Langmuir 1996, 12, 5143-5147
5143
Pillaring of a High Iron Content Saponite with Aluminum Polycations: Surface and Catalytic Properties Miguel Angel Vicente* and Miguel Angel Ban˜ares-Mun˜oz Departamento de Quı´mica Inorga´ nica, Facultad de Quı´mica, Universidad de Salamanca, Plaza de la Merced S/N, 37008-Salamanca, Spain
Mercedes Sua´rez and Jose´ M. Pozas Area de Mineralogı´a y Cristalografı´a, Departamento de Geologı´a, Facultad de Ciencias, Universidad de Salamanca, Plaza de la Merced S/N, 37008-Salamanca, Spain
Juan de Dios Lo´pez-Gonza´lez Departamento de Quı´mica Inorga´ nica, Facultad de Ciencias, Universidad Nacional de Educacio´ n a Distancia, Senda del Rey S/N, 28040-Madrid, Spain
Jose´ Santamarı´a and Antonio Jime´nez-Lo´pez Departamento de Quı´mica Inorga´ nica, Facultad de Ciencias, Universidad de Ma´ laga, 29071-Ma´ laga, Spain Received March 26, 1996. In Final Form: July 10, 1996X A high iron content saponite from Griffith Park, CA, (griffithite variety) was pillared by aluminum polycation solutions with different Al/clay ratios. X-ray diffraction shows that the intercalation process begins when aluminum polycation solutions are added, being completed during the dialysis washing of the samples. The amount of Al fixed by the intercalated solids is about 1.6 mmol of Al/g of clay. The surface area of the intercalated solids is about 300 m2 g-1, decreasing about 20% for pillared samples (calcinated at 500 °C). The total acidity ranges between 470 and 615 µmol g-1, and the pyridine adsorption indicates the existence of only Lewis acid sites. The materials are very active in the dehydration of 2-propanol giving rise exclusively to propene, with activities of around 30 µmol g-1 s-1.
Introduction Pillared clays are obtained after calcination of the intercalated compounds prepared by insertion of metallic bulk polycations into the interlayer region of the clays. Polycations of Al, Zr, Ga, Cr, or Ti have been used. Pillared clays have good thermal stability and high porosity, which give them important catalytic applications, especially for the cracking of heavy oil fractions.1 Saponite is a tetrahedrally charged trioctahedral smectite, originating as a product of the hydrothermal alteration and weathering of basalts and ultramafic rocks. Its octahedral sites are usually occupied by Mg(II), but in its ferrous variety, a quantity of Fe(II,III) substitutes Mg(II) octahedral cations this substitution being important when the Mg/Fe ratio is lower than 5:1.2 The properties of saponite have been intensely studied in recent years. An excellent pillaring ability has been observed for this clay.3-15 Some of these papers show that saponite is better suited than other clays for studying the pillaring mechanism, especially by IR and solid state NMR * Corresponding author: e-mail,
[email protected]. X Abstract published in Advance ACS Abstracts, September 15, 1996. (1) Occelli, M. L. In: Keynotes in Energy-Related Catalysis. Stud. Surf. Sci. Catal. 1988, 35, 101, and references therein. (2) de la Calle, C.; Suquet, H. Vermiculite. In: Hydrous phyllosilicates. Rev. Miner. 1988, 19, 455. (3) Chevalier, S.; Suquet, H.; Franck, R.; Marcilly, C.; Barthomeuf, D. In Expanded clays and other microporous solids; Occelli, M. L., Robson, H. E., Eds.; Van Nostrand Reinhold: New York, 1992; pp 3246. (4) Chevalier, S.; Franck, R.; Suquet, H.; Lambert, J. F.; Barthomeuf, D. J. Chem. Soc., Faraday Trans. 1994, 90, 667. (5) Usami, H.; Tagaki, K.; Sawaki, Y. Chem. Lett. 1992, 1992, 1405. (6) Schoonheydt, R. A.; Leeman, H. Clay Miner. 1992, 27, 249.
