Thermogravimetric kinetic analysis of the Ce-Zr composite oxygen carrier prepared by ball milling

A series of zirconium-doped cerium-based composite oxygen carriers were prepared using the ball milling method. The results from X-ray powder diffraction (XRD), H-2-temperature programmed reduction experiments (H-2-TPR), and Brunauer-Emmett-Teller (BET) show that a solid solution, formed from CeO2 and ZrO2, possesses a mesoporous structure and exhibits excellent reaction performance. In addition, carbon nanotubes (CNTs) with an addition amount of 5 wt.% greatly increased the specific surface area of oxygen carriers, thereby improving the activity of solid solutions. In order to further understand the performance of oxygen carriers, the kinetics of H-2 reduction of oxygen carriers was studied by thermogravimetric analysis (TGA). The three-dimensional diffusion model showed the best fitting effect among four typical models (viz., the diffusion-controlled model, the unreacted shrinking core model, the uniform model, and the nucleation-nuclei growth model). Finally, the activation energies of CeO2, Ce9Zr1O delta, and 5 wt.% CNTs Ce9Zr1O delta were 223.92, 170.96, and 128.60 kJ/mol, respectively, which also correspond with the reactivity sequence of the oxygen carriers.

Automated summary

In this study, a series of zirconium-doped cerium-based composite oxygen carriers were prepared using the ball milling method. The addition of carbon nanotubes was found to greatly increase the specific surface area and activity of the oxygen carriers. The kinetics of H2 reduction of the oxygen carriers were best described by a three-dimensional diffusion model. Additionally, the activation energies of the oxygen carriers corresponded with their reactivity sequence.