A comparative study of precursor effect on manganese post-synthetic incorporation into the T-sites of dealuminated Β-zeolite

Manganese sites on zeolites are known to be catalytically active for a range of chemical reactions. The work here describes the post-synthetic incorporation of manganese (Mn) into the vacant silanol nests of β-zeolite. We show that markedly different material properties are obtained when the Mn(NO₃)₂precursor is used as opposed to the Mn(Ac)₂precursor. Our DRIFT and XRD results show that the Mn(NO₃)₂does not promote the incorporation of the Mn into the vacant silanol nests. Rather we find, by XRD and HRSEM, that the Mn(NO₃)₂leads to the formation of poorly dispersed 14 ± 1 nm MnO₂crystals on the external surface of the dealuminated β-zeolite. On the contrary, when Mn(Ac)₂is used the XRD and DRIFT results clearly show the almost complete incorporation of Mn into the silanol nests and a significant effect on the microporous structure. HRSEM, DR-UV-Vis, H₂-TPR and N₂-physisorption show that the use of Mn(Ac)₂produces highly dispersed extra-framework Mn₂O₃and Mn₃O₄species inside and outside the pores of the dealuminated zeolite, where as in the case of Mn(NO₃)₂the pores maintain their original properties. The difference in behavior between the two precursors is correlated to the intrinsic properties of the respective precursor and its interactions with the underlying zeolite support.