Catalytic decomposition of nitrous oxide over perovskite type solid oxide solutions and supported noble metal catalysts

Abstract

The catalytic decomposition of nitrous oxide to nitrogen and oxygen has been investigated over various solid oxide solutions (SOS), La0.8Sr0.2MO3−δ (M=Cr, Fe, Mn, Co or Y), La1.8Sr0.2CuO4−δ and supported Pd, Pt catalysts. The reaction was carried out in a gradientless recycle reactor at 1 atm pressure with a feed gas containing about 0.5% N2O (in helium). Among the various solid solutions, La0.8Sr0.2CoO3−δ showed a maximum N2O conversion of 90% at 600‡C. The order of activity observed for N2O decomposition was La0.8Sr0.2CoO3−δ>La0.8Sr0.2FeO3−δ>La1.8Sr0.2CuO4−δ> La0.8Sr0.2MnO3−δLa0.8Sr0.2CrO3−δ≈La0.8Sr0.2YO3−δ. The activity of La0.8Sr0.2CoO3−δ was compared with supported Pd, Pt and also with unsubstituted LaCoO3 catalysts under similar reaction conditions. Among all the catalysts tested in this study, Pd/Al2O3 showed the lowest light-off temperature for N2O decomposition. The activity of La0.8Sr0.2CoO3−δ was found to be comparable to Pd/Al2O3 catalyst at temperatures above 500‡ C. The influence of added oxygen (about 4%) in the feed was examined over La0.8Sr0.2CoO3−δ and Pd/Al2O3 catalysts and only in the case of cobalt catalyst was the conversion of N2O decreased by ∼13%. By choosing varied sintering conditions, La0.8Sr0.2CoO3−δ of different BET surface areas were prepared and the light-off temperature was found to decrease with increase in surface area. The results obtained over solid solutions are discussed on the basis of the cation mixed valency and oxygen properties of the catalyst.