The heterogeneous structure of activated carbon is studied by using a pore size distribution concept. The pore size is related to the adsorbate-adsorbent interaction energy by the Lennard-Jones potential. The competition of different species for a given pore is considered via their own interaction strength with the local micropore. A pore and surface diffusion model taking into account the pore size distribution is proposed to investigate the effect of surface heterogeneity on the prediction of binary sorption kinetics. The results are compared with those previously obtained using a uniform energy distribution.