Institute for Chemical Technology and Polymer Chemistry University of Karlsruhe

Modeling and Simulation of NOModeling and Simulation of NOxx Abatement with Abatement with Storage/Reduction Catalysts for Lean Burn and Storage/Reduction Catalysts for Lean Burn and

Diesel EnginesDiesel Engines

Jan Koop and Olaf Deutschmann

Institute for Chemical Technology and Polymer ChemistryUniversity of Karlsruhe, Germany

2 2007-01-1142

IntroductionIntroduction

demand for new types of catalytic exhaust-gas aftertreatment, e.g.

Diesel Particle Filter (DPF)Urea-SCRNOx-storage catalyst (NSC)

Increasing number of vehicles

More stringent Emission Regulations (specially in Europe and California)

Solution: Lean operated engines less fuel consumption

Exhaust-gas treatment of the E 320 BLUETEC

Source: Umicore

3 2007-01-1142

IntroductionIntroduction

Exhaust-gas treatment of the E 320 BLUETEC

Advanced DeNOxcatalytic converter

DOC

DPF SCR

Source: DaimlerChrysler

4 2007-01-1142

NOx

TimeLean Rich Lean

Storage Storage

Reduction

NOx atcatalyst entrance

NOx atcatalyst exit

FunctionFunction of of thethe NONOxx StorageStorage and and ReductionReduction CatalystCatalyst

Lean phase – O2 rich Rich phase – O2 deficit

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Model SpecificationsModel Specifications

NO [ppm]

NO2 [ppm]

O2 [Vol.-%]

C3H6

[ppm] CO

[Vol.-%] CO2

[Vol.-%] H2O

[Vol.-%] H2

[Vol.-%] Mager 200 40 12 60 0,04 7 10 0

Fett 200 40 0,9 60 2,1 7 10 0,7

Lean

Rich

Isothermal Flatbed Reactor

NOx Long-Term Storage Experiments

Lean/Rich Cycling 300s/15s and 60s/5s (realistic time scale)

SV= 40000 h-1

T= 250 - 450°C

Well-defined Model Catalysts: Pt/Al2O3 and Pt/Ba/Al2O3

Dimension: 3 cm (Width), 20 cm (Length)

Realistic Exhaust-gas Composition:

6 2007-01-1142

TEMTEM--Images of Platinum and Barium ParticlesImages of Platinum and Barium Particles

Platinum Barium

Pt/Ba/AlPt/Ba/Al22OO33 CatalystCatalyst ((agedaged: 4h, 700: 4h, 700°°C, 10% HC, 10% H22O)O)

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Hierarchical Modeling of a NSCHierarchical Modeling of a NSC

Courtesy of J. Eberspächer GmbH& Co

8 2007-01-1142

Simulation Program DETCHEMSimulation Program DETCHEMRESERVOIRRESERVOIR

DETCHEM-Library

Washcoat-Models (optional)

CHANNEL

Complexity0d 2d / 3d

Storage Mechanism RESERVOIR1d-Concentration profile of

the storage media(transient, isothermal)

si•

diffusion jis ~ ji i•

diffusion term

reaction rate

mic

rosc

opic

mac

rosc

opic

2D Steady-State Profile for a Laminar Flow usingBoundary-Layer-Approx.

Reaction MechanismsThermodynamic Properties

Transport Coefficients

ji = η Fcat/geo Mi si

Mod

el L

evel

Tischer, S. and O. Deutschmann (2005). Catalysis Today 105(3-4): 407-413

9 2007-01-1142

ElementaryElementary--step Mechanism on Platinumstep Mechanism on Platinum

Hydrocarbons Carbon monoxide Nitric oxide

D. Chatterjee, O. Deutschmann and J. Warnatz (2001). Faraday Discussions 119 :371-384

70 Elementary-step Reactionswith 35 surface species and 10 gas-phase species

10 2007-01-1142

Development of heterogeneous reaction mechanismsDevelopment of heterogeneous reaction mechanisms

