Layer cross-linking in pillared clays

Pinnavaia, Thomas J.; Landau, Steven D.; Tzou, Ming Shin; Johnson, Ivy D.; Lipsicas, M.

doi:10.1021/ja00310a102

Cited by 108 publications

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“…Besides catalytic activities, Malla et al (1989) and Komarneni (1990a, 1990b) observed a definitive variation in water sorption isotherms for pillared montmorillonite, nontronite, hectorite, and saponite. Although cross-linking was not observed in minerals having a negative charge in the octahedral sheet, Pinnavaia et al (1985b) observed an inversion of Si tetrahedra and cross-linking between the A1 in the pillars and the tetrahedral Si in calcined pillared fluorohectorite. This was attributed to the presence of F in the octahedral sheet of this material.…”

Section: Introductionmentioning

confidence: 71%

“…Similarly, the peak at 91.4 ppm can be thought of as being composed of peaks at -90.8 and -94.5 ppm. The peak broadening can be attributed to at least one or both of the following reactions: 1) initiation of hydrolytic splitting of Si-O-A1 linkages which modifies the Si environment and 2) initiation of inversion of SiO4 tetrahedra and its bonding with A1 v~ of the pillar which place the Si in the Q4(1A1) environment as suggested by Pinnavaia et al (1985b) for fluorohectorite. The effect of the former reaction is to broaden the Si(1A1) peak and that of the latter is to broaden the peak centered at -96.6 ppm due to overlapping of two Si(0A1) peaks, that is, Q3(0AI) (-95.5 ppm) and Q4(Si)(1AI) (-97.4 ppm).…”

Section: Cross-linkingmentioning

confidence: 97%

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Properties and Characterization of Al₂O₃ and SiO₂-TiO₂ Pillared Saponite

Malla

Komarneni

1993

Clays and clay miner.

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Abstract--A saponite pillared with a single (AlzO3) or a mixed (SiO~-TiO:) oxide exhibited basal spacings of 16-19 and 30-40/~, respectively. The pillared structures were found to be stable up to 700~ Water, nitrogen, and high resolution argon adsorption were used to study the effect of thermal treatments on surface chemistry, pore structure, and surface area of these pillared clays. The pillared saponites exhibited a hydrophobic behavior at temperatures > 500~ whereas such behavior was observed at >300~ for montmorillonite. Most of the micropores in the A1203 pillared clays were < 10 A, whereas the SiO2-TiO2 pillared clays showed a broad distribution of pores in both micropore and mesopore regions. The SiO2-TiO2 pillared samples possessed higher surface area compared with A1203 pillared clays. The percent decrease in surface area was smaller for pillared saponites compared with pillared montmorillonites when calcined from 300 ~ to 700~ indicating a higher thermal stability of the former. The pillared clays were also characterized by solid state 27A1 and 295i magic-angle spinning nuclear magnetic resonance (MAS/ NMR) spectroscopy. There was no direct evidence of cross-linking (covalent bonding between the clay layer and pillar) in montmorillonite irrespective of the types of pillars. In saponite, however, a significant structural modification took place. 27A1 spectra of A1203 pillared saponite heated at >300~ appear to indicate an increase in A1 vl as a result, at least in part, of initiation of hydrolytic splitting of Si-O-AI bonds. The actual release of A1 from the tetrahedral sheet probably occurred at a temperature > 500~ and completed around 7000C with the formation of Si-O-Si linkages. The decreased intensity of peak due to Si(1A1) in 29Si spectra of the sample heated at 700~ corroborates the 27A1 MAS/NMR results. Additionally, the 295i spectra indicated a cross-linking between SiO4 (clay sheet) with A1203 pillars, which could be achieved by inverting some silica tetrahedra into the interlayer. 27A1 and 295i spectra of SiOzTiO2 pillared saponite also showed the trend similar to that exhibited by A1203 pillared saponite, indicating that the crystal chemistry of the host may be more important than the nature of pillars in the structural modification and cross-linking behavior of thermally treated pillared clays.

