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• Core–shell Al@Al2O3 was used as the support in supported Ni catalysts. • The Al@Al2O3 is better than γ-Al2O3 to develop a highly efficient Ni-based catalyst. • The deposition–precipitation method outperforms the wet impregnation method. • Higher Ni dispersion resulted in better catalytic performance for CO methanation. • The higher density of medium basic sites increases the CO 2 methanation activity. Core–shell Al@Al 2 O 3 , which was obtained by hydrothermal surface oxidation of Al metal particles, was used as the support in supported Ni catalysts for CO and CO 2 methanation. The core–shell micro-structured support (Al@Al 2 O 3) helped develop a highly efficient Ni-based catalyst compared with conventional γ-Al 2 O 3 for these reactions. Moreover, the deposition–precipitation method was shown to outperform the wet impregnation method in the preparation of the active supported Ni catalysts. The catalysts were characterized using various techniques, namely, N 2 physisorption, H 2 chemisorption, CO 2 chemisorption, temperature-programmed reduction with H 2 , temperature-programmed desorption after CO 2 adsorption, X-ray diffraction, inductively coupled plasma-atomic emission spectroscopy, high-resolution transmission electron microscopy, and in situ diffuse reflectance infrared Fourier transform spectroscopy. Higher Ni dispersion when using Al@Al 2 O 3 as the support and the deposition–precipitation method resulted in better catalytic performance for CO methanation. Furthermore, the higher density of medium basic sites and enhanced CO 2 adsorption capacity observed for Ni/Al@Al 2 O 3 helped increase catalytic activity for CO 2 methanation. [ABSTRACT FROM AUTHOR]

• The effect of promoter was evaluated for CO and CO 2 methanation. • Mn, Ce, Mg, V, and Zr are beneficial for both CO and CO 2 methanation activity. • CO 2 methanation is related to the Ni dispersion and relevant CO 2 adsorption. • Ni-V/Al@Al 2 O 3 with the highest Ni dispersion is the best for CO methanation. • The promotional effect of Mn is remarkable for both CO and CO 2 methanation. Effects of metal promoter on CO and CO 2 methanation were examined over Ni-M (M = Mn, Ce, Zr, Mg, K, Zn, or V)/Al@Al 2 O 3 catalysts prepared by the co-impregnation method. Ni-M (M = Mn, Ce, or Zr)/γ-Al 2 O 3 catalysts were also investigated for comparison. The prepared catalysts were characterized with a variety of techniques such as N 2 physisorption, CO 2 chemisorption, H 2 chemisorption, temperature-programmed reduction with H 2 (H 2 -TPR), temperature-programmed desorption of CO 2 (CO 2 -TPD), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Among different promoters, Mn, Ce, Mg, V, and Zr are beneficial to enhance both CO and CO 2 methanation activity due to the improvement of the Ni dispersion. The Ni-V/Al@Al 2 O 3 catalyst performs the highest CO methanation activity due to the largest Ni sites. However, it is not the best one for CO 2 methanation among tested catalysts because of the much decrease in CO 2 adsorption capacity. The promotional effect of Mn is the most remarkable for both CO and CO 2 methanation. On the other hand, the negative effect of K and Zn was observed on both CO and CO 2 methanation by the small number of active Ni sites and the decrease in the amount of basic sites. The CO 2 methanation mechanism over Ni-Mn/Al@Al 2 O 3 catalyst is elucidated by the transform route: adsorbed carbonate species – formate species – methane under hydrogenation process. [ABSTRACT FROM AUTHOR]