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

Leading a Transformation in the Industry