Microwave Hydrothermal Synthesis of Bimetallic (Ti-V) Ions Modified MCM-41 for Epoxidation of Styrene
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Microwave Hydrothermal Synthesis of Bimetallic (Ti-V) Ions Modified MCM-41 for Epoxidation of Styrene Yajie Guo, Guangjian Wang*, Yuran Wang, Zhengwang Liu, Guangqing Liu, Yiwu Liu. a School of Chemistry and Materials Science, Huaibei Normal University, Huaibei 235000, P.R. China b School of Chemistry and Chemical Engineering, Shanghai Jiaotong University, Shanghai 200030, P.R. China ABSTRACT Mesoporous molecular sieves MCM-41 modified by single (Ti) and bimetal (Ti-V) ions with highly ordered hexagonal arrangement of their cylindrical channels were prepared by direct synthesis under microwave–hydrothermal (M–H) conditions at 403K. Characterizations with powder X-ray diffraction (XRD), 29Si magic-angle spinning (MAS) NMR, N2 adsorption– desorption, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelcctron spectra(XPS) and transmission electron microscopy (TEM) showed that Ti and V ions were introduced into MCM41 under M-H conditions and Ti/V-Si bond was formed. Results revealed that all the samples were of a typical hexagonal arrangement of mesoporous structure. The modified materials were high active and selective in the epoxidation of styrene at 343 K in comparison with singlefunctional MCM-41. Moreover, compared to conventional method, the presented microwave hydrothermal synthesis of molecular sieves greatly improved the selectivity to styrene oxide, e.g., it reached 58.6% at styrene conversion of 18.7% over Ti-V-MCM-41 (50). Keywords: Microwave hydrothermal synthesis; Mesoporous molecular sieves; Ti-V-MCM-41; Epoxidation; Styrene 1 INTRODUCTION The successful syntheses of the M41S family of ordered mesoporous materials in 1992 sparked worldwide interest in their synthesis and applications, specially in heterogeneous catalysis and separation science [1]. In order to improve the catalytic activity of the mesoporous materials, especially to create redox active sites, active sites were incorporated into the silica framework or grafted on the surface [2]. The incorporation of transition metal ions was a common method for introducing active sites in MCM-41. And it could isolate these active centers and thus make them highly efficient. Transition metal ions such as Ti [3-7], V [8-12], Zr [13-15] and Mn [15,16] have been successfully incorporated into the MCM-41 framework. These modified MCM-41 materials exhibited outstanding catalytic activity in selective oxidation reactions using hydrogen peroxide or alkylhydroperoxides at mild conditions. The incorporation of two different metal ions might therefore create new hybrid materials with different or original redox and acid properties. However, only few studies concerned the synthesis and catalysis of bimetallic ions modified mesoporous molecular sieves [15, 17, 18, 19] based on synergistic effect of two metal ions. So far, to the best of our knowledge, successful attempts, on the basis of synergistic effect of different metal ions, for one-step direct synthesis of Ti-V-MCM-41 have not b
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