KL分子筛的碱性对Pt/KL催化剂上正己烷芳构化的影响

Effect of Basicity of KL Molecular Sieves on n-Hexane Aromatization over Pt/KL Catalysts

采用水热晶化法合成了KL分子筛,并采用XRF,XRD,BET,CO2-TPD等方法表征了骨架掺杂Fe原子改性和负载碱金属盐改性对KL分子筛结构以及碱性位分布状态的影响。通过H2-TPR表征和正己烷芳构化反应,考察了负载Pt后相应催化剂上的Pt颗粒状态及催化剂的芳构化性能。实验结果表明,骨架掺杂Fe原子增加了分子筛的弱碱性位数量,而负载碱金属盐增加了分子筛的强碱性位数量;碱性位分布情况影响Pt在载体上的分散情况及电子状态。强碱性位数量的增多使Pt颗粒分散得更加均匀且呈现出富电子状态,明显提高了Pt/KL催化剂的芳构化性能,相应的Pt负载量为0.5%(w)的Pt/K-KL催化剂在450℃、WHSV=3 h-1、n(H2)∶n(n-C6)=3的条件下,正己烷转化率达70%以上,苯选择性为85%左右。

KL molecular sieve was synthesized by hydrothermal crystallization method and then K-KL and Fe KL molecular sieves were prepared by the modification of KL with K and Fe,respectively. The Pt/KL,Pt/K-KL and Pt/Fe KL catalysts were prepared by impregnation method. The molecular sieves and catalysts were characterized by means of XRF,XRD,BET,CO2-TPD and H2-TPR. The catalysts were used in the aromatization of n-hexane. The weak basic sites on the molecular sieves increased with Fe doping in the hydrothermal synthesis,while the strong basic sites increased with the introduction of K＋ by ion exchange method. The increase of the strong basic sites led to more uniform Pt particles and electron-rich Pt species,which improved the aromatization performances of the Pt/KL catalyst. The conversion of n-hexane was more than 70% and the selectivity to benzene was about 85% under the conditions of Pt/K-KL with Pt loading of 0.5%（w） as the catalyst,450 ℃,WHSV 3 h^-1 and n（H2）∶n（n-hexane） 3.