Abstract: Ni/La₂O₃/γ-Al₂O₃ and Ni/La₂O₃/α-Al₂O₃ catalysts were prepared by the incipient wetness impregnation and evaporation methods. Their catalytic properties for the dry reforming of methane without a diluting gas were studied. The fresh and used catalysts and deposited carbon were characterized by H₂ temperature-programmed reduction, N₂ adsorption-desorption, X-ray diffraction, transmission electron microscopy, thermogravimetry coupled to differential scanning calorimetry, and temperature-programmed hydrogenation. The results showed that there were four carbon species that existed as three types, namely, amorphous (polymeric), filamentous, and graphitic carbon. The amount and type of carbon species on the catalysts depended on the size of Ni particles and texture of the support. The formation and morphology of filamentous carbon were clearly related to the size of Ni particles. Ni particles less than 15 nm suppressed the formation and deposition of filamentous carbons, decreased the amount of carbon deposition, and had more active C_α species, resulting in a better activity and higher stability of the catalysts.

Key words: nickel, lanthanum oxide, alumina, supported catalyst, dry reforming, methane, carbon deposition