Regulation of Oxygen Activity by Lattice Confinement over NixMg1−xO Catalysts for Renewable Hydrogen Production

The chemical looping steam reforming (CLSR) of bioethanol is an energy-efficient and carbon–neutral approach of hydrogen production. This paper describes the use of a NixMg1−xO solid solution as the oxygen carrier (OC) in the CLSR of bioethanol. Due to the regulation effect of Mg2+ in NixMg1−xO, a three-stage reaction mechanism of the CLSR process is proposed. The surface oxygen of NixMg1−xO initially causes complete oxidation of the ethanol. Subsequently, H2O and bulk oxygen confined by Mg2+ react with ethanol to form CH3COO* followed by H2 over partially reduced NixMg1−xO. Once the bulk oxygen is consumed, the ethanol steam reforming process is promoted by the metallic nickel in the stage III. As a result, Ni0.4Mg0.6O exhibits a high H2 selectivity (4.72 mol H2 per mole ethanol) with a low steam-to-carbon molar ratio of 1, and remains stable over 30 CLSR cycles. The design of this solid-solution OC provides a versatile strategy for manipulating the chemical looping process.