Activating effect of cerium in hydrotalcite derived Cu-Mg-Al catalysts for selective ammonia oxidation and the selective reduction of NO with ammonia

Hydrotalcite originated mixed metal Cu-Mg-Al oxide system was doped with various amounts of cerium (0.5 or 3.0 wt%) and tested in the role of catalysts for the selective catalytic oxidation of ammonia to dinitrogen (NH3-SCO) and the selective catalytic reduction of NO with ammonia (NH3-SCR). The activating effect of cerium was observed in both studied processes. However, the CeO2 loading is a very important parameter determining catalytic performance of the studied samples. It was shown that an introduction of cerium into Cu-Mg-Al mixed oxide resulted in its significant activation in the low-temperature NH3-SCR process, independently of the CeO2 loading and a decrease in the efficiency of the NO reduction at higher temperatures, which was more significant for the catalyst with the lower cerium content. In the case of the NH3-SCO process, the introduction of cerium into Cu-Mg-Al mixed oxide resulted in the activation of the low temperature reaction, which was more intensive for the catalyst with lower cerium content. These effects were related to the presence of cerium in the form of crystallites of various size and therefore their different reducibility.