Mechano-synthesis of a AgSrFeO₃ catalyst for epoxidation of ethylene in a chemical looping set-up

The catalyst AgSrFeO₃(imp), used in chemical looping epoxidation of ethylene-to-ethylene oxide (EtO), is usually synthesised via a conventional impregnation method. We have used a mechano-chemical method to synthesise the catalyst, AgSrFeO₃(ss), by initially homogenising Fe₂O₃, SrCO₃ and AgNO₃ (15 wt% loading of Ag) and ethanol (0.25 mL g⁻¹ precursor) as a binder in a mortar and pestle, followed by ball milling at 500 Hz for 1 h and drying at 120 °C. The AgSrFeO₃(ss) thus produced was characterized using XRD, XPS, TGA, and SEM analyses after calcination and tested in a reactor setup that allowed the silver active site in the catalyst to receive oxygen from the active solid support and not from a gas stream for the epoxidation reaction. The ethylene epoxidation conversion rate for our AgSrFeO₃(ss) was 9-12% but with a superior selectivity of 42-62% and a conversion rate that was sustained for at least 20 cycles compared to the conversion rate of 10-15% for AgSrFeO₃(imp) that kept decreasing after the first cycle. We have thus demonstrated a more straightforward way to make AgSrFeO₃, with a better yield of EtO with AgSrFeO₃(ss) compared to the AgSrFeO₃(imp) catalyst, which shows superior performance for chemical looping epoxidation of ethylene to what has been reported so far.