(393h) Multiscale Methodology for Prototyping of Porous Catalysts

The microstructure of the support determines a key
property of porous catalysts---effective diffusivity. Typically,
supporting materials with bimodal pore size distribution are used that
involve both meso- and macro-pores. Spatial distribution of active
metal crystallites within the porous support then influences reaction
rates and conversions. In order to optimize the catalyst support
microstructure and ultimately the whole catalyst, it is necessary to
relate quantitatively the morphological features of the porous
structure both to its preparation conditions and to the final transport
properties and catalyst performance under reaction conditions.

In this paper we demonstrate
the application of novel models based on the generalized
volume-of-fluid method and 3D digital reconstruction of porous
structure. The procedure includes simulation of porous support
formation (virtual packing of primary particles of defined shapes and
sizes), drying and crystallization of impregnated metal solution
(growth of metal nano-particles), and solution of reaction and
transport within the final virtual catalyst structure to obtain
volume-averaged reaction rates that are then used in full-scale model
of catalytic monolith reactor. A parametric study is performed to
investigate the effects of the sizes of primary particles (influencing
the meso- and macro-porosity and pore sizes) and active metal
impregnation conditions (influencing the distribution of active
catalytic surface area) on the macroscopic activity of a catalytic
monolith with Pt/g-Al2O3 washcoat used for automotive exhaust gas
aftertreatment.