  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 $A\to B$ 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.
