Experiment Study On The Selective Catalytic Reduction Of NO By CH₄ Over Fe Modified Co-FER Catalysts

With the increasing consumption of energy,more and more nitrogen oxides are emitted,and countries around the world are paying more and more attention to the harm of NO_x to the human body and nitrogen oxide control technologies.Since CH₄ is the main component of natural gas and safe and easy to obtain,so the CH₄-SCR technology that uses CH₄ as a reducing agent to selectively catalytically reduce NO has become a frontier research hotspot.At present,CH₄-SCR has low reactivity,and has problems such as poor water and sulfur resistance,so it is difficult to achieve industrial practical applications.Co-FER has achieved certain performance in the CH₄-SCR reaction,but still has disadvantages such as poor water and sulfur resistance.The previous research of the research group showed that Fe showed good water and sulfur resistance in the experiment of reducing NO with low carbon hydrocarbons.Therefore,this article used Fe modified Co-FER to prepare Fe/Co-FER catalysts,conductd denitration activity test,and used UV-vis,XPS to characterize and analyze the pore characteristics,acidic distribution,and reaction path of the catalyst.In addition,the effect of loading sequence and operating conditions（reaction space velocity,reaction time,etc.）on catalyst activity was further studied.The main research results are as follows:（1）After an appropriate amount of Fe was introduced into the Co-FER catalyst,it had a higher ability to catalyze the reduction of NO by CH₄ and the ability to resist water and sulfur under oxygen-rich conditions.The Co-FER catalyst modified with an appropriate amount of Fe can improved the NO conversion rate,N₂ selectivity,and water and sulfur resistance.With 0.46Fe/Co-FER under oxygen-rich conditions and 500°C,the NO conversion rate reached 64.9%and the N₂selectivity reached 100%.After adding 0.02%SO₂,the NO conversion rate of the 0.46Fe/Co-FER catalyst could still maintain about 58.5%.After cutting off the SO₂,the NO conversion rate had rebounded,which was slightly lower than the efficiency before the introduction of SO₂.After adding5%H₂O,the NO conversion rate of the 0.46Fe/Co-FER catalyst decreased by only 15%,and the catalyst poisoning caused by H₂O was reversible.（2）By characterizing the catalyst,it could be seen from the results of N₂ adsorption and desorption that the introduction of an appropriate amount of Fe into Co-FER could effectively increase the specific surface area and pore volume of the catalyst,reduce the pore size of the catalyst,and after adding a small amount of Fe,The structure of Co-FER had little effect.XPS and UV-vis results showed that 0.46Fe/Co-FER contained more free Fe³⁺and Fe₂O₃,and free Fe³⁺promoted the low-temperature activation of CH₄.It was an important low-temperature active material and contained more Co²⁺ions.Co²⁺was the active center of CH₄-SCR.The H₂-TPR results showed that the temperature corresponding to the reduction peak of 0.46Fe/Co-FER was lower,indicating that an appropriate ratio of Co to Fe can promote the reduction of the peak to low temperature,thereby improving its catalytic activity.The Py-FTIR resulted show that the catalyst surface contained a large amount of Br（?）nsted acid and Lewis acid,and the introduction of Fe significantly increased the Br（?）nsted acid content of the catalyst.Therefore,Co-FER modified with an appropriate amount of Fe can effectively improved the catalytic activity of CH₄-SCR.（3）The results of in-situ infrared experiments showed that NO forms various nitrogen-containing adsorption species（ads）on the acidic site of the 0.46Fe/Co-FER catalyst surface.When O₂ was added,it promoted the oxidation of adsorbed NO and generate more nitrogen-containing adsorption Species（ads）.Under aerobic conditions,CH₄ existed on the surface of 0.46Fe/Co-FER catalyst in molecular form and formate oxide.CH₄ and NO will continue to react on the surface of the catalyst.As the reaction temperature rises,reaction intermediates will continue to form.During the reaction,the hydroxyl group（[Co-OH]⁺）generated by H₂O at the Co²⁺site was the main SCR Active site,where an important reaction intermediate Co²⁺-NCO was formed,and then Co²⁺-NCO reacted with NO adsorption species and CH₄ to form N₂,CO₂ and H₂O.（4）The change of the ion exchange sequence affected the denitration performance of the catalyst.The Fe/Co-FER catalyst loaded with Co first and then Fe had the best out-of-stock performance.Within the reaction temperature window of 300-600°C,the order of denitration efficiency of the three catalysts was:Fe/Co-FER>Fe&Co-FER>Co/Fe-FER.The N₂ adsorption-desorption results showed that Fe/Co-FER had a larger specific surface area,a smaller average pore size,and more micropores.The results of H₂-TPR indicated that the different loading order of Co and Fe will lead to the formation of active metals on the catalyst surface.The 0.46Fe/Co-FER catalyst had the best denitration performance at a space velocity of 12000h^-1.the 0.46Fe/Co-FER catalyst had good reaction stability.the 0.46Fe/Co-FER catalyst had catalytic performance under0.1%NO reaction conditions.