Pt/H-ZSM-5 zeolites (Si/Al ratio of 50) with a Pt loading of 0.28 wt.% were successfully synthesized and employed as catalysts for the selective hydrodealkylation of C-9+ aromatics to benzene, toluene, and xylenes (BTX). Five different crystallite sizes (40, 20, 10, 5, 2 mu m) were prepared using different aging times before crystallization. The influence of crystallite size on catalytic activity was investigated, and the catalysts synthesized were physicochemically characterized by XRD, BET, SEM, and ICP-OES. Hydrodealkylation was performed in a conventional fixed bed reactor, and the influences of crystallite size on ethyltoluene (ET) isomer conversion and on the recovery yields of trimethylbenzene (TMB) isomers were examined. Conversion of ET isomers was always higher than that of TMB isomers. The distribution of products obtained was strongly influenced by Pt/H-ZSM-5 crystallite size, that is, ET isomer conversion decreased and TMB isomer recovery yield increased with crystallite size. Catalyst crystallite size was found to dictate catalytic activity with respect to selective hydrodealkylation. Pt/H-ZSM-5 with a crystallite size of 5 mu m exhibited the best catalytic performance for the selective hydrodealkylation of C-9+ aromatics to BTX. (C) 2015 Elsevier B.V. All rights reserved.