Experimental Research On Removal Of Nitrogen Oxides By Modified Zeolitic Imidazolate Frameworks Catalyst

At present,the emission peak and carbon neutrality goals proposed by the government of China have brought new challenges to the emission reduction of coal-fired power plants.Under the background of flexible peak shaving in coal-fired power plants,flue gas pollution control equipment is still required to ensure efficient,continuous,and stable operation.In a variety of pollution control facilities,the load changes caused by flexible peak shaving have a particularly significant impact on the flue gas denitrification system.Since the existing commercial denitration catalysts need to operate under high temperature conditions and do not have a wide temperature window,it is necessary for a wide temperature window denitrification catalyst suitable for coal-fired power plants to be developed to solve the above problems and the catalyst can also be used for nitrogen oxide control in steel,building materials,and civil boilers.In this paper,through a large number of literature surveys and experimental studies,three ZIFs catalysts,namely Cu@ZIF-11,Cu@ZIF-7,and Cu/Ce@ZIF-7,were prepared using ZIFs in MOFs as supports.,and a ZIFs-based catalyst for removing NO from flue gas was constructed.The reaction system and many flue gas denitrification experiments have been carried out.The results provide an important theoretical basis and reference for the development of a wide temperature window flue gas denitrification technology.The main research contents of this paper are as follows:（1）A variety of preparation conditions were investigated experimentally,and three catalysts Cu@ZIF-11,Cu@ZIF-7,and Cu/Ce@ZIF-7 were prepared respectively.A certain concentration of SO₂ and H₂O were added to the three catalysts to study the sulfur resistance and water resistance properties of the catalysts.Combined with the removal experimental data and the catalyst characterization before and after the reaction,it is shown that SO₂ and H₂O have roughly similar effects on the catalytic performance of Cu@ZIF-11 and Cu@ZIF-7.The bimetallic Cu/Ce@ZIF-7 catalyst is less affected by SO₂ and H₂O,and its sulfur resistance and water resistance are improved by 11%and 9.9%,respectively.（2）A series of experiments were carried out on the effects of various factors,such as catalyst addition,flue gas flow,ammonia-nitrogen molar ratio,and reaction temperature on the NO removal effect.The results show that the optimal temperature range for denitration of Cu@ZIF-11 catalyst can be selected as 350-375 ℃,and the highest NO removal efficiency in this temperature range is 95.0%;the optimal denitration temperature range of Cu@ZIF-7 catalyst In this temperature range,the NO removal efficiency is 96.9%;the optimal denitration temperature range of the bimetallic Cu/Ce@ZIF-7 catalyst is 325-350℃,and the NO removal efficiency is within this temperature range can reach to 96.6%,the temperature range above can meet the ultra-low emission requirements of coal fired power plant.In practical applications,considering the requirements of different regions and different coal-fired boilers for the emission limit of nitrogen oxides,the optimal temperature range of the three catalysts can also be moderately relaxed to 325-400℃,250-425℃,and 275-400℃.Considering the catalyst’s sulfur resistance,water resistance,thermal stability,and denitration efficiency,a new wide-temperature flue gas denitration process based on the bimetallic Cu/Ce@ZIF-7 catalyst was proposed in this paper.（3）Using X-ray diffraction（XRD）,scanning electron microscope（SEM）,transmission electron microscope（TEM）,X-ray photoelectron spectroscopy（XPS）,thermogravimetric analysis（TG）,NH3 temperature programmed desorption（NH3TPD）and H₂ temperature programmed reduction（H₂-TPR）to study the changes in the composition and structural properties of Cu@ZIF-7 and bimetallic Cu/Ce@ZIF-7 catalysts before and after the selective catalytic reduction reaction.The results show that the Cu element on the surface of Cu@ZIF-7 mainly exists in the form of Cu²⁺,and has abundant acid sites and redox sites in the temperature range of 250-425℃;the addition of the Ce element enhances the Cu/Ce The thermal stability of the@ZIF-7 catalyst changes the distribution of acid sites and redox sites of the catalyst,the acid sites and redox sites of the catalyst decrease in the low temperature region and increase in the high temperature region,which may be the reason for this catalyst The main reason for the decrease of NO removal efficiency in the low temperature region.（4）The reaction mechanism of Cu@ZIF-7 catalyst and Cu/Ce@ZIF-7 catalyst in the denitration process was investigated by in-situ diffuse reflection Fourier transform infrared（In stiu DRIFTS）characterization.The Cu@ZIF-7 catalyst is dominated by the E-R mechanism during the denitration process.The bimetallic Cu/Ce@ZIF-7 catalysts have both E-R and L-H reaction mechanisms in the denitration process.On this basis,the specific reaction processes of the two catalysts were deduced by combining the physical and chemical properties of the two catalysts.