Understanding the Distributed Intra-Catalyst Impact of Sulfation on Water Gas Shift

in a Lean NOx Trap Catalyst

Bill Partridge1, Jae-Soon Choi1, Josh Pihl1, Todd Toops1, Jim Parks1, Nathan Ottinger2, Alex Yezerets2 , Neal Currier2

1: Oak Ridge National Laboratory2: Cummins Inc

DEER 2010 ConferenceEmissions Control TechnologiesMarriott Renaissance CenterSeptember 28, 2010Detroit, Michigan

U.S. DOE Program Management Team:Ken Howden, Gurpreet Singh, Steve Goguen

2

• Background & Motivation

• Experimental Approach

• Sulfation Results NSR: NOx Storage & Reduction OSC: Oxygen Storage Capacity WGS: Water Gas Shift

• Global Conceptual Model

• Conclusions

Outline

3

Background

H2

HC

NOO2

NO2NO2

O2NO CO2 Substrate

Washcoat

Pt

KNO2,3

K2CO3

Substrate

Washcoat

Pt

KNO2,3

K2CO3NO2HC,CO,H2

NO2HC,CO,H2 H2O

N2CO

Storage

RegenerationH2

HC

NOO2

NO2NO2

O2NO CO2 Substrate

Washcoat

Pt

KNO2,3

K2CO3

Substrate

Washcoat

Pt

KNO2,3

K2CO3NO2HC,CO,H2

NO2HC,CO,H2 H2O

N2CO

Storage

Regeneration

• LNT catalysts are sensitive to sulfur poisoning• Sulfates more stable than nitrates: SO2 + 1/2O2 + Pt + BaO ----> Pt + BaSO4

2NO + 3/2O2 + Pt + BaSO4 ----> Ba(NO3)2 + Pt + SO3

Sulfation changes reaction distributions

• High-temperature DeS can damage catalyst Irreversible thermal aging: e.g., Pt sintering Fuel penalty cost of process

Choi, et al., Appl. Catal. B 77 (2007) 145.

• LNTs (e.g., Pt/Ba/Al2O3) operate in cyclic mode LEAN-phase storage:2NO + 3/2O2 + Pt + BaO ----> Pt + Ba(NO3)2

RICH-phase reduction:5H2 + Pt + Ba(NO3)2 ----> N2 + 5H2O + Pt + BaO Internal spatial & temporal variations

●

4

Motivation• Need to minimize high-T DeS events

Basic control commands DeS too often and too long

• WGS enables advanced control Cummins OBD Patent (US Patent App. 20080168824) Active on-board assessment of catalyst state Only DeS when & for as long as required

Better efficiency (lower fuel penalty) Better durability (catalyst & engine last longer)

Intake Air

TurboExhaust LNT

Catalyst

Parks, Swartz, Huff, West. ORNL. DEER 2006, August 20-24, 2006, Detroit, MI

UEGO Sensors

LNT WGS α Ageing

UEGO Signal α WGS

UEGO has unique H2 cross sensitivity

0.94

0.95

0.96

0.97

0.98

0.99

1

1.01

1.02

1.03

0.97 0.98 0.99 1 1.01 1.02 1.03SCAT LAMBDA

LAM

BDA

SENS

OR

O2 (0.96)

CO (0.76)

NO (1.34)

C3H6 (0.51)

H2 (3.02)

(Gradient)

O2, CO, NO, C3H6

H2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2

95000 100000 105000 110000 115000 120000 125000 130000

Time / ms

Sens

or V

olta

ge /

V

InletOutlet

LEAN

RICH

STOIC

LNT In

LNT Out

α WGS

H2

COTHC

●

5

• Background & Motivation

• Experimental Approach

• Sulfation Results NSR: NOx Storage & Reduction OSC: Oxygen Storage Capacity WGS: Water Gas Shift

• Global Conceptual Model

• Conclusions

Outline

6

Approach: Controlled Bench Reactor Experiments with Spatially & Temporally Resolved Gas Analyses

