Study on the redox performance of Cu and Ce‐doped CoFe ₂ O ₄ as oxygen carriers for chemical looping hydrogen generation

Abstract

Summary In the chemical looping hydrogen generation process, CoFe2O4 is regarded as one of the most excellent candidates for oxygen carriers (OCs). In this paper, the synergistic effect of Cu and Ce added to CoFe2O4 was studied. The doping of Cu and Ce improved the reactivity of CoFe2O4 with methane, and also increased the hydrogen yield and purity. The results indicated that the introduction of Cu and Ce facilitated the deep reduction of CoFe2O4, which was ascribed to the enhanced migration capacity of lattice oxygen. In addition, the addition of Cu inhibited the decomposition of CH4 and alleviated carbon deposition. The Cu4Ce4‐CoFe had a suitable Cu/Ce mass ratio, which was more conducive to the formation of excellent synergistic effect to enhance hydrogen production and weaken carbon deposition. The Cu4Ce4‐CoFe exhibited outstanding H2 yield (15.42 mmol·g−1) and H2 purity (99.13%). In addition, the reactivity of OC decreased to some extent with the cyclic experiment when the Cu4Ce4‐CoFe was used, the H2 yield decreased from ∼15.21 to ∼10.86 mmol·g−1 over 10 experimental cycles. In conclusion, Cu and Ce co‐doping is an effective strategy to obtain OCs with preeminent hydrogen production performance and anti‐carbon deposition performance.

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

“…However, the intensity of CoFe 2 O 4 peaks increased, and the characteristic diffraction peak corresponding to the (311) crystal plane narrowed after cycling (Figure b), suggesting an increase in the crystal size of CoFe 2 O 4 . The average crystal size of CoFe 2 O 4 shown in Table is calculated from the most intensive (311) plane according to the Scherrer formula. , The crystal size of LCF increases from 54.2 to 80.5 nm. Also, the characteristic peak shifts to higher 2θ angles due to the contraction of the cell, which is strongly associated with the sintering stresses generated during high-temperature cycling.…”

“…220), (311), ( 222), (400), ( 422), (511), (440), and (533) crystal planes, respectively. 18,45 The diffraction peaks assigned to the LaFeO 3 (121), (220), and (202) crystal planes are located at 32.2, 39.6, and 46.1°, respectively. The reduced sample shows three distinct peaks at 44.9, 65.3, and 82.7°, which are associated with the CoFe alloy (JCPDS 49-1568) phase (Figure 7a).…”

“…The average crystal size of CoFe 2 O 4 shown in Table 6 is calculated from the most intensive (311) plane according to the Scherrer formula. 18,29 The crystal size of LCF increases from 54.2 to 80.5 nm. Also, the characteristic peak shifts to higher 2θ angles due to the contraction of the cell, which is strongly associated with the sintering stresses generated during high-temperature cycling.…”

“…Among many composite metal oxides, spinel-type ferrites (MFe 2 O 4 , M = Co, Cu, Mn, Ni, Zn, etc.) offer the advantages of compositional flexibility, structural stability, and adjustable redox properties. ,, Also, cobalt ferrite (CoFe 2 O 4 ) has attracted attention for its excellent oxygen transport capacity. , Researchers have further enhanced the redox activity of CoFe 2 O 4 by adopting active metal doping or partial substitution strategies, such as Cu x Co 1– x Fe 2 O 4 , Mn x Co 0.6– x Fe 2.4 O 4 , A 0.25 Co 0.25 Fe 2.5 O y (A = Cu, Ni, and Mn), etc. Generally speaking, the deep reduction of OCs is the basis for enhancing the hydrogen production capacity and the reduction level of OCs determines the final hydrogen yield.…”

“…Therefore, as high-temperature (>800 °C) redox cycles proceed, OCs inevitably suffer from severe sintering, reduced oxygen transfer capacity, and structural collapse. Meanwhile, CoFe 2 O 4 has also suffered severe sintering and loss of activity during high-temperature cycles. , This requires further enhancement of its thermal stability.…”