intra-catalyst reductant chemistry in lean nox traps: a ...intra-catalyst reductant chemistry in...

Intra-catalyst Reductant Chemistry in Lean NOx Traps:A Study on Sulfur Effects

Jim Parks ([email protected]), Matt Swartz, Shean Huff, Brian WestOak Ridge National LaboratoryFuels, Engines, Emissions Research Center

DEER 2006August 20-24, 2006Detroit, MI

Sponsor: U.S. Department of Energy, OFCVTProgram Managers: Ken Howden, Gurpreet Singh, Kevin Stork

8/17/2006

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

Study Focus Area: Sulfur Effects on Reductant Utilization by Lean NOx Trap Catalysts

• Lean NOx Trap (LNT) catalysts are effective at reducing NOx fromdiesel engines but need…− Periodic “regeneration” (rich exhaust) with suitable reductants− Durability against negative sulfur effects

Sulfur degrades performance over time by poisoning NOx sitesdeSulfation (high temperature clean up) recovers lost site activity

• ORNL has studied regeneration chemistry on a light-duty diesel engine platform with in-cylinder combustion techniques− Intra-catalyst sampling has been applied to characterize reductant

utilization [SAE 2006-01-1416, SAE 2005-01-3876, SAE 2004-01-3023]

• Study presented here focuses on the effects of sulfur on intra-catalyst chemistry during in-cylinder regeneration


Two engine control strategies for achieving intermittent rich combustion for regeneration of LNT

main

pilot

“Delayed andExtended Main”

(DEM)

main

pilot

“Post 80 Injection”(P80)

post

Two LNT Regeneration Strategies Chosen Based on Difference in Chemistry• Delayed and Extended Main (DEM):

− Throttle for reduced air flow− Extra fuel injected near main injection timing to achieve rich conditions

• Post 80 Injection (P80):− Throttle for reduced air flow− Extra fuel injected after main injection later in cycle to achieve rich conditions


0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Spec

ies

Con

cent

ratio

n (%

)

0

5

10

15

20

25 Inlet Airflow

(g/s)CO

HC

H2

Airflow

CO

H2

Airflow

DEMHC

0 5 10 15 20 25 30

Time (sec)

Two engine control strategies for achieving intermittent rich combustion for regeneration of LNT

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0 5 10 15 20 25 30

Time (sec)

Spec

ies

Con

cent

ratio

n(%

)

15

10

5

0

5

10

15

20

25

Inlet Airflow

(g/s)

CO

HC

H2

Airflow

CO

H2

Airflow

P80HC

• Delayed and Extended Main (DEM):

− High H2 and CO− Low HC− High PM

• Post 80 Injection (P80):− Moderate CO and H2

− High HC− Low PM

0102030405060708090

DEM P80

Reg

ener

atio

n R

educ

tant

(mm

ols/

rege

n)

and

Sm

oke

(a.u

.) H2

CO

HC

Smoke


Experimental setup allows full exhaust species characterization throughout the catalyst system• DOC upstream of LNT catalyst• UEGO2 sensor is feedback point for A/F

control• Exhaust samples obtained at ¼, ½, and ¾

intra catalyst locations in LNT• Analysis for: H2, CO, HC, NOx, CO2, O2

Engine DOC LNT

Engine OutBench(SS1)

UEGO1 UEGO2 UEGO3

SS2

NOxSensor #1

NOxSensor #2

Turbo

1/4 LNT

1/2 LNT

3/4 LNT

FTIRGC/MS bag

(dilute)

Air

Bench 2

SpaciMS

TailpipeBench(SS3)


Exhaust Speciation: DEM Strategy, 60s Cycle (DEM, 60s)

0

100

200

300

400

500

NO

x (p

pm)

Engine OutLNT Out

10

15

20

25

30

35

A/F

UEGO Sensor

0102030405060

Opa

city

(%) Celesco

0

1

2

3

4

5

0 60 120 180 240 300

Time (sec)

Red

ucta

nts

(%)

Engine Out COEngine Out H2Engine Out HC

DEM, 60s

•NOx Reduction Efficiency(NRE)=96.9%

•Mean LNT Temp=329ºC•Minimum A/F=13.5

•60 second Cycle:•57 seconds Lean•3 seconds Rich


Strategy and Cycle Time Combinations in Study Engine OutLNT Out

0

100

200

300

400

500

0 60 120 180

Time (sec)

NO

x (p

pm)

DEM, 60s

0

100

200

300

400

500

0 60 120 180

Time (sec)

NO

x (p

pm)

