Applied Energy, Vol.225, 912-921, 2018
Effects of supports on reduction activity and carbon deposition of iron oxide for methane chemical looping hydrogen generation
Chemical looping hydrogen generation is a promising technology which has the potential to efficiently produce hydrogen and capture CO2 with the aid of iron-based oxygen carriers. The properties of the iron-based oxygen carrier, such as carbon resistance, redox activity, and cycle stability, are critical factors for the development of CLHG process. In this study, four different supports, MgAl2O4, CeO2, ZrO2, and CeZrO4, were incorporated with iron oxide by a co-precipitation method. The reduction activity, carbon resistance and redox stability of the oxygen carriers with methane were investigated in a bench-scale fluidized bed reactor. The redox activity and oxygen transfer capacity were also tested by temperature programmed reduction (TPR) and temperature programmed oxidation (TPO). Carbon formation was observed during the reduction period through the methane decomposition reaction. It was revealed that the carbon resistance of the oxygen carriers was partially determined by the oxygen transfer capacity. For the fresh oxygen carriers, the incorporation of MgAl2O4 led to a better carbon resistance because more lattice oxygen can be released compared to the other supports before carbon deposition. After 10 redox cycles, the Fe2O3/CeZrO4 oxygen carrier performs the best oxygen transfer capacity, but the oxygen transfer capacity of the Fe2O3/MgAl2O4 oxygen carrier reduced obviously. In addition, the specific surface area could dramatically affect the reduction activity of the oxygen carriers. Crystalline graphite was observed on the reduced oxygen earners, which posed a negative effect on the reduction activity, leading to sintering of the oxygen carriers.