Abstract
Computational fluid dynamics (CFD) is coupled with reaction and transport in a micro-scale pellet simulation to study CO oxidation over Rh/Al2O3 catalyst. The macro-pores are explicitly modeled to study the interaction of these phenomena in both the solid and fluid phases. A catalyst layer is computationally reconstructed using a distribution of alumina particles and a simple force model. The constructed geometry properties are validated using the existing data in the literature. A surface mesh is generated and modified for the geometry using the shrink-wrap method and the surface mesh is used to create a volumetric mesh for the CFD simulation. The local pressure and velocity profiles are studied and it is shown that extreme changes in velocity profile could be observed. Furthermore, the reaction and species contours show how fast reaction on the surface of the solid phase limits the transport of the reactants from the fluid to meso- and micro-porous solid structures and therefore limits the overall efficiency of the porous structure. Finally, the importance of using a bi-modal pore structure in the diffusion methods for reaction engineering models is discussed.
Highlights
CO oxidation is one of the most studied catalytic reaction mechanisms
Given the emphasis of different studies on the importance of coupling different phenomena on the catalyst surface, here we introduce a framework to generate a micro-scale porous structure and use it to develop a resolved pore Computational fluid dynamics (CFD) simulation of CO oxidation over Rh/Al2O3
For the given velocity it seems that pressure change is not signifificant, it should be noted that almost 14 Pa pressure change in a 42 μμm ssttrruucture ccoould bbee ccoonnssiderable
Summary
CO oxidation is one of the most studied catalytic reaction mechanisms. The simple and fast mechanism of the reaction is suitable to investigate reaction and transport interactions on the catalyst surface both computationally and experimentally. In one of their most important studies Matera and Reuter show how heat and mass transfer can mask intrinsic reactivity of the catalyst for normal modern in situ experiments under typical gas phase conditions [10] They show that coupling the gas phase transport with surface reaction could lead to multiple steady-states in case of CO oxidation on RuO2. The study emphasizes the effects of external and internal mass transfer limitations on the reaction rate measurements and how surface science experiments should be aware of these limitations for such a fast reaction These important findings show how sophisticated the experimental procedures should be designed to be able to truly investigate the active phase behavior, and highlight the importance of integrating flow and transport with the reaction in all the different stages of design of catalytic systems
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