scholarly journals Measures to Reduce the N2O Formation at Perovskite-Based Lean NOx Trap Catalysts under Lean Conditions

Catalysts ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 917
Author(s):  
Sabrina I. Ecker ◽  
Jürgen Dornseiffer ◽  
Stefan Baumann ◽  
Olivier Guillon ◽  
Henny J. M. Bouwmeester ◽  
...  
Keyword(s):  
Catalytic Reduction ◽  
Operation Mode ◽  
Oxidation Catalyst ◽  
Lean Nox Trap ◽  
N2o Emissions ◽  
Incipient Wetness Impregnation ◽  
N2o Formation ◽  
Lean Burn ◽  
Nox Storage Capacity ◽  
Lean Nox

The net oxidising atmosphere of lean burn engines requires a special after-treatment catalyst for NOx removal from the exhaust gas. Lean NOx traps (LNT) are such kind of catalysts. To increase the efficiency of LNTs at low temperatures platinised perovskite-based infiltration composites La0.5Sr0.5Fe1-xMxO3-δ/Al2O3 with M = Nb, Ti, Zr have been developed. In general, platinum based LNT catalysts show an undesired, hazardous formation of N2O in the lean operation mode due to a competing C3H6-selective catalytic reduction (SCR) at the platinum sites. To reduce N2O emissions an additional Rh-coating, obtained by incipient wetness impregnation, besides the Pt coating and a two-layered oxidation catalyst (2 wt.% Pd/20 wt.% CeO2/alumina)-LNT constitution, has been investigated. Though the combined Rh-Pt coating shows a slightly increased NOx storage capacity (NSC) at temperatures above 300 °C, it does not decrease N2O formation. The layered oxidation catalyst-LNT system shows a decrease in N2O formation of up to 60% at 200 °C, increasing the maximum NSC up to 176 µmol/g. Furthermore, the NSC temperature range is broadened compared to that of the pure LNT catalyst, now covering a range of 250–300 °C.

scholarly journals Improved NOx Storage/Release Properties of Ceria-Based Lean NOx Trap Compositions with MnOx Modification

Materials ◽  
2019 ◽  
Vol 12 (13) ◽  
pp. 2127 ◽  
Author(s):  
Marcos Schöneborn ◽  
Thomas Harmening ◽  
Javier Giménez-Mañogil ◽  
Juan Carlos Martínez-Munuera ◽  
Avelina García-García
Keyword(s):  
Storage Capacity ◽  
Nox Storage ◽  
Pt Catalyst ◽  
Lean Nox Trap ◽  
Incipient Wetness Impregnation ◽  
Nox Trap ◽  
Remarkable Effect ◽  
Nox Storage Capacity ◽  
Nox Adsorption ◽  
Lean Nox

Ceria/spinel-based lean NOx trap compositions with and without barium were modified with MnOx via incipient wetness impregnation. The effect of the MnOx layer on the aged materials (850 °C) as to the NOx storage and release properties was investigated via NOx adsorption (500 ppm NO/5% O2/balance N2) carried out at 300 °C in a dual-bed with a 1% Pt/Al2O3 catalyst placed upstream of the samples to generate sufficient amounts of NO2 required for efficient NOx storage. Subsequent temperature programmed desorption (TPD) experiments were carried out under N2 from 300 °C to 700 °C. The addition of MnOx to the barium free composition led to a slightly reduced NOx storage capacity but all of the ad-NOx species were released from this material at significantly lower temperatures (ΔT ≈ 100 °C). The formation of a MnOx layer between ceria/spinel and barium had a remarkable effect on ageing stability as the formation of BaAl2O4 was suppressed in favour of BaMnO3. The presence of this phase resulted in an increased NOx storage capacity and lower desorption temperatures. Furthermore, NOx adsorption experiments carried out in absence of the Pt-catalyst also revealed an unexpected high NOx storage ability at low NO2/NO ratios, which could make this composition suitable for various lean NOx trap catalysts (LNT) related applications.

Effect of Butanol on the Performance of DeNOx Aftertreatment Systems of a Diesel Vehicle Under WLTC Driving Conditions

2021 ◽  
Author(s):  
Alejandro Calle-Asensio ◽  
Juan José Hernández ◽  
José Rodríguez-Fernández ◽  
Víctor Domínguez-Pérez
Keyword(s):  
Catalytic Reduction ◽  
Nox Reduction ◽  
Climatic Conditions ◽  
Transport Sector ◽  
Lean Nox Trap ◽  
Diesel Vehicles ◽  
Medium Speed ◽  
Emission Regulations ◽  
Lean Nox ◽  
Light Duty Vehicles

Abstract Advanced biofuels and electrofuels, among which are medium-long chain alcohols, have gained importance in the transport sector with the enforcement of the EU Renewable Energy Directive (2018/2001). In parallel, last European emission regulations have become much more restrictive regarding NOx, so vehicle manufacturers have been forced to incorporate lean NOx trap (LNT) and/or selective catalytic reduction (SCR). Thus, the combination of modern DeNOx devices and the upcoming higher contribution of sustainable biofuels is a new challenge. In this work, two Euro 6 diesel vehicles, one equipped with LNT and the other with ammonia-SCR, have been tested following the Worldwide harmonized Light-duty vehicles Test Cycle (WLTC) at warm (24°C) and cold (−7°C) conditions using conventional diesel fuel and a diesel-butanol (90/10% vol.) blend. While the effect of butanol on the LNT efficiency was not significant, its influence on the SCR performance was notable during the low and medium-speed phases of the driving cycle, mainly under warm climatic conditions. Despite of the lower NOx concentration at the catalyst inlet, the worst efficiency of the SCR with butanol could be attributed to hydrocarbons deposition on the catalyst surface, which inhibits the NOx reduction reactions with ammonia. Moreover, the LNT was not sensitive to the ambient temperature while the SCR performance greatly depended on this parameter.

