Activity of Ag/CeZrO2, Ag+K/CeZrO2, and Ag-Au+K/CeZrO2 Systems for Lean Burn Exhaust Clean-Up

Herein, the activity of Ag and bimetallic Au-Ag catalysts, supported over Ce0.85Zr0.15O2(CZ), was investigated in a complex stream, whose components included CO, C3H8, NO, O2, and,optionally, an injection of water vapor. In such a stream, three of the possible reactions that canoccur are CO oxidation, propane combustion, and NO oxidation. The aim of these studies was toexplore whether silver, due to its strong affinity to oxygen, will counteract the stabilization of oxy-gen by potassium. The effect of the presence of potassium ions on the activity of the monometallicsilver catalysts is beneficial in the complex stream without water vaporin all three studied reactions,although it is negligible in the model CO stream. It has been shown that water vapor strongly sup-presses the activity of the Ag+K/CZ catalyst, much more so than that of the Ag/CZ catalyst. Thesecond purpose of the work was to determine whether the negative effect of potassium ions on theactivity of nanogold catalyst can be countered by the addition of silver. Studies in a model streamfor CO oxidation have shown that, for a catalyst preloaded with gold, the effect of potassium isnulled by silver, and the activity of AuAg + 0.15 at%K/CZ and AuAg + 0.30 at%K/CZ is the same asthat of the monometallic Au catalyst. Conversely, when the reaction is carried out in a complexstream, containing CO, C3H8, NO, O2, and water vapor, the presence of water vapor leads to higherCO conversion as well as increased NO2 formation and slightly suppresses the C3H8 combustion