First-Principles-Based Reduction Kinetics of CuO Oxygen Carrier in Commercial TGA

The gas diffusion in a commercial thermogravimetric analyzer (TGA) is crucial for the reduction kinetics of the oxygen carrier, which could make the conversion rate drop to almost 1/3. To eliminate the gas diffusion in the crucible, a multiscale methodology is established based on CFD simulation and multiscale modeling of concentration modification of the TGA crucible, gas diffusion in a sample layer, the reduction reaction of CuO particles, and intrinsic kinetics at the gas–solid interface. During the initial stages of the reduction reaction, the logistic function expression is proposed to modify the H2 concentration at the top/bottom surface of the TGA crucible. As for the interaction between CuO and H2, density functional theory calculations indicate that the reduction of H2 involves a two-step surface reaction and ion diffusion in the bulk. The intrinsic kinetics of these processes are directly calculated by the first-principles method, rather than experimental fitting. Kinetic modeling can well predict the CuO reduction reaction rate with H2 at different temperatures and concentrations. In the innermost region of the particles, the proportion of H2O gas reached approximately 25 vol %, while few H2 gas particles were found in the internal region. Gaseous H2 is absent from the surface of particles to the inward depth of 1/5 of the radius, indicating that the H2 reduction was governed by a typical internal diffusion control mechanism.