STRUCTURAL STATE OF BORON IN MFI-TITANIUM BORALITES AND THEIR CATALYTIC PROPERTIES

A series of titanium boralites with the MFI structure has been synthes ized. The catalysts were characterized using X-ray diffraction (XRD), IR and magic-angle spinning (MAS) NMR spectroscopic techniques and the incorporation of boron into the framework in the presence of titanium has been investigated in as-synthesized and in calcined samples. Tetr ahedral framework boron was determined quantitatively by B-11 MAS NMR. The activity of titanium boralites in the oxidation of hexane using h ydrogen peroxide as oxidizing agent was evaluated. In the as-synthesiz ed samples, boron and titanium were simultaneously incorporated into t he siliceous MFI framework. At constant boron loading, a higher titani um loading leads to a higher fraction of boron removed from its framew ork position after calcination. The lower activity and H2O2 selectivit y toward oxyfunctionalization products when boron is present are relat ed to the mild acidic Bronsted sites of the boralite. Acid leaching se lectively removes boron and allows a partial recovery of the activity of the titanium silicalite.