Effects of Promoters on the Structure, Performance, and Carbon Deposition of Ni-Al₂O₃ Catalysts for CO₂–CH₄ Reforming

Abstract

Modified Ni-Al₂O₃ catalysts with Ca, Co, and Ce species as promoters were prepared by the combustion method, and the structure, morphology, reduction characteristic, and CO₂-CH₄ reforming of the catalysts were discussed by X-ray diffraction (XRD), H₂-temperature-programmed reduction (H₂-TPR), energy-dispersive X-ray (EDX) mapping, NH₃-temperature-programmed desorption (NH₃-TPD), N₂ adsorption-desorption, thermogravimetric-differential thermal analysis (TG-DTG), and temperature-programmed hydrogenation (TPH) methods. The crystal size of Ni on Ca-Ni-Al₂O₃ was 16.97 nm, and the active component and additive were distributed well in the catalyst. Co-Ni-Al₂O₃ presented a surface area of 65.70 m²·g^-1 and a pore diameter of 161.60 nm. Ce-Ni-Al₂O₃ showed relatively stable nickel-aluminum spinel (NiAl₂O₄), which could not be easily reduced to the active component Ni. Evaluation results demonstrated that the performance of the catalysts followed the order Co-Ni-Al₂O₃ > Ca-Ni-Al₂O₃ > Ni-Al₂O₃ > Ce-Ni-Al₂O₃. Carbon deposition analysis showed that the carbon resistance of Ca-Ni-Al₂O₃ was poor and graphitic carbon was generated on the catalyst. However, Ce-Ni-Al₂O₃ showed less carbon deposition, which might have resulted from the lower activity of the catalyst.