Partial substitution of lanthanum with silver in the LaMnO3 perovskite: Effect of the modification on the activity of monolithic catalysts in the reactions of methane and carbon oxide oxidation

Partial substitution of lanthanum with silver in the LaMnO3 perovskite deposited onto a monolithic metal support enhances catalytic activity in the oxidation of CH4 and CO. The optimal silver content (x) in the La1−xAgxMnO3 perovskite amounts to 0.2 and ranges from 0.1 to 0.3 for CH4 combustion and CO oxidation, respectively. Methane conversion obtained over the monolithic catalyst with the most active perovskite (La0.8Ag0.2MnO3) at 750 °C totals 98.9% and falls slightly (to 97.6%) after 130 h on stream. Ageing at 900 °C accounts for a distinct decline in methane conversion, which drops to 67% at 750 °C. The decrease in the activity of this catalyst during the run is attributable to the decreasing SSA and decreasing proportion of Ag+ to Ag0 and to the reduction of Mn4+ to Mn3+ on the perovskite surface. When the catalyst is aged at 900 °C, the processes are enhanced; the metallic silver that segregates onto the surface tends to form agglomerates, and the composition of the catalyst surface is similar to the composition of the LaMnO3 perovskite.

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