Double perovskite (La2-xCa-Bax)NiO4 oxygen carriers for chemical looping reforming applications

Abstract Double perovskites La2-xNiO4-δ doped with Ca and Ba were synthesized via microwave-assisted combustion method and studied as an alternative oxygen carrier (OC) for chemical looping reforming processes (CLR). The OCs, La2NiO4, La1.8Ca0.2NiO4, La1.8Ba0.2NiO4 and La1.8Ca0.1Ba0.1NiO4 were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature-programmed reduction and oxidation (TPR/TPO) and cyclic thermogravimetric analysis (TGA). Rietveld's refinement, performed after each redox cycle, confirmed that doping allows smaller amounts of nickel to migrate from the perovskite structure. The double perovskites synthesized for the chemical looping reforming process behave as simple nickel oxide and are considered as alternative oxygen carriers to solve the problems of deactivation due to the interaction of NiO with the support. The Ca-doped OC (La1.8Ca0.2NiO4) showed lower NiO concentration outside the structure and smaller crystallite size after the redox cycles, which was associated with a change in the crystal structure, presenting superior performance and stability. The results show that all perovskites have high reactivity in both reduction and oxidation reactions, however the perovskites were not able to uncouple oxygen, which is an unsual behavior for perovskites.