Reduction and oxidation properties of Fe2O3/ZrO2 oxygen carrier for hydrogen production

Fe2O3 is a promising oxygen carrier for hydrogen production in the chemical-looping process. A set of kinetic studies on reduction with CH4, CO and H2 respectively, oxidation with water and oxygen containing Ar for chemical-looping hydrogen production was conducted. Fe2O3 (20 wt.%)/ZrO2 was prepared by a co-precipitation method. The main variables in the TGA (thermogravimetric analyzer) experiment were temperatures and gas concentrations. The reaction kinetics parameters were estimated based on the experimental data. In the reduction by CH4, CO and H2, the reaction rate changed near FeO. Changes in the reaction rate due to phase transformation were observed at low temperature and low gas concentration during the reduction by CH4, but the phenomenon was not remarkable for the reduction by CO and H2. The reduction rate achieved using CO and H2 was relatively faster than achieved using CH4. The Hancock and Sharp method of comparing the kinetics of isothermal solid-state reactions was applied. A phase boundary controlled model (contacting sphere) was applied to the reduction of Fe2O3 to FeO by CH4, and a different phase boundary controlled model (contacting infinite slab) was fit well to the reduction of FeO to Fe by CH4. The reduction of Fe2O3 to Fe by CO and H2 can be described by the former phase boundary controlled model (contacting sphere). This phase boundary controlled model (contacting sphere) also fit well for the oxidation of Fe to Fe3O4 by water and FeO to Fe2O3 by oxygen containing Ar. These kinetics data could be used to design chemical-looping hydrogen production systems.