Advances and Environmental Perspectives of Oxygen Carriers and Catalysts in Methane-Based Chemical Looping for Hydrogen Production: A Review

The accelerating global demand for clean energy has placed hydrogen as a pivotal vector for achieving carbon neutrality. However, over 95% of current hydrogen is still derived from fossil-based routes such as steam methane reforming (SMR), which remains energy-intensive and carbon-emitting. Chemical looping technology (CLT) has emerged as an innovative low-carbon pathway capable of inherently separating CO2 during hydrogen generation. This review systematically examines recent advances in methane-based CLT, emphasizing oxygen carrier (OC) design, process efficiency, and environmental implications. Across different CLT configurations, the technology shows excellent performance, with CH4 conversion above 95% and H2 purity reaching 99.9%. It also achieves 10–15% higher thermal efficiency than conventional SMR with carbon capture. Among key variants, CLPO produces syngas with a H2/CO ratio of ∼2, CLSR yields 90–95 vol % pure H2, and CLCHP achieves >97% CO2 capture with >90% OC regeneration sustained over 100 cycles. Meanwhile, CLMC enables theoretical 100% CH4 conversion at 1000 °C without CO2 emissions and produces valuable solid carbon. Environmentally, Fe2O3-based OCs outperform Ni- or Co-based counterparts due to low toxicity, thermal stability (750–950 °C), and a reduction in lifecycle emissions to 3009 g CO2-eq/kg H2. The review identifies research priorities for scalable deployment, including the development of durable OCs, system integration with waste heat or biomass, and reactor optimization capable of reducing capital costs by up to 37%.