TiO 2 supported cobalt oxide for olefin epoxidation reaction - characterization, catalytic activities and mechanism - using a DFT model.

Metal oxide catalysts are known to trigger C-H bond activation selectively, indicating their suitability for olefin epoxidation. Nano-structured Co 3 O 4 supported on TiO 2 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 m 2 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 (H 2 O 2 ) 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.