Manganese-containing silica-based microporous molecular sieve MnS-1: Synthesis and characterization

Abstract

Manganese-containing silicalite-1 (MnS-1) was synthesized hydrothermally in the presence of the structure-directing agent (template) tetraethylammonium hydroxide (TEAOH) for the first time. The highly crystalline MnS-1 crystallized from a gel with a molar composition of 2:1:1:50:25:935 Na2O:K2O:MnO:SiO2:TEAOH:H2O at 175 degreesC after 3 days. The product was thermally stable up to 700 degreesC in air. The template-free MnS-1 was prepared by calcination at 550 degreesC in an oxygen flow. The incorporation of manganese into the framework sites of silicalite-1 was suggested by elemental, thermogravimetric, and cation exchange analyses. The X-ray absorption spectroscopic methods XANES and EXAFS confirmed the incorporation of Mn3+ into a silicalite-1 framework. FT-IR spectroscopic studies of CO adsorption at 100 K on the MnS-1 revealed the Lewis acidity of the sample and the presence of both Mn3+ and Mn2+ cations in the structure.