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Ni/SiC and Ni/SiO2 catalysts prepared by both wet impregnation (WI) and deposition-precipitation (DP) methods were compared for CO and CO2 methanation. The prepared catalysts were characterized using N2 physisorption, temperature-programmed reduction with H2 (H2-TPR), H2 chemisorption, pulsed CO2 chemisorption, temperature-programmed desorption of CO2 (CO2-TPD), transmission electron microscopy, and X-ray diffraction. H2-TPR analysis revealed that the catalysts prepared by DP exhibit stronger interaction between the nickel oxides and support than those prepared by WI. The former catalysts exhibit higher Ni dispersions than the latter. The catalytic activities for both reactions over Ni/SiC and Ni/SiO2 catalysts prepared by WI increase on increasing the Ni content from 10 to 20 wt%. The Ni/SiC catalyst prepared by DP shows higher catalytic activity for CO and CO2 methanation than that of the Ni/SiC catalyst prepared by WI. Furthermore, it exhibits the highest catalytic activity for CO methanation among the tested catalysts. The high Ni dispersion achieved by the DP method and the high thermal conductivity enabled by SiC are beneficial for both CO and CO2 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]