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Infra-red studies of ammoniation of pillared montmorillonites

¹ Faculty of Chemistry, Jagiellonian University, ul. Ingardena 3, 30-060 Cracow, ² Regional Laboratory of Physicochemical Analyses and Structural Research, ul. Ingardena 3, 30–060 Cracow, ³ Department of Mineralogy and Geochemistry, Academy of Mining and Metallurgy, al. Mickiewicza 30, 30–059 Cracow, Poland, and ⁴ Institute of Physical Chemistry, Friedrich Schiller University, Lessingstrasse 10, 07–743 Jena, Germany

^* E-mail: dyrek{at}trurl.ch.uj.edu.pl

(Received 20 November 1998; revised 16 August 1999)

Ammoniation of montmorillonites pillared with polyhydroxo-complexes of Al was performed in flow conditions at 773–1073 K and monitored by IR spectroscopy. Interaction of the clay with ammonia revealed exchange of terminal and bridging -OH groups by NH₂-, NH- and N-species depending on the reaction temperature. Amination begins at 773 K while formation of NH groups starts at 873 K. Transformation of NH- into N-species occurs at 973 K. A mechanism for the ammoniation reaction is proposed and the series of the relative reactivity of OH groups was established: Si–OH > Mg–OH–Mg > Al–OH–Mg > Al–OH–Al. This series was rationalized in terms of accessibility of the OH groups.

KEYWORDS: IR, ammoniation, pillared montmorillonite, polyhydroxo complexes