The accessibility in aluminas considered to be representative of matrices used in FCC resid catalysts, with mean pore sizes between 64 and 201 A, was characterized through a kinetic approach by means of the conversion of 1,3,5-tri-isopropylbenzene (TIPB) at 500 degrees C in a CREC Riser Simulator fluidized bed laboratory reactor. The product distribution was essentially the same as that observed on an equilibrium commercial FCC catalyst, but the activity of the aluminas was much lower. The main products (propylene, benzene, isopropylbenzene, di-isopropylbenzenes) showed that a series cracking mechanism prevailed in the conversion of TIPB. The apparent first order kinetic constants assessed and the conversion profiles allowed establishing a ranking of activities that could be associated directly to accessibilities and not to the number of acid sites (Lewis nature), which was proportional to the specific surface area of the alumina. The sequence of accessibilities followed the same trend as the mean pore size of the aluminas. (c) 2006 Elsevier B.V. All rights reserved.