Global Chemistry for an Oxidation Catalyst in Oxygen-Deficient

Environments: With Application to LNT+SCR system

Doohyun Kim

GT-SUITE Conference11/7/2011

UNIVERSITY OF MICHIGANCOLLEGE OF ENGINEERINGMECHANICAL ENGINEERING

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Acknowledgements

• Prof. Dennis Assanis – UM

• John Hoard – UM

• Dr. Richard Blint – N2Kinetics

• Rob Middleton, Kyoung Hyun Kwak – UM

• Funding– Michigan Economic Development Company (MEDC)

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Background

• NOx emissions from automobile– Photochemical smog– Acid rain– Respiratory diseases

• Stringent NOx regulation – Light-Duty: 0.07 g/mile (Tier 2)– Heavy-Duty: 0.20 g/bhp-hr (2010)– Much lower than what can be

achieved with in-cylinder combustion control

• NOx control for diesel engine– Challenging due to excess oxygen in

exhaust (8%~12%)– Novel NOx control system required

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LNT + SCR NOx Reduction System• LNT + SCR dual stage NOx reduction

– Lean NOx Trap (LNT) as main NOx reduction device– Downstream Selective Catalytic Reduction (SCR)

takes advantage of NH3 formed in LNT during its regeneration – no urea injection needed

– Requires periodic LNT regeneration by rich exhaust– Applicable to diesel and lean gasoline system

• Oxidation Catalysts in LNT + SCR system– DOC or cDPF– Oxidize CO, HC, NO during lean operation– Provide exotherm to DPF for its active regeneration– Increase NO2/NO ratio for DPF passive regeneration

and for better SCR performance– Operates in rich exhaust during LNT regeneration– NH3 flows through during LNT regeneration

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SCR

cDPF

LNT NH3

DOC: Diesel Oxidation Catalyst

DPF: Diesel Particulate Filter

cDPF: Catalyzed DPF

Novel challenges!!

DOC Modeling• Diesel Oxidation Catalyst (DOC)

– Platinum Group Metal catalysts on monolith wall

– Required in every diesel aftertreatment system for oxidation of CO, HC and NO during lean operation

• Global chemistry in DOC models– Fundamentals: Voltz et al. (1973)

Oh and Cavendish (1982)– Current models: Triana et al. – MTU (2003)

Koltsakis et al. – AUT (2005)Sampara et al. – UM (2007)

– Only covers lean oxidations by oxygen

5

22

222

22

5.0

5.0

NOONOOHCOOHC

COOCO

↔++→+

→+

Rich chemistry needed for LNT+SCR

system

Previous Works – NO reduction• Catalytic reduction of NO

– Most important catalytic converter chemistry in rich exhaust– Fundamentals: Ayen and Peters (1962)

Kobylinski and Taylor (1974)– Early TWC: Montreuil et al. – Ford (1992)

Koltsakis et al. – AUT (1998)

– Recent TWC: Tsinoglou et al. (2002)

– Recent LNT: Depcik et al. – UM (2008)

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22 5.0 NCONOCO +→+

222

22

22

25.0

NCOONCOONCONOCO

NCONOCO

+→++→++→+

222

22

22

5.02

5.0

NOHNOHONCONOCO

NCONOCO

+→++→++→+

Previous Works – NH3 formation• NH3 formation over precious metal catalyst

– Reaction between H2 and NO in rich exhaust

– Kobylinski and Taylor (1974), Abdulhamid et al. (2004), Depcik et al. – UM (2008), Koci et al. – ICT (2009)

• Barium-associated NH3 formation in LNT models– Reaction of stored NOx on Barium with reductants

– Nova et al. (2008), Koci et al. – ICT (2009)

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OHNHNOH 232 2225 +→+

32223 2838)( NHCOBaOOHCONOBa ++→++

32223 258)( NHOHBaOHNOBa ++→+

Model - Chemistry

• NO reduction mechanism implemented with CO, H2 and NH3

• New NO reduction mechanism proposed

– Two-step version of – N2O as an intermediate

• NH3 formation reaction added

• Surface reactions neglected

8

22

2

:22:1

NROONRONRONOR

+→++→+

OHNHNOH 232 2225 +→+

25.0 NRONOR +→+

Model - Chemistry

• Langmuir-Hinshelwood reaction rate form

– 2 kinetic parameters per reaction – G: inhibition by CO, HC, NO

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OHNHNOHRNOHONHR

ONOHNOHRNOHONNHR

ONOHNONHRNCOONCOR

ONCONOCORHCOOHCOR

232

2222

222

2223

223

222

22

222

2225:8:7

2:64332:5

5382:4:3

2:2:1

+→++→++→+

+→++→+

+→++→++↔+

CO-NO reduction

H2-NO reduction

NH3-NO reduction

Water-Gas Shift (WGS)

