Kinetics of Oxygen Exchange and N2O Decomposition Reaction over MeOx/CeO2 (Me = Fe, Co, Ni) Catalysts

MeOx/CeO2 (Me = Fe, Co, Ni) samples were tested in an O-18(2) temperature-programmed isotope exchange and N2O decomposition (deN(2)O). A decrease in the rate of deN(2)O in the presence of oxygen evidences the competitive adsorption of N2O and O-2 on the same sites. A study of isotope oxygen exchange revealed dissociative oxygen adsorption with the subsequent formation of surface oxygen species. The same species, more probably, result from N2O adsorption and the following N-2 evolution to the gas phase. We supposed the same mechanism of O-2 formation from surface oxygen species in both reactions, including the stages responsible for its mobility. A detailed analysis of the kinetics of isotope exchange has been performed, and the rates of one-atom (R-I) and two-atom (R-II) types of exchange were evaluated. The rate of the stage characterizing the mobility of surface oxygen was calculated, supposing the same two-step mechanism was relevant for both types of exchange. The effect of oxygen mobility on the kinetics of deN(2)O was estimated. An analysis of the possible pathways of isotope transfer from MeOx to CeOx showed that direct oxygen exchange on the Me-Ce interface makes a valuable contribution to the rate of this reaction. The principal role of the Me-Ce interface in deN(2)O was confirmed with independent experiments on FeOx/CeO2 samples with a different iron content.