In situ study of structural modifications in Ni-Fe/MgAl2O4 catalysts employed for ethanol steam reforming

Abstract

In situ XRD and XANES experiments were used to analyze structural changes influencing the catalytic activity of Ni-Fe/MgAl2O4 catalysts during the ethanol steam reforming (ESR) reaction. Activation with H2 reduced nickel and iron oxides to their metallic forms, producing Ni-Fe alloy on the bimetallic catalysts. Phase composition changes during activation depended on the Ni:Fe ratio. Catalysts with Ni ≥ Fe showed no FexOy XRD peaks, while when Ni < Fe, these peaks were exhibited during reduction. In situ XANES showed higher reduction for bimetallic catalysts, compared to monometallic catalysts, with the reduction decreasing as more iron was added. Catalytic tests were performed in conventional ESR and H2-added (ESRH) atmospheres. The in situ techniques revealed restructuring during ESR, where contact with the reactants resulted in the Ni-Fe particles being slightly oxidized. As the temperature increased, iron migrated and was oxidized to FexOy, while nickel re-reduced. The extent of restructuring depended on reactant composition and iron content. A milder impact was exhibited in ESRH, leading to catalyst stabilization. This phenomenon enabled elucidation of the catalytic features linked to the accessibility of metallic sites responsible for cleaving C–C and C–H bonds. Furthermore, FexOy aided oxidation of the carbon residue, leading to lower carbon accumulation and greater stability of the bimetallic catalyst.