Sulfur Poisoning Effects on Modern Lean NOx Trap Catalysts Components

In the present work, a series of different materials was investigated in order to enhance the understanding of the role of modern lean NOx trap (LNT) components on the sulfur poisoning and regeneration characteristics. Nine different types of model catalysts were prepared, which mainly consisted of three compounds: (i) Al2O3, (ii) Mg/Al2O3, and (iii) Mg/Ce/Al2O3 mixed with Pt, Pd, and Pt-Pd. A micro flow reactor and a diffuse reflectance infrared Fourier transform spectrometer (DRIFTS) were employed in order to investigate the evolution and stability of the species formed during SO2 poisoning. The results showed that the addition of palladium and magnesium into the LNT formulation can be beneficial for the catalyst desulfation due mainly to the ability to release the sulfur trapped at relatively low temperatures. This was especially evident for Pd/Mg/Al2O3 model catalyst, which demonstrated an efficient LNT desulfation with low H2 consumption. In contrast, the addition of ceria was found to increase the formation of bulk sulfate species during SO2 poisoning, which requires higher temperatures for the sulfur removal. The noble metal nature was also observed to play an important role on the SOx storage and release properties. Monometallic Pd-based catalysts exhibited the formation of surface palladium sulfate species during SO2 exposure, whereas Pt-Pd bimetallic formulations presented higher stability of the sulfur species formed compared to the corresponding Pt- and Pd-monometallic samples.

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Modelling of a Lean NOx-Trap system with NO/NO2 differentiation and sulfur poisoning

SAE International Journal of Fuels and Lubricants ◽

10.4271/2010-01-1554 ◽

2010 ◽

Vol 3 (2) ◽

pp. 414-424 ◽

Cited By ~ 3

Author(s):

Alexis Manigrasso ◽

PIerre Darcy ◽

Patrick Da Costa

Keyword(s):

Sulfur Poisoning ◽

Lean Nox Trap ◽

Nox Trap ◽

Trap System ◽

Lean Nox

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A Temperature-Based Analysis Technique and Distributed Model Lean NOx Trap Catalyst

Dynamic Systems and Control, Parts A and B ◽

10.1115/imece2006-14887 ◽

2006 ◽

Author(s):

Shawn Midlam-Mohler ◽

Yann Guezennec

Keyword(s):

Chemical Reactions ◽

Measurement Technique ◽

Spatial Information ◽

Sulfur Poisoning ◽

Distributed Model ◽

Practical Reasons ◽

Lean Nox Trap ◽

Nox Trap ◽

Lean Nox ◽

The Rich

The management of an automotive Lean NOx Trap (LNT) catalyst requires periodic, brief periods of net rich exhaust to regenerate the catalyst by reducing the stored NOx. During the regeneration event, the fuel rich gas first affects the front of the catalyst then, as reductants are available, reach the downstream sections of the catalyst. In a typical engine test cell, it is not feasible to witness these distributed effects by simultaneously measuring multiple points in a catalyst bed due for a number of practical reasons. This is inconvenient because it is often desired to have a continuous or distributed lump model of the catalyst, which is difficult to calibrate without spatially and temporally resolved measurements. A novel measurement technique is presented which uses internal catalyst temperature measurements to detect the gross chemical reactions occurring in the catalyst during the rich reduction phase. The magnitude of the temperature change is shown to correlate with the mass of NOx and O2 reduced from the catalyst substrate. This information is available at each temperature measurement location, allowing spatial information to be collected non-intrusively. Furthermore, the technique contains temporal information regarding the key reactions. The type of information made available, as well as the convenience of the measurement system, makes the technique useful for a number of applications. The basis of the measurement technique is first presented from a theoretical basis, relating the temperature rise of the substrate to the various gross chemical reactions. Experimental validation of the method is then provided, illustrating the good correlation between the mass of stored NOx and O2 estimated by the method and the mass of stored NOx calculated from traditional gas analyzer measurements during the NOx storage phase. After demonstrating the applicability of the method, several applications are suggested including use of the technique for LNT modeling, LNT regeneration control, and sulfur poisoning detection.

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Chapter 4. Lean NOx Trap Performance Degradation – Reversible Sulfur Poisoning and Irreversible Thermally-induced Sintering

Catalysis Series - NOx Trap Catalysts and Technologies ◽

10.1039/9781788013239-00104 ◽

2018 ◽

pp. 104-126 ◽

Cited By ~ 1

Author(s):

William S. Epling

Keyword(s):

Performance Degradation ◽

Sulfur Poisoning ◽

Lean Nox Trap ◽

Nox Trap ◽

Thermally Induced ◽

Lean Nox

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Sulfur Poisoning and Desulfation of the Lean NOx Trap

10.4271/2001-01-2503 ◽

2001 ◽

Cited By ~ 19

Author(s):

J. Li ◽

J. Theis ◽

W. Chun ◽

C. Goralski ◽

R. Kudla ◽

...

Keyword(s):

Sulfur Poisoning ◽

Lean Nox Trap ◽

Nox Trap ◽

Lean Nox

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Mitigation of Sulfur Effects on a Lean NOx Trap Catalyst by Sorbate Reapplication

ASME 2007 Internal Combustion Engine Division Fall Technical Conference ◽

10.1115/icef2007-1628 ◽

2007 ◽

Author(s):

James E. Parks

Keyword(s):

Natural Gas ◽

Catalyst Activity ◽

Sulfur Poisoning ◽

Lean Nox Trap ◽

Nox Trap ◽

Gas Engine ◽

Natural Gas Engine ◽

Washing Process ◽

Lean Nox ◽

The Rich

Lean NOx trap catalysis has demonstrated the ability to reduce NOx emissions from lean natural gas reciprocating engines by >90%. The technology operates in a cyclic fashion where NOx is trapped on the catalyst during lean operation and released and reduced to N2 under rich exhaust conditions; the rich cleansing operation of the cycle is referred to as “regeneration” since the catalyst is reactivated for more NOx trapping. Natural gas combusted over partial oxidation catalysts in the exhaust can be used to obtain the rich exhaust conditions necessary for catalyst regeneration. Thus, the lean NOx trap technology is well suited for lean natural gas engine applications. One potential limitation of the lean NOx trap technology is sulfur poisoning. Sulfur compounds directly bond to the NOx trapping sites of the catalyst and render them ineffective; over time, the sulfur poisoning leads to degradation in overall NOx reduction performance. In order to mitigate the effects of sulfur poisoning, a process has been developed to restore catalyst activity after sulfur poisoning has occurred. The process is an aqueous-based wash process that removes the poisoned sorbate component of the catalyst. A new sorbate component is reapplied after removal of the poisoned sorbate. The process is low cost and does not involve reapplication of precious metal components of the catalyst. Experiments were conducted to investigate the feasibility of the washing process on a lean 8.3-liter natural gas engine on a dynamometer platform. The catalyst was rapidly sulfur poisoned with bottled SO2 gas; then, the catalyst sorbate was washed and reapplied and performance was reevaluated. Results show that the sorbate reapplication process is effective at restoring lost performance due to sulfur poisoning. Specific details relative to the implementation of the process for large stationary natural gas engines will be discussed.

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