Collect. Czech. Chem. Commun. 1999, 64, 168-176

Role of Zinc in Zn-Loaded ZSM-5 Zeolites in the Aromatization of n-Hexane

Edita Rojasová*, Agáta Smiešková, Pavol Hudec and Zdenek Židek

Department of Petroleum Technology and Petrochemistry, Faculty of Chemical Technology, Slovak University of Technology, Radlinského 9, 812 37, Bratislava, Slovak Republic


Aromatization of n-hexane over zinc-modified ZSM-5 zeolites was investigated. It was shown that incorporation of zinc by ion exchange into cationic positions of NH4-ZSM-5 zeolite causes acid-site strength redistribution and generation of new relatively strong Lewis acid sites in zeolite increasing the selectivity of n-hexane aromatization in comparison with the parent NH4-ZSM-5 zeolite. Simultaneous presence of Lewis and Broensted acid sites in ZSM-5 zeolite does not affect the strength of Broensted acid sites in zeolite. For the activity/selectivity of aromatization of n-hexane on Zn-modified ZSM-5 zeolites, the amount of Zn and its localization in the cationic positions are decisive. The reaction of n-hexane can be also initiated by the Zn species alone in the cationic positions. ZnO species alone as an extraframework phase was found inactive in the catalyst for aromatization of n-hexane. The influence of ZnO addition on the performance of pure ammonium forms of ZSM-5 zeolites in n-hexane conversion is a result of partial migration of zinc into cationic positions of zeolite by solid-state ion exchange.

Keywords: ZnZSM-5; Acidity; Aromatization; n-Hexane; Solid-state ion exchange; Zeolites; Heterogeneous catalysis.