Enhanced performance of hematite oxygen carrier by CeO2 for chemical looping hydrogen generation

Natural hematite is a promising oxygen carrier for chemical looping hydrogen generation (CLHG) owing to its abundance and low price. However, the reactivity of hematite is poor compared with the artificial oxygen carriers. To solve this problem, modified hematite with different CeO2 loading amounts were prepared, and the redox reactivity, cyclic stability, sintering and carbon deposition resistance were investigated with the original hematite (0%CeO2) as the control group. It was found that the CeO2-modified hematite presented far higher H2 yield and purity than 0%CeO2, and the hematite with CeO2 loading amount of 20 wt % (20%CeO2) displayed the highest reactivity, carbon deposition resistance, and satisfactory cyclic stability. The H2 yield of 20%CeO2 was 110% higher than that of 0%CeO2, and the H2 purity of the former was 99.71% vs 98.36% for the latter. The desirable performance of 20%CeO2 could be ascribed to the promotion effects of CeO2 on the lattice oxygen mobility. Specifically, the cubic fluorite CeO2 and the generated perovskite CeFeO3 provided channels for the lattice oxygen transport, enhancing the redox reactivity. The CeO2 modification could also inhibit the Fe outward migration to particle surface and thus increase the sintering resistance. The generation of cerium silicate could be inimical to the oxygen mobility, however, it could restrain the growth of CeO2 crystallite. Moreover, the interaction between CeO2 and Fe2O3 could decrease their crystallite sizes and further promote the sintering resistance.