不同拓扑结构分子筛催化剂上正十二烷异构化反应性能比较研究

Comparative study on the performance of n-dodecane isomerization reaction on molecular sieve catalysts with different topological structures

采用硅铝比相近的Y分子筛、ZSM-5分子筛和β分子筛分别负载贵金属约0.5%Pt制备催化剂,通过XRD、XRF、TEM、N_(2)物理吸附-脱附、NH_(3)-TPD、Py-FTIR、^(27)Al核磁等手段研究了不同拓扑结构分子筛晶体结构、元素组成、孔结构、酸性以及Al分布的差异,进而考察了拓扑结构对催化剂催化正十二烷异构化反应性能的影响。结果表明,当硅铝比接近时,ZSM-5分子筛总酸量及骨架铝比例最高、平均孔径最小,Y分子筛总酸量及骨架铝比例最低、平均孔径最大,而β分子筛的总酸量、骨架铝比例以及平均孔径介于两者之间,说明不同拓扑结构分子筛硅铝原子组合方式不同,不仅影响孔道结构和孔口尺寸,而且会因为铝所处位置的不同而影响酸性;在正十二烷异构化反应中,Pt/ZSM-5催化剂活性最高且主要发生的是外表面无选择性反应,Pt/Y催化剂活性最低且异构化反应主要在孔道内,而Pt/β催化剂活性介于两者之间,异构化反应发生于孔口处以锁匙反应为主。

The catalysts were prepared by loading about 0.5%Pt noble metal on Y molecular sieves,ZSM-5 molecular sieves andβmolecular sieves with similar Si/Al ratios.The crystal structures of the molecular sieves with different topologies,elemental compositions,pore structures,activities,and Al distributions were investigated by means of XRD,XRF,TEM,N_(2) physical adsorption and desorption,NH_(3)-TPD,Py-FTIR,and ^(27)Al NMR.And then the effect of topology on the catalytic performance of n-dodecane isomerization reaction was investigated.The results showed that when the Si/Al ratios were close to each other,the ZSM-5 molecular sieve had the highest total acid and skeleton Al ratio and the smallest average pore size,the Y molecular sieve had the lowest total acid and skeleton Al ratio and the largest average pore size,and theβmolecular sieve's total acid,skeleton Al ratio,and average pore size were between the two others,which indicated that different topologies of the molecular sieves with different combinations of Si/Al atoms affected not only the structure of the pores and the size of the pore but also the number of acidity.In the n-dodecane isomerization reaction,the Pt/ZSM-5 catalyst had the highest activity and the main reaction occurred on the outer surface without selectivity,the Pt/Y catalyst had the lowest activity and the isomerization reaction mainly occurred inside the pores,while the Pt/βcatalyst had the activity between the other two catalysts and the isomerization reaction occurred dominantly at the pore opening as the key-locking reaction.