Aromatization of light alkanes over ZSM-5 catalysts
Aromatization of light alkanes over ZSM-5 catalysts
复制标题
DOI：
10.1016/j.apcata.2004.03.043
复制
发表时间：
2004-08
影响因子：
5.5
通讯作者：
A. Smiešková;E. Rojasová;P. Hudec;Luboš Šabo
中科院分区：
文献类型：
--
作者：
A. Smiešková;E. Rojasová;P. Hudec;Luboš Šabo
本文研究了由两种不同粒径（≤1 μ m和≤ 4μm）的ZSM-5分子筛经离子交换制备的ZnZSM-5催化剂（0.04-0.369mmolZn/g分子筛）在低碳烷烃芳构化反应中的活性和选择性。使用正己烷作为探针分子。酸性HZSM-5样品的组成（0.101-0.11mmolAl/g）和酸度（0.92-0.91mmolacidsites/g）相当。Zn的引入对TPDA法测定的总酸度没有明显影响，但引起了酸中心类型的重新分布。从ZnZSM-5催化剂的活性/选择性，然后通过将Zn引入到HZSM-5沸石中，芳构化通过双功能机理进行非常显著的进行。结果表明，ZnZSM-5催化剂的活性/选择性强烈地依赖于沸石颗粒大小、酸性、骨架中铝的分布以及沸石阳离子位置上锌物种的数量和类型的协同作用。Zn物种的类型强烈地受沸石骨架中Al原子的分布的影响。据报道，根据骨架中相邻铝原子之间的距离，可以在ZSM-5沸石中形成孤立的Zn 2+或氧桥连的Zn-O-Zn 2+物种，并且这种物种在芳构化中具有非常不同的活性。得出的结论是，在低Zn浓度下所观察到的所研究的ZnZSM-5催化剂的性能的差异是由沸石颗粒的不同尺寸引起的，并且在较高量的Zn下是由沸石样品的骨架中的Al原子的不同分布引起的。
Activity/selectivity of ZnZSM-5 catalysts (0.04–0.369mmolZn/g zeolite) prepared by ion-exchange from two samples of ZSM-5 zeolites having different size of particles (≤1 and ∼4μm) in aromatization of light alkanes have been investigated. As a probe molecule n-hexane was used. Acid HZSM-5 samples have comparable composition (0.101–0.11mmolAl/g) and acidity measured by TPDA method (0.92–0.91mmolacidsites/g). Introduction of Zn into zeolites does not significantly affect the total acidity determined by TPDA but causes the redistribution in the type of acid sites. From the activity/selectivity of ZnZSM-5 catalysts followed that by introduction of Zn into HZSM-5 zeolites the aromatization proceeds very significantly via bifunctional mechanism. Results showed that the activity/selectivity of ZnZSM-5 catalysts strongly depends on the synergism of the particle size, acidity, aluminum distribution in the zeolite framework, and of the amount and the type of Zn species located in the cationic positions in the zeolite. The type of Zn species is strongly affected by the distribution of Al atoms in the zeolite framework. It was published that isolated Zn2+or oxygen-bridged Zn–O–Zn2+species can be formed in ZSM-5 zeolite depending on the distance between the adjacent aluminum atoms in the framework and that this species have a very different activity in aromatization. It was concluded that the observed differences in the performance of the investigated ZnZSM-5 catalysts at low Zn concentration are caused by the different size of the zeolite particles and at higher amount of Zn by the different distribution of Al atoms in the framework of the zeolite samples.