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Abstract:
The high-temperature interaction between H-ZSM-5 zeolite and solid MnCl2, MnSO4, Mn(CH3CO2)2 and Mn3O4 has been studied by temperature-programmed desorption of ammonia, IR, EPR and mass spectrometry. It has been shown that the degree of solid-state ion exchange for MnCl2 is strongly affected by the temperature of the heat treatment. Depending on the amount of manganese cations present in the zeolite–salt mixture, at 770 K an exchange degree of 60–85% can be obtained. The solid-state reaction of MnSO4 at the same temperature leads only to 20% exchange of Mn2+ ions, while that of Mn3O4 results in ca. 50% exchange of Mn2+. Owing to its decomposition above 520 K to Mn oxides, Mn(CH3CO2)2 behaves similarly to these oxides; only part of the bridging OH groups are replaced by Mn ions. For all the Mn compounds studied, the solid-state reaction, resulting in replacement of protons of acidic skeletal OH groups by Mn2+ ions, appears to take the same course: most of the Mn2+ ions are exchanged in the initial stage of the reaction and then the reaction rate considerably decreases, levelling off to zero.
