H-Gallosilicate (MFI) propane aromatization catalyst: influence of calcination temperature on acidity and deactivation due to coking

Abstract

H-Gallosilicate (MFI) (bulk Si/Ga = 33) calcined at different temperatures (600-1100° C) has been characterized for its acidity/acid strength distribution (by step wise thermal desorption and chemisorption of pyridine at 100-400° C), acid function by acid catalyzed model reactions (viz. isooctane cracking (at 400° C) for external acid sites and o-xylene isomerization (at 400° C) and toluene disproportionation (at 500° C) for overall acid sites), crystallinity by XRD, incorporation of Ga in the zeolite framework by ⁷¹Ga MAS NMR and FTIR, and framework and non-framework Ga by ²⁹Si MAS NMR and bulk chemical analysis. Influence of the calcination temperature on the catalytic activity/selectivity and catalyst deactivation due to coking in the propane aromatization process (at 550° C) has also been thoroughly investigated. The acidity, framework Ga, crystallinity and catalytic activity and catalyst deactivation in the propane aromatization are found to be strongly influenced by the calcination temperature, mostly because of the extensive degalliation of the zeolite, depending upon the calcination temperature. The product selectivity, shape selectivity and dehydrogenation activity relative to cracking activity, of the zeolite in the propane aromatization are influenced strongly by the calcination temperature and also by the catalyst deactivation due to coking.