Bifunctional properties of Al-TS-1 synthesized by wetness impregnation of amorphous Al2O3-TiO2-SiO2 solids prepared by the sol-gel method

Abstract

Ti-containing ZSM-5 (Al-TS-1) has been synthesized by wetness impregnation of amorphous Al2O3-TiO2-SiO2 solids with TPAOH solutions and subsequent crystallization under autogenous pressure at 170°C. The cogel containing aluminum, titanium and silicon oxides used as raw material has been prepared following a two-step (acid-base) sol-gel process which leads to the formation of Si-O-Ti and Si-O-Al bonds previously to the zeolite crystallization. X-ray diffraction (XRD) confirms the high crystallinity of TS-1 and Al-TS-1 obtained by this procedure whereas thermogravimetric analysis (TGA) of TPAOH-containing samples andnC6 adsorption measurements show the purity of the different samples. Fourier transformed infrared spectroscopy (FTIR) evidences the incorporation of Ti and NH3 temperature programmed desorption confirms the acidic properties of Al-TS-1. Diffuse reflectance ultraviolet-visible spectroscopy (DR UV-VIS) shows that Ti atoms occupy tetrahedral positions in the Al-TS-1 and TS-1 lat-tices whereas bulk anastase and/or extraframework Ti species are not detected.29Si and27Al magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy indicate the presence of Al occupying tetrahedral positions in the Al-TS-1 framework. Therefore, the simultaneous incorporation of Ti and Al provides the Al-TS-1 samples with bifunctional properties showing high catalytic activity forn-hexane oxyfunctionalization with H2O2 and for alcohols etherification reactions. When it is compared to the conventional procedures of Al-TS-1 preparation by hydrothermal crystallization of a liquid gel, the method studied here is simpler, requires a lower reaction volume and proceeds with shorter synthesis time. In addition Al-TS-1 prepared through this alternative method exhibits better catalytic properties than the material synthesized following a recipe based on hydrothermal crystallization of a liquid gel.