Study on Catalytic Soot Oxidation over Spinel Type ACo2O4 (A = Co, Ni, Cu, Zn) Catalysts

ABSTRACT

In this study, a series of spinel type ACo₂O₄ (A = Co, Ni, Cu, Zn) catalysts were synthesized via a citric acid complex method for catalytic soot oxidation. The effects of A sites on the removal of soot particles and CO₂ selectivity was investigated. The best performances for soot oxidation was achieved over ZnCo₂O₄ with the T₅₀ of 569°C. The textural and redox properties of the ACo₂O₄ catalysts were tested using BET, XRD, H₂-TPR, O₂-TPD, XPS. The substitution of A site caused the change of Co³⁺/(Co²⁺ + Co³⁺) ratios as well as the oxygen mobility in the spinel structure. Both Co²⁺ and Co³⁺ species were observed on the surface of ACo₂O₄ catalyst, and Co³⁺ species were more easily to be reduced to lower states, thus improved the catalytic performance. Compared to other catalysts, the interactions between Zn and Co species led to larger surface area, higher relative concentration of surface active Co³⁺ and more chemisorbed oxygen species. Additionally, the activity of the catalysts on soot oxidation were inhibited in the presence of sulfur dioxide and water vapor, while nitric oxide facilitated the catalytic activity.