Catalyst Design for Urea-less Passive Ammonia SCR Lean-Burn SIDI Aftertreatment System
Chang H. Kim, Kevin Perry, Wei Li, Kushal Narayanaswamy, and Michael Viola
Global Research & Development
Effective May 3, 2010 DOE Funded ProjectAward Number DE-EE-0003379
September 28, 2010
Fuel Efficiency vs. Emission Control
Conventional TWC - Poor NOx efficiency
with DFCO / Lean-Idle
Urea-SCR- Secondary urea tank
with injection system- Urea Solution Freezing
Lean NOx Trap- High PGM Cost- Sulfur Poisoning- Desulfation Required
Passive Ammonia SCR System
PASS - How Does It Work?
Use H2 and CO to generate NH3 over TWC and store NH3 in multiple SCRs
Use the stored NH3 for lean NOxconversion
DURING RICH: DURING LEAN:
Urea-Free SCR System
NH3
NOx
RICH
LEAN
H2O
N2
TWC• Front Brick: 0.8 L
200 g/ft3, 0/200/0• Rear Brick: 1.2 L
70 g/ft3, 0/60/10
SCR• 2.0 L
Cu-based
Poor NOx conversion over TWC during NEDC
TWC produced NH3with rich operation
Engine Out NOx
Post-TWC NOx
TWCConverter
WRAF
SCRConverter NH3
NOxRICH
LEAN
100
Vehi
cle
Spee
d (k
m/h
)
Euro VI
Dynamometer data based on: European Passenger Car – I4, Manual Transmission
NEDC Results from Stratified Charge Application – Extended Lean Operation
NEDC Results from Stratified Charge Application – Extended Lean Operation
Post-TWC NOx
Tailpipe NOx
TWCConverter
WRAF
SCRConverter
TWC• Front Brick: 0.8 L
200 g/ft3, 0/200/0• Rear Brick: 1.2 L
70 g/ft3, 0/60/10
SCR• 2.0 L
Cu-based
100Ve
hicl
e Sp
eed
(km
/h)
Euro VI
NH3 Formation over TWC
Post-TWC NH3
NH3/NOx ratio is always greater than 1 over SCR for maximum conversion efficiency
15.0
Engi
ne O
ut N
Ox
and
0.1*
H2
Post
-TW
C N
H3
Engine Air / Fuel Ratio14.0 13.0
Engine Out NOx
Engine Out H2
Post-TWC NH3
Post-TWC NOx
The Multiple Roles for TWC
Hydrocarbon
Oxidation
CO
Conversion
NOx
Conversion
CO+ O2 CO2
NOx + CO CO2 + N2
CxHy + O2 CO2 + H2O
NOx + H2 NH3 + H2O
Lean Stoic. Rich
CO+ H2O CO2 + H2
CxHy + H2O CO2 + H2
Engine Operation
TWC design is critical for PASS
• Engine: 2.2L, stratified-charge developed by GM R&D• Controller: d-SPACE with Micro-autobox• Transient Dynamometer Equipped with Horiba Emission
Benches, MKS FTIRs, and V&F H2/O2 Analyzer
Experimental Design
Pd/R
h
PdPd PdPdPd
Pd/R
h
Pd Pd
Pd/R
hI:
II:
• Pd Brick: no OSC200 g/ft3, 0/200/0
• Pd/Rh Brick: Std. OSC70 g/ft3, 0/60/10
• Aged in RAT H cycle for 50 hrsInvestigate the effect of Rh
and OSC for NH3 formation
Investigate the effect of Pd, Rh, and OSC for NOx reduction & CO/HC Oxidation
A B C
Modular Converters for TWC Design
Modular testing allows to characterize the individual components in TWC
Sampling Ports
NH3 Formation over Pd-only vs. Pd-Rh
Pd/Rh catalyst with OSC makes much less NH3 compared to Pd only catalyst
Pd-Only
Pd-Rh/OSC
1000
1000
0
0
Sampling position
CO and HC Efficiency
HC conversion efficiency over Pd only catalyst was much higher than that over Pd/Rh with OSC
Pd-Only
Pd-Rh/OSC
NOx Reduction Efficiency over TWC
Not much benefit of using Rh in terms of NOx efficiency under lean environment
Pd-Only
Pd-Rh/OSC
(Shinjoh et al., 2004)
NOx reduction in Lean Exhaust
Rh
Post-TWC NOx
OSC Effect on CO and HC Efficiency
HC conversion efficiency was great over Pd-only catalyst, however CO efficiency is strongly linked with Rh and OSC
Pd-Only
Pd-Rh/OSC
CO Conversion during Rich Operation
CO is removed by water gas shift reaction over Rh/OSC
WGSCO + H2O
↔ H2 + CO2
WGS
Challenges
• High NH3Efficiency
• PGM & OSC Optimization
• NH3 storage beyond 450 C
• High Temp. NOxEfficiency
• Stable TWC under Lean Env.
• Stable SCR under Reducing Env.
TWC Technology
Pd-only, No OSCPd+Rh, Low OSCPd+Rh, High OSC
SCRTechnology
~ Zero Storage Capacity beyond
450°C
Cu-SCR
Fe-SCR
100 200 300 400 500
Capa
city
°C
Thermal Durability
200 300 400 500 600 700 °C
NO
xCo
nver
sion
After Lean/Rich (RAT) Aging at 750 C
DegreenedSCR
PAS
SO
xygen Tolerant Universal A
ftertreatment
• PASS concept: a universal, oxygen tolerant aftertreatmemt system for SI engines– Minimize PGM while improving fuel economy potential
• TWC technology that maximizes NH3 production and CO/HC conversion under slightly rich conditions is the most important element in PASS– Modular TWC experiments guided us how EO emission
interacts with Pd, Rh, and OSC components in TWC– Most NH3 was produced from the Pd only catalyst– WGS reaction may be the most effective way to reduce CO
during rich operations
Summary