Enhancement mechanism of Ce-Ni-modified vanadium–titanium magnetite in chemical looping hydrogen production

Vanadium-titanium magnetite concentrate (VTM) oxygen carriers suffer from inherently low redox activity and sluggish oxygen migration rate, which severely constrain their application in high-efficiency chemical looping hydrogen production. To overcome these limitations, this study introduces Ce–Ni bimetals via mechanical ball milling for synergistic modification. The enhancement mechanism of hydrogen production performance in modified VTM was systematically investigated with emphasis on phase evolution, reduction behavior, and oxygen vacancy regulation. Ni doping promoted the formation of a new NiFe 2 O 4 phase and drove the transformation of Fe 3 O 4 to Fe 2 O 3 , thereby optimizing the redox system of the oxygen carrier. Ce doping effectively increased the oxygen vacancy concentration through local lattice distortion. The H 2 -TPR and CH 4 -TPR results consistently show that the modified oxygen carrier exhibited a reduced reduction temperature and significantly enhanced methane activation capacity. At 900 ℃, the hydrogen yield of the 10Ce20Ni sample reached 11.39 mmol/g, approximately 10.4 times higher than that of the raw ore, with a purity of 98.32%. XPS analysis further verified that Ce-Ni co-doping optimized the distribution of oxygen species on the oxygen carrier surface. Among all the samples, 10Ce20Ni possessed the highest ratio of defective oxygen (1.61), indicating the formation of a more abundant oxygen-vacancy structure. Meanwhile, the coexisting multivalence system of Ni/Ce/Fe provides an efficient electron transfer channel for lattice oxygen migration and interfacial reactions, which serves as the core intrinsic factor for improving the activity.