The purpose of this study was to investigate the synthesis and properties of oxyaluminum pillared montmorillonites prepared using the controlled hydrolysis of aluminum isopropoxide as the source of pillaring species and to evaluate pillared montmorillonites as supports for hydrodesulfurization (HDS) catalysts. Several synthesis schemes were evaluated for the preparation of pillared montmorillonites. Successful pillaring was accomplished by addition of cyclohexane solutions of aluminum isopropoxide to aqueous montmorillonite suspensions. The pillared montmorillonite preparation was optimized for maximum interlayer spacing by variation of experimental parameters. Samples were characterized by x-ray diffraction and BET surface area. After dehydration a maximum interlayer spacing of approximately 6 A was obtained. As the ratio of aluminum isopropoxide to clay increased the surface area decreased. The interlayer limit was attributed to the primary pillaring species being a plate-like oxyaluminumcation having a boehmite layer structure whose thickness was about 6.1 A. Decreasing surface area for increasing aluminum to clay ratio probably resulted from exchange of larger cationic oxyaluminum plates into the interiayer volume. It was suggested that at the limit of very low surface area with a layer separation of about 6 A, the montmorillonite-oxyaluminum material consisted of alternating montmorillonite and 'boehmitem layers. / Ph. D.