Enhanced Thermal Stability of Al-Pillared Smectites Modified with Ce and La

J.L. Valverde, P. Cañizares, M.R. Sun Kou1 and C.B. Molina
Chemical Engineering Department, Faculty of Chemistry, University of Castilla-La Mancha, Campus Universitario s/n. 13004, Ciudad Real, Spain
1 Chemical Department, Faculty of Science and Engineering, Pontificia University Catholic of Peru, Av. Universitaria, Cuadra 18, San Miguel, Lima 100, Perú
E-mail of corresponding author: jlvalver@inqu-cr.uclm.es

Abstract: 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 were subsequently modified with Ce and La. Several Al/metal ratios (5 and 9) were used to investigate the effects on the thermal and hydrothermal stability of these synthetic clays. The structure of these materials was studied by X-ray diffraction. Isotherms were determined by N2 adsorption. Thermal stability was determined using thermogravimetric (TG) measurements and ammonia-TPD (temperature programmed desorption) was used to obtain acidity data. These materials exhibited basal spacings from 16 to 20 Å, with surface areas from 239 to 347 m2 g−1, with microporosity contributing from 50 to 80% of the total surface area. Pillared clays prepared from F bentonite generally showed larger basal spacings and surface areas than those prepared from P bentonite. Pillared clays modified with Ce or La did not show any apparent structural changes relative to the Al-pillared clays. Pillared clays modified with Ce and La had similar acid properties as Al-pillared clays. In contrast, the thermal and hydrothermal stabilities of these materials were greater than Al-pillared clays. However, Ce-pillared clay appears to be more effective than La-pillared clay in delaying the dehydroxylation of pillared clays with increasing temperature. The intercalation of Ce and La into Al-pillared clays improved the thermal stability, which may increase the utility of these materials as catalysts.

Key Words: Bentonite • Ce • La • Pillared Clays

Clays and Clay Minerals; August 2000 v. 48; no. 4; p. 424-432; DOI: 10.1346/CCMN.2000.0480402
© 2000, The Clay Minerals Society
Clay Minerals Society (www.clays.org)