Co-Mn-Al mixed oxides as catalysts for ammonia oxidation to N2O

Abstract

Mixed oxide catalysts containing Co, Mn, and Al in a molar ratio of 4:1:1 were prepared by heating precursors obtained by a mechanochemical method (when appropriate nitrates were milled with ammonium hydrogen carbonate) or by coprecipitation. The precursors and related mixed oxides obtained at 500 °C were characterized by XRD, TG/DTA, UV–Vis, IR spectroscopy, TPR and NH3-TPD, and were tested for activity and selectivity in ammonia oxidation to N2O. The precursors prepared by mechanochemical reaction showed very similar phase composition to that of the coprecipitated product. All examined mixed oxide catalysts were active in the low temperature range (100 % conversion of NH3 was achieved at 250 °C), but the selectivity was sensitive to catalyst composition and the method used for preparation of the precursors. Non-modified Co–Mn–Al mixed oxide catalyst obtained from the coprecipitated precursor exhibited higher selectivity towards N2O formation than the calcined product prepared by the mechanochemical method. Modification of the latter mixed oxide catalysts with cesium promoter (1 wt%) significantly increased their selectivity to nitrous oxide. The yield of N2O at 250 °C was close to 100 %.