Synthesis, characterization and catalytic performance of Mo-TUD-1 catalysts in epoxidation of cyclohexene

A new, 3-D mesoporous amorphous molybdenum-containing silica, denoted Mo-TUD-1, was prepared with variable Mo-loading via direct hydrothermal treatment using triethanolamine as a template. Elemental analysis, N-2 sorption measurements, NMR spectroscopy, XRD, UV-Vis spectroscopy, SEM, HR-TEM, and Raman spectroscopy indicated that as a function of increasing loading, the morphology of Mo changes from isolated sites to nano particulates, and finally to crystalline MoO3 at a loading higher than 5 wt%. The catalytic performance of the Mo-TUD-1 samples was investigated in the liquid phase epoxidation of cyclohexene with TBHP as an oxidant. Mo-TUD-1 with a low molybdenum loading showed a higher TON as compared to samples with a high loading, suggesting that isolated Mo-sites are more active than particulate MoO3. Stability and reusability of the catalyst containing isolated sites were also investigated. While leaching was observed initially, stable performance was obtained in as many as three subsequent catalytic runs.