Incorporation of Aluminium and Iron into the Zeolite MCM‐58

AbstractThe 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 Brønsted 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)