Enhanced catalytic performance of Co–Sn composite oxide in styrene epoxidation with air

A simple calcination process was used to obtain Co–Sn composite oxides, the structure of which was confirmed by the XRD analysis. For comparison, the pure cobalt oxide was also prepared under the same calcination condition. According to TEM measurements, the composite oxide prepared in the presence of Sn had lower particle size than pure cobalt oxide. Accordingly, the presence of Sn increased the specific surface area as evidenced by the BET analysis data. The as-prepared Co–Sn composite oxides were applied as heterogeneous catalysts in the epoxidation of styrene with air and exhibited catalytic activity with 77.9 mol % of styrene converted and 87.1% selectivity for epoxide. These results exceed those obtained for pure cobalt oxide. However, the addition of ions of other metals such as Fe, Ni, Cu, Zn and Mn to the catalyst had a detrimental effect on the styrene epoxidation. The mechanistic considerations are also presented and suggestion is given that the DMF solvent plays a key role in the catalytic epoxidation. Results of the study indicate that Co–Sn composite oxides are efficient heterogeneous catalysts for the epoxidation of styrene with air in DMF.