  We simulated models of diffusion and aggregation in long pores of small
widths in order to represent the basic mechanisms of coke deposition in
catalysts' pores. Coke precursors are represented by particles injected at the
pore entrance. Knudsen diffusion, which is usually expected inside the pores,
is modeled by ballistic motion of those particles. The regime of molecular
diffusion is also analyzed via models of lattice random walks biased along the
pores. The aggregation at the surface or near previously aggregated particles
was modeled by different probabilistic rules, accounting for the possibilities
of more compact or more ramified deposits. In the model of Knudsen diffusion
and in some cases of molecular diffusion, there is an initial regime of uniform
deposition along the pore, after which the deposits acquire an approximately
wedge shape, with the pore plugging near its entrance. After the regime of
uniform deposition and before that of critical pore plugging, the average
aggregation position slowly decreases with the number N of deposited particles
approximately as N^{-0.25}. The apparently universal features of deposits
generated by microscopic models are compared with those currently adopted in
continuum models.
