1. Alternative of Acid Treatement to Expand the Micropore
Volume of a Natural Clinoptilolite Zeolite
Gerardo Rodriguez-Fuentesa and Louis Charles de Ménorvalb
a Laboratorio de Ingeniería de Zeolitas, Instituto de Materiales y Reactivos (IMRE), Universidad de La Habana, Habana 10400, Cuba,
b Laboratoire des Agrégats Moléculaires et Matériaux Inorganiques (LAMMI), UMR 5072-CNRS, Université Montpellier II, 2 Place Eugène Bataillon. CC-15, Montpellier Cédex 05, France,
ABSTRACT
The acid treatment of zeolites with high silicon content has been recurrently used to increase the volume of microporous. The acid treatment usually is conducted with hydrochloric acid and it can be qualified as efficient for the enlargement of zeolites cavities. However, the extraction of aluminum atoms from the structure also takes place as a reaction not well controlled. In some zeolites like clinoptilolite (IUPAC code HEU) the extraction of aluminum atoms produces collapse of the structure at low temperature. The present work studies the treatment of the purified natural clinoptilolite NZ from Tasajera deposit of Cuba with orthophosphoric acid as an alternative to expand the volume of microporous.
Multinuclear NMR Study
31P MAS NMR
27Al MAS NMR Room temperature spectra of: (a) NZ, (b) NZH, (c) OPAZ, (d) Fe2+-OPAZ, (e) Fe 3+-OPAZ samples.
Experimental
29Si MAS NMR
% Fe content
X ray diffraction
Al Extraction
129Xe NMR
Chemical Analysis and BET measurements
Réferences
1.      G. Vessalini, FEZA 4th Euroworkshop, Natural Zeolites: Occurrence, Properties, Use, Lectures and Poster Abstracts, FEZA, (1997).
2.    G. Rodriguez-Fuentes, E. Reguera, F. Machado, D. Moronta, F. Chávez Rivas, R. Zamorano, Memorias II Congreso Mexicano de Zeolitas Naturales (2001) paper 11.
3.    G. Rodríguez Fuentes, A.R. Ruiz Salvador, M. Mir, G. Quintana, M. Delgado, O. Picazo, Microporous and Mesoporous Materials 20 (1998) 269
4.    A. Rivera, T. Farías, A. R. Ruiz-Salvador and L. C. de Ménorval, Micropor. Mesopor. Mater. 61 (2003)
5.    E. Lippmaa, M. Mägi, A. Samoson, M. Tarmak, G. Engelhardt, J. Am. Chem. Soc. 103 (1981) 4992.
6.    M. Kato, S. Satokawa and K. Itabashi, Progress in Zeolite and Microporous Materials, Chon, Ihm and Uh eds, Stu. Surf. Sci. Cat. Vol.105, Elsevier Science (1997)
Conclusions
The orthophosphoric acid treatment produced the almost total extraction of iron atoms from the tetrahedral coordination to silicon atoms in the clinoptilolite framework, while a low content of aluminum was released from tetrahedral coordination (55 ppm in 27Al-MAS/NMR spectra) to aluminum sites in extra-framework octahedral coordination probably linked to defective OH nests and close to structural silicon. The final sample was named OPAZ. The volume of microporous of NZ was enlarged from to cm3.g-1 in OPAZ. The thermal resistance of the clinoptilolite structure was reduced about 300º C. However, the reinsertion of iron atoms in the structure keeps constant the volume of microporous ( cm3.g-1) and restores the thermal resistance.