2010 DEER Conference

Pt-free, Perovskite-based Lean NOx Trap Catalysts

Gongshin Qi, Chang H. Kim, and Wei Li

GM Global Research & Development

2010 DEER Conference

Overview

LNT Chemistry

NO Oxidation on Perovskite Catalysts

PGM-free LNT Catalysts

Pt-free LNT Catalysts

2010 DEER Conference

Lean NOx Trap (LNT) Chemistry

NO + O2 NO2 (Pt site)

NO2 + BaO Ba(NO3)2 (Ba site)

NOx + H2 N2 + H2O (Pt site)

NOx + CO N2 + H2O (Pt site)

Lean Rich

NOx stored as nitrate/nitrite NOx released & reduced

RegenerationStorage

Critical step

Goal: Reduce Pt usage and total PGM cost

2010 DEER Conference

Perovskite Oxides Catalysts

PerovskiteGeneral formula: ABO3

A: Rare earth metal (i.e. La)B: Transition metal (i.e. Co, Mn, and Fe)Promoters: Sr, Ba, and Ce promote catalytic properties

Benefits• Low cost & easy synthesis

• Excellent thermal stability

Issues• Low surface area

• Susceptible to sulfur poisoning

Perovskite As Automotive Catalysts

• Three way catalysts for gasoline application - HC, CO oxidations- NO/CO reactions

• “Intelligent” catalysts (TWC)- Pd self-regeneration- Limited cost reduction

2010 DEER Conference

00.10.20.30.40.50.60.70.80.9

1

150 200 250 300 350 400 450

NO

to N

O2

Con

vers

ion

Temperature (°C)

NO Oxidation and NOx Storage

La0.9Sr0.1CoO3

Pt-basedCatalyst

500 ppm NO, 10% O2, GHSV: 30,000 h-1

Perovskite

0

50

100

150

200

250

150 200 250 300 350 400 450 500 550 600

Con

cent

ratio

n (p

pm)

Temperature (oC)

NONO2NOx

NO Inlet concentration

NOx = NO+NO2

Perovskite catalysts are active for NO oxidation to NO2

Perovskite based LNT shows good NOxstorage capacity in lean condition

NOx adsorption capacity: 0.75 g/L

[NO] = 200 ppm, [CO2] = [H2O] = [O2] =10%, SV=50,000 h-1, ramp rate = 10 C/min, catalyst degreened at 700 oC for 2.5 hrs

AbsorptionDesorption

2010 DEER Conference

-20

80

180

280

380

480

580

680

780

2000 2050 2100 2150 2200

Con

cent

ratio

n (p

pm)

Time (s)

NH3

NO

Perovskite Based LNT Regeneration

Conditions: [CO2] = [H2O] =10%, 200 ppm NO, SV=50,000 h-1; Lean/Rich = 60s/5s; Lean 10% O2; Rich 3%CO+1%H2

300oC

Stored NOx can not convert to N2 or NH3 in rich condition on perovskite based LNT without PGM

Perovskite based LNT containing Pd/Rh looks promising

NO

Perovskite

NOx + H2/CO N2/NH3

PerovskiteX

N2 not monitored

-20

380

780

1180

1580

1980

750 800 850 900 950

Con

cent

ratio

n (p

pm)

Time (S)

NH3

300oC

NO

NOx + H2/CO N2/NH3

Pd/Rh

√

w/o PGM

w/ Pd/Rh

2010 DEER Conference

Conditions: lean-rich cycles (60s/5s) with 2 ppm SO2; 200 ppm NO, [CO2] = [H2O] =10%, SV=50,000 h-1; Lean 10% O2; Rich 3%CO+1%H2

Sulfur Poisoning and Desulfation

20

40

60

80

100

0 1 2 3 4 5 6 7 8 9

NO

con

vers

ion

(%)

Time (hour)

After loading 1 g/L sulfur

After Desulfation at 700oCunder rich conditions, NOx conversion drops from 80% to 70%

