Mn containing 3D mesostructured FDU-5 (Ia3d) silicates with varying Si/Mn ratios were synthesized for the first time via evaporation induced self assembly (EISA) technique under acidic conditions at room temperature, employing Pl23 triblock copolymer as a structure directing agent. This method facilitates complete incorporation of higher amounts of Mn in the framework and extraframework locations of FDU-5 even under highly acidic synthesis conditions. The Mn-FDU-5 samples possessed surface areas of 300–500 m2/g, pore volumes of 0.42–0.55 cm3/g and narrow pore size distributions of 4.1–4.9 nm. Homogeneous dispersion of Mn species and aggregated Mn oxide clusters were evidenced from FIB-SEM micrographs. Complementary analytical techniques such as diffuse reflectance UV–Vis, FTIR, TPR and EPR analyses provide insights into the nature of the different types of Mn species (Mn2+, Mn3+ and Mn3O4 nanoparticles) that co-exist in FDU-5. The Mn-FDU-5 material is shown to be active for the epoxidation of trans-stilbene (TS, ~60 % conversion) to trans-stilbene epoxide (~64 % selectivity) with TBHP as oxidant. Although the activity of Mn-FDU-5 (~45 % TS conversion) is similar to those observed with MCM-41 and MCM-48 supports containing similar amounts of Mn (1 wt%), higher epoxide selectivity (~64 %) was observed with Mn-FDU-5. The mixed oxidation states of Mn (Mn2+, Mn3+) along with the extraframework Mn3O4 are found to be beneficial in catalyzing TS epoxidation.
Manganese FDU-5 Epoxidation trans-Stilbene
I. G is thankful for a research fellowship from UGC No. F.40-8(C/M)/2009(SA-III/MANF). Financial Assistance from University Grants Commission, New Delhi [F. No. 39-730/2010 (SR)] is also acknowledged. The authors also acknowledge Dr. Sridevi, Chemical Physics laboratory, CLRI for helping with EPR analysis and Dr. R. M and I. G thank DST (FIST), UGC (SAP) Department of chemistry for providing laboratory facilities at Anna University.