DEM, 20s

NRE=96.9%LNT Temp=329ºCPM(relative)=0.46


0

100

200

300

400

500

0 60 120 180

Time (sec)

NO

x (p

pm)

0

100

200

300

400

500

0 60 120 180

Time (sec)

NO

x (p

pm)


NRE=99.3%LNT Temp=434ºCPM(relative)=0.09P80, 60s P80, 20s


Catalyst chemistry characterized under sulfated and desulfated conditionsSulfation procedure• Degreened in air• BP15 fuel • 1% bottled SO2 at 3.4slpm• Three loading states (fuel S +

bottled S)− 3.06g S ≈ 2888 miles− 5.63g S ≈ 5319 miles− 9.63g S ≈ 9087 miles

• Full characterization done at each loading state

Desulfation procedure• Engine based desulfation

− Target 700°C / 14AFR− Fixed boost to 0kPa− Use RPM to control airflow− Control catalyst inlet AFR using in-

pipe injection• 20 minute desulfation event

Fuel loadingFuel Flowrate 0.6 g/sFuel Economy (assumed) 45 mi/galBP 15 Sulfur Content 0.0015%Fuel Density 0.143 gal/lb Miles per gram S 944 mi/ggrams S /min 0.00054 g/min

Bottle loadingMolecular Weight of S 32.06 g/mol S1% SO2 flowrate 3.4 slpmSO2 concentration 1.00%S flowrate 0.0486 g/min

state 1 state 2 state 31% SO2 Injected (min) 28 45 60Injected S (g) 1.35 2.18 2.92Cumulative Engine S (hrs) 52.8 64.9 98.0Cumulative Engine S (g) 1.71 2.10 3.18Running Total S (g) 3.06 5.63 9.63Equivalent miles 2888 5319 9087


Catalyst chemistry characterized under sulfated and desulfated conditionsSulfation procedure• Degreened in air• BP15 fuel • 1% bottled SO2 at 3.4slpm• Three loading states (fuel S +

bottled S)− 3.06g S ≈ 2888 miles− 5.63g S ≈ 5319 miles− 9.63g S ≈ 9087 miles

• Full characterization done at each loading state

Desulfation procedure• Engine based desulfation

− Target 700°C / 14AFR− Fixed boost to 0kPa− Use RPM to control airflow− Control catalyst inlet AFR using in-

pipe injection• 20 minute desulfation event

Engine Intake

exhaust manifold cooler

Hi-FlowEEGRvalve

DOC LNT

air

fuel

waste gate

intercooler

turbo

UEGO

thermocouples

UEGO UEGO

throttle

Engine Intake

exhaust manifold cooler

Hi-FlowEEGRvalve

DOC LNT

air

fuel

waste gate

intercooler

turbo

UEGO

thermocouples

UEGO UEGO

throttle


S/deS Effect on Strategy Performance

• P80 strategies (Higher in HCs, Lower H2/CO) appear to degrade more with S/deS; Why???

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Fresh

2900

Mile

s53

00 M

iles

9100

Mile

sde

Sulfate

d

Aged

NR

E

DEM, 20sP80, 20sDEM, 60sP80, 60s


Small downstream shift in reductant utilization with S exposure

0.00

0.01

0.02

0.03

0.04

0.05

EO

EO

AI

AI

LNT 1/4

LNT 1/2

LNT 3/4

TP TP

H2

and

CO

(mol

es d

urin

g re

gen)

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

HC

(mol

es d

urin

g re

gen)

H2COTHC

P80, 60s, Fresh

FRESH

P80, 60s



0.00

0.01

0.02

0.03

0.04

0.05

EO

EO

AI

AI

LNT 1/4

LNT 1/2

LNT 3/4

TP TP

H2

and

CO

(mol

es d

urin

g re

gen)

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

HC

(mol

es d

urin

g re

gen)

H2COTHC

P80, 60s, Fresh

0.00

0.01

0.02

0.03

0.04

0.05

EO

EO

AI

AI

LNT 1/4

LNT 1/2

LNT 3/4

TP TP

H2

and

CO

(mol

es d

urin

g re

gen)

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

HC

(mol

es d

urin

g re

gen)

H2COTHC

P80, 60s, Mild

2900 Miles

P80, 60s



0.00

0.01

0.02

0.03

0.04

0.05

EO

EO

AI

AI

LNT 1/4

LNT 1/2

LNT 3/4

TP TP

H2

and

CO

(mol

es d

urin

g re

gen)

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

HC

(mol

es d

urin

g re

gen)

