Influence of Molybdenum on Ceria Activity and CO2 Selectivity in Propene Total Oxidation

A total oxidation of propene into CO₂ is obtained on pure ceria at 673 K. However, in the presence of molybdenum, propene can be partially oxidized at room temperature. The Electron Paramagnetic Resonance (EPR) indicates changes in the oxidation state of molybdenum occurring upon interaction with propene. It has been found that the concentration of Mo(V) influences the propene conversion. The interaction between propene and molybdenum leads to the formation of surface species that, depending on the strength of their bonding to the surface, can be decomposed to ethene or coke. These results have been confirmed by infrared (FTIR) study. The oxidation reaction of propene is in competition with that of coke or ethene deposit on the catalyst surface, which can explain the decrease of the catalyst activity and selectivity in the presence of high molybdenum loadings.     

Formation of cereous sulphate phase upon interaction of So2 with ceria at room temperature

The adsorption of SO₂ gas on ceria solid at room temperature has been investigated by thermal analysis, Raman spectroscopy and electron paramagnetic resonance (EPR). The results confirm that SO₂ transformation into sulphate species occurs at 25°C with a concomitant reduction of Ce⁴⁺ to Ce³⁺ ions. The formation of Ce(III)-sulphate phase has been evidenced on ceria surface. The thermal analysis revealed a complete decomposition of cereous sulphate phase to CeO₂ at 785°C. The change of oxidation state of Ce(IV) to Ce(III) during the formation of sulphate phase has been confirmed also by EPR technique. This revised version was published online in August 2006 with corrections to the Cover Date.