Catalytic decomposition of N2O over monolithic supported noble metal-transition metal oxides

Abstract

The decomposition of nitrous oxide to nitrogen and oxygen using a series of monolithic (ceria-alumina washcoated cordierite) supported transition metal (Cu, Fe, Co, Ni, Mn) and noble metal (Ir, Rh) oxide catalysts has been studied using gas chromatography. The effect of combining a transition metal with a noble metal has also been investigated. A synergetic effect was observed between transition metal and noble metal oxides in the presence of a small amount of water for some of the catalysts. The synergy between Fe-Ir and Ni-Ir was also verified under dry conditions. X-ray photoelectron spectroscopic measurements on these catalysts indicate that Fe, Rh and Ir are present predominantly as Fe2O3, RhO2 and IrO2, while significant amounts of Co and Ni ions may migrate inside the support to form cobalt and nickel aluminate. Only the Fe-Ir catalyst showed a significant interaction between the noble metal and the transition metal. The effect of water, oxygen and carbon monoxide on the catalytic behaviour of the five most active catalysts (Ni-Ir, Ni-Rh, Fe-Ir, Co-Ir, Ir) has also been investigated. Oxygen and water were found to inhibit the catalytic activity, although the extent of oxygen inhibition is limited, presumably due to the presence of ceria in the monolith washcoat support. Conversely, carbon monoxide greatly enhances catalytic activity.