The Effect Of Partial Substitution Of Co In LaMnO₃for NO Oxidation And Hydrothermal Stability

There is increasing realization on the diesel vehical by means of highlyfuel-efficiecy properties, and then diesel exhaust aftertreatment tecknoledges is fastlydeveloped. Diesel exhaust emission levels are day by day stringent regulations.Because of including lots of oxygen, three way catalyst （TWC） can no efficientlyregulate and transform NO_xin lean diesel engine. Therefore, the development ofnew catalysts to reduce NO_x emissions is of great significance.In this paper, Co-doped perovskite oxides were synthesized by the sol-gel method,and then were hydrothermally treated at800oC. Crystal phase of all the samples wastested by XRD. The surface area of all the samples was characterized by BET, and thesurface NO_xadsorbed species, transition metal reducibility and NO catalytic oxidationactivity were investaged. The aim is the effect of Co partial substitution on physicalchemistry properties and catalytic oxidation activities.In H₂-TPR measurement, we find the interaction betreen Co ion and Mn ion, andthe content of Mn⁴⁺is in nonline with cobalt doped content. The effect of cobaltpartial substitution on relation of reducibility and active oxygen species to catalyticactivility is investigated by CO-O₂experiment. The result is that better transitionmetal reducibility and active oxygen species are favorable for NO oxidation catalyticproperties in lean conditions.The surface NO_xadsorbed species in presence of NO and O₂were studied byNO_x-DRIFTS measurement. We find that the formation of NO_xadsorbed species onthe surface of the samples is very easy. In these adsorbed species, monodentatenitrates which decomposed above300oC can desorb NO₂into gas phase. With regardto the effects of Co²⁺substitution on Mn³⁺, NO oxidation performances have beenimproved by gradually increasing the amount of Co in non-linear order. The catalyticactivities were enhanced significantly with cobalt substitution, and achieved the bestwhen y was0.1, but gradually decreased at higher y values. After hydrothermaltreatment, NO oxidation activities for all the samples were partially decreased.