Control Design of an Automotive Urea SCR Catalyst

2002 ◽  
Author(s):  
Devesh Upadhyay ◽  
Michiel Van Nieuwstadt
Keyword(s):  
Ammonia Oxidation ◽  
Catalytic Reduction ◽  
Nox Reduction ◽  
Control Design ◽  
Reaction Rates ◽  
Lumped Parameter Model ◽  
Lean Burn ◽  
Ammonia Sensing ◽  
Injection Process ◽  
Lean Nox

The leading aftertreatment technologies for NOx removal from the exhaust gas of lean burn engines, Diesels in particular, are urea based Selective Catalytic Reduction (SCR), Lean NOx Traps (LNT) and Active Lean NOx Catalysts (ALNC). It is generally believed that the SCR technique has the potential of providing the best NOx conversion efficiency relative to the other techniques. Nonetheless, it is crucial that the high conversion efficiencies be achieved with a minimum slippage of unreacted ammonia as tail pipe emissions. This necessitates a precise control over the urea injection process. The complex behavior of the catalyst substrate with respect to adsorption and desorption of ammonia in conjunction with a lack of “stored ammonia” sensing capabilities makes the control problem challenging. In this paper we present a model-based control design approach using a lumped parameter model of an SCR system that includes the essential dynamics of the plant. The model includes the adsorption, desorption and surface coverage dynamics, along with the NOx reduction and ammonia oxidation dynamics based on the relevant chemical reaction rates.

The Effects of Aging Temperature and Air-Fuel Ratio on the NOx Storage Capacity of a Lean NOx Trap

2004 ◽  
Author(s):  
Joseph R. Theis ◽  
Justin A. Ura ◽  
George W. Graham ◽  
Hung-Wen Jen ◽  
John J. Li ◽  
...  
Keyword(s):  
Aging Temperature ◽  
Storage Capacity ◽  
Nox Storage ◽  
Lean Nox Trap ◽  
Nox Trap ◽  
Fuel Ratio ◽  
Nox Storage Capacity ◽  
Lean Nox ◽  
Effects Of Aging

The Effects of Aging Temperature and PGM Loading on the NOx Storage Capacity of a Lean NOx Trap

2005 ◽  
Author(s):  
Joseph R. Theis ◽  
Justin A. Ura ◽  
Christian T. Goralski ◽  
Jon Caine ◽  
Marcus Davies ◽  
...  
Keyword(s):  
Aging Temperature ◽  
Storage Capacity ◽  
Nox Storage ◽  
Lean Nox Trap ◽  
Nox Trap ◽  
Nox Storage Capacity ◽  
Lean Nox ◽  
Effects Of Aging

scholarly journals Lean and rich aging of a Cu/SSZ-13 catalyst for combined lean NOx trap (LNT) and selective catalytic reduction (SCR) concept

2019 ◽  
Vol 9 (9) ◽  
pp. 2152-2162 ◽  
Author(s):  
Xavier Auvray ◽  
Ann Grant ◽  
Björn Lundberg ◽  
Louise Olsson
Keyword(s):  
Selective Catalytic Reduction ◽  
Catalytic Reduction ◽  
Lean Nox Trap ◽  
Nox Trap ◽  
Scr Catalyst ◽  
Lean Nox

In the combined lean NOx trap (LNT) and selective catalytic reduction (SCR) concept, the SCR catalyst can be exposed to rich conditions during deSOx of the LNT.

NO2 Reaction Pathways With NH3 on an Fe-Zeolite SCR Catalyst

2011 ◽  
Author(s):  
Michael A. Smith ◽  
Christopher D. Depcik ◽  
Stefan Klinkert ◽  
John W. Hoard ◽  
Stanislav V. Bohac ◽  
...  
Keyword(s):  
Flow Reactor ◽  
Catalytic Reduction ◽  
Nox Reduction ◽  
Catalyst System ◽  
Lean Nox Trap ◽  
Scr Catalyst ◽  
Nh3 Scr ◽  
Nox Conversion ◽  
Lean Nox ◽  
System Part

One approach for nitrogen oxides (NOx) emission control of medium duty diesel engines is through the use of a combination Lean NOx Trap and Selective Catalytic Reduction (LNT-SCR) catalyst system. In this system, part of the NOx conversion occurs via an NH3 SCR catalyst that is dependent on the NO2 to NOx ratio of the feed gas with NO2 being a more advantageous oxidizer. One benefit of using this system is the conversion of NO to NO2 over the LNT which increases the NO2:NOx ratio of the feed gas to the SCR catalyst. An experimental study has been performed to investigate the NO2-NH3 reaction for an Fe-based zeolite SCR catalyst using a bench top flow reactor. The increase in NO2 concentration at the inlet of the SCR results in the formation of large quantities of N2O from 200°C to 400°C. Further experiments determined that N2O and NH3 react above 350°C. This has led to a hypothesis that one primary SCR reaction (Slow SCR) can be replaced with two reaction steps featuring NH3, NO2, and N2O. As a result, this paper proposes five NOx reduction reactions as part of a global mechanism, which would account for the observed experimental behavior.

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