Effect of promoters in Co–Mn–Al mixed oxide catalyst on N2O decomposition

Catalytic decomposition of N2O over calcined Co–Mn–Al layered double hydroxide (LDH) modified with slight amount of alkali (Li, Na, K), rare earth (La, Ce), or noble metals (Pd, Pt) was studied. Two methods of promoter addition were applied: impregnation of LDH-related Co–Mn–Al mixed oxide by a promoter-containing solution and incorporation of the promoter during coprecipitation of the LDH precursor. The method of preparation affected the reducibility of the obtained mixed oxide catalysts but its effect on the surface area (with the exception of a cerium-contained sample) and N2O conversion was less evident. The modification of the Co–Mn–Al mixed oxide with K or Na increased N2O conversion, while no effect or a decrease in the N2O conversion was observed over the other examined catalysts. Alkali metals act as electron promoters; therefore, the differences in catalytic activity may be related to changes of oxygen-transition metal bond strength. The Co–Mn–Al mixed oxides with 1.8 wt% K exhibited a high catalytic activity even under the simultaneous presence of O2, H2O and NOx. The laboratory stability test revealed maintenance of the beneficial effect for 360 h.