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Direct decomposition of nitric oxide (NO) proceeds over Co−Mn−Al mixed oxides promoted by potassium. In this study, answers to the following questions have been searched: Do the properties of the K-promoted Co−Mn−Al catalysts prepared by different methods differ from each other? The K-precipitated Co−Mn−Al oxide catalysts were prepared by the precipitation of metal nitrates with a solution of K₂CO₃/KOH, followed by the washing of the precipitate to different degrees of residual K amounts, and by cthe alcination of the precursors at 500 °C. The properties of the prepared catalysts were compared with those of the best catalyst prepared by the K-impregnation of a wet cake of Co−Mn−Al oxide precursors. The solids were characterized by chemical analysis, DTG, XRD, N₂ physisorption, FTIR, temperature programmed reduction (H₂-TPR), temperature programmed CO₂ desorption (CO₂-TPD), X-ray photoelectron spectrometry (XPS), and the species-resolved thermal alkali desorption method (SR-TAD). The washing of the K-precipitated cake resulted in decreasing the K amount in the solid, which affected the basicity, reducibility, and non-linearly catalytic activity in NO decomposition. The highest activity was found at ca 8 wt.% of K, while that of the best K-impregnated wet cake catalyst was at about 2 wt.% of K. The optimization of the cake washing conditions led to a higher catalytic activity.