Effect of Potassium Nitrate Modification on the Performance of Copper-Manganese Oxide Catalyst for Enhanced Soot Combustion

An enhanced catalytic activity and improved reusability were achieved by applying facile KNO₃ modification during the synthesis of a copper-manganese mixed oxide (CuMnO). Upon KNO₃ modification, the characteristic finishing temperature (T_f) of catalytic soot combustion was decreased from 360 °C for CuMnO to 338 °C for the K-modified product CuMnO(K). Moreover, this T_f value for CuMnO(K) remained remarkably low (346 °C) even after five runs of an activity test. The excellent performance of CuMnO(K) is attributed to its well-dispersed nanoparticle morphology, which is totally different from the microspherical features of CuMnO and is beneficial for its sufficient contact with the soot particles. Additionally, an interesting phase evolution of CuMnO(K) was observed for the first time from Cu_1.5Mn_1.5O₄ to the mixed phases of CuO, K₂Mn₄O₈, and MnO_x during the consecutive test runs. These mixed phases are believed to be responsible for the enhancement and stabilization of the catalytic activity. Furthermore, the mechanism for the morphology transformation upon KNO₃ modification and for the phase evolution during soot combustion was investigated.