Abstract
A continuum modeling approach is used to compare the yield of catalyst
particles called monodisperse, and containing only nanopores (i.e.,
micropores or narrow mesopores), to the yield of the same nanoporous
particles to which larger diffusion channels have been introduced
in various ways. Bidisperse and bimodal pore size distributions are
considered; in the bimodal case, the large diffusion channels are
allowed to vary in size throughout a particle, while in the bidisperse
case they are all of the same size. Model-based optimization is performed
with respect to the overall yield of a first-order reaction, optimizing
the spatial distributions of both the volume fraction and the diameter
of the diffusion channels. It is found that the yield of catalysts
with an optimized bidisperse pore size distribution may be at least
an order of magnitude increased with respect to the original monodisperse
distribution, thanks to the optimized introduction of large pore
channels. Remarkably, however, local variations in pore diameter
and porosity in bimodal pore networks do not lead to significant
further improvements. This calls for the synthesis of bidisperse
catalysts with a carefully optimized size of the large pore channels
and thickness of their nanoporous catalytic walls.
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