The progressive deactivation of various HNaY zeolite catalysts (Si/Al=2.4),
during methylnaphthalene isomerisation, was studied at 573-663 K. The acti
vity decay was expressed as a function of time-on-stream (t-o-s) and of cok
e content (C-c). In both cases very simple exponential equations, whose par
ameters depend on the degree of decationation of the zeolite and temperatur
e were satisfactorily used to fit the experimental data. Coke analysis was
performed on the most acidic catalyst (HNaY-98) at T=633 K and the composit
ion of the coke soluble in methylene chloride was determined. The influence
of temperature and ion-exchange degree on the coke deposition rate was als
o examined. (C) 1999 Elsevier Science B.V. All rights reserved.