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.
Highlights
Soot particulate is one of the primary components of atmospheric aerosols, which is mainly emitted from diesel engines (Srivastava et al, 2011; Sitarski, 2012)
Harrison et al (2003) reported that diesel soot particles could be burnt over Co3O4 catalyst at 683 K under tight contact, which was much lower than non-catalytic soot combustion
Spinel oxides constituted by Ni and Co resulted in a smaller SBET compared to other catalysts, whereas the largest SBET was obtained over the ZnCo2O4 catalyst with a value of 16.4 m2 g–1, which was comparable with the results of Abu-Zied et al (2015)
Summary
Soot particulate is one of the primary components of atmospheric aerosols, which is mainly emitted from diesel engines (Srivastava et al, 2011; Sitarski, 2012). A series of spinel type ACo2O4 (A = Co, Ni, Cu, Zn) catalysts were synthesized via a citric acid complex method for catalytic soot oxidation. For ZnCo2O4 catalyst, the TPR curves showed two reduction peaks attributed to two types of oxygen species.
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