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

Abstract

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 potyoxymetal cations of A1 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 programmedodesorption) was used to obtain acidity data. These materials exhibited basal spacings from 16 to 20 A, with surface areas from 239 to 347 m 2 g-~, 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, Cepillared 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.

Comments on “Enhanced Thermal Stability of Al-Pillared Smectites Modified with Ce And La” By J.L. Valverde, P. Cañizares, M.R. Sun Kou, and C.B. Molina

“…The basal spacings reported by Valverde et al (2000) are in a similar range to those reported by others for Al-pillared smectites (Kloprogge, 1998 and references therein), but -6--7 A smaller than those reported for the A1 and rare-earth element (A1/REE) large-pore pillared smectites (McCauley, 1988; Sterte, 1991a Sterte, , 1991bBooij et al, 1996aBooij et al, , 1996b. This indicates that rare earth elements do not form an integral part of the pillars within the interlayer.…”

“…Unfortunately, Valverde and coworkers (Valverde et aL, 2000) missed most of the important publications on the thermally stable large-pore pillared clays based on AI pillars modified by Ce or La. The basal spacings reported by Valverde et al (2000) are in a similar range to those reported by others for Al-pillared smectites (Kloprogge, 1998 and references therein), but -6--7 A smaller than those reported for the A1 and rare-earth element (A1/REE) large-pore pillared smectites (McCauley, 1988;Sterte, 1991aSterte, , 1991bBooij et al, 1996aBooij et al, , 1996b.…”

“…Several other studies on the combination of A1 pillars with Ce or La resulted in the formation of pillared clays with basal spacings characteristic of Al-pillared clays. However, catalytic activity is enhanced owing to Ce or La (e.g., Gonz~ilez et al, 1992;Mendioroz et aL, 1993;Trillo et al, 1993).Unfortunately, Valverde and coworkers (Valverde et aL, 2000) missed most of the important publications on the thermally stable large-pore pillared clays based on AI pillars modified by Ce or La. The basal spacings reported by Valverde et al (2000) are in a similar range to those reported by others for Al-pillared smectites (Kloprogge, 1998 and references therein), but -6--7 A smaller than those reported for the A1 and rare-earth element (A1/REE) large-pore pillared smectites (McCauley, 1988; Sterte, 1991a Sterte, , 1991bBooij et al, 1996aBooij et al, , 1996b.…”

“…Although the thermal stability of these pillared clays is enhanced, the access to the catalytically active sites in the pillared clays may be severely hindered. However, Valverde et al (2000) did not report any catalytic testing on their materials. Valverde et al (2000) also reported on the infrared spectra of their pillared clays after calcination at various temperatures for 2 h. These spectra are quite different from those reported in other studies.…”

“…However, Valverde et al (2000) did not report any catalytic testing on their materials. Valverde et al (2000) also reported on the infrared spectra of their pillared clays after calcination at various temperatures for 2 h. These spectra are quite different from those reported in other studies. Teagarden et aL (1981) and Kloprogge et aL (1992) reported the infrared spectra of the A113-sulphate salt with OHstretching and bending modes of H20 at --3247 and -1640 cm -1, A1-OH stretching mode at -3440 cm -t, and the A1-O mode at --713 cm 1.…”