Effect of ceria promotion on the catalytic performance of Ni/SBA-16 catalysts for CO2 methanation

Abstract

Ni/SBA-16 catalysts doped with Ce having cage-like mesopores were synthesized and tested in the CO₂ methanation reaction. The effect of the Ce promoter (10 and 20 wt%) on the catalytic performance of Ni/SBA-16 catalysts for CH₄ formation was evaluated. The catalysts were characterized by N₂ sorption, XRD, TEM, HRTEM, XPS, H₂-TPR, and CO₂-TPD methods. It was found that the Ni and Ce particles were well confined inside the cage-like mesopores of SBA-16. The methanation tests indicated that Ni/Ce/SBA-16 (10 or 20 wt%) showed better catalytic performance than Ce-free Ni/SBA-16. The best CO₂ conversion (68.9%) and highest CH₄ selectivity (96.4%) were obtained over 10Ni/10Ce/SBA-16 at 350 °C, which was attributed to the highly dispersed Ni and Ce species over SBA-16, the small particle size of metallic Ni and CeO₂, the highest Ce³⁺/(Ce³⁺ + Ce⁴⁺) ratio and the largest number of medium basic sites. On increasing the Ce loading to 20 wt%, the catalytic activity decreased, which was assigned to a decrease in Ce dispersion, an increase of Ni⁰ particle size, an increase of the number of Ni particles outside the SBA-16 support and inhomogeneous dispersion of Ce, a decrease of the Ce³⁺/(Ce³⁺ + Ce⁴⁺) ratio, and finally a decrease of the medium basicity.