The hydrogenation of aromatic compounds is mainly controlled by diffusion; hence, the diffusion of reactants into the pores of a catalyst has a significant effect on the catalytic reaction. However, the diffusivity of reactant molecules is poorly characterized due to the limitations of experimental technology. In this study, the diffusion behavior of benzene, naphthalene, and anthracene in alumina pores of three different sizes, namely, 3.1 nm, 5.2 nm, and 6.8 nm pores, at 623.15-723.15 K is investigated using a molecular dynamics (MD) method. The effects of temperature and pore size on the diffusion performance were investigated. The three aromatic hydrocarbons were distributed parallel to the pore surface through electrostatic interactions. The Arrhenius equation can accurately fit the relationship between temperature and the self-diffusion coefficient, and the calculated diffusion activation energy shows that the diffusivity of the larger molecules is more sensitive to temperature variation. Furthermore, the self-diffusion coefficients of three aromatic hydrocarbons and their corresponding dynamic diameters show a good linear relationship. The larger molecules showed smaller variations in their self-diffusion coefficients with an increase in pore size. The results reported herein provide theoretical guidance for the characterization of the diffusion behavior of different aromatics in catalyst pores. (C) 2019 Elsevier Ltd. All rights reserved.