CATALYTIC DECOMPOSITION OF NITROUS-OXIDE OVER PEROVSKITE-TYPE SOLID OXIDE SOLUTIONS AND SUPPORTED NOBLE-METAL CATALYSTS

The catalytic decomposition of nitrous oxide to nitrogen and oxygen has been investigated over various solid oxide solutions (SOS), La(0.8)Sr(0.2)MO(3-delta) (M = Cr, Fe, Mn, Co or Y), La1.8Sr0.2CuO4-delta 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-delta showed a maximum N2O conversion of 90% at 600 degrees C. The order of activity observed for N2O decomposition was La0.8Sr0.2CoO3-delta >La0.8Sr0.2FeO3-delta>La1.8Sr0.2CuO4-delta>La(0.8)Sr(0.2)CrO(3-delta)approximate to La0.8ST0.2YO3-delta. The activity of La0.8Sr0.2CoO3-delta 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-delta was found to be comparable to Pd/Al2O3 catalyst at temperatures above 500 degrees C. The influence of added oxygen (about 4%) in the feed was examined over La0.8Sr0.2CoO3-delta and Pd/Al2O3 catalysts and only in the case of cobalt catalyst was the conversion of N2O decreased by similar to 13%. By choosing varied sintering conditions, La0.8Sr0.2CoO3-delta 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.