Kinetic Monte Carlo modeling of heterogeneous catalysis on silica thermal protective materials based on reactive molecular dynamics simulation

Heterogeneous catalytic recombination of chemically dissociated atoms occurring on thermal protective materials significantly increases the thermal load borne by high-speed aircraft, but the intricate nature of microscopic reaction dynamics poses a formidable challenge in its analysis within the context of macroscopic heat and mass transfer calculations. Reactive molecular dynamics (RMD) method is helpful in simulating the complicated chemical mechanisms of the gas-surface interaction, while the high computational cost limits its application to larger spatial and temporal scales. To quickly obtain the time evolution of surface catalysis of dissociated atoms on thermal protective materials and provide reactive boundary conditions for numerical simulation of the high-speed flow field, a kinetic Monte Carlo (KMC) algorithm specified for this phenomenon was developed. Rate parameters of the elementary reaction steps were extracted from ReaxFF-based molecular dynamics simulation using proper post-processing method. Elementary reaction steps and active site configuration were integrated into the RMD-based KMC algorithm to cater to the characteristics of catalysis on silica thermal protective materials. The RMD-based KMC modeling method was proved to be accurate and efficient in predicting the recombination coefficients and surface configuration, with an error of less than 15 %. Compared to RMD simulations, the KMC modeling significantly reduces the computational cost of surface reaction dynamics by approximately 2 × 10⁵ times. RMD-based KMC method can contribute to the cross-scale coupling between molecular-level research and continuum computation.