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Decrease Thermal Exposure While Shorten DeSOx Time During LNT DeSOx

IP.com Disclosure Number: IPCOM000125179D
Publication Date: 2005-May-23
Document File: 2 page(s) / 85K

Publishing Venue

The IP.com Prior Art Database

Abstract

Lean NOx Trap (LNT) technology is based on chemical reactions that store NOx under lean conditions and reduce it under rich conditions. There are two major factors affecting LNT durability; one is sulfur poisoning and the other one is thermal deactivation. Sulfur poisoned LNTs can be restored by decomposing these sulfates (de-sulfation or deSOx) under rich conditions at high temperature. However, exposure to high temperatures will cause the thermal deactivation on LNT results in irreversible destruction of the NOx storage features. The thermal deactivation caused by deSOx is permanent and becomes a major concern for all LNTs. At this point, reducing the thermal damage on LNT during deSOx seems important to extend the thermal durability of LNTs. The temperature and the time of deSOx are the two factors that can be controlled during LNT deSOx to reduce the thermal damage on LNT. The key point of current method is to increase the rich duration in deSOx L/R cycling, to reduce the deSOx temperature as well as reduce the deSOx time (time to exposure at deSOx temperature) while maintain the same deSOx efficiency.

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Decrease Thermal Exposure While Shorten DeSOx Time During LNT DeSOx

Lean NOx Trap (LNT) technology is based on chemical reactions that store NOx under lean conditions and reduce it under rich conditions.  There are two major factors affecting LNT durability; one is sulfur poisoning and the other one is thermal deactivation.  Sulfur poisoned LNTs can be restored by decomposing these sulfates (de-sulfation or deSOx) under rich conditions at high temperature. However, exposure to high temperatures will cause the thermal deactivation on LNT results in irreversible destruction of the NOx storage features.

The thermal deactivation caused by deSOx is permanent and becomes a major concern for all LNTs. At this point, reducing the thermal damage on LNT during deSOx seems important to extend the thermal durability of LNTs. The temperature and the time of deSOx are the two factors that can be controlled during LNT deSOx to reduce the thermal damage on LNT. The key point of current method is to increase the rich duration in deSOx L/R cycling, to reduce the deSOx temperature as well as reduce the deSOx time (time to exposure at deSOx temperature) while maintain the same deSOx efficiency.

Method

The flowing figures show the cumulative weight percent of sulfur released during the deSOx period of a LNT with different rich duration, L/R=5s/60s, L/R=5s/30s, and L/R=5s/15s. Prior to each deSOx, the LNT was cleaned and loaded the same amount of sulfur. The deSOx starts when the catalyst temperature reaches 600ºC, and the deSOx continues while the temperature kept ramping at 5ºC/min till 800ºC. The X axis can either be in the temperature or in time scale, since the temperature was linearly increased with time. The Figure 1 is plotted in the temperature scale, and the results showed that the catalyst temperature was decreased for desulafting or removing the same amount of stored sulfur with the increasing of the rich duration in deSOx L/R cycling. For deSOx at L/R=5s/15s, the catalyst temper...