Study On The Three-Dimensional Ordered Macroporous Ce-Based Catalysts For Selective Catalytic Reduction Of NO_x With NH₃

Nitrogen oxides（NO_x）,as one of the main air pollutants,cause serious harm to the ecological environment and human production and life.Selective catalytic reduction（SCR）is the most widely used and mature technology for flue gas denitration.In this study,Ce-based oxides were combined with three-dimensional ordered macroporous（3DOM）materials to improve the NH₃-SCR performance of Ce-based denitration catalysts by optimizing the pore structure and metal doping modification.In this paper,the physical and chemical properties of3DOM Ce-based catalysts were comprehensively studied,the structure-activity relationship of the catalysts and the interaction between active components were analyzed and discussed,and the reaction mechanism of SCR was deeply studied.The main research results are as follows:（1）In this paper,monodisperse polystyrene（PS）microspheres were firstly synthesized by soap-free emulsion polymerization,and then colloidal crystal templates were prepared by evaporation self-assembly method.On this basis,3DOM Ce O₂-MO_x（M=W,Mo,Fe,Mn,Cr）binary mixed oxide catalysts were successfully prepared by filling metal alkoxide solution.The Ce-based binary catalysts doped with different metal elements showed distinct catalytic activities.The 3DOM Ce-W catalyst has the best NH₃-SCR activity,and the NO conversion is more than 90%in the range of 250-450℃at GHSV=90,000 h^-1.3DOM Ce-W catalyst has the highest concentration of Ce³⁺and chemisorbed oxygen,and the best Redox performance and acidity.（2）The effects of different Ce/W ratios on SCR performance of 3DOM Ce_xW_y catalysts were investigated.Among them,3DOM Ce₂W₁ catalyst has the best SCR activity,and shows excellent space velocity adaptability and water sulfur resistance.There is a strong interaction between Ce and W,which makes it have a high amount of chemisorption oxygen,excellent REDOX performance and sufficient acid sites.（3）The influence of different Nb content doping on the SCR performance of 3DOM Ce-W-Nb_x ternary catalysts was investigated.Nb doping improved the catalytic activity and water sulfur stability of catalyst.The Ce WNb_0.15 catalyst has the best SCR activity and a wider temperature window.The addition of Nb increased the number of active sites and dispersed more evenly,optimized the pore structure to a certain extent,and increased the specific surface area.On the one hand,the interaction between Nb₂O₅ and Ce O₂ promoted the increase of Oα,enhanced the redox capacity,and contributed to the good SCR activity at low temperature.On the other hand,the synergistic effect between Nb and W provided sufficient Lewis acid sites for3DOM Ce-W-Nb_x catalyst.（4）In situ DRIFTS analysis shows that the NH₃-SCR reactions of 3DOM Ce-W and3DOM Ce-W-Nb catalysts all follow Eley–Rideal（E–R）and Langmuir–Hinshelwood（L–H）mechanism simultaneously.The doping of Nb is beneficial to promote the adsorption of NH₃and the generation of active NO_x species on the catalyst surface,improve the reaction activity and optimize the reaction path.