicalite-1 (TS-1) is a zeolite used as a catalyst in partial oxidation reactions, whose synthesis is often performed under hydrothermal conditions by exploiting alkoxides as Ti and Si precursors. A rational study of the synthesis procedure of TS-1 using the experimental design approach was performed. Seven variables (i.e. times and temperatures of the various synthesis steps) were explored, by fixing the reagents ratio to establish which of them could affect the Ti incorporation and speciation. The syntheses were chosen following a D-optimal experimental design strategy, and each variable was explored at two levels and one center point. The responses monitored were: the yield of the synthesis; the total Ti content of the catalyst; the wavelength for the onset of the Ligand-to-Metal Charge Transfer (LMCT) transition involving Ti; and the vibrational fingerprint of tetrahedral Ti (centred at 960 cm−1 in the IR spectra). It was found that a few variables affect the Ti content and speciation (time and temperature of the hydrothermal treatment and the time of hydrolysis of the Ti precursor), whereas the yield is determined by the time of crystallization.