Enhanced Catalytic Soot Oxidation over Co-Based Metal Oxides: Effects of Transition Metal Doping

A series of Co-M (M = Fe, Cr, and Mn) catalysts were synthesized by the sol-gel method for soot oxidation in a loose contact mode. The Co-Fe catalyst exhibited the best catalytic activity among the tested samples, with the characteristic temperatures (T10, T50, and T90) of 470 degrees C, 557 degrees C, and 602 degrees C, respectively, which were 57 degrees C, 51 degrees C, and 51 degrees C lower than those of the CoOx catalyst. Catalyst characterizations of N2 adsorption-desorption, X-ray diffraction (XRD), X-ray photo-electron spectrometry (XPS), and the temperature programmed desorption of O2 (O2-TPD) were performed to gain insights into the relationships between the activity of catalytic soot oxidation and the catalyst properties. The content of Co2+ (68.6%) increased due to the interactions between Co and Fe, while the redox properties and the relative concentration of surface oxygen adsorption (51.7%) were all improved, which could significantly boost the activity of catalytic soot oxidation. The effects of NO and contact mode on soot oxidation were investigated over the Co-Fe catalyst. The addition of 1000 ppm of NO led to significant reductions in T10, T50, and T90 by 92 degrees C, 106 degrees C, and 104 degrees C, respectively, compared to the case without the NO addition. In the tight contact mode, the soot oxidation was accelerated over the Co-Fe catalyst, resulting in 46 degrees C, 50 degrees C, and 50 degrees C reductions in T10, T50, and T90 compared to the loose contact mode. The comparison between real soot and model Printex-U showed that the T50 value of real soot (455 degrees C) was 102 degrees C lower than the model Printex-U soot.