Effect of Supports on the Performance of La-Modified CoFe2O4 Oxygen Carriers in Chemical Looping Hydrogen Generation from Hydrogen-Rich Syngas
The redox activity and thermal stability of oxygen carriers (OCs) during multi-cycle processes are important performance criteria. In this paper, the effects of three supports, i.e., ZrO2, TiO2, and YSZ (yttria-stabilized zirconia), on the reactivity, redox stability, hydrogen recovery capacity, and purity, as well as the sintering behavior of La-modified CoFe2O4 (LCF) OCs, were investigated. The results indicated that the unsupported LCF had severe sintering behavior, the aggregation of grains, the collapse of pore structure, and surface densification after multiple cycles led to a significant reduction in its activity. Meanwhile, the interaction between different supports and active components had a remarkable influence on fuel conversion and hydrogen recovery capacity. The formation of Fe2TiO5 in LCF6T4 weakened the initial reduction activity of the OC. Also, phase separation occurred after multiple cycles, forming separated Fe2O3 and TiO2, which further accelerated the sintering and resulted in irreversible deactivation. In contrast, LCF6Z4 and LCF6YZ4 exhibited excellent initial activity and cyclic stability, which was attributed to their improved pore structure and surface properties. Interestingly, the generated La2Zr2O7 pyrochlore structure was also conducive to the enhancement of cyclic stability properties for OCs. In addition, all OCs displayed high-purity hydrogen (>99.5%) generation properties. Overall, the ion-conductive YSZ-supported OC showed excellent reactivity and stability. After 11 cycles, the fuel conversion deactivation and hydrogen production deactivation for LCF5YZ5 were merely 6.23 and 8.26%, respectively.
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