Conversions of Methane to Synthesis Gas over Co/γ-Al2O3 by CO2 and/or O2

Abstract

The goal of the paper was to investigate the effect of the catalyst precursor on the catalytic activity. For this reason, the structure, the reducibility and the reaction behavior of γ-Al₂O₃-supported Co (24 wt%) catalysts as a function of calcination temperature (T _c) were investigated using X-ray diffraction, temperature-programmed reduction, CO chemisorption, pulse reaction with pure CH₄, and the catalytic reactions of methane conversion to synthesis gas. Depending on T _c, one, two, or three of the following Co-containing compounds, Co₃O₄, Co₂AlO₄, and CoAl₂O₄, were identified. Their reducibility decreased in the sequence: Co₃O₄>Co₂AlO₄>CoAl₂O₄. Co₃O₄ was generated as a major phase at a T _c of 500°C and Co₂AlO₄ and CoAl₂O₄ at a T _c of 1000°C. The reduced Co/γ-Al₂O₃ catalysts, obtained via the reduction of the 500 and 1000°C calcined catalysts, provided high and stable activities for the partial oxidation of methane and the combined partial oxidation and CO₂ reforming of methane. They deactivated, however, rapidly in the CO₂ reforming of methane. Possible explanations for the stability are provided.