Synthesis and Characterization of Phase-Pure Manganese(II) and Manganese(III) Silicalite-2

Abstract

Manganese silicalite-2 was synthesized at high pH using the molecular cluster Mn 12O 12(O 2CCH 3) 16 as a Mn source. The silicalite-2 (ZSM-11) materials were synthesized using 3,5-dimethyl- N, N-diethylpiperdinium hydroxide as a structure-directing agent to produce phase-pure ZSM-11 materials. No precipitation of manganese hydroxide was observed, and synthesis resulted in the incorporation of up to 2.5 mol % Mn into the silicalite-2 with direct substitution into the framework verified by the linear relationship between the unit cell volume and loading. The Mn is reduced to Mn (II) during hydrothermal synthesis and incorporated into the silicalite-2 framework during calcination at 500 degrees C. Further calcination at 750 degrees C does not affect the crystallinity but oxidizes essentially all of the Mn (II) to Mn (III) in the framework. The large difference in oxidation temperatures between the II and III oxidation states provides a means of producing relatively pure manganese(II) and manganese(III) silicalite-2 materials for applications such as catalysis.