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Title: Intra-Catalyst Reductant Chemistry and NO x Conversion of Diesel Lean NO x Traps at Various Stages of Sulfur Loading

Abstract

Due to increasingly stringent emissions regulations, Lean NOX Trap (LNT) catalysts are being researched as a potential solution for diesel engine emissions reduction. LNTs are practical for diesel NOX reduction due to their ability to reduce NOX from the O2 rich environment produced by diesel engines. LNTs function by storing NOX on the catalyst surface during efficient lean operation then, under rich conditions, releasing and reducing the trapped NOX. One method of producing this rich environment which regenerates a LNT involves manipulating the fuel injection parameters and throttling the air intake. This process is called in-cylinder regeneration. Experiments will be described here in which a 1.7 L common rail diesel engine has been used to regenerate LNTs at various stages of sulfur exposure, a known poison of the LNT. In-cylinder regeneration strategies were used to produce a range of reductant chemistries which enabled the study of the role of various reductants as NOX was converted across the LNT. This study gives insight into how to most efficiently regenerate the LNT. Sulfur poisoning of a fresh LNT was accelerated via the use of bottled SO2. Regeneration studies at various states of sulfation and after catalyst desulfation are discussed, highlighting intra-catalyst measurementsmore » of reductant chemistry and NOX conversion through the catalyst. Results showed that as sulfur loading increased, NOX conversion efficiency decreased and reductant utilization shifted downstream. Hydrogen from in-cylinder combustion was consumed over the first half of the LNT then produced from other available reductants over the last half for some strategies and conditions. Hydrogen production over the last portion of the catalyst was found to be affected by sulfur.« less

Authors:
 [1];  [1];  [1];  [1]
  1. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Fuels, Engines and Emissions Research Center (FEERC); National Transportation Research Center
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
978219
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Conference
Resource Relation:
Conference: Society of Automotive Engineers Powertrain and Fluids Conference, Toronto, Canada, 20061015, 20061019
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; 33 ADVANCED PROPULSION SYSTEMS; AIR; CATALYSTS; CHEMISTRY; COMBUSTION; DIESEL ENGINES; EFFICIENCY; ENGINEERS; HYDROGEN; HYDROGEN PRODUCTION; POISONING; REGENERATION; REGULATIONS; SULFATION; SULFUR

Citation Formats

Parks, II, James E, Swartz, Matthew M, Huff, Shean P, and West, Brian H. Intra-Catalyst Reductant Chemistry and NOx Conversion of Diesel Lean NOx Traps at Various Stages of Sulfur Loading. United States: N. p., 2006. Web.
Parks, II, James E, Swartz, Matthew M, Huff, Shean P, & West, Brian H. Intra-Catalyst Reductant Chemistry and NOx Conversion of Diesel Lean NOx Traps at Various Stages of Sulfur Loading. United States.
Parks, II, James E, Swartz, Matthew M, Huff, Shean P, and West, Brian H. Sun . "Intra-Catalyst Reductant Chemistry and NOx Conversion of Diesel Lean NOx Traps at Various Stages of Sulfur Loading". United States. doi:.
@article{osti_978219,
title = {Intra-Catalyst Reductant Chemistry and NOx Conversion of Diesel Lean NOx Traps at Various Stages of Sulfur Loading},
author = {Parks, II, James E and Swartz, Matthew M and Huff, Shean P and West, Brian H},
abstractNote = {Due to increasingly stringent emissions regulations, Lean NOX Trap (LNT) catalysts are being researched as a potential solution for diesel engine emissions reduction. LNTs are practical for diesel NOX reduction due to their ability to reduce NOX from the O2 rich environment produced by diesel engines. LNTs function by storing NOX on the catalyst surface during efficient lean operation then, under rich conditions, releasing and reducing the trapped NOX. One method of producing this rich environment which regenerates a LNT involves manipulating the fuel injection parameters and throttling the air intake. This process is called in-cylinder regeneration. Experiments will be described here in which a 1.7 L common rail diesel engine has been used to regenerate LNTs at various stages of sulfur exposure, a known poison of the LNT. In-cylinder regeneration strategies were used to produce a range of reductant chemistries which enabled the study of the role of various reductants as NOX was converted across the LNT. This study gives insight into how to most efficiently regenerate the LNT. Sulfur poisoning of a fresh LNT was accelerated via the use of bottled SO2. Regeneration studies at various states of sulfation and after catalyst desulfation are discussed, highlighting intra-catalyst measurements of reductant chemistry and NOX conversion through the catalyst. Results showed that as sulfur loading increased, NOX conversion efficiency decreased and reductant utilization shifted downstream. Hydrogen from in-cylinder combustion was consumed over the first half of the LNT then produced from other available reductants over the last half for some strategies and conditions. Hydrogen production over the last portion of the catalyst was found to be affected by sulfur.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}

