Catalytic oxidation of diesel soot: New characterization and kinetic evidence related to the reaction mechanism on K/CeO2 catalyst

The oxidation of diesel soot using K/CeO2 catalysts is studied in this paper. The reaction system involved in the catalytic oxidation of soot is quite complex; therefore, the study of reaction mechanisms is particularly difficult to address and, consequently, there are few publications related to this topic. In this work, kinetic tests providing new information on this mechanism are shown. Using temperature-programmed oxidation experiments designed in order to get the combustion of only a fraction of the soot, it was possible to observe transient phenomena that demonstrate that the soot oxidation reaction involves many steps and intermediate species. Fourier transform infrared spectroscopy (FTIR), SEM and energy-dispersive X-ray analysis (EDX) characterization results obtained before and after partial burning experiments of soot, also provided information on catalysts morphological changes during the reaction. It was found that peroxide and superoxides associated to CeO2 are present on the catalyst during soot oxidation. On the other hand, carbonates are formed on the catalyst surface reaching a pseudo-steady-state. The formation of peroxides and superoxides and its surface diffusion explained the transient behavior observed during temperature-programmed experiments designed to burn a fraction of soot under isothermal condition.

Temperature-programmed oxidation analysis carried out up to intermediate temperatures (320–350 °C) made it possible to observe an unexpected result regarding the reaction rate for the catalytic soot oxidation. A maximum was observed in the rate of oxidation at constant temperature, which is explained taking into account the formation of different intermediates involving CeO2 and K unstable compounds.Figure optionsDownload as PowerPoint slide