Enhanced thermal stability of Al-pillared smectites modified with Ce and La

A commercial bentonite (primarily smectite) from Fischer Scientific Company (F bentonite) and a natural bentonite from Peru (P bentonite) were used in the preparation of pillared clays with polyoxymetal cations of Al that wer e subsequently modified with Ce and La. Several Al/metal ratios (5 and 9) w ere used to investigate the effects on the thermal and hydrothermal stabili ty of these synthetic clays. The structure of these materials was studied b y X-ray diffraction. Isotherms were determined by N-2 adsorption. Thermal s tability was determined using thermogravimetric (TG) measurements and ammon ia-TPD (temperature programmed desorption) was used to obtain acidity data. These materials exhibited basal spacings from 16 to 20 Angstrom, with surf ace areas from 239 to 347 m(2) g(-1), with microporosity contributing from 50 to 80% of the total surface area. Pillared clays prepared From F bentoni te generally showed larger basal spacings and surface areas than those prep ared from P bentonite. Pillared clays modified with Ce or La did not show a ny apparent structural changes relative to the Al-pillared clays. Pillared clays modified with Ce and La had similar acid properties as Al-pillared cl ays. In contrast, the thermal and hydrothermal stabilities of these materia ls were greater than Al-pillared clays. However, Ce-pillared clay appears t o be more effective than La-pillared clay in delaying the dehydroxylation o f pillared clays with increasing temperature. The intercalation of Ce and L a into Al-pillared clays improved the thermal stability, which may increase the utility of these materials as catalysts.