Titanium-silicalite molecular sieves were prepared from colloidal silica, tetraethyl orthotitanate, and tetrapropylammonium hydroxide as a templating agent.
X-ray diffraction patterns of titanium-silicalites were nearly the same as those of ZSM-5 zeolites. The FT-IR spectra and Si MAS NMR investigations showed that titanium is in the framework position. It was found that it does not possess ion exchange capacity due to the fact that titanium is in the Ti(IV) chemical state. No appreciable amount of Ti(III) species was detected by EPR spectroscopy.
Titanium-silicalite showed a little catalytic activities for typical acid catalyzed reaction such as isomerization of p-xylene and alkylation of toluene because of its week acid strength.
On titanium impregnated silicalite dehydration to propylene was more pronounced. Ti-silicalite displayed higher activity for dehydrogenation of 1-propanol than the silicalite although the selectivity to propionaldehyde was a little lower than that obtained with silicalite. As the reaction temperature was elevated, the selectivity to propionaldehyde decreased, while that to propylene increased. It seemed that the incorporation of titanium into the framework of silicalite had a positive effect in increasing the dehydrogenation activity.
