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.