A First-Principles Microkinetic Rate Equation Theory for Heterogeneous Reactions: Application to Reduction of Fe<sub>2</sub>O<sub>3</sub> in Chemical Looping
Zhenshan Li, Jinzhi Cai, Lei Liu
Abstract
How to couple the microscale surface reactions with the macroscale kinetic phenomenon and achieve a first-principles-based kinetics prediction is an unsolved problem in the field of chemical looping. This study proposes a first-principles-based theoretical model to calculate the heterogeneous reduction kinetics of an Fe2O3 oxygen carrier in chemical looping. At the atom scale, the surface reaction mechanism of H2 with Fe2O3 is investigated on the basis of density functional theory (DFT) calculations. The energetic data, frequency, and atomic structure obtained from DFT calculations are introduced into transition state theory (TST) to calculate the reaction rate constants. At the grain scale, a rate equation theory is developed and used to couple the surface reaction with the bulk diffusion of lattice oxygen, and the reaction mechanism and reaction rate constants obtained from DFT and TST are introduced into the rate equations to predict the reduction kinetics of Fe2O3. The theoretical prediction is validated by experimental data from thermogravimetric analysis, and it is demonstrated that the first-principles-based microkinetics rate equation theory can provide an accurate prediction of the reduction kinetics of Fe2O3 oxygen carrier in chemical looping.