TiO2 supported cobalt oxide for olefin epoxidation reaction – characterization, catalytic activities and mechanism – using a DFT model

Abstract

Metal oxide catalysts are known to trigger C–H bond activation selectively, indicating their suitability for olefin epoxidation. Nano-structured Co₃O₄ supported on TiO₂ was prepared for selective epoxidation of a number of olefins under optimized reaction conditions. An appropriate synthetic procedure yielded a catalytic material (Co–Ti (NP)^HT) with desired crystal size and interface conditions. Incorporation of Co into the Ti matrix resulted in an enhancement in the specific surface of Ti–Co nanoparticles (77.93 m² g⁻¹). XPS measurements evaluated the surface cobalt atom concentration (5.77%) in Ti–Co(NP)^HT, indicating more dispersion of cobalt oxide species. Catalytic application of the material, using various olefins (under optimized reaction conditions) shows higher conversion (>85%) in a 6-h time interval. The substrate : oxidant (H₂O₂) concentration in an optimized molar ratio of 1 : 2 shows high olefin conversion for the formation of olefin oxide. The reactivity of olefins was found to be in the order: cyclohexene > methylstyrene > styrene > chlorostyrene > p-nitrostyrene. A DFT model compared the HOMO–LUMO energies of styrene and its substituted forms. The reusability of Ti–Co (NP)^HT tested up to four continuous cycles of batch operations indicates a negligible loss (0.25–0.30%) of catalytic activity.