NH3 formation

G

CCRTEA

r cat

iacti

i

]][[exp 21,

−

=

Gas Flow Reactor Experiment

• UM gas flow reactor - Klinkert et al. (2009)• Synthetic gas blend through catalyst sample• Sample core: 200 CPSI, Pt/Pd=2:1, 15g/ft3

• Steady state experiment– Steady inlet composition, 8% CO2 and H2O for all experiments– Temperature ramp from 100°C ~ 550°C at 5°C/min

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Temperature-Controlled

Oven(catalyst sample)

AnalyzersFTIR

H-SenseO2 analyzer

Gas Bottles(N2, CO, NO, H2, CO2, H2O…)

Mass Flow Controllers

Manifold

GT-SUITE catalyst model

• GlobalReaction object in GT-SUITE 7.0– Without surface chemistry

• Catalyst-out gas concentration and catalyst wall temperature exported to MATLAB environment through Simulink

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GlobalReaction

SimuLink

Kinetic Parameter Determination• UM-built, MATLAB based optimizer utility for kinetic parameter

determination in catalyst modeling (Middleton, 2009)– Coupled with GT-SUITE catalyst model via Simulink– Loads experimental data and creates input text file for GT-SUITE model– Executes GT-SUITE catalyst model – Calculates error between experimental data and simulation results– Several optimization techniques in MATLAB can be chosen– Precise control over the objective function definition (species, weight)

•

• Each pathway fitted separately– Sequence: WGS -> CO-NO -> NH3-NO -> H2-NO

• Each pathway calibrated to 4 different experiment cases• Genetic Algorithm followed by the downhill simplex

– The downhill simplex started from the best point from the GA

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( )( )( )∑ ∑ ∑

−⋅=

iCases jspeciessimi XXwunctionObjectiveF

, ,

2exp

Results – CO-NO Pathway

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4 kinetic parameters

222

22

:32:2

NCOONCORONCONOCOR

+→++→+

]][[)/exp( 2,2

2 NOCOG

RTEAr catact−=

]][[)/exp(

23,3

3 ONCOG

RTEAr catact−=

A2 4.04 x 1010 [mol-K/cm³-sec]

A3 1.12 x 1013 [mol-K/cm³-sec]

Eact,2 85717 [J/mol]

Eact,3 112987 [J/mol]

1000ppm CO1000ppm NO

300ppm CO1000ppm NO

Results – CO-NO Pathway

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• Validity of new mechanism1. Good N2O formation prediction

o By reaction rate difference between R2 and R3

2. NO consumption > CO consumptiono Consumption of NO and CO will

be exactly the same with one reaction mechanism

3. Max NO reduction > available COo 450 ppm vs 300 ppm o With one reaction mechanism,

maximum NO reduction possible equals to available CO.

22 5.0 NCONOCO +→+

2

3

1

222

22

:32:2

NCOONCORONCONOCOR

+→++→+

vs

Results – NH3-NO Pathway

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4 kinetic parameters

2223

223

4332:55382:4

NOHONNHRONOHNONHR

+→++→+

]][[)/exp(

34,4

4 NONHG

RTEAr catact−=

]][[)/exp(

235,5

5 ONNHG

RTEAr catact−=

A4 2.68 x 1017 [mol-K/cm³-sec]

A5 4.09 x 1018 [mol-K/cm³-sec]

Eact,4 179998 [J/mol]

Eact,5 189060 [J/mol]

1000ppm NH3

1000ppm NO

300ppm NH3

300ppm NO

Results – H2-NO pathway

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6 kinetic parameters

OHNHNOHRNOHONHR

ONOHNOHR

232

2222

222

2225:8:7

2:6

+→++→++→+

]][[)/exp(

26,6

6 NOHG

RTEAr catact−=

]][[)/exp(

227,7

7 ONHG

RTEAr catact−=

]][[)/exp(

28,8

8 NOHG

RTEAr catact−=

Calibrated NH3-NO pathway

2223

223

4332:55382:4

NOHONNHRONOHNONHR

+→++→+

1000ppm H2

1000ppm NO

Results – CO-H2-NO case

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• All reactions turned on• Simulation with determined

kinetic parameters• 300ppm CO, 300ppm H2,

1000ppm NO• Model captures experiment

trend

Results – CO-NH3-H2-NO case

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• 500ppm CO, 300ppm H2, 300ppm NH3, 1000ppm NO

