Correlation of Soot Oxidation Kinetics to Catalyst Particle Nanostructure/Microstructure

Athanasios  Konstandopoulos, CERTH

Catalysts for direct soot oxidation in catalyzed diesel particulate filters (CDPFs) consist typically of various mixed oxide compositions (frequently with CeO2 as the dominant component) that assist soot oxidation by enhancing the supply of oxygen from the catalyst to the soot. Apart from the composition, the material morphological characteristics may also contribute to the catalytic activity. Different CeO2 nanoparticle catalysts have been obtained employing aerosol-based synthesis and sol–gel methods. The obtained catalyst particles have been characterized with respect to their physical and morphological properties as well as with respect to their catalytic soot oxidation activity. The results have been analyzed with the aid of a multi-population kinetics model motivated by the presence of distinct families of surface oxygen complexes (SOCs) on the carbon surface, which are involved in gasification reactions, in agreement with accepted mechanisms of soot oxidation in the literature.  The detailed kinetic data obtained are shown to correlate very well to a composite morphological parameter, derived here for the first time, combining the catalyst particle size, surface area, crystallite size, and porosity.  A similar study was conducted with sub-micron/micron sized, dense catalyst particles obtained by milling for various time intervals a CeO2 rich powder, resulting in a poly-disperse multimodal distribution.  In this case, the kinetic data are shown to correlate well with the total surface-weighted mean particle size (also known as the Sauter mean diameter in spray literature).  This study establishes to our knowledge for the first time a quantitative mechanistic link between catalyst particle structure and kinetic parameters, facilitating much the rational estimation of kinetic parameters in simulation studies of catalytic soot oxidation.