The synthesis and characterization of titanium silicalite-1

Abstract

This paper investigates the effect of the variation in alkoxide precursor ratio and templating agent concentration on the production of titanium silicalite (TS-1) through analysis using various physical characterisation techniques. X-ray diffraction showed clear evidence for the MFI zeolite structure and a high degree of crystallinity in all systems. For those materials prepared using a templating agent with ultra low alkali metal content, excellent agreement with previously reported unit cell parameters was obtained. For these same systems, 20% higher specific surface areas were also obtained by nitrogen adsorption. Analysis using an energy dispersive x-ray spectrometer coupled to a scanning electron microscope showed that the product typically contained between 60 and 90% of the titanium in the precursor and some dependence of titanium incorporation on the initial mixture composition was also observed. The results from Raman spectroscopy indicated titanium incorporation into the silicalite framework for all systems. For those materials produced using a templating agent with low alkali metal content, extra-framework anatase titanium dioxide was also identified at moderate Ti : Si mole ratios (>0.03) in the initial mixture. Due to its lower penetration depth, x-ray photoelectron spectroscopy (XPS) was used to characterise the titanium species in the surface layer. The XPS results indicated that a small amount of extra-framework titania was present in the surface of most of the TS-1 samples and the proportion of extra-framework material was observed to increase with both precursor alkali metal content and precursor titanium to silicon ratio.