The Effect of Extra-Framework Aluminum in Dealuminated ZSM-5 Zeolites on the Transformation of Aromatic Hydrocarbons

Abstract

H-ZSM-5 zeolite was dealuminated by steaming under "mild" and "severe" conditions at 675 and 975 K for 71.5 and 0.5 h, respectively. It resulted in a comparable number of Al atoms released from the zeolite framework, although of their different nature. The "mild" zeolite steaming yielded Al species easily removable from the zeolite by an acid leaching, in contrast to the zeolite steamed at "severe" conditions. The extra-framework Al species contributed to both a substantially higher para -selectivity in toluene disproportionation and its alkylation with ethylene and to an increased rate of side reactions leading to the zeolite deactivation by coke formation in toluene alkylation with ethylene.