Effects of K-dopant on structure and activity of KMn/Al₂O₃ catalysts for CO oxidation: Experimental evidence and DFT calculation

KMn/Al₂O₃ catalysts with different K:Mn molar ratios were synthesized by a facile impregnation method and attempted for CO oxidation. The correlation in between potassium-dopant amount and the structure/catalytic activity of KMn/Al₂O₃ catalysts were investigated. Doping small amount of potassium (K:Mn mole ratio less than 1:10) to Mn/Al₂O₃ catalyst efficiently enhanced the catalytic activity of Mn/Al₂O₃ catalyst. We found that the K₁Mn₁₀/Al₂O₃ catalyst exhibited the best CO oxidation activity with the TOF of 1.5 × 10^-3 s^-1 for 100% CO conversion at 260 °C, which is 50 °C lower than that on Mn/Al₂O₃ catalyst. However, excessive amounts of potassium led to β-to-α-MnO₂ phase transformation and poor catalytic performance. DFT calculations combined with multiple characterization techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), O₂ temperature-programmed desorption (O₂-TPD) and hydrogen temperature-programmed reduction (H₂-TPR) were performed to provide a deep insight into the K-doping effect. The results suggested that the addition of an appropriate amount of potassium to Mn/Al₂O₃ catalyst improved the dispersion of manganese oxide, the mobility and reactivity of surface lattice oxygen, thus significantly improved the catalyst activity.