CATalytic – Post Processor (CAT-PP): A new methodology for the CFD-based simulation of highly diluted reactive heterogeneous systems

• A novel approach is proposed to simulate heterogeneous catalytic reactors with highly diluted streams.
• Reactor fluid dynamic is first computed in non-reactive conditions using commercial CFD simulator.
• The flow field is used to solve the chemical species transport equations.
• This approach is recommended when the reactor is affected by nonideal fluid-dynamic.
• The NOx storage over a Pt-BaO/Al2O3 catalyst within an operando reactor is the case study.

Scaling-up and -down of conventional ideal lab-scale catalytic reactors often introduces strong non-idealities in the flow field which may drastically affect the expected reactor performances and effectiveness. Computational fluid-dynamic (CFD) analysis is required to assess the extent of such non-idealities. In the case of reactive systems, and in particular in the case of heterogeneous catalytic processes, however, computational efforts are huge and, due to the wide range of space and time scales, may become hardly sustainable when detailed chemical kinetics have to be implemented and solved for transient processes. A specific case, encountered in most of the applications of environmental catalysis, is represented by highly diluted process streams, where reactants and products have concentrations of the order of hundreds of part per million and the reaction duty is extremely low. In this case, the reactor fluid dynamic is not affected by the occurrence of chemical reactions, while the activity of the system can be significantly affected by the reactor hydrodynamics. A new simulation approach, named CATalytic – Post-Processor (CAT-PP), is proposed in this paper to treat those systems. Such approach results in a numerical tool which acquires the flow-field data from non-reactive CFD simulations, performed by a commercial code (ANSYS Fluent) and post-processes them by solving the species transport equations with a detailed kinetic scheme. The potential of the proposed approach is demonstrated through its application to the dynamic analysis of a FTIR-operando reactor-cell loaded with a lean-NOx-trap catalyst. It is shown that CAT-PP allows to effectively simulate a transient diluted catalytic process taking care of the actual reactor hydrodynamics even implementing detailed surface (or gas/solid) kinetic schemes.