Microkinetic analysis of reactions between CO and CuO in chemical looping combustion

Abstract

Since the gas diffusion in the thermogravimetric analyzer crucible significantly limits the reactivity of samples, a down-top multi-scale kinetic model is proposed to predict the reduction rate in a diffusion-limited crucible, by considering the gas diffusion during the entire crucible domain. To improve the adaptability of kinetic parameter, the reaction kinetics are directly calculated by the first-principle method, rather than fitting the experimental data. The oxidation process of CO takes into account three-step reversible reaction (i.e., adsorption, interface reaction, and desorption) on the surface and the diffusion of oxygen ions in the bulk. The impact factors, i.e., particle polydispersity, gas diffusion, oxygen diffusion, and surface reaction, are all adequately considered, which can be easily extended to the different kinds of diffusion-limited crucibles of various commerce devices. Density functional theory calculations are used to analyze the mechanisms of CO oxidation on the surface of copper oxide, and the optimal adsorption site is the triple coordination copper top site. The corresponding kinetic parameters are then obtained via harmonic transition state theory. The multi-scale model can accurately predict the actual reduction rate of copper oxide in a commercial thermogravimetric analyzer under various operation conditions. Using the particle-resolved simulations, the effect of different physical properties is further studied to provide theoretical support for the design of copper-based oxygen carrier in fuel reactor. Results reveal that there is the optimal grain size for CuO reduction, and Cu-based oxygen carrier with the grain size of 30∼50 nm exhibits almost the same reaction performance.