Sintering of Montomorillonites Pillared by Hydroxy-Aluminum Species

Abstract--Three montmorillonite samples, from Wyoming (particle size <0.2 tzm, 4.6 wt. % FezO3), Greece (<14 ~tm, 6.5 wt. % Fe203), and Poland (0.5 wt. % Fe203, two fractions <2 tzm and 2-10 um) were intercalated with hydroxy-A1 species. The amount of hydroxy-Al cations exchanged by the clays depended on the particle size: it decreased from 31 vet. % A1203 for 0.2 um in size to 22.6 vet. % for >2 t~m. The X-ray powder diffraction (XRD) pattern showed that most of the material was not intercalated after refluxing at 80"C for 2 hr; several redispersions of the pillared clay in hot water were required to obtain a single sharp XRD line at 18.6 A. The diffusion of the A1 cations therefore limited the cationexchange process. The addition of NH4 § to the pillaring solution decreased the amount of A1 fixed by the clay from 31 (no NH4 § to 26 wt. % (NH4+/A1 = 10), but increased slightly the microporous volume of the resulting pillared material from 0.13 to 0.14 ml/g. The competition between NH4 + and Al-hydroxy cations for ion-exchange sites forced the A1 species into the interlayer space and increased the homogeneity of the resulting pillared material. The influence of particle size on the amount of Ai exchanged was then reduced. After calcination in air at 700"C the pillared Wyoming clay retained a microporous volume of 0.09 ml/g if no NH4 + was added, compared with 0.i I mug for a NH4+/A1 ratio of I0. The Fe content of the clay affected the thermal stability of pillared clays at 800"C: for two samples prepared by competitive ion exchange (NHa § = 10) the microporous volume increased from 0.06 ml/g for 6.4 wt. % Fe203 to 0.08 ml/g for 0.5 wt. % Fe203. The acidity of the pillared clay was determined by calorimetric adsorption of ammonia at 150"C, on samples calcined at 500"C. Pillared montmorillonite prepared using noncompetitive intercalation showed a weak acid strength: most sites adsorbed ammonia with an enthalpy of 65 kJ/mole. The intercalation of the same original clay using competitive ion exchange yielded a solid that possessed both weak (heat = 60 kJ/mole) and strong (120 kJ/mole) acid sties. Competitive ion exchange appears to be a simple means of preparation of large quantities of pillared clays of reasonable thermal stability and higher acidity than those obtained by conventional methods.Key Words--Competitive ion exchange, Hydroxy-A1, Intercalation, Montmorillonite, Pillared clays, Thermal stability, X-ray powder diffraction.Rtsum~--Trois montmorillonites provenant du Wyoming (taille des particules <0,2 urn, 4,6% en poids de Fe203), de Grace (taille < 14 #m, 6,5% Fe203) et de Pologne (0,5% Fe203, deux fractions <2/~m et 2-10/zm), ont 6t6 intercaltes par des complexes cationiques hydroxylts de raluminium. La quantit6 d'A1 6chang~e par l'argile d~pend de la taiUe des particules: elle dtcroit de 31% A1203 pour une taille de 0,2 um it 22,6% pour >2 t~m. Le spectre de diffraction des rayons X montre que la majeure partie du mattriau n'est pas intercalte apr~s reflux it 80~ pendant 2 hr; plusieurs redispersions de...

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 91%

Use of Competitive Ion Exchange for Intercalation of Montmorillonite with Hydroxy-Aluminum Species

Figuéras

Kłapyta

Massiani

et al. 1990

“…There was an intensity reduction of the main peaks, especially in the stretching mode of the hydroxyl groups at 3627 cm-k This is attributed to the condensation of terminal hydroxyl groups from the polymeric ions in the pillars with the structural hydroxyl groups in the 2:1 layers (Tichit et aL, 1988). Also, there was an intensity reduction of Ai-OH-A1 and AI-OH-Mg vibrational modes at 910 and 842 cm -~, respectively, accompanied by a broadening of the band centered at 1047 cm -1, which is similar to ion-exchanged clays (Tennakoon et al, 1986).…”

Section: Infrared Studiesmentioning

confidence: 95%

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

Valverde

Cañizares

Kou

et al. 2000

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.

“…Valverde et al (2000) however reported a broadening of the Si-O band at 1047 cm -1, which they ascribed to the formation of Si-O-A1 bonds. These authors did not observe the formation of a new A1-O band at ~722 cm -~ owing to the conversion of the A1 polyoxocation to its oxide equivalent as indicated by Tichit et al (1988) and by .…”

mentioning

confidence: 93%

“…Tichit et al (1988) observed that exchange with Al~3 had no effect on the tetrahedral sheet of the montmorillonite based primarily on the absence of changes in the 1125-cm -I (Si-OaP ~"1 stretching mode), the 1035-cm ~ (combined stretching and bending modes Si-Ob"~"~), and 935-cm-~ (A1-OH) bands. A slight shift of the 710-cm -a band towards 735 cm -~ was the only change in the infrared spectrum.…”

mentioning

confidence: 96%

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

Kloprogge

Veen

Booij

et al. 2001

Valverde et al. (2000) recently reported on the preparation and characterization of Al-pillared smectites modified with Ce and La. Pillaring of clays with A1 polyoxocations (Keggin type Al~3 ) and a large variety of other complexing cations has been reported many times since the seventies. McCauley (1988) described in a patent the preparation of thermally stable pillared clays with large basal spacings of -28 A, followed by publications by Sterte (1991aSterte ( , 1991b and Booij and coworkers (Booij et al., 1996a(Booij et al., , 1996b. These authors used hydrothermally treated or refluxed solutions containing the A1 polyoxocation and the rare earth elements in the form of their chloride salts. The presence of cerium or lanthanum seems to promote polymerization of the A1 polyoxocation. Until now however, nobody has been able to assess the structure of the newly formed pillaring molecules. Although the interlayer spacing is about twice that of the normal A1-pillared clay, chemical analyses indicate smaller amounts of Ce and La than expected from polymerization of the A1 polymer alone. 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. This indicates that rare earth elements do not form an integral part of the pillars within the interlayer. Although the surface areas are in the order of what is expected for a pillared clay, the micropore volume is significantly lower as, for example, observed for Al-pillared montmorillonite SWy-1 (Kloprogge et al., 1994). However, their micropore volume is much higher than that of large-pore A1/REE pillared clays in which no micropores are present at all because the average pore diameter is --60-70 A (Booij et aL, 1996b). The relatively low micropore volume can probably be explained by the incorporation of a relatively large amount of Ce or La in the interlayer between the pillars during the synthesis of the pillared clays where initial REE/A1 ratios of --<1.8 were maintained. 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 s...