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.