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

Abstract

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 can occur are CO oxidation, propane combustion, and NO oxidation. The aim of these studies was to explore whether silver, due to its strong affinity to oxygen, will counteract the stabilization of oxygen by potassium. The effect of the presence of potassium ions on the activity of the monometallic silver catalysts is beneficial in the complex stream without water vapor in all three studied reactions, although it is negligible in the model CO stream. It has been shown that water vapor strongly suppresses the activity of the Ag+K/CZ catalyst, much more so than that of the Ag/CZ catalyst. The second purpose of the work was to determine whether the negative effect of potassium ions on the activity of nanogold catalyst can be countered by the addition of silver. Studies in a model stream for CO oxidation have shown that, for a catalyst preloaded with gold, the effect of potassium is nulled by silver, and the activity of AuAg + 0.15 at%K/CZ and AuAg + 0.30 at%K/CZ is the same as that of the monometallic Au catalyst. Conversely, when the reaction is carried out in a complex stream, containing CO, C3H8, NO, O2, and water vapor, the presence of water vapor leads to higher CO conversion as well as increased NO2 formation and slightly suppresses the C3H8 combustion.

Reducibility Studies of Ceria, Ce0.85Zr0.15O2 (CZ) and Au/CZ Catalysts after Alkali Ion Doping: Impact on Activity in Oxidation of NO and CO

“…It can be seen that these elements are distributed evenly on the surface of the sa Furthermore, the distribution of gold is not changed by the addition of sodium ( 8a,b), although the predeposited gold influences the distribution of sodium (Figure The intensity of the sodium signal from the surface is stronger in the case of the go alyst. A similar observation was made with the other alkali metal ions deposited ceria-zirconia preloaded with gold and with the sequential deposition of gold and onto ceria-zirconia [19]. Studies in the complex stream, which, apart from CO, contains other componen the detailed composition, see Materials and Methods), show that although the ef potassium ions on the activity of a gold catalyst in CO oxidation is detrimental ( 9a), as reported by us earlier [11], its effect on the availability of oxygen for oxida NO is not correlated with the reducibility of the catalyst (Figure 9b).…”

“…The intensity of the sodium signal from the surface is stronger in the case of the gold catalyst. A similar observation was made with the other alkali metal ions deposited onto ceria-zirconia preloaded with gold and with the sequential deposition of gold and silver onto ceria-zirconia [19].…”

“…Among the research on ceria-based low-temperature CO oxidation catalysts is a study on the effect of doping the support with Fe, La and Zr on the activity of the catalyst [16], which showed that the best effect is observed when ceria contains zirconia. An interaction of the active phase with the support can sometimes be observed when considering the C 3d region in X-ray photoelectron spectroscopy (XPS) spectra and profiles in temperature-programmed reduction (TPR) studies, as in the case of Ag-CeZrO 2 and Au-Ag/CeZrO 2 catalysts [19]. Moreover, in the case of palladium catalysts for low-temperature CO oxidation, it has been shown that the active sites are formed thanks to the interaction of Pd with CeO 2 [15].…”

A comparison of dry and wet condition CO oxidation activity of a supported silver catalyst at low temperature

“…66 Similarly, Glinski and coworkers also reported significant suppression of CO oxidation activity on Ag/CeO 2 –ZrO 2 catalyst in the presence of water but the catalytic performance remained unaffected after the incorporation of potassium in the system. 67 Here, we evaluated the effect of water vapor on the catalytic performance of Ag/TiO 2 -3, which shows outstanding activity in the absence of water. The feed gas containing 5 vol% of water was passed through a water saturator before being introduced into the reactor after maintaining the above-mentioned reaction conditions (flow rate = 33 ml min −1 ; WHSV = 10 000 ml g (cat) −1 h −1 ).…”