Model LNT Catalyst

● Substrate: 300-cpsi cordierite

● Washcoat: Pt/Ba/Al2O3

● No Oxygen-Storage Capacity

(OSC) such as Ce

● Evaluated as a 3/4” x 3” core

Procedure● Baseline: 0 g/L S

● Performance evaluationNeutral; OSC; NSR

● 1st S dosing: 0.85 g/L S

● Performance evaluationNeutral; OSC; NSR

● 2nd S dosing: <1.7 g/L S

● Performance evaluationNeutral; OSC; NSR

● Post mortem analysisDRIFTSMicro Reactor

In Situ Intra-Channel Speciation

SpaciMS

0 76L (mm)Cat-In

SamplingCapillary

Cat-Out

Gas Flow

7

WGS converts CO to H2 via: CO + H2O → H2 + CO2

Lean-phase composition dictates CO reaction possibilities NSR: WGSR vs. OSC vs. LNT regeneration OSC: WGSR vs. OSC Neutral: WGSR only

Fast Cycling (60:5-s lean:rich cycling) Temperature: 325°C

Systematically Vary WGS Competition for CO Reductant

RICH (5s) LEAN (60s)

CO H2O NO O2 H2O

NSR 2% 5% 300ppm 10% 5%

OSC 2% 5% 0 10% 5%

Neutral 2% 5% 0 0 5%

8

• Background & Motivation

• Experimental Approach

• Sulfation Results NSR: NOx Storage & Reduction OSC: Oxygen Storage Capacity WGS: Water Gas Shift

• Global Conceptual Model

• Conclusions

Outline

9

Baseline (0 gS / Lcat): NSR in front ½

Back ½ unused

1st Sulfation (0.85 gS / Lcat): Front ¼ inactive

NSR in back ¾

2nd Sulfation (<1.7 gS / Lcat): Front ½ inactive

NSR in back 1/2

Sulfation Progressively Poisons NSR in Plug-Like Fashion

0

20

40

60

80

100

0.00 0.25 0.50 0.75 1.00

Relative Axial Catalyst Location (\)

% N

Ox

Trap

ped

Baseline0.85 gS / L< 1.7 gS / L

NSR CyclingNOx Storage

10

• Background & Motivation

• Experimental Approach

• Sulfation Results NSR: NOx Storage & Reduction OSC: Oxygen Storage Capacity WGS: Water Gas Shift

• Global Conceptual Model

• Conclusions

Outline

11

0.00

0.25

0.50

0.75

1.00

0.00 0.25 0.50 0.75 1.00Relative Axial Catalyst Location (\)

CO

2 fro

m O

SC (%

)

Baseline0.85 gS / L< 1.7 gS / L

OSC due to Pt redox No Ce or support OSC

~ active Pt area

OSC ~ uniform along catalyst i.e., uniform Pt distribution

Minor sulfation impact on OSC ~3-17% loss max minor OSC on Ba?

OSC active in sulfated zone Pt remains S free cf. poisoned NSR!

Can change input to NSR zone

Sulfation Has Little Impact on “OSC”

OSC Cycling

“OSC”: Pt Area

~17% Loss max

gS/Lcat 1st Q. 2nd Q. 3rd Q. 4th Q.

0 NSR unused

0.85 Inactive degraded

<1.7

Qualitative Pictorial Representation of NSR Activity

●

12

• Background & Motivation

• Experimental Approach

• Sulfation Results NSR: NOx Storage & Reduction OSC: Oxygen Storage Capacity WGS: Water Gas Shift

• Global Conceptual Model

• Conclusions

Outline

13

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.00 0.25 0.50 0.75 1.00

Relative Axial Catalyst Location (\)

H2 C

once

ntra

tion

(%)

Baseline

0.85 gS / L

< 1.7 gS / L

Baseline (0 gS / Lcat): WGS throughout

1st Sulfation (0.85 gS / Lcat): Front ½ : “Max” degradation

~90-95% loss from Baseline

WGS in back ½

2nd Sulfation (<1.7 gS / Lcat): Front 3/4 : “Max” degradation

WGS in back ¼

WGS S-front leads NSR S-front by ~ ¼ catalyst

WGS inactive upstream of NSR

WGS more sensitive to S than NSR

WGS Very Sensitive to Sulfur Degradation

Neutral Cycling

WGS

~95% Loss

0

20

40

60

80

100

0.00 0.25 0.50 0.75 1.00

Relative Axial Catalyst Location (\)

