Recent Advances in Diesel Particulate Emission Control

Abstract

Diesel Particulate Filters are the most complex component of today's emission control systems as they need to incorporate different and often conflicting functionalities such as high soot nanoparticle filtration efficiency, low pressure drop behavior, direct catalytic soot oxidation activity, high oxidation activity for Carbon Monoxide, Hydrocarbons and Nitrogen Oxide, as well as ability to reduce Nitrogen Oxides. Significant progress has been made employing both fundamental research as well as applications-oriented approaches. These have led to an improved understanding of the coupled physicochemical transport and reaction phenomena occurring in DPFs. We have researched new materials, designs and control approaches for enhancing the design and reliability of future Diesel Particulate Emission Control systems. An enabling technology has been the development and synthesis of nanostructured catalysts and their incorporation into a multifunctional reactor for Diesel Emission. Apart from the composition, the material morphological characteristics also contribute to the catalytic activity. As an example we present different nanoparticle catalysts characterized with respect to their physical and morphological properties as well as with respect to their catalytic soot oxidation activity. 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. Likewise when sub-micron/micron sized, dense catalyst particles were obtained by milling for various time intervals, resulting in a poly-disperse multimodal distribution, the kinetic data correlate well with the total surface-weighted mean particle size. 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.