Surface science studies(TPD, XPS, AES, TEM, FEM, FIM

STM, SFG …)

Theory(ab-intio, DFT, BOC-MP, UBI-QEP, TS, Collision)

Analogy to gas phase kinetics, organometallics

Comparison of measured and computed data

Lab experiments(conversion, selectivty,

ignition/extinction temperatures,spatial & temporal profiles,

coverages)

Revised mechanism

Mechanism (Idea)

Modeling of lab reactors(including appropriate models for gas

phase kinetics and heat & mass transport

Sensitivity analysis &Evaluation of crucial

parameters

Reliable mechanism

11 2007-01-1142

Lean/Rich Cycle (300s/15s) and Axial Profiles for Pt/AlLean/Rich Cycle (300s/15s) and Axial Profiles for Pt/Al22OO33

0

50

100

150

200

250

300

350

0 50 100 150 200 250 300

t [s]

y NO

x, y C

3H6 [

ppm

]

0

50

100

150

200

250

300

350

0 50 100 150 200 250 300

t [s]

y NO

x, y C

3H6 [

ppm

]

0

50

100

150

200

250

300

350

0 50 100 150 200 250 300

t [s]

y NO

x, y C

3H6 [

ppm

]

NO2

NO C3H6

NO Mole Fraction

NO2 Mole Fraction

C3H6 Mole Fraction

Channel length [m]

SimulationExperiment

250°C 350°C 450°C

12 2007-01-1142

SimulatedSimulated SurfaceSurface CoveragesCoverages on on PlatinumPlatinum

Lean PhaseLean Phase Rich PhaseRich Phase

Model enables the prediction of the concentration profiles along the channel length and gives detailed insight into the surface coverages of the lean/rich phase

13 2007-01-1142

StorageStorage ReactionsReactions on Bariumon Barium

BaCO3 + 2NO2 + ½O2 Ba(NO3)2 + CO2

BaCO3 + 2NO + ½O2 Ba(NO2)2 + CO2

Ba(NO2)2 + O2 Ba(NO3)2

BaCO3 + 3NO2 Ba(NO3)2 + NO + CO2

Modeled as Global Reactions with Shrinking Core Model, due to Diffusion Limitation during Storage Process

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ShrinkingShrinking CoreCore Model Model withwith an an InactiveInactive CoreCore

rcDrR Sdiff ∂∂

∗∗= 24π

diffParticleBaONO

Nitrate

RArrr=∗

=

−− 22&

Olsson, L., R. J. Blint, et al. (2005) Industrial & Engineering Chemistry Research 44(9): 3021-3032.Tuttlies, U., V. Schmeisser, et al. (2004) Chemical Engineering Science 59(22-23): 4731-4738.

At the interface Nitrate-Carbonate:

50 nm

15 2007-01-1142

ShrinkingShrinking CoreCore Model Model withwith an an InactiveInactive CoreCore

tot

Nitrat

S rr

D∗=

lτ

½BaCO3 + NO2 + ¼O2 ½Ba(NO3)2 + ½CO2

Rate coefficients

Inhibition term:

Increasing inhibition term gives rise to a decreased rate coefficient

16 2007-01-1142

ReductionReduction ReactionsReactions on Bariumon Barium

Carbon Monoxide COBa(NO3)2 + 3 CO BaCO3 + 2 NO + 2 CO2

Hydrogen H2Ba(NO3)2 + 3H2 + CO2 BaCO3 + 2NO + 3H2O

Propylene C3H6Ba(NO3)2 + 1/3C3H6 BaCO3 + 2NO + H2O

Modeled without Shrinking Core Model, no Diffusion Limitationduring Regeneration

17 2007-01-1142

Parameterization of Storage/Reduction Reactions on Pt/Ba/AlParameterization of Storage/Reduction Reactions on Pt/Ba/Al22OO33

0

50

100

150

200

250

300

350

0 200 400 600 800

t [s]

y NO

x [pp

m]

0

50

100

150

200

250

300

350

0 200 400 600 800

t [s]

y NO

x [pp

m]

