Collect. Czech. Chem. Commun.
1999, 64, 168-176
https://doi.org/10.1135/cccc19990168
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
Abstract
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.
