Sulfur effects on spatiotemporal distribution of reactions involved in a commercial lean NO_x trap operation

The effects of sulfur on the spatiotemporal distribution of reactions and temperature inside a monolithic lean NO_x trap (LNT) were studied. A commercial LNT monolith core sample in a bench-flow reactor with simulated engine exhaust was evaluated. The obtained spatiotemporal profiles, combined with integral catalytic performance data, provided useful information about sulfation and its impact on LNT reactions such as NO_x storage, oxygen storage, reductant utilization, and byproduct formation. Sulfur tended to accumulate in a plug-like fashion in the reactor and progressively inhibited NO_x storage capacity along the axis. The NO_x storage/reduction reactions occurred over a relatively short portion of the reactor. Oxygen storage capacity was poisoned by sulfur also in a progressive manner but to a lesser extent. Global selectivity for N₂O remained low at all sulfur loadings, but NH₃ selectivity increased significantly with sulfur loading. Sulfation also led to significant changes in reductant consumption trends and temperature profiles in a manner that was consistent with the progressive poisoning of the LNT. This is an abstract of a paper presented at the 2007 AIChE Annual Meeting (Salt Lake City, UT 11/4-9/2007).