A mechanism-based finite-rate surface catalysis model for simulating reacting flows

A mechanism-based finite-rate wall boundary condition is implemented in a state-of-the- art finite volume CFD thermochemical nonequilibrium code to study a high enthalpy CO₂ flow over blunt bodies. All the relevant surface processes responsible for the catalytic behavior of the wall are accounted for, including adsorption and desorption (both atomic and molecular), and Eley-Rideal and Langmuir-Hinshelwood recombinations. The model only requires the specification of the reaction rates for each of the processes considered, and the law of mass action is used to compute surface coverages and mass fluxes produced or consumed at the wall due to its catalytic activity. The kinetic rates are chosen to describe a platinum surface, with a fairly high degree of catalycity with respect to CO oxidation. As expected, the predicted heat flux is intermediate between the two extrema, namely the non-catalytic and supercatalytic wall assumptions. Because the only input of the model are the reaction rates, which are usually unavailable or affected by a large experimental uncertainty, the use of Molecular Dynamics simulations employing the Quantum Chemistry based reactive force field ReaxFF is proposed as a novel approach to both determine and characterize each of the underlying processes which collectively cause the wall catalytic activity. Because (dissociative) adsorption is a fundamental step leading to surface recombinations, the sticking of O₂ on Pt(111) is studied using ReaxFF Molecular Dynamics simulations.