On the stability of alkali metal promoters in Co mixed oxides during direct NO catalytic decomposition

Abstract

Co-Mn-Al mixed oxide and Co3O4 catalysts with alkali metal promoters (K, Cs) were tested for direct NO decomposition with the aim to determine their activity and stability. The catalysts were prepared by coprecipitation with subsequent impregnation by alkali metal salts and characterized by AAS, MP-AES, XRD, N-2 physisorption and species-resolved thermal alkali desorption (SR-TAD). Long-term experiments of NO catalytic decomposition performed above the temperature of alkali metal desorption showed slow deactivation which has not yet been reported by other authors, since only short laboratory tests of NO catalytic decomposition have been presented. The reason for the observed deactivation was identified as volatilization of alkali metal promoters from the catalyst surface, which was revealed by SR-TAD and chemical analysis of alkali metals. Measurements conducted below the temperature of alkali metal desorption yielded an increase in NO conversion during the initial period of measurement, which can be explained by rearrangement of surface species.