H2COTHC

P80, 60s, Fresh

0.00

0.01

0.02

0.03

0.04

0.05

EO

EO

AI

AI

LNT 1/4

LNT 1/2

LNT 3/4

TP TP

H2

and

CO

(mol

es d

urin

g re

gen)

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

HC

(mol

es d

urin

g re

gen)

H2COTHC

P80, 60s, Mild

0.00

0.01

0.02

0.03

0.04

0.05

EO

EO

AI

AI

LNT 1/4

LNT 1/2

LNT 3/4

TP TP

H2

and

CO

(mol

es d

urin

g re

gen)

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

HC

(mol

es d

urin

g re

gen)

H2COTHC

P80, 60s, Mild

5300 Miles

P80, 60s



0.00

0.01

0.02

0.03

0.04

0.05

EO

EO

AI

AI

LNT 1/4

LNT 1/2

LNT 3/4

TP TP

H2

and

CO

(mol

es d

urin

g re

gen)

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

HC

(mol

es d

urin

g re

gen)

H2COTHC

P80, 60s, Fresh

0.00

0.01

0.02

0.03

0.04

0.05

EO

EO

AI

AI

LNT 1/4

LNT 1/2

LNT 3/4

TP TP

H2

and

CO

(mol

es d

urin

g re

gen)

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

HC

(mol

es d

urin

g re

gen)

H2COTHC

P80, 60s, Mild

0.00

0.01

0.02

0.03

0.04

0.05

EO

EO

AI

AI

LNT 1/4

LNT 1/2

LNT 3/4

TP TP

H2

and

CO

(mol

es d

urin

g re

gen)

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

HC

(mol

es d

urin

g re

gen)

H2COTHC

P80, 60s, Mild

0.00

0.01

0.02

0.03

0.04

0.05

EO

EO

AI

AI

LNT 1/4

LNT 1/2

LNT 3/4

TP TP

H2

and

CO

(mol

es d

urin

g re

gen)

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

HC

(mol

es d

urin

g re

gen)

H2COTHC

P80, 60s, 9100mile

9100 Miles

P80, 60s



deSulfated

0.00

0.01

0.02

0.03

0.04

0.05

EO

EO

AI

AI

LNT 1/4

LNT 1/2

LNT 3/4

TP TP

H2

and

CO

(mol

es d

urin

g re

gen)

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

HC

(mol

es d

urin

g re

gen)

H2COTHC

P80, 60s, Fresh

0.00

0.01

0.02

0.03

0.04

0.05

EO

EO

AI

AI

LNT 1/4

LNT 1/2

LNT 3/4

TP TP

H2

and

CO

(mol

es d

urin

g re

gen)

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

HC

(mol

es d

urin

g re

gen)

H2COTHC

P80, 60s, Mild

0.00

0.01

0.02

0.03

0.04

0.05

EO

EO

AI

AI

LNT 1/4

LNT 1/2

LNT 3/4

TP TP

H2

and

CO

(mol

es d

urin

g re

gen)

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

HC

(mol

es d

urin

g re

gen)

H2COTHC

P80, 60s, Mild

0.00

0.01

0.02

0.03

0.04

0.05

EO

EO

AI

AI

LNT 1/4

LNT 1/2

LNT 3/4

TP TP

H2

and

CO

(mol

es d

urin

g re

gen)

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

HC

(mol

es d

urin

g re

gen)

H2COTHC

P80, 60s, deS

0.00

0.01

0.02

0.03

0.04

0.05

EO

EO

AI

AI

LNT 1/4

LNT 1/2

LNT 3/4

TP TP

H2

and

CO

(mol

es d

urin

g re

gen)

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

HC

(mol

es d

urin

g re

gen)

H2COTHC

P80, 60s, 9100mile

P80, 60s

H2COTHC


Significant changes observed in N2 selectivity with S/deS

0.0

0.2

0.4

0.6

0.8

1.0

1.2

EO

EO

AI

AI

LNT 1/4

LNT 1/2

LNT 3/4

TP TP

NO

x (g

) [C

ycle

Ave

rage

]

0

5

10

15

20

25

30

NH

3 (p

pm)

NOx (g)NH3 (ppm)

P80, 60s, Fresh

Note: NH3 and NOx not in same units. EO NOx ~ 500ppm

FRESH

P80, 60s


0.0

0.2

0.4

0.6

0.8

1.0

1.2

EO

EO

AI

AI

LNT 1/4

LNT 1/2

LNT 3/4

TP TP

NO

x (g

) [C

ycle

Ave

rage

]

