Enhanced syngas production from CH₄-CO₂ chemical looping over A-site Ce³⁺-modified brownmillerite oxygen carriers

Chemical looping methane reforming coupled with CO₂ splitting enables efficient co-conversion of CH₄ and CO₂, but its application is limited by the activity and cyclic stability of oxygen carriers. In this study, an A-site Ce-doped perovskite oxygen carrier (Ca_2-x Ce _x Fe_1.4Al_0.6O₅) is successfully synthesized, and by optimizing the gas hourly space velocity, a favorable balance between methane decomposition and lattice oxygen supply is achieved. At 850 °C and a space velocity of 6000 h⁻¹, Ca_1.95Ce_0.05Fe_1.4Al_0.6O₅ exhibits stable performance over 20 cycles, with a CH₄ conversion of 74.6 %, CO selectivity of 96.1 %, syngas yield of 8.2 mmol g⁻¹, CO₂ conversion of 96.2 %, and CO yield of 4.6 mmol g⁻¹. The performance enhancement mainly results from lattice distortion and oxygen vacancy regulation induced by trace Ce³⁺ doping, which strengthens the Fe-O-Ce bridging structure, promotes oxygen ion migration, and accelerates the reoxidation of Fe²⁺ during CO₂ splitting. However, excessive Ce doping leads to the formation of CeO₂, which suppresses Fe active sites and aggravates carbon deposition. Kinetic analysis and density functional theory calculations further confirm that trace Ce doping significantly reduces the apparent activation energy, oxygen vacancy formation energy, and reaction energy barrier, fundamentally optimizing the electronic structure of the material. This work provides theoretical guidance and a novel design strategy for the green and sustainable co-conversion of CH₄ and CO₂.