La0.9Sr0.1CoO3 -based LNT can not recover activities after desulfation

300oC

NO conversions as a function of sulfur loadingCommercial Pt based LNT

2010 DEER Conference

TPR/XRD of PerovskitesXRD patterns of LaMO3 (M = Fe, Co and Mn)

LaCoO3 is not stable at 700oC in 5%H2/N2, likely needed for desulfation

LaMnO3/LaFeO3 could be stable at 700oC in 5%H2/N2

100 200 300 400 500 600 700

Sign

al In

tens

ity (a

.u)

Temperature (oC)

LaFeO3LaCoO3LaMnO3

Condition: 50 mg LaMO3(M = Fe, Co Mn), ramp rate = 10oC/ min under 5%H2/N2

H2-TPR of LaMO3(M = Fe, Co, Mn)

Oxidized at 550oC in air after reduction at 700oC in 5%H2/N2 for 30 min.

2010 DEER Conference

NO Oxidation over Perovskites

[NO] = 200 ppm, [CO2] = [H2O] = [O2] =10%, SV = 50,000 h-1.

NO oxidation activity: LaCoO3 > LaMnO3 > LaFeO3 LaMnO3 may be the best choice for LNT considering both NO oxidation efficiency and durability in rich conditions

CeO2-ZrO2

LaMnO3

BaOPd/Rh

NO +O2

NO2

NO3-

Lean

CO/H2

N2+H2O

Rich

CeO2-ZrO2

LNT Catalyst• Pd: 50g/ft3

• Rh: 5g/ft3

• Monolith: 400/4 cordierite substrate• Aged at 750°C/72 hrs with10%H2O/Air

0

10

20

30

40

50

60

70

250 300 350 400 450

NO

con

vers

ion

to N

O2

(%)

Temperature (oC)

LaCoO3

LaMnO3

LaFeO3

2010 DEER Conference

Perovskite-based LNT vs. Platinum-based LNT

Pt/Pd/Rh: 45/8/5 g/ft3Pt/Pd/Rh: 0/50/5 g/ft3

0

20

40

60

80

100

250 300 350 400 450

NO

xco

nver

sion

(%)

Temperature (oC)

Before sulfr loading

After loading 1.0 g/L Sulfur

After desulfation

[CO2] = [H2O] =10%, SV=50k/hr; Lean: 200 ppm NO +10% O2; Rich: 200 ppm NO+3%CO+1%H2; Lean/Rich =60s/5s

Comparable NOx reduction performance

Sulfur poisoning characteristics similar to a commercial LNT

0

20

40

60

80

100

250 300 350 400 450N

Ox

conv

ersi

on (%

)Temperature (oC)

Before sulfur loading

After loading 1.0 g/L sulfur

After desulfation

2010 DEER Conference

Desulfation Comparison

Perovskite-based LNT

[CO2] = [H2O] =10%, SV=50k/hr; 3%CO+1%H2; temperature ramp 300-700C at 10C/min

Pt-based LNT

200

300

400

500

600

700

800

0

5

10

15

20

25

30

35

40

45

50

5 15 25 35 45 55Te

mpe

ratu

re (o

C)

H2S

Con

cent

ratio

n (p

pm)

Time (min)

H2S concentration

Temperature

200

300

400

500

600

700

800

0

5

10

15

20

25

30

35

40

45

50

5 15 25 35 45 55H

2S c

once

ntra

tion

(ppm

)Time (min)

H2S concentration

Temperature

Tem

pera

ture

(oC

)

Similar desulfation characteristics to a Pt-based LNT… most sulfur is likely adsorbed on BaO sites

2010 DEER Conference

Summary

Co and Mn-based Perovskite oxides are active for NO oxidation to NO2

Perovskite based LNT without PGM stores NOx effectively under lean conditions; however, it is not effective in reducing NOx to N2/NH3 under rich conditions

Integration of perovskite-based LNT with a TWC formulation leads to efficient NOx conversions

LaMnO3-based LNT shows similar sulfation and desulfationcharacteristics to a Pt-based LNT

This family of materials may offer significant PGM reduction opportunity for diesel catalysts