硅铝比对Cu/SSZ-13分子筛低温催化性能的影响

Effect of Si/Al ratio on catalytic reduction performance of Cu/SSZ-13 zeolite for NH_(3)-SCR at low temperature

采用水热法和液态离子交换法制备了一系列硅铝比(摩尔比)不同的Cu/SSZ-13分子筛[n(Si)/n(Al)=47,30,20,15],探究了硅铝比对NH 3选择性催化还原(NH 3-SCR)的影响,并通过XRD,ICP,N 2吸脱附,SEM,H 2-TPR,NH 3-TPD等表征分析对样品的物化性质进行了系统研究。活性测试结果表明,不同硅铝比分子筛的NH 3-SCR性能具有显著差异,特别是低温范围,其中催化剂起燃温度T_(50)(转化效率≥50%时的温度)顺序为n(Si)/n(Al)=20<n(Si)/n(Al)=15<n(Si)/n(Al)=30<n(Si)/n(Al)=47。从表征结果可知,硅铝比会影响分子筛催化剂的表面形貌、晶体结构,进而影响样品中Cu物种的分布和数量及酸性。4种分子筛催化剂中n(Si)/n(Al)-20具有最多的孤立Cu 2+以及弱L酸位数量,有利于低温NH 3-SCR反应的进行。

A series of Cu/SSZ-13 zeolites with different Si/Al ratios[n(Si)/n(Al)=47,30,20,15]were prepared by hydrothermal method and liquid ion exchange technology.The influence of Si/Al ratio on selective catalytic reduction of NO x with NH 3(NH 3-SCR)was investigated.The physicochemical properties of the samples were systematically characterized by XRD,ICP,SEM,N 2 adsorption-desorption,H 2-TPR and NH 3-TPD.It shows that NH 3-SCR performances of different n(Si)/n(Al)ratios are significantly different,especially in the low-temperature range.The light off temperature T_(50)(temperature when conversion efficiency≥50%)fellows the order of n(Si)/n(Al)=20<n(Si)/n(Al)=15<n(Si)/n(Al)=30<n(Si)/n(Al)=47.The characterization results show that different n(Si)/n(Al)could affect the surface morphology and crystal structure of the zeolite catalysts,and futher exert an influence on distribution and quantity of Cu species as well as the acidity.Among the four zeolite catalysts,Si/Al-20 possesses the largest number of isolated Cu 2+and weak L acid sites,which are conducive to the low-temperature NH 3-SCR activity.