NOx-assisted soot oxidation with alkaline-earth metals (Ca, Sr, Ba) loaded on Ag/2MnOx-1CeO2

Previously, we demonstrated that Ag/2MnOx-1CeO2 is the optimal catalyst for NOx-assisted soot oxidation and that the amount of NOx adsorption is major factor for NOx-assisted soot oxidation activity. Thus, in this study, alkaline-earth metals were introduced into Ag/2MnOx-1CeO2 to promote NOx-assisted soot oxidation activity by increasing NOx adsorption. As a results, Ag(Er)/2MnOx-1CeO2 catalysts exhibited enhanced NOx adsorption, which improved their NOx-assisted soot oxidation activity compared with that of Ag/2MnOx-1CeO2. Among them, AgSr/2MnOx-1CeO2 and AgBa/2MnOx-1CeO2 exhibited high NOx adsorption capacity. In particular, AgSr/2MnOx-1CeO2 greatly improved NOx-assisted soot oxidation activity by desorbing NOx at an appropriate temperature (approximately 350 °C). On the other hand, AgBa/2MnOx-1CeO2 adsorbed NOx even at high temperature, so its NOx-assisted soot oxidation activity was lower than that of AgSr/2MnOx-1CeO2. Therefore, the T20 of AgSr/2MnOx-1CeO2 decreased to 80 °C compared with Ag/2MnOx-1CeO2. Consequently, the developed AgSr/2MnOx-1CeO2 catalyst is an optimal catalyst for NOx-assisted soot oxidation activity compared to existing catalysts. Finally, this study demonstrates that the increase in NOx adsorption enhances the NOx-assisted soot oxidation activity, but the NOx desorption temperature is a more important factors for improving the NOx-assisted soot oxidation activity.