The reduction mechanism and kinetics of Fe2O3 by hydrogen for chemical-looping hydrogen generation

Abstract

Low-grade hydrogen-containing gases can be converted into high-value pure hydrogen by chemical-looping hydrogen generation. Iron-based oxygen carrier is believed to be the most suitable oxygen carrier for CLHG. It is essential to investigate the reduction mechanism and kinetics of Fe2O3 with hydrogen. The reduction of Fe2O3 by H2 was conducted in a thermogravimetric analyzer at 973–1172 K. The phase analysis of reduction products in different reduction stages illustrated that Fe2O3 → Fe3O4 and Fe3O4 → FeO proceed simultaneously; hence, the reduction process is a two-step reaction, in the sequence of Fe2O3 → FeO and FeO → Fe. To investigate the reaction mechanisms for the two steps, the Hancock–Sharp method and the nonlinear fitting approach were applied to select the kinetic models. The reaction mechanisms of Fe2O3 → FeO can be described by nucleation and growth model. The activation energy is 36.74 ± 1.09 kJ mol−1, and reaction rate equation derived from Arrhenius law is estimated for Fe2O3 → FeO. As for FeO → Fe, the first stage is controlled by the phase-boundary reaction, and the oxygen diffusion affects the last stage of the reduction process.