Effect of Ni/Co Molar Ratio on the CO Oxidation Activity of NixCo3−xO4 Catalysts

A series of NixCo3−xO₄ (x = 0.75, 1, 1.5, 2, 2.25) catalysts with different Ni/Co molar ratios was fabricated via the co-precipitation method. The catalytic performance for CO oxidation and SO₂ resistance of the prepared catalysts was systematically investigated, and their physicochemical properties were characterized by XRD, SEM, BET, H₂-TPR, CO-TPD and in situ DRIFTS. The experimental results reveal that the Ni₂.₂₅Co₀.₇₅O₄ catalyst exhibits the optimal CO oxidation activity, achieving a CO conversion of 93.25% at 120 °C. The superior catalytic performance can be attributed to its large specific surface area, low reduction temperature, and easily activated lattice oxygen species. When exposed to SO₂ at a concentration 10 times the industrial emission limit, all catalysts exhibited varying degrees of activity loss. Among them, NiCo₂O₄ exhibited the slowest deactivation rate and showed the greatest recovery in CO conversion after SO₂ was cut off, suggesting relatively better sulfur tolerance and recoverability among the investigated catalysts. In conclusion, tuning the Ni/Co molar ratio can effectively optimize the low-temperature CO oxidation activity and sulfur resistance of Ni-Co composite oxides. This work provides a useful reference for the structural composition design and practical application of such catalysts in flue gas purification.