Silica-embedded metal oxide nanoparticles as epoxidation catalysts: batch and continuous flow systems

Catalytic epoxidation of olefins gives epoxide chemicals for several end-user products. With the technological advancements of these processes (especially for light olefins), which have importantly contributed to the epoxides market expansion, challenges remain in developing adequate heterogeneous catalysts for converting bulkier olefins, using simple catalyst synthesis procedures, and, on the other hand, studying the catalytic performances under different operation modes. Hence, heterogeneous epoxidation catalysts are prepared via simple one-pot procedures, with the necessary versatility to tune the material properties for batch and continuous flow operation. Specifically, silica-embedded nanoparticles of molybdenum oxide (Si/Mo(x), x = Mo loading) and silica-embedded nanoparticles of binary transition metal oxides (Si/MoM, M = Ta, Nb or W) are synthesized, and promoted the epoxidation of cis-cyclooctene with tert-butylhydroperoxide as oxidant, at 70 °C. Epoxide yields in the range of 90%–100% are reached within 4 h, at 70 °C, under batch operation. Under continuous flow, steady state conditions (fixed bed reactor), catalyst Si/MoNb led to ca. 44% epoxide yield, at 70 °C. At 90 °C, Si/MoNb exhibited multifunctionality leading to 51% cyclooctanone yield. It represents the first fully inorganic heterogeneous Mo-catalyst for continuous flow olefin epoxidation and the first heterogeneous Mo-catalyst for integrated olefins-to-cycloalkanones with hydroperoxides.