Gas-phase epoxidation of propylene over iron-containing catalysts: the effect of iron incorporation in the support matrix

Abstract

The gas-phase epoxidation of propylene using iron as a catalytically active metal has been studied. The XRD-amorphous silica nanopowder was found to host active as well as redox-silent iron species, using nitrous oxide as an oxidizing agent. The presence of iron oxide nanoparticles was proven in the most active catalysts, indicating that the epoxidation proceeds over nanoparticles rather than over isolated iron atoms. A combination of XPS, TEM and voltammetric techniques elucidated the mechanism of the formation of catalytically active forms of iron oxide, distinguishing selective forms from unselective and inactive ones in the epoxidation reaction. Transition response experiments showed a good correlation between epoxidation activity, N₂O decomposition and electrochemical specification of iron oxides.