Improved iron oxide oxygen carriers for chemical looping hydrogen generation using colloidal crystal templated method

Iron oxide has been widely studied in chemical looping hydrogen generation (CLHG) process as an oxygen carrier, but fast decline of its activity in redox cycles due to sintering and agglomeration is one of the main drawbacks. In this work, the colloidal crystal templated (CCT) method was applied to synthesize Fe2O3/CeO2 oxygen carrier and the mole ratio of Fe/Ce was 8:2, aiming to inhibit adjacent grains from agglomerating and improve the contact between the fuel gas and the oxygen carrier. The redox performances were evaluated with CO as fuel in a batch fixed bed reactor for 20 redox cycles, with oxygen carriers prepared by co-precipitation (CP) and sol-gel (SG) methods as references. X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), and H-2-temperature programmed reduction (H-2-TPR) were used for characterization. The results showed that the calcination temperature lower than 750 degrees C was suitable for the CCT. The redox experiments showed that the H-2 yield and the redox stability for the oxygen carrier prepared by CCT were higher than those by co-precipitation and sol-gel methods. The H-2 yield of CCT oxygen carrier kept stable from the 3rd cycle and was 8.5 mmol/gOC in the 20th cycle. The pore structures resulting from CCT were different from another two oxygen carriers before and after the cycles, but maintained well through SEM images, leading to high activity and stability during redox cycles. The crystallite sizes of Fe2O3 and CeO2 before and after redox cycles were the smallest for the CCT oxygen carrier from XRD patterns. In addition, H-2-TPR demonstrated that CCT oxygen carrier exhibited the highest reactivity. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.