Preparation Of ZIFs Derivatives And Core-shell Materials And Its CO-SCR Denitration Performance

Since the Economic Reform and open up,China’s economy has developed rapidly,and people’s living needs have been increasing,resulting in a rapid increase in the number of motor vehicles,and motor vehicle exhaust has become one of the main"culprits"that damage the atmospheric environment.Among them,nitrogen oxides（NOx）and carbon monoxide（CO）in exhaust gas are two typical atmospheric pollutants,which have a huge impact on the atmospheric environment.Carbon monoxide selective catalytic reduction technology（CO-SCR）can eliminate NO and CO at the same time and convert them into CO₂ and harmless N₂.This technology not only does not require the addition of external reducing agents but also has no secondary pollution,which has become a popular technology in recent years.Research hotspots.The selection of catalyst is the top priority of CO-SCR.In this paper,based on ZIF-67,a variety of ZIFs derivatives and their core-shell material derivatives were designed and developed,and a series of low-temperature CO-SCR denitration activity experiments were carried out in simulated flue gas;various characterization methods were used to explore the carbonization temperature.and the effect of oxidation temperature on the microstructure and physicochemical properties of the catalyst,the catalyst with the best low-temperature denitration performance was selected to study the water resistance,sulfur resistance and oxidation resistance;finally,the in-situ FTIR technology was used to deeply explore the intermediate species in the CO-SCR reaction to reveal the reaction mechanism.The main research conclusions are as follows:（1）Co₃O₄ nanoparticles（NPs）embedded in porous carbon（CoO_x@PC-T）were synthesized by carbonization and oxidation with ZIF-67 as a sacrificial template.The morphology of CoO_x@PC-T maintained the dodecahedral structure of ZIF-67,and its CO-SCR activity was tested by using a fixed-bed quartz tube reactor.The effect of carbonization temperature on the microstructure and physicochemical properties of the catalyst was explored through a series of characterizations.The results show that the carbonization temperature has a great influence on the structure of the catalyst,which affects the exposure and oxidation of CoNPs on the surface of the sample.When the carbonization temperature rises to 800°C,the catalyst exhibits excellent low-temperature CO-SCR catalytic efficiency and thermal stability,which can reach 93.3%at 150°C,and can still reach more than 99%when the temperature reaches 300°C.The higher chemisorbed oxygen concentration,Co³⁺/Co²⁺and larger specific surface area are the reasons for the enhanced low temperature SCR activity.Furthermore,CO reacts with adsorbed NOx species to generate N₂ and CO₂ by in situ FTIR technique,and the reaction follows the Mv K mechanism at<200°C and the Eley-Rideal（E-R）mechanism at 200-300°C.Resistance experiments showed that CoO_x@PC-800 was highly stable,but easily affected by SO₂,H₂O and O₂.（2）The carbonized ZIF-67 was further oxidized at 350°C to obtain Co₃O₄@PC-T porous carbon nanoparticles.The catalytic efficiency of Co₃O₄@PC-800 reaches 83%at 175℃,and the catalytic efficiency reaches 98.8%at 200℃,showing a good low-temperature denitration efficiency.This is mainly due to its larger specific surface area,higher Co³⁺/Co²⁺ratio,as well as higher concentration of active surface adsorption of oxygen.In situ FTIR tests showed that NO was preferentially adsorbed on the catalyst surface in the CO-SCR reaction and reacted to generate a series of intermediate active species,which in turn generated N₂.The reaction follows the E-R mechanism.The Co₃O₄@PC-800 has high stability,good water resistance and a certain degree of oxidation resistance.（3）Using ZIF-67 as the core,CoO_x@Cs-T MOFs core-shell derived materials were prepared.The catalyst can achieve a NO conversion rate of more than 90%at 225℃,and the reaction follows the E-R mechanism.Resistance experiments show that it has excellent catalytic performance under a certain oxygen concentration.The best catalytic efficiency was exhibited when the oxygen concentration was 0.5%.At 100°C,the catalytic efficiency can reach more than 83%,showing excellent low-temperature out-of-stock performance.The catalytic efficiency reaches a maximum of 99%at250°C.This is due to the presence of the carbon shell which enhances the adsorption of oxygen and provides an extremely large surface area for the reaction.