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This paper develops a detailed analysis of reaction-diffusion processes within a porous rhodium-alumina catalyst washcoat. Focused-ion-beam-scanningelectron-microscope (FIB-SEM) techniques are developed and applied to reconstruct the actual catalyst-support microstructure. Three-dimensional transport processes within washcoat micro-pore structures are modeled using a dimensionless representation of reaction and diffusion rates based on the Damköhler number. Three-dimensional computational solutions for particular porous microstructures are modeled and interpreted. In a companion paper, these microstructural results are used to assist development of largerscale models that can be incorporated into reactor-scale simulations.

a b s t r a c tThis paper extends the in situ adaptive tabulation (ISAT) algorithm for accelerating the simulation of complex heterogeneous chemical kinetics within transient, three-dimensional, computational fluid dynamics (CFD). The ISAT algorithm, initially developed for homogeneous combustion kinetics, takes advantage of the fact that initial conditions for the chemistry in a particular cell (i.e., temperature and composition) may have been present in this cell or another cell earlier in the simulation. In such cases, the solution can be extracted from a tabulation of prior solutions more efficiently than solving the local kinetics problem. The ISAT algorithm uses efficient tabulation and retrieval algorithms, greatly accelerating the solution process. Illustrative results are based on the simulation of methane reforming in a catalytic microchannel reactor, considering coupled fluid mechanics, catalytic chemistry, and conjugate heat transfer.

This paper first develops a two-dimensional Thiele-type cylindrical-pore model that predicts catalytic washcoat performance, albeit for idealized cylindrical pores. The primary purpose for the cylindrical-pore model is to serve as a basis of comparison with three-dimensional models of catalytic performance in actual geometrically complex washcoat pores that are tomographically reconstructed from focused-ion-beam-scanning-electron-microscopy (FIB-SEM) measurements. In both models, the reaction-diffusion processes are characterized by a Damköhler number that is based on a pore diffusion coefficient and a single first-order reaction rate. Performance metrics include effective product flux from the pores, pore effectiveness, and reaction depth within the pore. In all cases, the models are generalized by casting the conservation