SYNTHESIS OF CANCRINITE UNDER APPLICATION OF ORGANIC SOLVENTS:
AN OPPORTUNITY TO ACHIEVE A TEMPLATE-FREE CHANNEL SYSTEM?

Britta Posnatzki¹, Michael Fechtelkord, Josef- Christian Buhl

Institut für Mineralogie, Universität Hannover, Welfengarten 1, D - 30167 Hannover, Germany

e-mail: B.Posnatzki@mineralogie.uni-hannover.de

Keywords: Hydrothermal synthesis, organic solvents, cancrinite, MAS NMR spectroscopy

Cancrinite is a well-known natural zeolite having a Si/Al- ratio of unity which is readily synthesized in systems consisting of Na₂O - SiO₂ - Al₂O₃ - H₂O in the presence of a large variety of salts [1]. The characterizing structural feature is a single 12- ring channel parallel to the c- axis [2]. This one-dimensional channel system with a diameter of 6.8 A is a perfect matrix for the enclathration of orientated molecules [3, 4]. The insertion of organic macromolecules as reactive compounds for later catalytic reactions is possible. Furthermore, the application of small organic precursor molecules is desirable which can be removed by heating to provide a template-free channel system. In cancrinites prepared under well-studied hydrothermal conditions the pores are blocked up by anions like CO₃^2-, NO₃^- or SO₄^2-. Attempts to remove these templates by calcination lead to decomposition of the framework structure.

Fig.1: XRD-pattern of cancrinite synthesized in a NH₃- solution

Synthesis of zeolites in organic systems is a common way for the formation of novel structures, compositions or special characteristics. Since Bibby and Dale [5] prepared silica-sodalite in ethylene glycol, several zeolites with known structures have been synthesized in organic, non-aqueous media. Reports on cancrinite syntheses in organic solvents are scarce:

Tab. 1: Reaction compounds

Milestone et al. [6] and Liu et al. [7] report about the formation of sodalite and cancrinite in 1,3- and 1,4-butane-diol. These cancrinites can absorb water, hexane and cyclohexane [7]. Vaughan [8] has developed ECR-5 - a cancrinite structure-type material - under application of ammonia and aqueous ammonia solutions. ECR-5 is distinguish by a high silica content and an increased adsorption capacity compared to conventional cancrinite.

In this paper we report about synthesis of cancrinite under application of organic solvents. The reaction compounds used are listed in Table 1. Syntheses were carried out in coated stainless steel autoclaves at temperatures from 373 K to 473 K for a duration up to 2.5 weeks.

The products were analysed by X-ray powder diffraction, IR- and MAS NMR spectroscopy.

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[4] Barnakov, Y.A. et al., Inorg. Mater., 31 (1995), 748
[5] Bibby, D.M., Dale, M.P.; Nature; 317; (1985); 157
[6] Milestone, N.B., Hughes S. M. and Stonestreet P. J., Stud. Surf. Sci. Catal., 98, (1995) 42
[7] Liu, C., Li, S., Tu K. and Xu R., J. Chem. Soc. Chem. Commun., (1993) 1645
[8] Vaughan, D.E.W., E. Patent A - 190,90, (1986)