Reaction distributions in diesel emissions catalysts

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UNDERSTANDING DIESEL EMISSIONS CATALYSTS      Current predictions indicate that diesel engines for passenger vehicles will increase relative to gasoline engines. Coincidentally, upcoming environmental policy throughout most of the world is imposing significant decreases in tailpipe NOX and particulate emissions from diesel engines. New technologies are being developed to meet these demands. One such technology is NOX storage/reduction (NSR) where NOX is stored as nitrates on a catalyst and periodically reduced to N2. Another is catalyzed particulate filters, where particulate matter (soot) is trapped on a filter and periodically oxidized to CO2. With both of these technologies, there is a break with traditional catalyst performance characterization in that there is no steady-state related operation and there are significant axial distributions of reaction kinetics, surface species and temperature. These parameter gradients need to be understood in order to successfully model, control and optimize NOX reduction and particulate removal. Our proposed, short-term objectives with respect to diesel emission control include: - the development of a mechanistic description of the NSR cycle; - evaluation of the interaction of sulfur with the NSR catalyst system; and - demonstration of the propagation of soot oxidation on a soot filter. A programmatic goal of this research effort is the development and validation of experimental methodologies for evaluating catalytic reaction processes as a function of axial position inside a catalyst system. The success of this program will facilitate the implementation of NSR and soot filter technologies onto diesel engines and result in significantly cleaner exhaust. Furthermore, if the NSR technology does prove effective, it is then applicable to lean-burn gasoline engines as well, which would result in CO2 emissions reductions and fuel savings thereby dampening current fuel demands.