一步水热合成Cu-SSZ-13分子筛选择性催化C3H6还原NO

采用铜胺配合物(Cu²⁺-四乙烯五胺,Cu-TEPA)作为结构导向剂,通过一步水热法合成不同铜铝比(n_Cu/n_Al)和硅铝比(n_Si/n_Al)的Cu-SSZ-13分子筛催化剂,研究其在贫燃条件下丙烯选择性催化还原NO(C₃H₆-SCR)的性能。当n_Cu/n_Al=2、n_Si/n_Al=6时2.0Cu-SSZ-13(6)催化剂具有最好的低温脱硝活性,200℃时NO转化率超过80%,在250~300℃可实现100%脱硝效率和~100%N₂选择性,同时具有较强的抗水、抗硫性能。为研究不同n_Cu/n_Al和n_Si/n_Al对催化剂物理化学特性的影响,通过X射线衍射(XRD)、扫描电子显微镜(SEM)、N₂吸附-脱附测试、H₂程序升温还原(H₂-TPR)、氨气程序升温脱附(NH₃-TPD)、紫外可见光谱(UV-Vis)等手段对样品进行表征。结果表明,2.0Cu-SSZ-13(6)具有最佳的脱硝性能,这是因为其具有最大的比表面积、最强的表面酸性和分布最多的孤立态Cu²⁺离子。Cu-SSZ-13上丰富的酸性位可以有效促进C₃H₆和NO的吸附和活化,SSZ-13分子筛八元环中孤立的Cu²⁺离子具有良好的氧化还原性能,是C₃H₆-SCR反应的主要活性位。随着n_Cu/n_Al的增加,孤立的Cu²⁺离子会在分子筛表面迁移、集聚形成CuO物种,从而导致C₃H₆-SCR活性下降。

Selective Catalytic Reduction of NO with C3H6 over One-Step Hydrothermal Synthesized Cu-SSZ-13 Catalysts

To investigate the performance of Cu-SSZ-13 for selective catalytic reduction of NO with C₃H₆under lean-burn conditions,Cu-SSZ-13 with different n_Cu/n_Aland n_Si/n_Alwere prepared by one-step hydrothermal synthesis meth-od using Cu²⁺-tetraethylenepentamine(Cu-TEPA)as a structure directing agent.The Cu-SSZ-13 catalyst with n_Cu/n_Al=2 and n_Si/n_Al=6 had the best low-temperature activity,which could reach over 80%NO conversion at 200℃,and100%NO conversion and~100%N₂selectivity at 250~300℃.In addition,it also exhibited moderate resistance to SO2 and H₂O.The influence of different n_Cu/n_Aland n_Si/n_Alon the physicochemical properties of the catalysts were investigated by X-ray diffraction(XRD),scanning electron microscopy(SEM),N2 adsorption-desorption test,temper-ature programmed reduction of H₂(H₂-TPR),temperature programmed desorption of ammonia(NH₃-TPD),ultraviolet-visible spectroscopy(UV-Vis)and other characterization methods.According to the results of characterizations,the excellent catalytic activity of 2.0 Cu-SSZ-13(6)obtained with n_Cu/n_Al=2 and n_Si/n_Al=6 may relate to the largest specific surface area,the strongest surface acidity and the highest distribution of isolated Cu²⁺ions.Abundant acid sites on Cu-SSZ-13 can effectively promote the adsorption and activation of C₃H₆and NO.The isolated Cu²⁺ions in the 8-membered rings of SSZ-13 had great redox performance,which were the main active sites for the C₃H₆-SCR reaction.As the n_Cu/n_Alincreased,the isolated Cu²⁺ions would migrate and accumulate on the surface of the zeolite catalysts to form CuO species,resulting in the decrease in the activity of C₃H₆-SCR reaction.