Kinetic Analysis Of Catalytic Soot Oxidation Process Over CeO₂-Based Catalyst

Soot particulates emitted from the diesel engines have caused serious harm on environment and human health.Up to now,diesel particulate filters combined with oxidized catalysts have become the most promising soot elimination technology.Hence,it is necessary to carry out the kinetic analysis of soot oxidation over catalysts in order to clarify the reaction mechanism,which can provide reference for the development of oxidation catalysts and the design of diesel particulate filters.In order to define the effects of CeO₂ on soot oxidation,this work is aimed to investigate the kinetic behavior of soot oxidation over CeO₂-based catalysts.The nanostructured CeO₂ with different morphologies were synthesized by a facile hydrothermal method.In order to define the effects of crystal planes of CeO₂,the kinetic analysis of soot oxidation was carried out through the Friedman isoconversional method and the distributed activation energy model（DAEM）.The kinetic results indicate that soot oxidation consists of catalytic and non-catalytic processes under loose contact condition,corresponding to the active oxygen species activated by the exposed planes and gaseousO₂ directly involved in the reaction,respectively.On the basis of the DAEM,the activation energy（E_a）of the exposed（100）,（111）planes and non-catalytic gaseousO₂ on soot oxidation distributes in the range of 60-100,100-150,and 150-250k J mol^-1,respectively.CeO₂ nanocubes with abundant（100）planes exhibited the lowest E_a and the highest catalytic activity due to the higher intrinsic activity of（100）plane than that of（111）plane.This work develops a new methodology of kinetic analysis to investigate the soot oxidation reaction,which could be potentially extended to other complex oxidation systems.A series of Zr,Pr,Co and Mn doped CeO₂-based complex oxide catalysts were synthesized by a facile sol-gel method.Compared with the pure CeO₂,the quantity and the intrinsic activity of active oxygen species on the doped CeO₂-based catalysts can be improved,which is beneficial for soot oxidation.In addition,the kinetic analysis of soot oxidation over the CeO₂-based catalysts was investigated via the Friedman,KAS,OFW and Starink isoconversional methods based on the thermalgravimetric analysis（TGA）.It can be found that the activation energy values obtained via the Friedman method are the most accurate.Hence,the CeO₂-based catalysts with higher catalytic activity can lower the activation energy value of soot oxidation.The evaluation and selection for the catalysts can be achieved by the comparison of the activation energy values obtained via the Friedman method.