Solid-state incorporation of Mn2+ ions in H-ZSM-5 zeolite

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.