Key Takeaways & Executive Findings
- •• • Fe58Cu2Al achieved an oxygen storage capacity of 6.5 mmol/g and the highest oxygen loss of 12.1 g/100 g oxygen carrier during CH4 reduction, indicating superior lattice oxygen availability for syngas production. • • The 2% Cu-modified carrier produced 5.13 mmol/g H2 in the first cycle, 1.51 times that of pristine Fe60Al, with purity exceeding 98%, demonstrating enhanced hydrogen yield and quality. • • After ten redox cycles, Fe58Cu2Al maintained H2 yield of 3.61 mmol/g, surpassing the single-cycle yield of Fe60Al (3.39 mmol/g), confirming excellent cyclic stability and resistance to deactivation. • • Cu addition promoted formation of spinel CuFe2O4, which facilitated deeper reduction of Fe2O3, whereas La and Ce formed less reactive phases (LaFeO3, CeO2), ranking reactivity as Fe58Cu2Al > Fe60Al > Fe58La2Al > Fe58Ce2Al.
Abstract
Chemical looping methane steam reforming (CL-MSR) enables sequential production of high-selectivity syngas and high-purity hydrogen via redox cycling, yet single iron-based oxygen carriers suffer from poor cycling stability, low reactivity, and sintering. This study modified Fe2O3/Al2O3 oxygen carriers with Cu, La, and Ce additives via dip-coating, and systematically characterized their physicochemical properties, reactivity, and hydrogen production performance. Results showed that spinel-phase CuFe2O4 exhibited higher reactivity than perovskite LaFeO3 and CeO2, promoting deeper reduction of Fe2O3. Fe58Cu2Al achieved an oxygen storage capacity of 6.5 mmol/g. During CH4 reaction, Fe58Cu2Al exhibited the highest oxygen loss of 12.1 g/100 g oxygen carrier, with syngas yield of 5.15 mmol/g—1.33 and 1.59 times that of Fe60Al. In hydrogen production, the 2% Cu-modified carrier yielded 5.13 mmol/g H2, 1.51 times that of pristine Fe60Al, with purity exceeding 98%. After ten cycles, H2 yield remained at 3.61 mmol/g, surpassing the single-cycle output of pristine Fe60Al (3.39 mmol/g), demonstrating superior dispersion and coking resistance. The study establishes Cu modification as an effective strategy to enhance reactivity and cyclic stability of iron-based oxygen carriers for CL-MSR hydrogen production.
1. Introduction
Conventional steam methane reforming (SMR) remains the dominant industrial hydrogen production route, yet its multi-step nature—desulfurization, reforming, water-gas shift, and pressure swing adsorption—incurs high energy penalties, substantial CO2 emissions, and operational complexity. Chemical looping methane steam reforming (CL-MSR) offers a compelling alternative by splitting the overall reaction into separate reduction and oxidation stages, enabling inherent CO2 separation and high-purity hydrogen production without downstream purification. However, iron-based oxygen carriers, while inexpensive and environmentally benign, suffer from poor redox stability, low reactivity, and sintering at elevated temperatures, limiting their industrial viability.
This study addresses these bottlenecks by incorporating Cu, La, and Ce additives into Fe2O3/Al2O3 oxygen carriers via a dip-coating method. The additives induce distinct crystalline phases—CuFe2O4, LaFeO3, and CeO2—which alter oxygen mobility and reduction behavior. Systematic evaluation under fixed-bed redox conditions reveals that Cu modification significantly enhances oxygen storage capacity and hydrogen yield, achieving 5.13 mmol/g H2 with >98% purity in the first cycle and retaining 3.61 mmol/g after ten cycles. These findings provide a clear pathway to designing more durable and reactive oxygen carriers for scalable CL-MSR hydrogen production.
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YANG Liangnuo, LI Yilong, ZHOU Zheng, DENG Chunhuan, MA Hao, DING Zisheng, LI Guoliang, LI Ming, GU Zhenhua (2026). Chemical-Looping Methane Hydrogen Production Performance of Cu, La, Ce Modified Fe2O3/Al2O3 Oxygen Carriers. Journal of Fuel Chemistry and Technology. https://doi.org/10.1016/S1872-5813(25)60630-X
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Frequently Asked Questions
What is the mechanistic role of CuFe2O4 spinel phase in enhancing the reduction of Fe2O3 compared to LaFeO3 or CeO2?
CuFe2O4 spinel phase exhibits higher oxygen ion conductivity and provides a more facile pathway for lattice oxygen release, promoting deeper reduction of Fe2O3. This is evidenced by Fe58Cu2Al achieving the highest oxygen loss (12.1 g/100 g) and syngas yield (5.15 mmol/g) during CH4 reduction, whereas LaFeO3 and CeO2 phases are less reactive, resulting in lower oxygen mobility and reduced performance.
How does the Cu-modified oxygen carrier maintain high hydrogen yield after ten redox cycles, and what are the underlying stability mechanisms?
Fe58Cu2Al retains a hydrogen yield of 3.61 mmol/g after ten cycles, surpassing the single-cycle yield of pristine Fe60Al (3.39 mmol/g). This stability is attributed to the formation of a well-dispersed CuFe2O4 phase that inhibits iron sintering and carbon deposition, as confirmed by superior dispersion and coking resistance compared to Fe60Al. The spinel structure likely acts as a structural stabilizer, preserving active surface area and oxygen storage capacity over repeated redox cycling.
What are the trade-offs between syngas yield and hydrogen purity when using Cu-modified oxygen carriers in CL-MSR?
Fe58Cu2Al achieves a syngas yield of 5.15 mmol/g during the reduction stage, which is 1.33 times that of Fe60Al, while maintaining hydrogen purity above 98% in the subsequent steam oxidation stage. The high syngas yield indicates efficient partial oxidation of methane, while the high hydrogen purity suggests minimal carbon formation and complete water splitting, demonstrating that Cu modification enhances both stages without compromising product quality.
How does the oxygen storage capacity of Fe58Cu2Al (6.5 mmol/g) compare to conventional iron-based oxygen carriers, and what implications does this have for reactor sizing?
The oxygen storage capacity of 6.5 mmol/g is notably high for iron-based systems, enabling a larger amount of lattice oxygen to be utilized per cycle. This translates to higher hydrogen productivity per mass of oxygen carrier, potentially reducing the required inventory in a commercial reactor and lowering capital costs. The enhanced capacity also allows for longer reduction times or higher methane throughput, improving overall process economics.
What are the potential scalability challenges for the dip-coating method used to prepare Cu-modified oxygen carriers, and how might they be addressed industrially?
Dip-coating is a simple and cost-effective method for laboratory-scale preparation, but scaling to industrial quantities may face challenges in uniformity and reproducibility. However, the method is inherently scalable as it involves standard impregnation and calcination steps, which are already used in catalyst manufacturing. The low additive loading (2% Cu) minimizes raw material costs, and the demonstrated stability over ten cycles suggests that the material can withstand repeated use, making it a viable candidate for large-scale fixed-bed or moving-bed reactors.
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