LNT Catalysis at Ford Motor Company – A Case History

LNT Catalysis at Ford Motor Company – A Case History

2017 CLEERS Workshop

Christine K. Lambert, Joseph R. Theis, Giovanni Cavataio

Ford Motor Co.

10/5/2017 2017 CLEERS WORKSHOP 1

Background

• Ford studied Lean NOx Traps (LNTs) for > 20 years

• Ford used LNTs successfully on diesel and gasoline vehicles

• Thermal stability of LNTs was improved

• Sulfur management of LNTs is critical to performance and durability

• LNTs generate NH3 for downstream SCR or SDPF on diesels

• LNT application to gasoline is very limited

• Should weigh potential fuel benefit against the cost of the catalyst system, including sensors for control and onboard diagnostics


Examples of LNT-containing systems


• LNT position determines the temperature window in which it will operate

• TWC or DOC for CO and HC light-off during cold start, or LNT may replace the DOC if space is limited

• Diesel systems include a filter

• LNT may be either the main NOx control device or an assisting device

Differences in LNT requirements (1/4)


Requirements Gasoline LNT Diesel LNT

Operational Normally stoichiometric

Lean operation when feasible

Rich operation easy

Naturally lean

Rich operation difficult


Functional LNT provides lean NOx control

LNT provides additional TWC activity during stoichiometric operation to supplement the close-coupled TWC(s)

LNT may be main NOx control device

LNT may replace DOC for HC, CO control and exothermgeneration for downstream filter

LNT may generate NH3 for downstream SCR

LNT may assist urea SCR system for cold start NOx control






Compositional Designed for higher temperature and high NOx storage capacity

NOx storing materials (Ba, optional alkali metals Cs, K, Na)

Precious metals (Pt, Pd, Rh)

Oxygen storage component (Ce-Zr)

Sulfur scavenger (Ni)

Support material (Al2O3)

Designed for lower temperature NOx storage and deSOx temperature

NOx storing materials (Ce, Ba)

Precious metals (Pt, Pd, Rh)

Support material (Al2O3)

Requirements Gasoline LNT Diesel LNTNOx Control Level Engine out NOx high

NOx conversion 95-99%

Engine out NOx low

NOx conversion 50-60% -Europe

NOx conversion 85-90% -U.S.




Important characteristics of LNTs:• operating window• precious metal content• ceria content• sulfur tolerance &

desulfation capability• total capacity• thermal stability

LNT Fundamentals

LNT Fundamentals




• At low temperatures, higher PGM is best• At high temperatures, lower PGM is best

LNT Fundamentals




Higher ceria levels promote more “purge NOx Release” by consumingreductants during rich purge.

MO: mixed oxide

LNT Fundamentals





LNT FundamentalsImportant characteristics of LNTs:• operating window• precious metal content• ceria content• sulfur tolerance &


Low temperature NOx storage limitedby purging and NO oxidation.


LNT FundamentalsImportant characteristics of LNTs:• operating window• precious metal content• ceria content• sulfur tolerance &


Low temperature NOx storage degradedby high temperature aging.

LNT + SCR = a way to use the ammonia


increased zoning

LNTs make NH3 add SCR to store and use the NH3 for further NOx conversion.

LNT/SCR “sandwich” designs

Ford’s research on lean burn gasoline

• 2003.5 - 2006 MY 1.8L European Mondeo

• Close-coupled TWC, underbody TWC, and LNT

• Research supporting this system included:• Four mode aging schedule for TWC represented high

mileage on TWC+LNT system

• Oxygen sensor was sufficient for NOx purge control

• Two-step NOx purges minimized emissions and total duration

• Low frequency air/fuel ratio modulation during deSOxminimized H2S make


Gasoline LNT

Passive lean NOx approaches (TWC+LNT+SCR) Ford-MTU-DOE program with 2.3L Miller cycle GTDI engine


Gasoline LNT


Gasoline LNT

single-zoneSCR

Passive lean NOx approaches (TWC+SCR) Ford-MTU-DOE program with 2.3L Miller cycle GTDI engine


Estimated lean burn fuel economy benefit (2.3L Miller cycle GTDI)

Gasoline LNT



Gasoline LNT


Gasoline LNT

• Fuel economy benefits were low relative to other technologies• Added costs of catalysts and sensors exceeded targets

• Stop-start idles• Stoich accelerations• Fuel shutoff on

decelerations• Lean burn limited to

cruises


Ford’s research on diesel LNT

• Pd added for greater thermal stability

• Ce added for low temperature NOx storage (not oxygen storage)

• Diesel exhaust treatment also includes a soot filter

• Often the LNT replaces a DOC and is used to generate heat for soot oxidation

• LNT desulfation requires hot, rich conditions

• DeSOx was developed in conjunction with desoot

• LNT applied to diesel passenger cars in Europe


Diesel LNT

Three-mode aging scheme for diesel LNTs


Diesel LNT

• Three modes used to age LNTs

• low temp sulfur

• high temp rich deSOx

• high temp lean desoot

• Represents high mileage

• DeSOx T determined by sulfur loading and TPD300°C

inlet

DeSOx T*

650°C bed

Improvements in diesel LNT deSOxthermal safety margin and control range


Diesel LNT

• Thermal safety margin improved by 190oC• Control of deSOx temperature on vehicle improved ±50oC

Later Status

System trade-off example for a Tier 2 midrange diesel application


Diesel LNT



Diesel LNT



Diesel LNT

• NOx conversion capability assessed at FUL (120K mi) on FTP-75• Fuel economy penalties were estimated for FTP only and metro-highway [M-H]• Deployment issues were noted, as well as new sensors needed for OBD

LNT Outlook

• Lean burn gasoline emission control cost is high vs the fuel benefit, which limits the application

• Real world driving conditions and extended mileage requirements make it more difficult to use LNT as the main NOx control device on diesels• LNT can assist cold start control of NOx for downstream

urea SCR system (i.e., LTNA)

• LNT may be modified for lower temperature performance and multiple functions (HC trap, DOC)


LNT Catalysis at Ford Motor Company – A Case History

Documents

Transcript of LNT Catalysis at Ford Motor Company – A Case History