We investigate the conditions for reactivity enhancement of catalytic processes in porous solids by use of molecular traffic control (MTC) as a function of reaction rate and grain size. With dynamic Monte-Carlo simulations and continuous-time random walk theory applied to the low concentration regime we obtain a quantitative description of the MTC effect for a network of intersecting single-file channels in a wide range of grain parameters and for optimal external operating conditions. The efficiency ratio (compared with a topologically and structurally similar reference system without MTC) is inversely proportional to the grain diameter. However, for small grains MTC leads to a reactivity enhancement of up to approximately 30% of the catalytic conversion A -> B even for short intersecting channels. This suggests that MTC may significantly enhance the efficiency of a catalytic process for small porous nanoparticles with a suitably chosen binary channel topology. (c) 2005 Elsevier B.V. All rights reserved.