% N

Ox

Trap

ped

Baseline0.85 gS / L< 1.7 gS / L

NSR CyclingNOx Storage

●

14

• Background & Motivation

• Experimental Approach

• Sulfation Results NSR: NOx Storage & Reduction OSC: Oxygen Storage Capacity WGS: Water Gas Shift

• Global Conceptual Model

• Conclusions

Outline

15

Global Model of Distributed S Impact on NSR, WGS & OSC

• Fully active in S-free zone

• Initial Sulfation:• WGS very sensitive to S - probably due

to changes in Pt-support interface structure

• NSR insensitive due to spillover, surface diffusion and NO2,gas accessing S-free Ba in field

• Progressive Sulfation:• Further incremental WGS degradation

to max • Progressive NSR degradation as field

Ba is sulfated• Ultimate NSR poisoning• Minor OSC degradation

Sulfated Ba Pt S-Free Ba

Poisoned Degraded Active

Progressively Degraded Active

Active

Maximum Degradation

Progressively Degraded

Sulfated Ba Pt S-Free Ba

Poisoned Degraded Active

Progressively Degraded Active

Active

Maximum Degradation

Sulfated Ba Pt S-Free BaSulfated Ba Pt S-Free Ba

Poisoned Degraded Active

Progressively Degraded Active

Active

Maximum Degradation

Progressively Degraded

16

• Background & Motivation

• Experimental Approach

• Sulfation Results NSR: NOx Storage & Reduction OSC: Oxygen Storage Capacity WGS: Water Gas Shift

• Global Conceptual Model

• Conclusions

Outline

17

Conclusions

• WGS occurs on Ba LNT catalysts (not just Ce-containing catalysts)

• Each LNT function has a different response to sulfation− WGS: very sensitive to initial S− NSR: Progressively degraded and poisoned− OSC: Minor degradation

• The S distribution is different w.r.t. each LNT function

• Conceptual model of distributed S impact on different LNT functions

• So what:– Improved understanding of LNT sulfation– Enable better models and catalyst system design (device size/capacity)– Enable improved OBD & control (cf. Cummins Control Patent)– Better emissions control, efficiency & durability

18

Acknowledgments

Sponsor:U.S. DOE Office of Vehicle Technologies,Ken Howden, Gurpreet Singh, Steve Goguen

Thank YouBill Partridge865-946-1234

partridgewp@ornl.gov

19

How doesSulfur

Degrade WGS?

20

Oxygen Mitigates Sulfur Degradation of WGS

OSC enhances WGS in Sulfated states

~5-10% gain vs. Neutral

Little recovery vs. ~95% loss w/ Sulfation

O2 readily displaces S from Pt

Sgas adsorbs on Pt during rich Based on DRIFTS measurements

Fridell et al., Topics in Catal. V16/17, 133, 2001

Pt is S free in OSC fast-cycling conditions

O2 improves WGS by desorbing S from Pt

S adsorption on Pt has minor impact on WGS degradation

Other non-Pt-S route accounts for primary WGS S-degradation

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.00 0.25 0.50 0.75 1.00Relative Axial Catalyst Location (\)

H2 C

once

ntra

tion

(%)

0.85 gS / L, OSC

0.85 gS / L, Neutral

<1.7 gS / L, OSC

<1.7 gS / L, Neutral

WGS

OSC & Neutral Cycling

●

21

Does S Degrade WGS by Changing Pt Electronic Structure?

S doesn’t change Pt-CO affinity cf. flat CO peak position

Pt electronic density ~ constant

Pt sites are available cf. flat CO peak area

consistent w/ other observations showing that Pt is available

0

2

4

6

8

10

1.000.750.600.35Relative S

CO

Pea

k A

rea

(a.u

.)

