Effect of Supports on the Performance of La-Modified CoFe₂O₄ Oxygen Carriers in Chemical Looping Hydrogen Generation from Hydrogen-Rich Syngas

Abstract

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., ZrO 2 , TiO 2 , and YSZ (yttria-stabilized zirconia), on the reactivity, redox stability, hydrogen recovery capacity, and purity, as well as the sintering behavior of La-modified CoFe 2 O 4 (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 Fe 2 TiO 5 in LCF 6 T 4 weakened the initial reduction activity of the OC. Also, phase separation occurred after multiple cycles, forming separated Fe 2 O 3 and TiO 2 , which further accelerated the sintering and resulted in irreversible deactivation. In contrast, LCF 6 Z 4 and LCF 6 YZ 4 exhibited excellent initial activity and cyclic stability, which was attributed to their improved pore structure and surface properties. Interestingly, the generated La 2 Zr 2 O 7 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 LCF 5 YZ 5 were merely 6.23 and 8.26%, respectively.