A comparative study on the catalytic properties of high Ni-loading Ni/SiO₂ and low Ni-loading Ni-Ce/SiO₂ for CO methanation

Two Ni-based catalysts of 13%Ni/SiO₂(13Ni/Si) and 7%Ni-2%Ce/SiO₂(7Ni-2Ce/Si, by weight) were prepared by the incipient-wetness impregnation method and characterized with N₂-sorption, XRD, H₂-TPR, FT-IR, TEM, H₂-TPD and CO-TPD techniques. It was shown that addition of Ce promoter generated an interaction among NiO, CeO₂ and SiO₂, which changed chemical environment of Ni-O-Si bond, enhanced the dispersion and reduction of NiO, and increased the active surface area. In particular, a new type of moderately strong CO adsorption sites was formed on the surface of the 7Ni-2Ce/Si catalyst. As a result, the low Ni-loading 7Ni-2Ce/Si catalyst exhibited higher CO adsorption capacity and CO methanation catalytic activity than the high Ni-loading 13Ni/Si. Under the reaction conditions of 1% CO (volume fraction in H₂ atmosphere), GHSV of 7 000 h^-1 and atmospheric pressure, the temperature for complete conversion of CO over the 7Ni-2Ce/Si catalyst was 230 ℃, being 30 ℃ lower than that found over the high Ni loading 13Ni/Si catalyst.