Ag/CeO₂, Ag/MnO_x, and Ag/CeMnO_x (at different Ce/Mn molar ratios) synthesized via citrate sol-gel method were investigated in soot oxidation. The presence of NO in the reaction mixture inhibited soot oxidation. By adding CO to the NO + O₂ reaction mixture no inhibition of soot combustion was observed, and NO was converted to N₂ via SCR with CO before its total oxidation to CO₂.

Abstract

This study investigates the effectiveness in soot oxidation under tight and loose contact of Ag/CeO₂, Ag/MnO_x, and Ag/CeMnO_x catalysts with different Ce:Mn molar ratios prepared by the citrate sol-gel method. The sol-gel method promoted the formation of a nanodomain structure in the CeMnO_x composite. The interaction between cerium and manganese oxides and the Ce/Mn ratio were the key factors to form such a nanodomain structure. A 1:1 Ce/Mn ratio provided high activity and stability by preventing CeO₂ nanoparticle sintering, while at different Ce/Mn ratios deactivation eventually occurred. The presence of NO in the reaction mixture inhibited soot oxidation, while the CO presence in the NO + O₂ mixture limited such effect. The most promising Ag/CeMnO_x catalyst with 1:1 Ce/Mn ratio was successfully applied to a cordierite monolith. Both powder and the monolithic catalysts selectively oxidized soot to CO₂ below 500 and 600 °C, respectively, demonstrating to be promising for practical applications in efficient soot oxidation.