• Good agreement with experiment up to 350°C

• CO and NH3 prediction off trend in high temperature

• NH3 wins competition over CO– Due to too fast NH3-NO pathway– Experiments shows NO is more

active with CO than NH3

• Improved results expected when all kinetic parameters are optimized simultaneously

Summary• Global chemistry of oxidation catalyst in rich exhaust tested

– NO reduction mechanism for CO, NH3, and H2 proposed and implemented

– NH3 formation adopted from previous works– Proposed global chemistry calibrated to flow reactor data– Successfully predicts experiment trends for separate pathways– Improvement is expected by additional reactions and by fitting

multiple pathways simultaneously– Applicable not just to DOC or cDPF, but to any other PGM-

loaded automotive catalyst (LNT, TWC) under rich condition

• UM optimization utility for GT-SUITE catalyst model used– GT-SUITE/Simulink coupling– Multiple cases, user-defined objective function– Calibration of multiple kinetic parameters performed

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References• Kinetic Study of Carbon Monoxide and Propylene Oxidation on Platinum Catalysts. Voltz, S.E.; Morgan, C. R.;

Liederman, D; Jacob, S. M. 1973, Ind. Eng. Chem. Prod. Res. Dev., Vol. 12(4), pp. 294-301.• Transient of monolithic catalytic converters: response to step change in feedstream temperature as related

controlling automobile emissions. Oh, S.H. and Cavendish, J.C. s.l. : Ind. Eng. Chem. Prod. Res. Dev., 1982, Vol. 21• Catalytic Reduction of Nitric Oxide. Ayen, R.J. and Peters, M.S. s.l. : Ind. Engng. Chem. Process Des. Dev., 1962,

1(3), pp. 204-207• The Catalytic Chemistry of Nitric Oxide II. Reduction of Nitric Oxide Over Noble Metal Catalysts. Kobylinski, T.P. and

Taylor, B.W. s.l. : J. Catal., 1974, 33, pp. 376-384• Performance of catalyzed particulate filters without upstream oxidation catalyst. Koltakis, G.C., et al. s.l. : SAE

2005-01-0952• An experimental and numerical study of the performance characteristics of the diesel oxidation catalyst in a

continuously regenerating particulate filter. Triana, A.P., et al. s.l. : SAE 2003-01-3176• Global kinetics for platinum diesel oxidation catalyst. Sampara, C.S., et al. s.l. : Ind. Eng. Chem. Res., 2007, Vol. 46• Modeling current generation catalytic converters: laboratory experiments and kinetic parameter optimization –

Steady State Kinetics. Montreuil, C.N. et al. s.l. : SAE 920096.• Three way catalytic converter modeling and applications. Koltsakis, G.C., Kandylas, I.P. and Stamatelos, A.M. s.l. :

Chem.Eng.Commun., 1998, Vol. 164.• Oxygen Storage Modeling in Three-Way Catalytic Converters. Tsinoglou, D.N.; Koltakis, G.C.; Jones, J.C.P., s.l. : Ind.

Eng. Chem. Res. , 2002, Vol. 41.• Influence of the type of reducing agent (H2, CO, C3H6 and C3H8) on the reduction of stored NOx in a Pt/BaO/Al2O3

model catalyst. Abdulhamid, H. et al. s.l. : Topics in Catal. , 2004, 30/31 161-168• A one-dimensional lean NOx trap model with a global kinetic mechanism that includes NH3 and N2O. Depcik, C.;

Assanis, D.N.; Bevan. K., 2008, Int. J Engine Res. Vol. 9(1), pp. 57-77.• Design of a Flow Reactor for Testing Multi-Brick Catalyst Systems Using Rapid Exhaust Gas Composition Switches.

Klinkert, S., et al. 2009. Proceedings of the ASME Internal Combustion Engine Division. Vols. ICEF2009-14016.• Framework for Modeling Automotive Aftertreatment Catalysts using Global Optimization Techniques, Middelton,

R., Masters Thesis, University of Michigan, 2009• Global kinetic model for the regeneration of NOx storage catalyst with CO, H2 and C3H6 in the presence of CO2 and

H2O, Koci et al., Catalysis Today, 147S, 2009• Mechanistic aspects of the reduction of stored NOx over Pt–Ba/Al2O3 lean NOx trap systems, Nova et al., Catalysis

Today, 136, 2008

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Thank you!!Any questions?