SYNTHESIS AND CHARACTERIZATION OF PILLARED CLAYS CONTAINING BOTH SI AND A1 PILLARS

A Wyoming montmorillonite clay has been intercalated using the competi tive ion exchange of aluminum hydroxy polycations and oligosilsesquiox anes. Whereas the intercalation of montmorillonite by the products of hydrolysis of trichlorosilylethylpyridine yields an heterogeneous soli d; with a large fraction non-intercalated, the X-ray diffraction shows that competitive intercalation permits a nearly complete intercalatio n of the material. The lattice spacing of 21.4 Angstrom after ion exch ange, is determined by the size of the largest oligosilsesquioxane cat ions. It is reduced to 17.4 Angstrom after calcination at 873 K where Si-29 and Al-27 MAS-NMR Show the existence of the two types of pillars with respectively the siloxane and Al-13 structure, After calcination at 973 K, a clear 001 XRD line is observed, and the microporous volum e is 0.13 ml g(-1), thus showing a good thermal stability. The number and strength of acid sites determined by adsorption of ammonia is comp arable to that of HY zeolites. This strong acidity is related in part to the stability of the structure, and to the retention of the individ uality of the Al-13 pillars. The tetrahedral aluminum atom of the pill ars is assumed to be responsible for this strong acidity.