Hydrogen production over partial oxidation of methane using NiMgAl spinel catalysts: A kinetic approach

NiMgAl–based catalysts were synthesized by coprecipitation, sol–gel, and impregnation methods, calcined at 700 °C for 4 h and tested in partial oxidation of methane in a temperature range of 500–800 °C. The fresh and used unsupported and supported samples were characterized by X-ray diffraction, nitrogen physisorption with Brunauer-Emett-Teller (BET) analysis, and H₂–temperature-programmed reduction. X-ray diffraction analysis showed, for all samples, the formation of spinel phases MgAl₂O₄ and/or NiAl₂O₄ with crystallite sizes of 6–14 nm. H₂–temperature-programmed reduction analysis showed reduction of two Ni²⁺ species (in octahedral and tetrahedral sites of a spinel structure) into metallic nickel known to be responsible for the methane activation. The 10 wt % Ni/MgAl₂O₄ impregnated catalysts exhibited the highest activity and stability in the partial oxidation of methane reaction, which led mainly to syngas (CO + H₂) at 800 °C with a methane conversion close to the thermodynamic equilibrium (95%). A kinetic model revealed that the oxidation of methane occurs on a thin layer of the catalytic bed in which oxygen is consumed and is followed by the production of CO and H₂ by methane steam reforming and water gas shift reactions.