A Dutch researcher has developed a reaction model describing the activity of new NOx Storage Reduction (NSR) catalytic converters used in conjunction with diesel or lean-burn gasoline engines. The model supports the development of a controller for the engine and emissions aftertreatment systems to optimize fuel consumption and NOx control.
While diesel and lean-burn gasoline engines offer beneficial reductions in fuel consumption compared to conventional gasoline engines, they also generate exhaust gases rich in NOx. One current approach to reducing NOx emissions in such engines is to incorporate trapping components like barium oxide in oxidation catalysts, thus enabling the storage of NOx as nitrates under oxygen-rich conditions for later reduction.
With this new type of NOx Storage Reduction (NSR) catalytic converter, NOx generated during a long oxygen-rich (lean-burn) period is stored in the barium component. When this component becomes saturated, the catalyst is regenerated during the short fuel-rich period. The NOx stored is released and subsequently reduced to nitrogen over a precious metal such as platinum.
Caren Scholz from the Eindhoven University of Technology investigated this NSR mechanism to gain a better understanding of how the storage component functions during the oxygen-rich and fuel-rich periods.
She studied the behavior of the catalyst in detail, analyzing the effect of the various forms in which barium occurs in the catalytic converter, the effect of the presence of carbon dioxide and water in the exhaust gas, and the effect of the various reducing agents, such as carbon monoxide, hydrogen, and ethylene on the NOx storage and reduction.
The research yielded insights into the function of various components in the catalytic converter. Scholz produced a practical mathematical model that describes the various chemical reactions in the device.
Using this reaction model, a controller in the car can determine when the maximum NOx capacity of the catalyst has been reached, followed by the length of time extra fuel must be injected to regenerate the catalyst.
The research was carried out in cooperation with PSA Peugeot Citroen, Toyota and Ford, the car development company PD&E Automotive Solutions, catalytic converter manufacturer Engelhard De Meern (now BASF), and with TNO Automotive, Shell, E.P. Controls and IPCOS.
C.M.L. Scholz, V.R. Gangwal, M.H.J.M. de Croon, J.C. Schouten, Influence of CO2 and H2O on NOx storage and reduction on a Pt-Ba/γ-Al2O3 catalyst, Appl. Catal. B, 71(-), 143-150, (2007)
C.M.L. Scholz, B.H.W. Maes, M.H.J.M. de Croon, J.C. Schouten, Influence of reducing agent (CO, H2 and C2H4) and of H2O on NOx reduction on a Pt-Ba/γ-Al2O3 catalyst, Appl. Catal. A, -(-), in press, (2007)
C.M.L. Scholz, V.R. Gangwal, M.H.J.M. de Croon, J.C. Schouten, Model for NOx storage/reduction in the presence of CO2 on a Pt-Ba/-Al2O3 catalyst, J. Catal., 245(1), 215-227, (2007)
V.R. Gangwal, C.M.L. Scholz, M.H.J.M. de Croon, J.C. Schouten, Modelling periodic NOx storage-reduction in the presence of CO2, Chem. Eng. Sci., -(-), in press, (2007)
C.M.L. Scholz, V.R. Gangwal, J.H.B.J. Hoebink, J.C. Schouten, NOx storage over lean-burn automotive catalysts, Appl. Catal. B, 70(1-4), 226-232, (2007)