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Section: Introductionmentioning

confidence: 71%

Section: Cross-linkingmentioning

confidence: 97%

Properties and Characterization of Al₂O₃ and SiO₂-TiO₂ Pillared Saponite

Malla

Komarneni

1993

Clays and clay miner.

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“…The 27A1 NMR spectroscopic investigation of pillared clays is obstructed by the difficulty of analysing quantitatively the tetrahedral and octahedral resonances (Diddams et al, 1984;Pinnavaia et al, 1985;Tennakoon et al, 1986a,b), and the changes of the resonances upon calcination. The 27A1 spectra of pillared montmorillonite show a decrease in intensity of the tetrahedral resonance upon calcination, indicating the disappearance of the central fourfold coordinated Al from the pillar.…”

Section: ~ 300~mentioning

confidence: 99%

The Effect of Thermal Treatment on the Properties of Hydroxy-Al and Hydroxy-Ga Pillared Montmorillonite and Beidellite

et al. 1994

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A B S T R A C T :The pillaring process of montmorillonite and beidellite with A1 and Ga polymers has been studied using XRD, IR, 27A1, 71Ga, and 29Si MAS NMR, TGA, TEM, N2 adsorption and chemical analyses.The A1 adsorption maximum for montmorillonite is close to 5.5 mEq A1/g clay, whereas the maximum for Ga is higher. Basal spacings of both Ga-and Al-pillared clays vary between 16.7 and 18.8 ~,. Freeze-drying of pillared products followed by calcination yielded more regular pillared structures. Pillaring montmorillonite increased the BET surface area from 35 m2/g to 350 m2/g mainly by the creation of micropores <20 • in diameter. The Al-pillared clays are thermally stable to ~700~ Calcination of pillared montmorillonite liberates protons from the pillar, which diffuse into the clay sheet, lowering the thermal stability. In pillared beidellite, mainly silanol groups are formed by breaking Si-O-AI bonds. No reaction is observed between pillars and montmorillonite upon calcination, whereas in pillared beidellite a structural transformation links the pillar to inverted tetrahedra of the tetrahedral sheet. The basal spacing of Ga-pillared montmorillonite collapses to 9.5/~ at 350~ due to the Ga polymer decomposing to Ga 3+ cations.

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“…Several factors have been proposed to control the stability of the structure. Tichit et al (1985) and Tokarz and Shabtai (1985) correlated the stability of Al-montmorillonite to the density of the pillars; however, the strength of the bond linking the pillars to the clay sheet was emphasized by Plee et al (1985), Pinnavaia et al (1985), and Sterte and Shabtai (1987). These authors related the high stability of beidellite pillared by AI species and of fluorhectorite pillared by silico-aluminum species to the formation of a covalent bond.…”

Section: Introductionmentioning

confidence: 99%

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

Figuéras

Kłapyta

Massiani

et al. 1990

Clays and clay miner.

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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...

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Layer cross-linking in pillared clays

Cited by 108 publications

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Properties and Characterization of Al₂O₃ and SiO₂-TiO₂ Pillared Saponite

Properties and Characterization of Al₂O₃ and SiO₂-TiO₂ Pillared Saponite

The Effect of Thermal Treatment on the Properties of Hydroxy-Al and Hydroxy-Ga Pillared Montmorillonite and Beidellite

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

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Layer cross-linking in pillared clays

Cited by 108 publications

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Properties and Characterization of Al2O3 and SiO2-TiO2 Pillared Saponite

Properties and Characterization of Al2O3 and SiO2-TiO2 Pillared Saponite

The Effect of Thermal Treatment on the Properties of Hydroxy-Al and Hydroxy-Ga Pillared Montmorillonite and Beidellite

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

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Properties and Characterization of Al₂O₃ and SiO₂-TiO₂ Pillared Saponite

Properties and Characterization of Al₂O₃ and SiO₂-TiO₂ Pillared Saponite