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

• Published in: Clays and clay minerals Vol. 48; no. 4; pp. 424 - 432
• Main Authors: Valverde, J. L, Canizares, P, Sun Kou, M. R, Molina, C. B
• Format: Journal Article
• Language: English
• Published: Boulder, CO Clay Minerals Society 01-08-2000
• Subjects: aluminosilicates; bentonite; cerium; chemical properties; chemical ratios; clastic rocks; clay mineralogy; clay minerals; crystal chemistry; crystal structure; Earth sciences; Earth, ocean, space; Exact sciences and technology; experimental studies; geochemistry; hydrothermal conditions; isotherms; lanthanum; metals; Mineralogy; rare earths; rock, sediment, soil; sed rocks, sediments; Sedimentary petrology; sedimentary rocks; sheet silicates; Silicates; smectite; stability; synthetic materials; thermal properties; X-ray diffraction data; experimental studies; adsorption; cerium; lanthanum; nitrogen; X-ray diffraction; thermogravimetric analysis; bentonite; isotherms; dehydroxylation; smectite; rare earths; sedimentary rocks; crystal structure; clay minerals; sheet silicates; silicates; desorption; hydrothermal conditions; stability; clastic rocks; infrared spectroscopy
• ISSN: 0009-8604; 1552-8367
• DOI: 10.1346/ccmn.2000.0480402

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.