CO methanation on Ni-Ce mixed oxides prepared by hard template method

• SBA-15-templated, rod-shaped NiO, CeO2, and NiO-CeO2 oxides were prepared.
• The NiO-CeO2 catalysts were very active and selective for CO methanation after reduction pretreatment at mild conditions.
• CH4 selectivity increased along with the Ni content.
• The growth in the size of Ni0 particles with the Ni loading suggests an influence of the crystal size on CH4 formation.
• The lower value of SCH4 on NiO, despite the large size of Ni0 crystals, reveals a role of CeO2 in favouring CH4 formation.

Hard-templated NiO-CeO2 samples with increasing Ni/Ce molar ratios, as well as hard-templated CeO2 and NiO oxides, were prepared. All samples were characterized by different techniques as to their chemical composition, structure, morphology, texture, and redox features. They were investigated in the CO methanation reaction after mild reduction pretreatment (H2 at 400 °C for 1 h). Catalytic testing was performed under atmospheric pressure, 300 °C and H2/CO molar ratios of 3.2 or 1.8. In the latter case, runs were carried out also at 200, 250, and 275 °C. Almost complete CO conversion and very high CH4 selectivity (up to 94 and 78 mol% at H2/CO = 3.2 and 1.8, respectively) were obtained at 300 °C over the NiCe mixed oxides, with CO2 as byproduct. CH4 selectivity was found to increase with the increase in Ni content. A growth in the size of Ni0 particles with the same parameter was also observed, suggesting an influence of the crystallite size on methane formation. In spite of its large Ni0 crystallite size, a lower CH4 selectivity (73 mol%, at H2/CO = 3.2) was obtained on pure NiO. This was explained by taking into account the role of CeO2 in limiting CO2 formation.

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