Formation and characteristic properties of carbonaceous species on nickel-magnesia solid solution catalysts during CH₄-CO₂ reforming reaction

Carbonaceous species formed during the reforming of CH₄ with CO₂ over a series of Ni_xMg_1-xO solid solution catalysts and MgO-supported Ni catalysts were characterized by temperature-programmed hydrogenation (TPH) method. Two peaks appeared in the TPH spectra: one between 550 and 700 K (α-carbon) and another above 873 K (β-carbon). It was found that a good relationship exists between the quantity of α-carbon species and the catalytic activity, indicating that α-carbon should be the reaction intermediate. In addition, the amount of β-carbon increased with increasing reaction time, especially on the supported Ni/MgO catalysts which make inactive carbon during the CH₄-CO₂ reforming reaction.