Conference:
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  • A set of elementary surface reactions is proposed for modeling the chemistry in a lean NOx trap during regeneration (reduction of stored NOx). The proposed reaction mechanism can account for the observed product distribution from the trap over a range of temperatures and inlet gas compositions similar to those expected for realistic operation. The mechanism includes many reactions already discussed in the literature, together with some hypothesized reactions that are required to match observations from temperature programmed reactor experiments with a commercial lean NOx trap catalyst. Preliminary results indicate that the NOx trap regeneration and byproduct formation rates can bemore » effectively captured by using a relatively compact set of elementary reactions.« less
  • We investigate the effects of initial sulfur loadings on the desulfation chemistry and the subsequent final activity of a commercial LNT catalyst. Identical total amounts of SO2 are applied to the samples, albeit with the frequency of desulfation varied. The results indicate that performance is better with less frequent desulfations. The greater the amount of sulfur deposited before desulfation, the more amount of SO2 evolution before H2S is observed during desulfation, which can be explained by two sequential reactions; initial conversion of sulfate to SO2, followed by the reduction of SO2 to H2S. After completing all sulfation/desulfation steps, the samplemore » with only a single desulfation results in a fairly uniform sulfur distribution along the z-axis inside of the monolith. We expect that the results obtained in this study will provide useful information for optimizing regeneration strategies in vehicles that utilize the LNT technology.« less
  • Lean NOx Trap (LNT) catalysts can effectively reduce NOx from lean engine exhaust. Significant research for LNTs in diesel engine applications has been performed and has led to commercialization of the technology. For lean gasoline engine applications, advanced direct injection engines have led to a renewed interest in the potential for lean gasoline vehicles and, thereby, a renewed demand for lean NOx control. To understand the gasoline-based reductant chemistry during regeneration, a BMW lean gasoline vehicle has been studied on a chassis dynamometer. Exhaust samples were collected and analyzed for key reductant species such as H2, CO, NH3, and hydrocarbonsmore » during transient drive cycles. The relation of the reductant species to LNT performance will be discussed. Furthermore, the challenges of NOx storage in the lean gasoline application are reviewed.« less
  • The regulated and non-regulated emissions of a current diesel passenger car and two light-duty diesel trucks with catalysts and particulate traps were measured to better understand the effects of aftertreatment devises on the environment. The passenger car, a 1.8 L IDI TC Sierra, was tested both with and without three different diesel oxidation catalysts (DOC) and with two fuel sulfur levels, 0 and 0.05 wt%. One light-duty truck, a 2.5 L DI NA Transit, was tested on one fuel, 0.05 wt% sulfur, with and without three different particulate trap/regeneration systems and with and without a urea lean NO{sub x} catalystmore » (LNC) system. A second similar Transit was tested on the 0.05 wt% sulfur fuel with an electrically regenerated trap system. The results are compared to each other, regulated emission standards, and to emissions from gasoline vehicles.« less
  • Periodical regeneration of NO x storage catalyst (also known as lean NO x trap) by short rich pulses of CO, H 2 and hydrocarbons is necessary for the reduction of nitrogen oxides adsorbed on the catalyst surface. Ideally, the stored NO x is converted into N 2, but N 2O and NH 3 by-products can be formed as well, particularly at low-intermediate temperatures. The N 2 and N 2O products are formed concurrently in two peaks. The primary peaks appear immediately after the rich-phase inception, and tail off with the breakthrough of the reductant front accompanied by NH 3 product.more » In addition, the secondary N 2 and N 2O peaks then appear at the rich-to-lean transition as a result of reactions between surface-deposited reductants/intermediates (CO, HC, NH 3, — NCO) and residual stored NO x under increasingly lean conditions.« less