Application Of Copper Based Small-pore Molecular Sieve Catalyst In Selective Catalytic Reduction Of NO_x By Ammonia

Nowadays,with the rapid development of science and technology in the world,the material living standard of human beings is constantly improving,but a series of environmental pollution and other problems have emerged.For example,the exhaust emissions from coal-fired power plants and large passenger cars and trucks dominated by diesel vehicles contain a large number of harmful substances,such as nitrogen oxides（NO_x）,which not only pose a great threat to human health,but also cause acid rain,Greenhouse Effect and other environmental problems.Therefore,it is urgent to find suitable NO_x catalytic purification technology and catalytic materials.The selective catalytic reduction of ammonia（NH₃-SCR）has been widely used to eliminate the emission NO_x of fixed sources such as coal-fired power plants.Meanwhile it is the most likely large-scale application in heavy diesel vehicle exhaust gas and other mobile source NO_xpurification technology.NH₃-SCR catalysts for commercialized large-scale applications are V₂O₅/Ti O₂ catalyst（adding WO₃ as the promoter）,but it has problems such as poor low temperature activity,low N₂ selectivity at high temperature,narrow temperature window and V₂O₅’s biological toxicity.Therefore,the development of catalytic materials with high catalytic activity and selectivity in a wide temperature range and HCs toxicity,and high stability are the efforts of researchers.Cu/Zeolites with chabazite（CHA）crystal structure have attracted much attention because of their large specific surface area,regular pore structure and better thermal stability.Due to the complex synthesis steps and high application cost of copper based pore molecular sieve,we prepared CHA Cu-based pore molecular sieve material Cu-SSZ-13 and Fe/Cu-SSZ-13 of iron modification by using one-step hydrothermal method environmentally friendly.The preparation method,composition structure,catalytic performance and surface adsorption reaction were studied systematically.This thesis mainly studied the following aspects:In the first part,the original Cu-SSZ-13 was prepared by one-step hydrothermal method with Cu-TEPA complex as structure guide agent formed by cheap and easily available template agent tetraethylenetetramine and copper sulfate pentahydrate.In order to reduce the Cu content of the catalyst,Cu-SSZ-13 with different Cu/Al and Cu-TEPA/Al was prepared by adjusting the amount of copper source and template used in the preparation conditions.Comparison of the conversion of nitrogen oxides in the range of 100-500℃for each catalyst,Cu-SSZ-13 with Cu-TEPA/Al=0.55 can achieve optimal catalytic performance.Not only can the low temperature activity be maintained,catalyst can achieve 80%conversion of nitrogen oxides at 125℃,but also the high temperature activity has been improved,even at 500℃,the NO_x%was significantly higher than that of the original Cu-SSZ-13.The second part is based on the above preparation of the CHA copper-based small pore molecular sieve Cu-SSZ-13.To further improve the NH₃-SCR performance and broaden the temperature window,it is an experimental idea that the introduction of other elements into the catalyst to modify.Because the iron-based molecular sieve has excellent high temperature activity.Based on this feature,the CHA copper-based small pore molecular sieve Fe/Cu-SSZ-13modified by iron was synthesized by introducing iron into the Cu-SSZ-13 before burning by simple ion exchange method.Change the concentration of iron source and exchange time explore the best exchange conditions.The NH₃-SCR reactivity of synthetic catalysts under different exchange conditions was investigated,the Fe/Cu-SSZ-13 prepared by exchanging 5 h with 0.05 M Fe（NO₃）₃ had the best performance.Not only the reaction temperature window is significantly widened,but also the hydrothermal stability of the sample is improved due to the introduction of iron elements.It can maintain 100%conversion in the range 175-350℃.Tthe NO_x%was about 30%higher than that of the original Cu-SSZ-13.