Composition-Tuned Ni–Ce Mixed Oxides with Inverse CeO 2 /Ni Structure for Enhanced Low-Temperature CO 2 Methanation

This work systematically investigates the effect of Ni/Ce molar ratios (0.3–2.9) on the structure–activity relationship of Ni/Ce mixed oxides for low-temperature CO2 methanation. As the Ni/Ce ratio increased, the rate of CO2 conversion gradually increased. At a GHSV of 12,000 mL·g–1h–1, all catalysts exhibited 100% CH4 selectivity. The best-performing NiCe-2.1 catalyst not only achieved 37.2% CO2 conversion at 200 °C but also maintained above 85% CO2 conversion during the stability test at 250 °C. Characterization (XRD, BET, TEM, H2-TPR/TPD, CO2-TPD, XPS) results revealed that when Ni/Ce 2.1, excessive independent NiO phases caused severe nickel agglomeration, inhibiting the formation of additional Ni–O–Ce interfaces. Finally, in situ DRIFTS results revealed that the CO2 methanation on NiCe-2.1 mainly followed the formate pathway (CO2* → HCO3* → HCOO* → CH4).