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

Nitrogen oxides (NOx)are one of the main atmosphere pollution. Nowadays, more and more people are paying more attention to the environmental problems of NO. Due to increasing awareness of the negative consequences of air pollution and human health, flue gas De-NOx technology has become another major gas pollution prevention and control projects after desulfurization. At present, selective catalytic reduction (SCR) is applied widely in controlling NOx. For NO, which mostly comes from come from thermal power plants or other stationary sources, there have been strong interests to develop highly active and highly anti-poison catalysts for low-temperature SCR and SCO. In this work, a novel catalyst Mn-Mg-Ox was prepared and applied for catalytic oxidation of NO in the presence of excessive oxygen at low temperature as well as for selective catalytic reduction (SCR) of NOx with ammonia. NO catalytic oxidation technology is use O2, mainly oxidation of NO into NO2, and get the rational proportion of NO2/NO. NO2is easier to be removed by absorption than NO and then recycling byproduct by ammonia absorption. The key is how to synthesize a catalyst has high catalytic activity to oxidation of NO into NO2.The results show that the transition metal oxide showed good NO catalytic oxidation activity, but the activity at low temperature need further improvement. Plasma modification as a novel catalyst method has drawn more attention of researchers, in recent years. Therefore, for the catalytic oxidation of NO in this work,the main contents of this paper is synthesize a novel catalyst modified by the non-thermal plasma for NO catalytic oxidation. In particular, the effect of the presence of SO2in the feed stream on the NO conversion was investigated.This paper investigated the activity of transition metal oxide for NO catalytic oxidation. Mn-Mg-Ox catalyst which was synthesized by low temperature solid phase reaction method(SP) was selected to follow study. At the same time, the influence of Mn/Mg ratio and calcination temperature was studied. The results showed that Mn/Mg=5and unroasted Mn-Mg-Ox catalyst showed good NO catalytic oxidation activityExperimental studies found that Mn-Mg-Ox catalyst modified by plasma has better low-temperature catalytic oxidation activity, and the NO conversion rate reached82%at200℃.After being treated with non-thermal plasma, the metal particles were highly dispersed and catalyst had a smaller crystallite size.For investigate the effect of different plasma treatment conditions on catalyst, the activity of NO catalytic oxidation for different plasma modified atmosphere (N2and O2), output voltage (5.6kV,7kV and8.5kV) and treatment time (0.5h,1h and2h) were investigated. The experimental results show that the catalytic performance of catalysts modified by N2plasma is better than O2plasma. Within certain range, increase the output voltage or extension of the treatment time is favorable for the increase of NO catalytic oxidation, but when the output voltage increased to8.5kV, treatment time is2h the catalytic oxidation activity decreased. Therefore, appropriate plasma treatment conditions are conducive to the catalytic oxidation of NO. The optimal plasma treatment conditions are as follows:nitrogen plasma,7kV output voltage, and1h treatment time. Under the optimum treatment conditions, the NO conversion achieved82%at200℃.For the SCR of NOx with ammonia, the effects of SO2, reaction temperature, space velocity,NO/NH3were studied on the base of optimized Mn-Mg-Ox catalyst preparation on SCO reaction.Results indicated that Mg/Mn ratio and NH3/NO ratio and space velocity have certain effect on the performance of Mn-Mg-Ox catalyst. The NO conversion is up to99%at150℃when Mg/Mn ratio is1, NH3/NO ratio is land space velocity is30000h-1.And a higher conversion of99%is obtained during the reaction temperature of100～175℃. Mn-Mg-Ox catalyst shows good SO2resistance, which can keep high activity when have100ppm SO2at low temperature.This paper investigated the effect of SO2on Mn-Mg-Ox catalyst treated by non-thermal plasma for NO catalytic oxidation. XRD patterns also showed that the degree of crystallinity of the catalyst was low, and basically the catalyst has amorphous structure. Additionally, XRD results showed that MnO2, Mn2O3and Mn3O4were the main components of the catalyst. From FTIR result,we inferred that the1115cm-1,1074cm-1and1040cm-1over aged Mn-Mg-Ox characterize the formation of surface sulfur species. Through XRD and FT-IR characterization, the high SO2tolerance of Mn-Mg-Ox could be attributed to the effective inhibition of the competitive adsorption between NOx and SO? on catalytic active site and the enhancement of SO2adsorption on the magnesia surface with MgO addition.