Preparation Of Bimetallic MOFs Based On Cu-BTC And Their Experimental Study For C₃H₆-SCR

Production activities such as petrochemicals,fossil fuel combustion,pesticides and fertilizers are the main sources of nitrogen oxides,which are the source of a series of"urban diseases"and seriously threaten human health and the ecological environment.Therefore,the research and development of efficient denitrification technology is of great significance for the construction of social economy and ecological civilization.Selective catalytic reduction technology is currently one of the most effective methods for reducing nitrogen oxide content.The use of hydrocarbons as reducing agents for selective catalytic reduction（HC-SCR）is an alternative technology for NH₃-SCR,which can achieve simultaneous removal of nitrogen oxides and hydrocarbons in flue gas,and has attracted widespread attention from researchers.In recent years,researchers have carried out a lot of research on catalysts such as metal oxides,precious metals,pillared clays,molecular sieves,and hydrotalcite to catalyze the reduction of NO by hydrocarbons,but there is a certain gap from practical industrial applications.For example,noble metal catalysts have poor low temperature activity,so the development of new and efficient catalysts is the main research direction of HC-SCR.Metal-organic frameworks（MOFs）have the advantages of abundant acidic sites,excellent specific surface area,etc.,and have received extensive attention from researchers in the field of SCR.In addition,related studies have shown that metal Cu has abundant chemical valence states and existing forms,and has good denitration activity in the HC-SCR reaction.Therefore,copper-based MOFs materials are selected for the research of HC-SCR.In this paper,based on Cu-BTC materials,using the advantages of different metals in the field of HC-SCR catalysis,xCu-Mn-BTC,xCo/Cu-BTC,and xCu-Co-BTC catalysts were prepared.The catalytic performance of C₃H₆ for the selective reduction of NO under conditions was investigated,and the effects of SO₂ and water vapor on the catalyst activity were investigated.The physicochemical properties of the catalyst were studied by means of XRD,N₂ adsorption-desorption,H₂-TPR,XPS,Py-FTIR,DRIFTS and other characterization techniques to further analyze the reaction mechanism;the main conclusions were drawn as follows:1.The effect of different MOFs activation temperatures on the catalytic activity was studied.The results showed that when the activation temperature was 200°C,the NO conversion rate was up to 42%,which was 10%higher than that of the unactivated catalyst.In this experiment,bimetallic xCu-Mn-BTC catalysts were successfully prepared by direct synthesis.The results show that all bimetallic xCu-Mn-BTC catalysts exhibit better C₃H₆-SCR performance than monometallic MOFs catalysts.Among them,3.2Cu-Mn-BTC shows good denitration performance and nitrogen selectivity,and can reach 80%conversion efficiency and 94%N₂ selectivity at 300°C.2.SO₂ and water vapor have a great influence on the catalytic activity of 3.2Cu-Mn-BTC,the effect of sulfur dioxide on the catalyst is irreversible,and the effect of water vapor on the catalyst activity is reversible3.The characterization results show that the large specific surface area,suitable pore structure,high content of adsorbed oxygen O_αand Cu²⁺and the synergistic effect between Cu and Mn ions make the catalyst have better catalytic activity.Prior to this study,there was no related research on bimetallic MOFs applied to C₃H₆-SCR.This study demonstrates the feasibility of using bimetallic MOFs as a novel catalyst for low temperature C₃H₆-SCR,synthesizing multimetallic MOFs and utilizing the advantages of each metal to improve the catalytic performance of C₃H₆-SCR may be the direction of future research.4.The C₃H₆-SCR reaction pathway on 3.2Cu-Mn-BTC was investigated by in-situ DRIFTS experiments:the formation of gas adsorption on the active site,such as ad-NO₂,N₂O₄,ad-C₃H₆,etc.,as well as monodentate,bidentate and bridging nitrates accumulate on the active site.When the temperature is increased,the adsorbed species will start to be converted into monodentate and bidentate nitrates.C₃H₆ is oxidized by surface nitrate species to acetate.Acetate is further reacted to form the organic nitro R-ONO.As the reaction proceeded further,R-ONO was converted to R-NCO,and finally R-NCO was converted to CO₂,N₂,and H₂O under NO and O₂conditions.5.xCo/Cu-BTC showed better denitration effect than xCu-Co-BTC.Among them,10%Co/Cu-BTC exhibited 61%NO conversion and 80%nitrogen selectivity at 300°C.The results of N₂adsorption-desorption characterization showed that when the loading of Co increased from 5%to15%,the specific surface area of the catalyst decreased rapidly,but the pore diameter increased on the contrary.It is found that the loading of Co makes the catalyst contain mesoporous properties.According to SEM and XRD characterization results,xCo/Cu-BTC and xCu-Co-BTC retain the Cu-BTC structure.The XPS characterization showed that Co did not enter the framework in the xCu-Co-BTC catalyst,indicating that Cu has stronger coordination for carboxylate than Co.For the xCo/Cu-BTC catalyst,more Co²⁺and adsorbed oxygen are one of the reasons for the better catalyst activity.According to the H₂-TPR results,the reduction peak of 10%Co/Cu-BTC shifts to a lower temperature than other catalysts,indicating that it has stronger redox ability,which may also be10%Co/Cu-One of the reasons why BTC activity is better.It can be seen from Py-IR that 10%Co-Cu-BTC contains more Lewis acid,which leads to better activity of the catalyst.