NOx Storage Materials and Traps Resistant to Thermal Aging

a technology of storage materials and traps, applied in the direction of physical/chemical process catalysts, metal/metal-oxide/metal-hydroxide catalysts, separation processes, etc., can solve the problems of catalysts that use baria for nosub>x /sub>storage, nosub>x /sub>storage capacity loss, and ineffective twc catalysts for reducing nosub>x /sub>emissions

Inactive Publication Date: 2008-05-29
BASF CATALYSTS LLC
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0009]In certain embodiments, the coating of the nitrogen oxide storage catalyst further comprises at least one member of platinum group metals selected from the group consisting of platinum, palladium, rhodium, iridium and mixtures thereof supported on refractory oxide particles. The refractory oxide particles may be selected from the group consisting of aluminum oxide, mixed aluminum oxide and zirconium oxide, mixed aluminum oxide and lanthanum oxide, mixed aluminum oxide and cerium oxide, mixed aluminum oxide and magnesium oxide, and alumina oxide mixed with one or more of zirconia and lanthana.
[0010]Another embodiment relates to a catalytic trap disposed in an exhaust passage of an internal combustion engine which operates periodically between lean and stoichiometric or rich conditions, for abatement of NOx in an exhaust gas stream which is generated by the engine. The catalytic trap comprises a catalytic trap material including a precious metal catalytic component effective for oxid

Problems solved by technology

Although lean-burn engines provide enhanced fuel economy, they have the disadvantage that conventional TWC catalysts are not effective for reducing NOx emissions from such engines because of excessive oxygen in the exhaust.
However, catalysts that use baria for NOx storage exhibit a problem in practical application, particularly when the catalysts are aged by exposure to high temperature

Method used

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  • NOx Storage Materials and Traps Resistant to Thermal Aging
  • NOx Storage Materials and Traps Resistant to Thermal Aging
  • NOx Storage Materials and Traps Resistant to Thermal Aging

Examples

Experimental program
Comparison scheme
Effect test

example 1

Preparation of NOx Storage Material

[0034]BaCO3 and CeO2 were intimately mixed and finely dispersed in a weight ratio of between about 1:3 and about 1:5. Cerium oxide having a BET surface area of between about 50-150 m2 / g was mixed with a solution of barium acetate such that the BaCO3 / CeO2 composite had a BaCO3 content of about 10-30 wt %. After mixing, the suspension of soluble barium acetate and CeO2 was then spray-dried at a temperature of between about 90° C. and 120° C. to obtain a solid mixture of barium acetate and ceria.

[0035]After spray-drying, the mixture was then heated at about 550° C. to 800° C. for about 2 hours to form particles of ceria having barium carbonate supported on the ceria particles. The resulting BaCO3 had a crystallite size of between about 20 and 40 nm. The BaCO3 and CeO2 crystallites formed particles with a size of between about 5 and 50 microns. The BET surface area of the particulate mixture is between about 30 and 80 m2 / g.

Preparation of Catalytic Comp...

example 3

NOx Storage Capacity Testing

[0040]Two catalytic traps were prepared, a first catalytic trap was prepared in accordance with Example 1 and a comparative catalytic trap was prepared in accordance with Comparative Example 2. Both catalytic traps A were evaluated after aging for 8 hours at 850° C.

[0041]Both catalytic traps were evaluated as follows. An engine was set to an air / fuel ratio of 11.6 for 2 minutes at the desired temperature to remove all stored NOx and oxygen from the catalyst. This mode represents rich engine operation. Subsequently, the engine was adjusted to an air / fuel ratio of 29.6 under constant NOx mass flow. This mode represents lean engine operation. During the whole test, the NOx concentration was measured before and after the NOx trap using a NOx analyzer.

[0042]After the 2 minute rich operation followed by a 60 second lean operation, the engine was set to a 3 second rich operation to remove stored NOx without having hydrocarbon and carbon monoxide tailpipe emissio...

example 4

Barium Concentration and Calcination Temperature

[0049]Different amounts of Ba were impregnated into ceria of different surface area, using the procedures described in Example 1. Ceria powders with different BET surface areas were used to determine the effect of the resulting Ba / Ceria composite powder.

[0050]Characterization of the impregnated powder included BET surface area measurement. In addition fully formulated NOx trap catalysts were prepared using the procedures described in Example 1 that contain the particular Ba / Ceria composite material as NOx storage component. The NOx storage properties of the catalysts have been evaluated after aging for 8 hours at 850° C. under air with 10% H2O in a laboratory reactor. The results are shown in Table I and Table II below.

[0051]Table I shows the result of a variation of the BaCO3 and CeO2 concentration together with a variation of the ceria used. After impregnation, all samples were calcined at 550° C. in air to decompose the impregnated ...

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Abstract

Nitrogen oxide storage materials and methods of manufacturing nitrogen oxide storage materials are disclosed. The nitrogen oxide storage materials can be used to manufacture catalytic trap disposed in an exhaust passage of an internal combustion engine which is operated periodically between lean and stoichiometric or rich conditions, for abatement of NOx in an exhaust gas stream which is generated by the engine. In one embodiment, the nitrogen oxide storage material comprises alkaline earth material supported on ceria particles having a crystallite size of between about 10 and 20 nm and the alkaline earth oxide having a crystallite size of between about 20-40 nm.

Description

TECHNICAL FIELD[0001]Embodiments of the invention relate nitrogen oxide storage materials and methods for their manufacture. More particularly, embodiments of the invention pertain to NOx storage materials that are resistant to thermal aging and methods of making such materials. The nitrogen oxide storage materials may be part of a catalytic trap used to treat exhaust gas streams, especially those emanating from lean-burn gasoline or diesel engines.BACKGROUND ART[0002]Emission of nitrogen oxides (“NOx”) from lean-burn engines (described below) must be reduced in order to meet emission regulation standards. Conventional three-way conversion (“TWC”) automotive catalysts are suitable for abating NOx, carbon monoxide a (“CO”) and hydrocarbon (“HC”) pollutants in the exhaust of engines operated at or near stoichiometric air / fuel conditions. The precise proportion of air to fuel which results in stoichiometric conditions varies with the relative proportions of carbon and hydrogen in the f...

Claims

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Application Information

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IPC IPC(8): F01N3/10B01J23/10C01B32/60
CPCB01D53/9422B01J37/0045B01D2255/1025B01D2255/204B01D2255/2065B01D2255/20715B01D2255/2092B01D2255/91B01D2255/9202B01J23/10B01J23/63B01J35/006B01J35/023B01J35/1014B01J35/1019B01J35/1038B01J35/1061B01D2255/1021Y02T10/12B01D53/94B01J21/04
Inventor HILGENDORFF, MARCUSROTH, STANLEYSTIEBELS, SUSANNE
Owner BASF CATALYSTS LLC
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