0

50

100

150

200

250

300

350

0 200 400 600 800

t [s]

y NO

x [pp

m]

0

50

100

150

200

250

300

350

0 100 200 300

t [s]

y NO

x [pp

m]

250°C 350°C 450°C

250°C 350°C 450°C

NOx Long-Term Storage Experiments

NOx Long-Term Storage Experiments

Lean/RichCycling

300s/15s

Lean/RichCycling

300s/15s

NO

NO2

NO

NO2

0

50

100

150

200

250

300

350

0 50 100 150 200 250 300

t [s]

y NO

x [pp

m]

0

50

100

150

200

250

300

350

0 50 100 150 200 250 300

t [s]

y NO

x [p

pm]

Parameterization of the Storage Reactions on LTS Experiments and Parameterization of the Reduction Reaction on Lean/Rich Cycles

SimulationExperiment

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Lean/Rich Cycle (60s/5s) for Pt/Ba/AlLean/Rich Cycle (60s/5s) for Pt/Ba/Al22OO33 at 350at 350°°CC

SimulationExperiment

NO2

NO

Good agreement between simulations and experiments for both lean/rich cycling and axial profiles

19 2007-01-1142

0

50

100

150

200

250

300

0 20 40 60 80 100 120 140 160 180 200

t [s]

y NO

x [pp

m]

0

20

40

60

80

100

0 20 40 60 80 100 120 140 160 180 200

t [s]

y NO

x [pp

m]

0

50

100

150

200

0 20 40 60 80 100 120 140 160 180 200

t [s]

y NO

x [pp

m]

1. Cycle 2. Cycle 3. Cycle

250°C250°C

350°C350°C

450°C450°C

SimulationExperiment

Lean/RichLean/Rich CyclingCycling (60s/5s) (60s/5s) forfor Pt/Ba/AlPt/Ba/Al22OO33

First three cycles in a row at different temperatures

Input conditions of 2nd

and 3rd are the surface coverages of the previous cycle

Model is able to predict concentrations profiles even for incomplete regeneration (250 and 350°C)

Problems with NO regeneration peak at 450°C

NONO2

20 2007-01-1142

PredictedPredicted FractionFraction withwith Ba(NOBa(NO33))22 on Pt/Ba/Alon Pt/Ba/Al22OO33 (2. (2. CycleCycle))

Predicted fractions during the 2nd lean/rich cycle along the channel length and as a function of cycling time

Incomplete regeneration at lower temperatures

Increasing nitrate fraction due to storage reactions

Non-uniform nitrate distribution along the catalyst length

Sharp decrease in the nitrate fraction indicates regeneration

Model enables detailed insight into the barium nitrate distribution for a simple NSC at various temperatures

Frac

tion

Ba(

NO

3) 2

x (m)

t (s)

250°C250°C 350°C350°C 450°C450°C

21 2007-01-1142

SummarySummary and and ConclusionConclusion

Summary:

2d and transient Model of a NOx-Storage Catalyst

Effectiveness Factor Washcoat Model

Realistic Exhaust-gas Composition

Detailed Reaction Mechanism on the Noble Metal

Shrinking Core Model for the Storage of Nitrogen Oxides on Barium

Outlook:

Development and implementation of an Oxygen Storage Model on Ceria

22 2007-01-1142

ForschungsvereinigungForschungsvereinigung VerbrennungskraftmaschinenVerbrennungskraftmaschinen e.Ve.V..(Chairman: Dr. D. (Chairman: Dr. D. ChatterjeeChatterjee, DaimlerChrysler), DaimlerChrysler)

for the financial supportfor the financial support

Delphi CatalystDelphi Catalystfor providing the model catalystfor providing the model catalyst

V. V. SchmeiSchmeißßerer and G. and G. EigenbergerEigenberger, University of Stuttgart, University of Stuttgartfor sharing the experimental resultsfor sharing the experimental results

Thank YouThank YouFor your AttentionFor your Attention

Acknowledgements:Acknowledgements: