Abstract
In the search for new applications of natural silicates, various F− treatments have been applied to sepiolite to increase its acidic properties and for use as a catalyst in reactions occurring via carbonium ions. Two types of treatments including hydrofluoric acid (HF) at different concentrations and 2 N NH4F have been utilized and the physicochemical characteristics of the resulting materials studied using standard techniques. The X-ray diffractogram (XRD) patterns indicate a decrease in crystallinity of the original material as well as the appearance of amorphous silica. SEM micrographs showed a shortening and aggregation of the sepiolitic fibers. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), thermogravimetric analysis/differential thermal analysis (TGA/DTA), N2 adsorption-desorption isotherms and Hg intrusion were used to study the changes occurring in the structure, surface area and pore distribution of samples and acidity was evaluated by IR and thermoprogrammed desorption (TPD) of adsorbed ammonia and pyridine. It was found that acidity increased in most of the samples after anionic and cationic interchange between the activating agents and the surface sites, or extralattice cations. Additionally, structural changes induced by treatments modified the Brönsted and Lewis acidity. Mild treatments with ammonium fluoride are more effective than HF treatments in acidity generation.
Similar content being viewed by others
References
Abdul-Latif N, Weaver ChE. 1969. Kinetics of acid dissolution of palygorskite (attapulgite) and sepiolite. Clays Clay Miner 17:169–178.
Barrett EP, Joyner LG, Halenda PP. 1951. The determination of pore volume and area distributions in porous substances. I. Computation from Nitrogen isotherms. J Am Chem Soc 73:373–380.
Barthomeuf D. 1985. Catalysis by acids and bases. Amsterdam: Elsevier. B. V. 89 p.
Blanco C, Herrero J, Mendioroz S, Pajares JA. 1988. Infrared studies of surface acidity and reversible folding in palygorskite. Clays Clay Miner 36:364–368.
Brückman K, Fijał J, Haber J, Kłapyta Z, Wiltowski T, Żabiński W. 1976. Influence of different activation methods on the catalytic properties of montmorillonite.Mineralogia Polonica 7:5–12.
Campelo JM, García A, Luna D, Marinas JM. 1989. Textural properties, surface chemistry and catalytic activity in cy-clohexene skeletal isomerization of acid treated natural sepiolites. Mater Chem Phys 24:51–70.
Corina A, Fornés V, Ortega E. 1985. The nature of acid sites on fluorinated γ-alumina. J Catal 92:284–295.
Corma A, Mifsud A, Pérez-Pariente J. 1986. Etude de l’attaque acide de la sepiolite: Modification des propriétés texturales. Clay Miner 21:69–84.
Corma A, Pérez-Pariente J. 1987. Catalytic activity of modified silicates: 1. Dehydration of ethanol catalyzed by acidic sepiolite. Clay Miner 22:423–433.
Dandy AJ, Nadiye-Tabbiruka MS. 1982. Surface properties of sepiolite and its catalytic activity for ethanol decomposition. Clays Clay Miner 30:347–352.
Farmer VC, Mortland MM. 1966. An infrared study of the coordination of pyridine and water to exchangeable cations in montmorillonite and saponite. J Chem Soc (A):344–351.
Fernández Alvarez T. 1972. Activación de la sepiolita conácido clorhídrico. Bol Soc Esp Cerám Vidr 11: 6.
Fijał J, Żyła H, Tokarz M. 1985. Chemical, sorptive and morphological properties of montmorillonite treated with ammonium bifluoride (NH4HF2). Clay Miner 20:81–92.
Folgado MA. 1983. Caracterización textural y estructural de una sepiolita natural y activada. [Ms.Sc. thesis], Madrid, Spain: Univ Complutense de Madrid. 128 p.
Fripiat JJ. 1988. High resolution solid state NMR study of pillared clays. Catal Today 2:281–295.
Gerberich H, Lutinskì FL, Hall WK. 1966. Studies of the hydrogen held by solids. X. Fluorided aluminas as acid catalysts. J Catal 6: 209.
