Experimental Study On The Removal Of Nitrogen Oxides From Flue Gas By Modified Zeolitic Imidazolate Frameworks

Nitrogen oxides（NOx）emitted from coal burning are important precursors to acid rain,photochemical smog,ozone and greenhouse gases.They cause serious impact on the human health and the ecological environment.In order to achieve efficient emission reduction of NOx,selective catalytic reduction（SCR）technology and equipment are generally used.Because of its mature process and high removal efficiency,it has been widely used in coal-fired power plants at home and abroad.However,the commercial SCR catalyst（V₂O₅-WO₃/Ti O₂）currently used has a narrow working temperature range,which can not adapt to the impact of load changes caused by flexible peak shaving of coal-fired power plants on the flue gas denitration system,and has certain toxicity.Therefore,it is urgent to develop suitable combustion wide temperature window or medium and low temperature denitration catalyst for coal-fired power plants.In this paper,a new high-efficiency NH₃-SCR catalyst with zeolite imidazolate frameworks（ZIFs）was prepared as the carrier,which achieved the goal of efficient removal of NOx at 250℃～425℃.At the same time,the catalyst was characterized and analyzed by XRD,XPS,SEM and BET.The main work of this paper is as follows:1.ZIF-4 was prepared from imidazole and zinc nitrate.ZIF-4 was used as a carrier,and metal Cu was introduced into ZIF-4 through ultrasonic and traditional impregnation to synthesize Cu@ZIF-4.At the same time,the effects of impregnation solution concentration,ultrasonic time and impregnation time on the catalytic activity were investigated.And the catalyst dosage,simulated flue gas flow,volume space velocity and SO₂ and H₂O on catalyst efficiency were further explored.The results showed that the conditions of impregnation solution concentration of 0.10mol/L,the ultrasonic immersion time is 45min,and the immersion time is 1.0h,the Cu@ZIF-4 has the highest activity,and the denitration efficiency reaches more than 90%.it was found that SO₂had a negative effect on Cu@ZIF-4 activity,and H₂O and SO₂ had a reversible effect on catalyst activity.Through a series of characterization,the physical and chemical properties of the catalyst before and after the reaction were analyzed,which showed that the crystal structure and surface elements of the catalyst had no obvious changes before and after the reaction,which preliminarily confirmed the stability of the catalyst.2.In order to further improve the sulfur and water resistance of Cu@ZIF-4 and improve the efficiency of low-temperature denitration,Ce was introduced into Cu@ZIF-4 through ultrasonic impregnation and traditional impregnation to synthesize Ce-Cu@ZIF-4.The effects of doping ratio of the two metals,ultrasonic time and impregnation time were investigated.The study found that the Ce-Cu@ZIF-4 catalyst prepared under the conditions of Ce/Cu molar ratio of 1:4,ultrasonication for 60min,and immersion for 1.5h had the highest activity.When the catalyst addition amount was0.20g,the highest efficiency could reach 94%.the experimental results of the sulfur resistance and water resistance show that Ce-Cu@ZIF-4 had excellent anti-poisoning performance and good stability.Through characterization analysis,it was concluded that the addition of Ce increased the types of active components,the content of reactive oxygen species and adsorption capacity on the catalyst surface,thus promoting the denitration efficiency.