Study On The Performance And Mechanism Of Oxidation Of NO By Mn-Based Catalysts

Because NO_X produced by coal combustion is a serious hazard to human health and can cause environmental damage,it has received more and more attention,so we need to find a suitable method to reduce NO_X emissions.Based on the current NO_X removal technology,whether it is the most researched and most mature selective catalytic reduction technology or the oxidation absorption technology with good application prospects,NO oxidation technology is the key,and the price of gas or liquid oxidant is expensive.For its large-scale industrial applications,NO oxidation catalysts have obvious price advantages.Therefore,the successful synthesis of the NO oxidation catalyst not only reduces the denitration cost,but also improves the efficiency of NO_X removal.Among many NO oxidation catalysts,Mn-based catalysts have attracted much attention due to their excellent catalytic performance and low price.However,the current research on Mn-based catalysts mainly focuses on Mn-based catalysts supported on different supports or doped other metals on Mn-based catalysts.The influence of morphology and valence state of Mn-based catalysts on catalytic oxidation of NO is still not sure.The controllable synthesis of nano-sized metal oxide catalysts with different morphologies is a hotspot of many scholars.The catalyst can be adjusted by the shape control of the catalyst,which is beneficial to the design of catalysts with high activity and high selectivity.Therefore,the?-Mn₂O₃catalysts with different morphologies were synthesized by hydrothermal method.The effects of operating conditions?temperatures,NO concentrations,O₂contents,flow rates?on the catalytic activity were investigated.The catalytic NO of cubic shape?-Mn₂O₃ catalyst was found.The oxidation capacity is the strongest,the concentration of NO is 500 ppm,the O₂ content is 5 vol%,N₂ is the equilibrium gas,the GHSV is 48 000 mL g^-1 h^-1,and the reaction temperature is 250?,?-Mn₂O₃-C catalyst can achieve a maximum NO conversion of 90.1%.By characterization,it is found that the surface of the?-Mn₂O₃ catalyst has the strongest ability to adsorb NO and O₂,so that more O₂ and NO can participate in the NO oxidation reaction,thus showing the best catalytic performance.The NO oxidation catalyst with the best morphology of?-Mn₂O₃-C catalyst was finally determined.Some scholars have found that the valence state of Mn has a certain influence on the activity of the catalyst in the process of NO oxidation,but the catalytic performance of different valence MnO_X in NO oxidation has not been systematically compared.Therefore,based on the?-Mn₂O₃-C catalyst with the best morphology,two different valence catalysts,MnO₂ and Mn₃O₄,were synthesized.Their catalytic properties for NO oxidation were compared.It was found that MnO₂ catalysts containing Mn⁴⁺ions were catalyzed.The activity is the highest,the concentration of NO is 500 ppm,the O₂ content is 5 vol%,N₂ is the equilibrium gas and the GHSV is 48 000 mL g^-1 h^-1,and the maximum NO conversion rate is 91.4%when the reaction temperature is 250?.XRD,SEM,N₂ adsorption-desorption,H₂-TPR,O₂-TPD and XPS characterization analysis determined that the high activity of MnO₂ catalyst is due to its high specific surface area,good mobility of oxygen species,and high surface adsorbed oxygen content.The reaction mechanism of the catalyst can reveal the reaction history,provide guidance for the improvement of catalyst performance,and lay the foundation for industrial production.Therefore,in this paper,the in-situ diffuse reflectance Fourier transform infrared spectroscopy technique was used to analyze the reaction mechanism and activity difference of different valence catalysts.It was found that the main reaction intermediates of NO introduced on the catalyst surface was bidentate nitrate and monodentate nitrate.Lattice oxygen is also involved in the NO oxidation process.The addition of gaseous oxygen can increase the adsorption of NO on the catalyst.The reason why the activity of MnO₂ catalyst is best is that the adsorbed substances on the surface are more easily desorbed,that is,because The reaction intermediate produced by the introduction of NO is finally desorbed to form NO₂,thereby increasing the catalytic activity.