0

5

10

15

20

25

30

NH

3 (p

pm)

NOx (g)NH3 (ppm)

P80, 60s, Mild


2900 Miles

P80, 60s Note: NH3 and NOx not in same units. EO NOx ~ 500ppm



9100 Miles


0.0

0.2

0.4

0.6

0.8

1.0

1.2

EO

EO

AI

AI

LNT 1/4

LNT 1/2

LNT 3/4

TP TP

NO

x (g

) [C

ycle

Ave

rage

]

0

5

10

15

20

25

30

NH

3 (p

pm)

NOx (g)NH3 (ppm)



deSulfated


0.0

0.2

0.4

0.6

0.8

1.0

1.2

EO

EO

AI

AI

LNT 1/4

LNT 1/2

LNT 3/4

TP TP

NO

x (g

) [C

ycle

Ave

rage

]

0

5

10

15

20

25

30

NH

3 (p

pm)

NOx (g)NH3 (ppm)

P80, 60s, deS

Note: NH3 and NOx not in same units. EO NOx ~ 500ppm


NH3 formation increases after deSulfation

DEM, 20s Cycle

0

50

100

150

200

250

300Ta

ilpip

e N

H3

P80, 20s Cycle

0

50

100

150

200

250

300

Tailp

ipe

NH

3

DEM, 60s Cycle

0

50

100

150

200

250

300

Tailp

ipe

NH

3

P80, 60s Cycle

0

50

100

150

200

250

300

Tailp

ipe

NH

3

Fresh 2900miles

9100miles

deSulfated

Fresh 2900miles

9100miles

deSulfated

Fresh 2900miles

9100miles

deSulfated

Fresh 2900miles

9100miles

deSulfated

• NH3 formation after deSulfation was higher for all cases

Potential causes:• Sintering of Sorbate

− suspect thermal sintering of sorbate may be the cause of higher NH3

− Castoldi et. al. Report NH3 formation corresponds with higher sorbate loading (bulk crystallites)

L. Castoldi, I. Nova, L. Lietti, P. Forzatti, “Catalysis Today” 96 (2004), pp. 43-52

• Change in Reductant:NOx ratio− CLEERS, Pihl, and other work on N2

selectivity show NH3 increases with increasing Reductant:NOx ratio

Pihl, et.al. SAE 2006-01-3441


H2 Produced In Catalyst During 20s Cycles

• In 20s cycles, H2 observed being created in catalyst most likely from reforming reactions (water-gas shift, etc.)

• Same process may occur in 60s data, but H2 may be consumed immediately for NOx reduction

0.00

0.01

0.02

0.03

0.04

0.05

EO EO AI AI LNT 1/4

LNT 1/2

LNT 3/4

TP TP

H2

and

CO

(mol

es d

urin

g re

gen)

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

HC

(mol

es d

urin

g re

gen)

H2COTHC

P80, 60s, Fresh

P80, 20s Cycle

0.00

0.01

0.02

0.03

0.04

0.05

EO EO AI AI LNT 1/4

LNT 1/2

LNT 3/4

TP TP

H2

and

CO

(mol

es d

urin

g re

gen)

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

HC

(mol

es d

urin

g re

gen)

H2COTHC

P80, 60s, Fresh

P80, 60s Cycle


Catalytic H2 production: Effect of S/deS

• Increase in catalytic-produced H2 greater for P80 strategy

• H2 production degrades with S/deS aging

• LNT performance may degrade more rapidly for strategies that depend on catalyst utilizing HCs from engine

0.000

0.005

0.010

0.015

0.020

0.025

Fresh

2900

mile

s

5300

mile

s

9100

mile

s

deSulf

ated

Aged

Exc

ess

H2

from

inte

rnal

WG

S o

n LN

T(T

ailp

ipe

H2

- min

imum

H2

in L

NT)

DEM, 20s

P80, 20s

DEM, 60s

P80, 60s


Summary

• In general, reductant utilization in LNT moved downstream only slightly with S/deS− Process is consistent; optimism for modeling

• NH3 formation increased after deSulfation process− Regeneration control strategies must adjust accordingly with age

• Strategies with high HC and low H2/CO (P80) may depend on catalytic H2/CO production for regeneration− S/deS degradation of catalytic H2/CO production may have greater

degradation impact on the effectiveness of P80-like strategies

• Preparing Paper for SAE Fall Powertrain and Fluids Conference

intra-catalyst reductant chemistry in lean nox traps: a ...intra-catalyst reductant chemistry in...

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