Radially graded porosity in La-based OCM catalysts: a CFD-driven framework for optimizing reaction-diffusion dynamics at the single-particle scale

Understanding the effects of pore size and porosity distribution on the diffusion-reaction relationship of the La-based oxidative coupling of methane is essential for better design and scale-up reactors. This study developed a framework integrating mathematical-based pore size and porosity distribution with multi-component diffusion and lumped kinetic models at the particle scale using the computational fluid dynamics (CFD) method. The simulation results demonstrated that OMC catalyst particles with pore size and porosity decreasing towards the particle core exhibit optimal performance. The effects of operating conditions were investigated using the optimal pore size and porosity distribution model, which shows that an optimal operating temperature exists, N₂ dilution and increased CH₄/O₂ ratios enhance C₂ selectivity, while the increase in flow rate within the single particle does not confer a significant advantage in terms of CH₄ reaction rate and C₂ selectivity. The reaction-diffusion relationship analysis shows that catalyst particles with higher external porosity and larger external pore size have better catalyst performance because of the highest external efficiency factor, the highest internal efficiency factor, and the lowest Damköhler number. The single-particle catalyst model can effectively represent the reaction-diffusion law and is meaningful for fluidized bed reactor design and optimization.