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:
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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
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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
14 2007-01-1142
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
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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
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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
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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
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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:
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