Understanding the Catalysis of Noble Metals in Reduction of Iron Oxide by Hydrogen: Insights from DFT Calculations

Abstract

Fe/FeOx redox couples have been widely used as an oxygen carrier for redox devices such as chemical looping reactors and solid oxide iron-air battery (SOIAB) because of their low cost and high oxygen capacity. However, a critical challenge is the sluggish reduction kinetics of FeOx in the intermediate temperature range, significantly limiting the devices’ achievable efficiency and service life. Here, we report on a combined theoretical and experimental study on the catalytic effect of noble metals (Ir, Ru, Rh, Pd and Pt) on the H2-reduction kinetics of FeOx. We first use density functional theory (DFT) to calculate the electron projected density of states (PDOS) near Fermi level (EF) of several noble metal (Ir, Pd, Ru, Rh, Pd)/Fe3O4 systems. We reveal that Ir offers the highest PDOS near EF among all noble metals studied, which provides abundant electrons for efficient cleavage of O-Fe bonds and low-energy dissociation of H2 molecules, thus resulting in significantly boosted reduction kinetics of Fe3O4. Experimentally, the results of temperature programmed reduction and SOIAB performance testing corroborate the theoretical predictions.