Regulation of Oxygen Activity by Lattice Confinement over Ni Mg1−O Catalysts for Renewable Hydrogen Production

Abstract

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 Ni x Mg 1− x O solid solution as the oxygen carrier (OC) in the CLSR of bioethanol. Due to the regulation effect of Mg 2+ in Ni x Mg 1− x O, a three-stage reaction mechanism of the CLSR process is proposed. The surface oxygen of Ni x Mg 1− x O initially causes complete oxidation of the ethanol. Subsequently, H 2 O and bulk oxygen confined by Mg 2+ react with ethanol to form CH 3 COO* followed by H 2 over partially reduced Ni x Mg 1− x O. Once the bulk oxygen is consumed, the ethanol steam reforming process is promoted by the metallic nickel in the stage III. As a result, Ni 0.4 Mg 0.6 O exhibits a high H 2 selectivity (4.72 mol H 2 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.