Application of NOX storage/release materials based on alkali-earth oxides supported on Al2O3 for high-temperature diesel soot oxidation

Alkali-earth oxides and nitrates supported on alumina were studied as model systems for NOX storage/release. Their impact on the high-temperature soot oxidation has been investigated. The stability of surface nitrates and temperature of NOX release increase parallel to the basicity of the cation. The presence of soot decreases the temperature of NOX release. The storage capacity depends on the several factors, such as basicity, dispersion of the cation, and pre-treating conditions. Adsorption of NO with O2 at 200 °C leads to the formation of surface nitrates that mainly exist as ionic nitrates. Stored nitrates contribute to the soot oxidation and assist to lower the temperature of soot oxidation up to almost 100 °C. In the presence of only NOX storage material the efficiency of NOX utilization is, however, quite low, around 30%. Therefore, the presence of an oxidation catalyst is essential to increase the efficiency of NOX utilization for soot oxidation up to 140% and selectivity towards CO2. A combination of oxidation catalyst with NOX storage materials enables to lower the temperature of soot oxidation more than 100 °C for the Sr- and Ca-based systems.