Catalytic Removal Of Diesel Soot Particulates Over LaCoO₃ Perovskite Load Silver Catalyst

Diesel engines exhaust gases mainly contain the air pollutants like nitrogen oxide and soot particulate. It is well known that the gases emission temperature range of diesel engines exhaust is175-400 ℃,but the burning temperature for soot particulate is 550-600 ℃. It is expected that soot particulate is catalyzed at lower temperature under exhaust emission standards. Due to the complexity composition and wide temperature range for exhaust emission, the catalysts for carbon black combustion should have following characteristics such as good thermal stability, high oxygen storage capacity, low price, high catalytic activity under 400 ℃and so on. Amount the various catalysts; perovskite-type catalyst is one of the most prospect systems which meet the above conditions very well. But, the temperature for soot combustion over pure perovskite catalyst is higher than 450 ℃. In recent years, researchers have made a lot of work in regard to the development of low temperature catalyst. It is found that the metal oxide combined with LaCoO3 can obviously reduce carbon black combustion temperature. Our group also has done a lot of work to improve catalytic activity for soot oxidation. Some results indicate that it is possible process to remove NOx and soot simultaneously under low temperature over some metal oxides. In this article, ABO3 type(LaCoO3) perovskite composite silver catalysts are used for simultaneous catalytic removal NOx and soot. The relation between the structure of catalysts and catalytic performance will be discussed based on the thermal stability, redox property, and Co species. Some meaningful results are listed as follows:1. The introduction of the silver significantly improved LaCoO3 performance for soot combustion. Compared with the LaCoO3 catalyst, the introduction of the silver reduces the maximum soot combustion temperature(Tp) about 125 ℃. 4.65 wt.% Ag/LaCoO3-700 keeps good catalytic activity after three catalytic reaction cycle under nitrogen oxide atmosphere, which indicates that the catalyst has the good stability and has potential application prospect.2. The catalytic performance for soot combustion was studied when B site was displaced by other metal element in perovskite-type(ABO3) LaCoO3 combined with silver catalyst. The results show that the different B elements has great influence on the Co species distribution and redox properties in the LaCoO3 perovskite, which further affect the soot combustion performance. Under the oxygen atmosphere soot combustion performance is associated with low temperature reducibility of catalysts, and Ag/LaCo0.9Cu0.1O3 showed higher activity for soot oxidation with Tp = 450 ℃, △T= 65 ℃; Under nitrogen oxide atmosphere, the key factors for catalytic properties are the formation of NO2 and their reaction with carbon black, and Ag/LaCo0.9Bi0.1O3 showed the highest activity with the lowest value Tp(406 ℃) and △T(116 ℃).