Study On Synthesis Of Cu Based Small-pore Zeolite For Catalytic Reduction Of NO_x

Diesel vehicles are an important source of NO_x emissions,and ammonia selective catalytic reduction（NH₃-SCR）is the most widely used technology for diesel exhaust NO_x removal.Among the catalysts in the field of NH₃-SCR,Cu Based Small-pore Zeolite catalysts are favored by researchers for their excellent catalytic activity,N₂ selectivity and hydrothermal stability.Among them,Cu-SSZ-13 with the CHA structure has excellent catalytic activity,N₂ selectivity and resistance to HCs poisoning,but there is a problem of catalytic performance degradation in high-temperature hydrothermal environment;Cu-SSZ-39 with the AEI structure has excellent medium and high temperature activity and hydrothermal stability,but the low-temperature SCR activity is relatively poor.Based on this,this paper explores the addition of glucose in the synthesis of SSZ-13,to modulate the grain size and enhance the hydrothermal stability of Cu-SSZ-13;the Ce Zr O_x with excellent oxidation ability is compounded with Cu-SSZ-39,to prepare Ce Zr O_x/Cu-SSZ-39 composite catalyst to improve the low-temperature NH₃-SCR activity of Cu-SSZ-39.The main findings were as follows:（1）The addition of the glucose during the synthesis of SSZ-13,reduced the grain size of SSZ-13（about 10μm to about 3μm）,and changed the rough and irregular spherical shape to a smooth and uniform cubic shape.The catalyst Cu-SSZ-13-Glu prepared by glucose conditioning exhibited better NH₃-SCR catalytic performance than conventional Cu-SSZ-13,and the characterization results revealed improved crystallinity,increased acidic sites and improved redox properties.Meanwhile,Cu-SSZ-13-Glu has excellent hydrothermal stability,which is significantly improved compared with conventional Cu-SSZ-13.Compared with traditional Cu-SSZ-13,Cu-SSZ-13-Glu has a more stable structure and can maintain higher crystallinity and more specific surface area and microporous volume after hydrothermal aging.Moreover,the Cu²⁺ions in Cu-SSZ-13-Glu are more stable and generate less Cu O_x species after hydrothermal aging,retaining more Cu（OH）⁺-Z species and acidic sites.（2）The low-temperature NH₃-SCR activity of Cu-SSZ-39 was enhanced by compounding Ce Zr O_x,which has excellent oxidation capacity,with Cu-SSZ-39.The NO conversion of Ce Zr O_x/Cu-SSZ-39 is on average nearly 18%higher than that of Cu-SSZ-39 in the low temperature range of 125-200℃.The characterization results revealed that the Ce Zr O_x/Cu-SSZ-39 catalyst has more active Cu（OH）⁺-Z species on it with improved redox properties,which promotes the NH₃-SCR reaction.And the Ce Zr O_x/Cu-SSZ-39 catalyst contains surface chemisorbed oxygen,which facilitates the oxidation of NO to NO₂ and thus promotes the fast SCR reaction.Meanwhile,Ce Zr O_x/Cu-SSZ-39 still maintained better catalyst activity after hydrothermal aging treatment and improved hydrothermal stability compared with Cu-SSZ-39.The Ce Zr O_x composite weakened the effect of hydrothermal conditions on Cu-SSZ-39,and the composite catalyst maintained better specific surface area and pore structure after hydrothermal aging,reducing the acidic sites and reducible species during hydrothermal aging.The loss of acidic sites and reducible species during hydrothermal aging was reduced.