Incorporation of Aluminium and Iron into the Zeolite MCM‐58

Abstract

The hydrothermal synthesis of zeolite MCM-58 is investigated with N-benzylquinuclidinium bromide as a structure-directing agent in order to isomorphously substitute aluminium or iron for silicon. Al-MCM-58 was synthesised in a wide range of nSi/nAl ratios (from 19 to 56), and Fe-MCM-58 was successfully prepared in a narrower range of nSi/nFe ratios (from 18 to 36). The obtained products were characterised by XRD, SEM, 27Al MAS NMR, 29Si MAS NMR, FTIR, and ESR spectroscopy. Two different calcination procedures, viz. in a stream of nitrogen and air or in a stream of ammonia, were used in order to modify the acid sites in the zeolite. FTIR spectroscopy before and after the adsorption of [D3]acetonitrile and pyridine was employed to determine the concentration and type of the acid sites. The acid forms of Al(Fe)-MCM-58 are characterised by the vibrations of bridging Si–OH–Al(Fe) groups at 3628 cm–1 and 3564 cm–1 (Al-MCM-58) or 3646 cm–1 and 3520 cm–1 (Fe-MCM-58). The acid sites of both zeolites Al-MCM-58 and Fe-MCM-58 are accessible for [D3]acetonitrile and pyridine, and all materials contain substantial numbers of Lewis sites (Al-MCM-58: 50 % of the total acid sites; Fe-MCM-58: 90 %) over the whole range of nSi/nAl (nSi/nFe) ratios studied. Only a small increase in the concentration of Bronsted acid sites was achieved after calcination of the as-synthesised samples in a flow of ammonia. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)