Modeling reaction–diffusion processes within catalyst washcoats: I. Microscale processes based on three-dimensional reconstructions

Abstract

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.

Modeling reaction–diffusion processes within catalyst washcoats: II. Macroscale processes informed by microscale simulations

“…The objective of this paper is to develop and apply geometrically simple models that can be used to assist the qualitative and quantitative interpretation of three-dimensional models that predict performance in geometrically complex pore microstructures that are reconstructed from an actual catalyst washcoat. A companion paper [1] The individual channel dimensions are typically on the order of a millimeter and the monolith is typically a few centimeters long. The thin catalyst washcoat, which covers the monolith walls, is typically a few tens of microns thick.…”

“…Considering Fig. 3 from the companion paper [1], penetrating holes may provide a better idealization than isotropic porous media. Such hole structures can be modeled using approaches based on the Thiele modulus [6,7].…”

“…To begin, an axisymmetric, cylindrical, pore model that is motivated by the well known one-dimensional Thiele analysis [6,7] is developed. This two-dimensional pore model is structured and non-dimensionalized in ways that are analogous to the approach in a companion paper that directly models actual geometrically complex pores [1]. By casting the models in compatible forms, insight from the complex microscale geometry can be used in the more traditional setting.…”

Mathematical model of Fischer-Tropsch catalyst pellet with pointed centers of synthesis

“…The boundary condition for equation (13) coincides with equation (10). We are looking for a solution of the problem in a spherical coordinate system (see figure 1).…”

“…In this case, a homogeneous approximation can be used to describe the reactions in the volume of the granules. A wide range of models designed for homogeneous reactions: shrinking core model, models taking into account the dynamics of change the pore structure, percolation and fractal models [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16].…”