Nature Of Intracrystalline Diffusion In Cu/SSZ-13 NH₃-SCR Catalysts

Ammonia-selective catalytic reduction?NH₃-SCR?has been widely implemented for NO_x reduction in stationery and mobile applications.A Cu-exchanged zeolite with chabazite?CHA?structure,Cu/SSZ-13,attracts extensive attention due to its better catalytic performance,higher hydrothermal stability,N₂ selectivity and better resistance to hydrocarbon poisoning.While the small size porous structure of zeolites is prone to diffusion limitation,and may affect the activity and selectivity of catalysts,and the effect of intracrystalline diffusion on NH₃-SCR over Cu/SSZ-13 catalysts is controversival.In this research,controllable preparation of Cu/SSZ-13 with different particle sizes and diferent Cu loading was achieved through optimizing the synthesis process.On this basis,the active site and the influence of intracrystalline diffusion of NH₃-SCR over Cu/SSZ-13 catalyst was studied.The characterization of Cu species and kinetics of Cu/SSZ-13 with various Cu contents confirmed that isolated Cu²⁺was the active site for NH₃-SCR in the temperature range of 220-265 ^oC.XRD?ICP?SEM?NH₃-TPD,NMR and H₂-TPR were used to probe the effect of particle size on physiochemical properties of catalysts,and showed that Cu/SSZ-13 catalysts with various particle sizes have similar physicochemical properties.Then the kinetic experiments were conducted to investigate the influence of intracrystalline diffusion on NH₃-SCR.And the kinetic experiment results indicated that the samples with various particle sizes had identical apparent activation energy?Ea?and turnover frequency?TOFs?.Therefore,this study unequivocally concluded that the reaction rates of NH₃-SCR reaction over Cu/SSZ-13catalysts are not limited by intracrystalline diffusion under the kinetic condition(500ppm NO,500 ppm NH_3,10%O_2,balanced with N₂,220-265?,316800h^-1).