Pt-free, Perovskite-based Lean NOx Trap CatalystsPerovskite-based lean NOx catalysts shown to...
Transcript of Pt-free, Perovskite-based Lean NOx Trap CatalystsPerovskite-based lean NOx catalysts shown to...
2010 DEER Conference
Pt-free, Perovskite-based Lean NOx Trap Catalysts
Gongshin Qi, Chang H. Kim, and Wei Li
GM Global Research & Development
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Overview
LNT Chemistry
NO Oxidation on Perovskite Catalysts
PGM-free LNT Catalysts
Pt-free LNT Catalysts
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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
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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
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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
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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
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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
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Con
cent
ratio
n (p
pm)
Time (S)
NH3
300oC
NO
NOx + H2/CO N2/NH3
Pd/Rh
√
w/o PGM
w/ Pd/Rh
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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
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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
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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
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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.
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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
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NO
con
vers
ion
to N
O2
(%)
Temperature (oC)
LaCoO3
LaMnO3
LaFeO3
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Perovskite-based LNT vs. Platinum-based LNT
Pt/Pd/Rh: 45/8/5 g/ft3Pt/Pd/Rh: 0/50/5 g/ft3
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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
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250 300 350 400 450N
Ox
conv
ersi
on (%
)Temperature (oC)
Before sulfur loading
After loading 1.0 g/L sulfur
After desulfation
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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
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mpe
ratu
re (o
C)
H2S
Con
cent
ratio
n (p
pm)
Time (min)
H2S concentration
Temperature
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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
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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