S0743-7463(96)00295-8 CCC: $12.00
techniques. Thus, synthetic saponites have been used as models for pillaring studies.11,12,15 Pillared saponites have been tested as catalysts in cracking reactions13,14 and in other reactions,5 and recently, their ability for the retention of metals from solution has been investigated.11 Moreover, the behavior of this mineral under acid treatment has recently been reported.16-18 Griffithite is a high iron content saponite from Griffith Park, CA. Recently, we have reported a high development in surface properties by acid activation of this clay, finding that both Mg(II) and Fe(III) cations are very easily removed by the acid treatment.16,17 The aim of the present study is to investigate the behavior of this high iron content saponite when it is pillared with aluminum polycations, (7) Schoonheydt, R. A.; van den Eynde, J.; Tubbax, H.; Leeman, H.; Stuyckens, M.; Lenotte, I.; Stone, W. E. E. Clays Clay Miner. 1993, 41, 598; 1994, 42, 518. (8) Li, L.; Liu, X.; Ge, Y.; Xu, R.; Rocha, J.; Klinowski, J. J. Phys. Chem. 1993, 97, 10389. (9) Malla, P. B.; Kormaneni, S. Clays Clay Miner. 1993, 41, 472. (10) Lambert, J. F.; Chevalier, S.; Franck, R.; Suquet, H.; Barthomeuf, D. J. Chem. Soc., Faraday Trans. 1994, 90, 675. (11) Bergaoui, L.; Lambert, J. F.; Suquet, H.; Che, M. J. Phys. Chem. 1995, 99, 2155. (12) Bergaoui, L.; Lambert, J. F.; Franck, R.; Suquet, H.; Robert, J. L. J. Chem. Soc., Faraday Trans. 1995, 91, 2229. (13) Chevalier, S.; Franck, R.; Lambert, J. F.; Barthomeuf, D.; Suquet, H. Appl. Catal. A: General 1994, 110, 153. (14) Suquet, H.; Franck, R.; Lambert, J. F.; Elsass, F.; Marcilly, C.; Chevalier, S. Appl. Clay Sci. 1994, 8, 349. (15) Bergaoui, L.; Lambert, J. F.; Vicente-Rodrı´guez, M. A.; Michot, L. J.; Villie´ras, F. Langmuir 1995, 11, 2849. (16) Vicente Rodrı´guez, M. A.; Sua´rez Barrios, M.; Lo´pez Gonza´lez, J. D.; Ban˜ares Mun˜oz, M. A. Clays Clay Miner. 1994, 42, 724. (17) Vicente Rodrı´guez, M. A.; Lo´pez Gonza´lez, J. D.; Ban˜ares Mun˜oz, M. A. Microporous Mater. 1995, 4, 25. (18) Vicente, M. A.; Sua´rez, M.; Lo´pez-Gonza´lez, J. D.; Ban˜aresMun˜oz, M. A. Langmuir 1996, 12, 566.
© 1996 American Chemical Society
5144 Langmuir, Vol. 12, No. 21, 1996
Vicente et al.
Table 1. Chemical Composition (wt %) of Natural and Intercalated Saponite and Al Fixed by Intercalated Solids sample
SiO2
Al2O3
MgO
Fe2O3
MnO
TiO2
CaO
Na2O
K2O
H2O
Al fixa
natural IS2.5 IS5.0 IS7.5
44.02 38.08 39.12 41.61
7.35 14.14 14.17 13.93
12.45 10.78 11.69 11.42
13.38 12.70 13.57 13.64
0.48 0.22 0.23 0.23
0.28 0.27 0.29 0.31
3.68 1.36 1.39 1.31
0.70 0.88 0.86 0.86
0.09 0.06 0.12 0.12
17.09 21.01 18.01 16.25
1.76 1.68 1.45
a
In mmol of Al/g of clay.
comparing the results obtained with that found in the literature for the pillaring of natural and synthetic low iron content or iron free saponites and specially to study the superficial acidity of the pillared samples using ammonia, pyridine, and isopropyl alcohol as probe molecules. Experimental Section Pillaring of Saponite. The
