A study about the use of Co or Mn-based nanocatalysts for styrene epoxidation reaction

Epoxides are very useful synthetic intermediates as they can be easily converted into a wide variety of products through different chemical transformations on the reactive oxirane ring. Despite many methodologies for the synthesis of epoxides have been reported, efficient and selective epoxidation of olefins remains a challenge. Currently, research is focused on easy-to-use and environmentally friendly oxidants such as O₂, TBHP, air or H₂O₂, together with a transition metal catalyst that helps to improve the reactivity and selectivity of the oxygen transfer process. In this work, Mn- or Co-based nanocatalysts have been studied for styrene epoxidation. These earth-abundant and low-cost metals are known to be part of biologically relevant complexes, such as porphyrins with a pivotal role in oxidation reactions. Co or Mn nanoparticles (NPs) were synthesized by fast reduction of the corresponding metal chlorides, with an excess of Li sand and a catalytic amount of an arene as electron carrier. The metal NPs thus obtained were immobilized on different materials: celite, zeolite, C act., CeO₂, ZnO, MgO and Nb₂O₅. Reaction conditions were optimized by testing different solvents (CH₂Cl₂, DMF and ACN), reaction temperatures, oxidizing agents (O₂, H₂O₂ and TBHP) and optimal catalyst loading. The progress of the reaction is controlled by CG-MS. The use of CoNPs/MgO as the catalyst and TBHP as co-oxidant, in refluxing ACN, allowed total conversion with high selectivity to the corresponding styrene oxide, after 24 hours of reaction time.