González L, Ibarra LM, Rodríguez A, Moya JS, Valle FJ. 1984. Fibrous silica gel obtained from sepiolite by HCl attack. Clay Miner 19:93–98.
González F, Pesquera C, Blanco C, Benito I, Mendioroz S, Pajares JA. 1989. Structural and textural evolution of Aland Mg- Palygorskites. I Under acid treatment. Appl Clay Sci 4:373–388.
López-González JD, Ramírez-Sáenz A, Rodríguez-Reinoso F, Valenzuela-Calahorra C, Zurita Herrera L. 1981. Activación de una sepiolita con disoluciones diluádas de HNO3 y posteriores tratamientos térmicos. I. Estudio de la superficie especffica. Clay Miner 16:103–113.
Matulewicz ERA, Kerkhof FR Moulijn JA, Reìstma HJ. 1980. Structure and activity of fluorinated alumina. I. Determination of the number of protonic sites by an IR study of adsorbed pyridine. J Colloid Interface Sci 77:110–120.
Mendioroz S, Pajares JA, Benito I, Pesquera C, Gonzalez F, Blanco C. 1987. Texture evolution of montmorillonite under progressive acid treatment. Change from H3 to H2 Type of Hysteresis. Langmuir 3:676–681.
Nagata H, Shimoda S, Toshio S. 1974. On dehydration of bound water of sepiolite. Clays Clay Miner 22:285–293.
O’Reily DE 1966 Sbornik “Kataliz”. Moscow: Moscow Ed. Mir. 55 p.
Preisinger A. 1963. Sepiolite and related compounds: Its stability and application. Clays Clay Miner 10:365–371.
Prost R 1976. Spectre infrarouge de l’eau présente dans l’attapulgite et la sepiolite. Bull Grpe Fr Argiles 25:53–56.
Rey-Bueno F, Villafranca-Sanchez M, González-Pradas E, López-González JD. 1985. Adsorción de amoniaco, meti-lamina y etilamina sobre una sepiolita. An Quim 81B:18–21.
Rich AD. 1960. Industrial minerals and rocks, 3rd edition. New York: AIME. 62 p.
Ruíz-Hitzky E, Casal B. 1985. Epoxide rearrangements on mineral and silica-alumina surfaces. J Catal 92:291–295.
Serna C, Van Scoyoc GE. 1978. Infrared study of sepiolite and palygorskite surface. In: Mortland MM, Farmer VC, editors. Proc Int Clay Conf; 1978; Oxford, UK. Amsterdam: Elsevier, p 99–109.
Serna C, Van Scoyoc GE, Ahlrichs JL. 1976. Uncoupled water found in palygorskite. J Chem Phys 65:3389–3390.
Serratosa JM. 1979. Surface properties of fibrous clay minerals (palygorskite and sepiolite). In: Mortland MM, Farmer VC, editors. Proc Int Clay Conf; 1978; Oxford, UK. Amsterdam: Elsevier, p 99–109.
Sing KSW, Everett DH, Haul, RAW, Moscou L, Pierotti RA, Rouquero IJ, Siemieniewska T. 1985. Reporting physisorption data for gas/solid systems with special reference to determination of surface area and porosity. Pure Appi Chem 58:603–919.
Theng BKG. 1974. The chemistry of clay-organic reactions. London: London Hilger. 343 p.
Urabe K, Sakurai H, Izami Y. 1988. Cation-exchanged synthetic saponite as a “heat-stable” acidic clay catalyst. J Chem Soc Chem Commun: 1520.
Villafranca-Sánchez M, Valverde-García A, González-Pradas E, Rey-Bueno F. 1987. Estudio del proceso de retención de anilina por una sepiolita. An Quim 83B:151–156.
Washburn EW. 1921. Note on a method of determining the distribution of pore sizes in a porous material. Proc Natl Acad Sci USA 7:115–120.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Belzunce, M.J., Mendioroz, S. & Haber, J. Modification of Sepiolite by Treatment with Fluorides: Structural and Textural Changes. Clays Clay Miner. 46, 603–614 (1998). https://doi.org/10.1346/CCMN.1998.0460601
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1346/CCMN.1998.0460601