A NEW METHOD FOR PREPARING MICROPOROUS TITANIUM PILLARED CLAYS

A new method for reproducible preparation of Ti-pillared montmorillonite with microporous structure, high surface area and high thermal stability is reported. The <2 mum fraction of a physically purified Wyoming Na+-Ca2+-montmorillonite (commercial designation, Volclay SPV 200) was used as starting material. The pillaring agent was prepared by mixing a TiCl4/ethanol solution with a solution of glycerin and water. XRD analyses of the pillared clays showed that the as-synthesized sample had a basal spacing of 21.3 angstrom, that shrank to 17.7 angstrom after calcination at 773 K and to 17.4 angstrom after calcination at 973 K. By subtracting the basal thickness of clay, the interlayer spaces of 10.8, 8.2 and 7.9 angstrom were obtained. These distances implied that Ti was incorporated into the interlayers in some form of polynuclear clusters. The pillared clays had specific surface areas of 379, 365 and 286 m2/g after calcination at 573, 773 and 973 K, respectively. The N2 adsorption/desorption isotherms indicated that the corresponding samples contained both the micro- and meso-porous structures. The diameters of the micropores were consistent with the interlayer spaces obtained from XRD patterns. The micropores contributed approximately 88% to the total pore volume of the sample calcined at 573 K, that was found to be retained after calcination at 773 K but reduce to approximately 65% of its origin after calcination at 973 K. The presence of glycerin in the preparation procedure was found to be essential in order to prepare Ti-pillared clay of high thermal stability.