Modified CeO2 as active support for iron oxides to enhance chemical looping hydrogen generation performance

Abstract

Chemical looping hydrogen generation (CLG) is a promising pathway that can offer both the high purity hydrogen as well as the efficient CO2 capture capability. However, this process was significantly hindered by the lack of active oxygen carriers at relatively low temperatures. Mixed ionic-electronic (MIEC) supported iron oxides exhibit desirable redox performance for the improved oxygen-ion conductivity. In this work, we prepared several AxCe1-xO2-δ (A = Gd, La; x = 0, 0.1, 0.3) supported Fe2O3 for hydrogen production at 750 °C. It was shown that Fe2O3/Gd0.3Ce0.7O2-δ shows the highest hydrogen generation performance and stability over 50 redox cycles. The reactivity follows the sequence of: Fe2O3/Gd0.3Ce0.7O2-δ > Fe2O3/La0.1Ce0.9O2-δ > Fe2O3/Gd0.1Ce0.9O2-δ > Fe2O3/La0.3Ce0.7O2-δ. The fundamental investigation shows that the doping of rare earth (Gd, La) into CeO2 contributes to the formation of oxygen vacancies, thus improving the lattice oxygen diffusion. The enhanced hydrogen generation performance attributes to the high lattice oxygen diffusion to improve the reactivity and inhibiting outward diffusion of Fe. The roughly linear relation between the oxygen vacancy concentration and chemical looping performance can be extended to predict the performance of oxygen carriers for other chemical looping applications, methane reforming, combustion, and ethane dehydrogenation, etc.