2050

2060

2070

2080

2090

2100

CO

Pea

k Po

sitio

n (c

m-1

)

AreaPosition

CO DRIFTS @ 325C

Maybe initial S is detrimental to Pt-support\Ba interface Not yet verified for Pt\Ba\Al2O3 catalyst

But,…Pt\Ce extensively studied for WGS & Reverse WGS

&…common theme is importance of metal-support interface & activation on Pt

●

22

S May Concentrate or Minute S is Detrimental to Interface Structure Necessary for WGSR

Nonlinear S impact on WGS Small initial S dose has major impact on WGS (Fresh vs. 4th Q) 4th Q has significant NOx capacity

S has significant but limited impact i.e., non-zero asymptote0%

5%

10%

15%

20%

Fresh 4th Q, S

3rd Q, S

2nd Q, S

1st Q, SCO2

(% of feed)Catalyst Section & S State

WGSR Activity, 300 C

Increasing S

Sakamoto et al., J of Catal. 238, 361, 2006

Surface N Surface S

Different N & S deposition N goes through Pt N concentrated around Pt

S goes down everywhere

Lean will oxidize S on Pt Likely deposited close to Pt

May concentrated S around Pt

Goguet Model of WGS Carbon Poisoning

(Goguet et al., J. Phys. Chem. B 108, 20240, 2004)

Advancing Carbon Front

Pt“Ring of Active Area”

C-Island Radius

Curve shape uncertain

Non

-Ze

ro

Lim

it

0

WG

S Ac

tivity

C forms at Pt

C island grows around Pt

Proximal C impacts WGS

No impact of distal C

Looks like S impact

We don’t yet know……Further fundamental research needed●

23

0

20

40

60

80

100

0.00 0.25 0.50 0.75 1.00

Relative Axial Catalyst Location (\)

% N

Ox

Trap

ped

Baseline0.85 gS / L< 1.7 gS / L

Baseline (0 gS / Lcat): NSR in front ½

Back ½ unused

1st Sulfation (0.85 gS / Lcat): Front ¼ inactive

NSR in back ¾

Broadened NSR zone

(not perfectly “plug like”)

2nd Sulfation (>1.7 gS / Lcat): Front ½ inactive

NSR in back 1/2

Sulfation Progressively Poisons NSR in Plug-Like Fashion

gS/Lcat 1st Q. 2nd Q. 3rd Q. 4th Q.

0 NSR unused

0.85 Inactive degraded Degraded???

<1.7

NSR Cycling; 0, 0.85 & <1.7 g-S / LcatNOx Storage

Qualitative Pictorial Representation of NSR Activity

24

0.00

0.25

0.50

0.75

1.00

0.00 0.25 0.50 0.75 1.00Relative Axial Catalyst Location (\)

CO

2 fro

m O

SC (%

)

Baseline0.85 gS / L< 1.7 gS / L

OSC due to Pt redox No Ce or support OSC

~ active Pt area

OSC ~ uniform along catalyst i.e., uniform Pt distribution

Minor sulfation impact on OSC ~3-17% loss max minor OSC on Ba?

OSC active in sulfated zone Pt remains S free cf. poisoned NSR!

Sulfation Has Little Impact on “OSC”

OSC Cycling

“OSC”: Pt Area

~17% Loss max

25

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.00 0.25 0.50 0.75 1.00

Relative Axial Catalyst Location (\)

H2 C

once

ntra

tion

(%)

Baseline

0.85 gS / L

< 1.7 gS / L

Baseline (0 gS / Lcat): WGS throughout

1st Sulfation (0.85 gS / Lcat): Front ½ : “Max” degradation

~90-95% loss from Baseline

WGS in back ½

2nd Sulfation (<1.7 gS / Lcat): Front 3/4 : “Max” degradation

WGS in back ¼

WGS S-front leads NSR S-front By ~ ¼ catalyst

WGS & NSR S degradation differs

WGS more sensitive to S than NSR

WGS Very Sensitive to Sulfur Degradation

Neutral Cycling

WGS

~95% Loss

0

20

40

60

80

100

0.00 0.25 0.50 0.75 1.00

Relative Axial Catalyst Location (\)

% N

Ox

Trap

ped

Baseline0.85 gS / L< 1.7 gS / L

NSR CyclingNOx Storage

●