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

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.