Efficient epoxidation of styrene within pickering emulsion-based compartmentalized microreactors

The epoxidation of styrene is an important route to synthesize organic intermediate, but how to effectively promote the formation of target superoxide radicals and then regulate the production of styrene oxide in two-phase reaction system remains an urgent challenge. In this study, MnOx nanocatalysts with abundant oxygen vacancies were fabricated using reverse-micelle as template, and then were endowed with an amphiphilic surface through post-modification. With such MnOx catalysts, Pickering emulsion could be formulated, in which numerous compartmentalized droplet microreactors were created for the epoxidation of styrene. The rich oxygen defects on MnOx were found to be useful to improve the chemisorption of t-butylhydroperoxide, and the active complexes formed by coordination of Mn3+ with N, N-dimethylformamide favored the generation of preferable superoxide radicals for the synthesis of styrene oxide. Moreover, it was also found that compartmentalization effects arising from Pickering emulsion droplets modifies the radicals reaction path, significantly improving the catalytic efficiency and selectivity. As a result, in the Pickering emulsion system, 90.0% selectivity towards styrene oxide and a turnover frequency of 581 h-1 could be obtained, which were higher than ever reported results. The Pickering emulsion-based compartmentalized microreactors can provide versatile platforms to efficiently control the epoxidation of styrene involving free radicals.