Systematic comparison of a saponite clay pillared with Al and Zr metal oxides

Alumina and zirconia pillared Ballarat saponites have been prepared by cation exchange of the saponite in aluminum chlorhydrate and zirconyl chloride solutions, respectively. The nature of the pillaring species and the method of preparation have been varied in order to examine their effect on the amount of occluded oxide, as well as the thermal stability, surface area, and acidic properties of the resulting pillared clays. Higher reaction (cation exchange) temperature (80 degrees C) enhances the degree of polymerization, increases the mobility of the pillaring species, and results in greater incorporation between the sheets of the saponite. In general, it is observed that the alumina-pillared saponites have a higher thermal stability than their zirconia-pillared analogues and retain an ordered layered structure even after calcination at 700 degrees C. Infrared spectroscopy of adsorbed pyridine suggests the presence of Bronsted acid sites and two types of Lewis acid sites (of different strength) for the alumina-pillared materials. Only single types of Bronsted and Lewis acid sites, however, were detected for the zirconia-pillared saponites. The thermal desorption of cyclohexylamine and dehydration of pentan-1-ol were used as further probes to monitor the acidity of the different pillared saponites.