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

Co-Mn-Al Mixed Oxides Promoted by K for Direct NO Decomposition: Effect of Preparation Parameters

“…Selected experimental parameters (K content, specific surface area, particle size and unit cell parameter) for the investigated fresh and used catalysts. A small loss of K (12.5%) was also observed during the catalytic tests, which corresponds to the results published in our previous work [11]. However, this trend was surprisingly not confirmed for all sets of the catalysts (not shown), which can be caused by a non-homogenous distribution of potassium in the samples (caused by its bulk and surface migration and/or vaporization) and the complexity of potassium content determination.…”

“…It means that processes that take place during calcination differ from processes taking place during the stabilization period of NO catalytic decomposition and the latter processes are connected with reaction itself-in other words with the adsorption/desorption processes, the surface coverage by reactants or reaction intermediates or the reaction-induced surface reconstruction, rather than with strictly physical processes. In previous studies it was proposed that the stabilization period is connected with alkali metal vaporization [11], which surely takes place within the time on stream. However, it is interesting that the stabilization process in all cases consists of two parts.…”

“…Many catalysts for direct NO decomposition have been tested; however, none of them have been sufficiently stable, active and selective at economically feasible temperatures yet. The studied catalysts are mainly based on precious metals (Pt, Pd, Rh) [3][4][5], zeolites [6][7][8] or single [9,10] and mixed oxide catalysts [11][12][13]. The results suggest that further increase in catalytic activity would be difficult to achieve with metals or alloys alone or simple metal oxides.…”

“…Co-based mixed oxides promoted by alkali metals were used as catalysts for various reactions and they showed interesting results in NO decomposition [9,11]. From previous studies, it is known that alkali metals volatilize from transition metal oxides at temperatures higher than 500 • C [16][17][18], which could affect long-term stability of the catalyst [11]. The above mentioned results imply that the stability of alkali metal promoters has to be improved for viable application of these catalysts.…”

Precipitated K-Promoted Co–Mn–Al Mixed Oxides for Direct NO Decomposition: Preparation and Properties

“…As shown in [5], the method of catalyst preparation affects its activity and stability. Pacultova et al [15] found out that potassium modified Co-Mn-Al mixed oxide catalysts prepared from hydrotalcite-like precursors could efficiently catalyze the decomposition reaction, as it proceeds successfully in the temperature region of 600-700 • C. The durability of the activity of the catalyst can be influenced by stability of potassium in the catalysts at the applied reaction conditions. The co-precipitation of metal nitrates by a Na 2 CO 3 /NaOH water solution and subsequent impregnation of the resulting wet cake by KNO 3 solution (the K-impregnation of wet cake is labeled as BP) led to a higher activity and stability of the catalyst than the other examined methods, like the impregnation of the calcined Co-Mn-Al precursor with a solution of KNO 3 or the calcination of corresponding metal nitrates.…”