Research On Catalysts Treated By Non-thermal Plasma For Nitrogen Oxide Reduction

Nitric oxide (NO), as one of the major pollutants of stationary combustion sources, has been aroused wide attention. Because of the environmental problems of NO, denitrification has become another major gas pollution control issues after desulfurization. At present, selective catalytic reduction (SCR) is the main exhaust gas denitration method. But this method has high investment and operating costs because of the extra plus reducing agent NH3, and is likely to cause secondary pollution. For NO of thermal power plants and other stationary sources, the paper adopts catalytic oxidation. NO catalytic oxidation technology is mainly the oxidation of NO to easily absorbed NO2, using O2in the flue gas, and get the right proportion of NO2/NO, and then recycling byproduct by ammonia absorption. Now, absorption technology is basically mature, but there are still some difficulties in the first step—NO catalytic oxidation. The key is how to prepare catalyst for low-temperature catalytic oxidation of NO to NO2.The results show that the transition metal oxide has preferably NO catalytic oxidation effects, but their activity at low temperature is to be further improved. As a novel catalyst approach method in recent years, plasma modification attracted more and more attention of researchers. Therefore, the main contents of this paper is preparation of novel catalyst for NO catalytic oxidation by plasma.This paper systematically investigated the activity of transition metal oxide for NO catalytic oxidation. Mn-Co catalyst which was prepared by low-temperature solid-phase method was selected to follow study. At the same time, the influence of doped Ce and K was studied. The results showed that added Ce and K could improve NO catalytic oxidation activity of catalyst.Experimental studies found that plasma modified Mn-Co catalyst has better low-temperature NO catalytic oxidation activity and stability, and the NO conversion rate reached73%at150℃, and the activity did not declined after continuous reaction24h. The plasma treated catalyst had a smaller crystallizes size, and the metal particles highly dispersed, and the agglomeration phenomenon of particle on the surface of catalyst was reduced.In order to study the impact of different plasma modification conditions on catalyst, the activity of NO catalytic oxidation for different plasma modified atmosphere (N2and O2) and output voltage (5.6kV,7kV and8.5kV) and modified time (30min,1h and2h) of the catalysts were investigated. The experimental results show that catalytic activity of catalysts modified by N2plasma is better than that of O2plasma; increase the output voltage as well as extension of the modification time is conducive to the improvement of NO catalytic oxidation, but when the output voltage increased to8.5kV, the catalytic oxidation activity decreased significantly. Therefore, appropriate plasma modification conditions are conducive to the catalytic oxidation of NO. The optimum plasma modified conditions are as follows:nitrogen plasma,7kV modified output voltage, and lh modified time. Under this condition, the NO conversion achieved84%at150℃. The TEM characterization revealed that there were two states-round particulate and flaky structure in the catalysts, and the catalysts seemingly presented acicular structure. XRD results also showed that the degree of crystallinity of the catalyst was very low, and basically the catalysts were amorphous state. Additionally, XRD results showed that MnO2, Mn2O3and CO3O4were the main components of the catalyst. XPS characterization results also showed MnO2, Mn2O3and CO3O4were the main components of the catalyst. Mn atoms, Co atoms, Mn2O3and Co2+played major role in NO catalytic oxidation reaction, and their concentration determined the activities of the catalyst. Nitrogen plasma could effectively restore metal Mn and Co and reduce the valence, and consequently increased Mn2O3and Co2+concentration and then enhanced catalytic activity.