Numerical study of reaction in porous catalysts under composition modulation

A numerical simulator for modeling heterogeneous catalysis is developed to study the transient response of gas-solid kinetics in porous catalysts under composition modulation. A lumped system and a one-dimensional model are built in this numerical simulator. The numerical simulator, Transcat, is a general solver, which can handle unlimited components, arbitrary kinetics and various type of boundary conditions. An original algorithm of element constraint method is developed and also successfully integrated in Transcat to ensure the conservation of total mass and element in a numerical computation. With multiple numerical methods and the theory of stiffness-reduced modeling, Transcat can compute stiff problems efficiently. This general solver is validated by case studies of partial-equilibrium assumption, steady-state profiles and analytical solution of Fisher-Kolmogorov equation. Carbon monoxide oxidation over Pt/Al₂O₃ catalyst under periodic forcing is studied by numerical simulation using Transcat. Transcat is capable of fitting the experiment data and explain the behavior of CO oxidation under transient operation conditions. Frequency optimization of various input signal to maximize the turnover rate of CO is performed in a series of numerical experiments in Transcat. At optimum frequency, the characteristic spatiotemporal pattern of turnover rate is continuous, symmetric and boundary-attached, and the saturated storage of CO over the catalytic site is at minimu