Characterization of Carbon Oxidation Kinetics for Particulate Matter Reduction Technologies

Licentiate thesis, 2010

Transport related emissions of particulate matter (PM) represent a significant health risk and are therefore strictly regulated in most developed countries. An efficient technique to reduce emissions of combustion particles is to capture the particles in a filter, which must be subsequently regenerated by oxidation of the carbonaceous fraction of the PM. Although sophisticated filter regeneration systems and specialized catalysts are available, further optimization and cost reduction still represent major challenges, which motivate further in-depth studies on the oxidation characteristics of PM. An experimental method facilitating studies of the intrinsic oxidation kinetics of PM has been developed. The specific advantages with this method are; precise temperature and heat- and mass transfer control, possibility to directly analyze automotive PM samples on commercial filters and a high reproducibility that enables detection of small differences in reactivity. The oxidation profiles and global kinetic parameters of O2 based oxidation of a commercial carbon obtained with this method are comparable to previously published data. The global kinetic parameters show considerable dependence on degree of conversion, which limits the applicability of a global kinetic model. In specific, the changes in number of reactive carbon atoms during burnout could not be described by a simple global expression. Moreover, the direct catalytic activity of platinum on the oxidation of solid carbon is confirmed, and is shown to linearly depend on the mass of platinum. The promoting mechanism further seems to involve extensive oxygen or platinum crystallite / carbon particle mobility.