The kinetics of desorption of 1,3,diisopropylbenzene and 1,3,5-triisopropylbenzene in FCC catalyst pellets is reported employing the ZLC method as the measurement device: 20 by weight NaY zeolite (0.9 mu m diameter) and 80% by weight silica alumina matrix are combined to form the FCC catalyst particles (45-55 mu m diameter). The large hydrocarbon molecules 1,3-diisopropylbenzene and 1,3,5-triisopropylbenzene are adsorbed in both the zeolite and alumina matrix, influencing the equilibrium adsorption, and the desorption curves. Accordingly, the desorption plots of 10(c/c(0)) versus time for the NaY zeolite alone and for the FCC catalyst particles differ significantly in equilibria but not in the long time diffusion solutions. The intercept of the long time asymptotic diffusion plots is larger for the NaY zeolite than for the FCC catalyst particles, Signifying that more sorbate is desorbed in the ease of the FCC particles. For kinetics, the long time asymptotic diffusion plots are parallel indicating that the resistance for both the zeolite and FCC particles is similar. The time constants for diffusion for both systems are similar at the same temperatures, indicating that both systems are micropore (i.e., zeolitic) controlled.