Confinement of Mn3+ redox sites in Mn-KIT-6 and its catalytic activity for styrene epoxidation

Abstract

In the present study, a series of manganese (Mn) containing 3D cubic mesoporous KIT-6 materials with different Si/Mn ratio (100, 50 25 & 10) having Ia3d space group were synthesized for the first time by a facile one-pot hydrothermal process. The synthesized materials were methodically characterized by various analytical techniques including XRD, N2 sorption, HR-TEM, diffuse reflectance UV–vis (DRS-UV-vis), EPR and FT-IR. The well ordered mesoporous nature of Mn incorporated KIT-6 materials are realized by XRD, N2 adsorption-desorption isotherm and HR-TEM analysis. Surface area, pore volume and pore size of Mn-KIT-6 with different Si/Mn ratio are in the range of 451–786 m2/g, 0.57–0.9 cm3/g and 4.5–4.9 nm respectively. The incorporation of Mn3+ in the framework and fine dispersion of Mn2+ species over silica matrix of Mn-KIT-6 are confirmed by the results of UV-DRS, FT-IR and EPR. Further, the presence of higher amount of Mn2+ extra-framework species in Mn-KIT-6(10) is realized by the presence of high amplitude signal and the contraction in H1 hysteresis loop as shown in EPR and BET isotherm respectively. Catalytic behavior of Mn-KIT-6 material was evaluated for the epoxidation of styrene with various oxidants in which t-butyl hydro peroxide (TBHP) promotes the desired formation of styrene oxide under mild liquid phase conditions. Mn-KIT-6 shown to be highly stable and active which mainly depends on the framework substituted Mn3+ sites.