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

Ni/SBA-16 catalysts doped with Ce having cage-like mesopores were synthesized and tested in the CO(2)methanation reaction. The effect of the Ce promoter (10 and 20 wt%) on the catalytic performance of Ni/SBA-16 catalysts for CH(4)formation was evaluated. The catalysts were characterized by N(2)sorption, XRD, TEM, HRTEM, XPS, H-2-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 CO(2)conversion (68.9%) and highest CH(4)selectivity (96.4%) were obtained over 10Ni/10Ce/SBA-16 at 350 degrees 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 Ni(0)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.