Sept 29, 2011 1

Critical Materials in Catalysis:

Precious vs Base Metals in

Automotive Catalyst Systems

Christine Lambert Ford Research and Advanced Engineering

The Role of Chemical Sciences in Finding Alternatives to Critical

Resources Workshop

September 29th-30th, 2011

The National Academy of Sciences

Sept 29, 2011 2

Outline

• Overview of modern automotive catalysts

• Why Base Metals are not effective TWCs

• Where Base Metals do work

• Example of a Cu/zeolite catalyst system

• Other Base Metal catalyst research

• Summary

Sept 29, 2011 3

What are Automotive Catalysts?

http://www.umicore.com/en/cleanTechnologies/autocats/

Catalysts are used to reduce

the amount of regulated

pollutants from gasoline and

diesel vehicles:

• hydrocarbons (HC)

• carbon monoxide (CO)

• nitrogen oxides

(NOx = NO + NO2)

• particulate matter (PM)

N2, CO2 and H2O

Sept 29, 2011 4

Automotive Three-Way Catalyst “Staying in the Window”

Catalytic converter:

Typical operating conditions:

• 350 – 650 C (extremes: ambient to 1050 C)

• near-stoichiometric exhaust gas

• 60 – 300 ms contact time

Heck and Farrauto

Shelef and McCabe

<1% oxygen at stoichiometry

Sept 29, 2011 5

Modern Automotive TWC Electron microprobe view of washcoat (2000):

Typical catalyst composition (2000):

cordierite 70 wt%

-Al2O3 13

CeO2 6

ZrO2 4

La2O3/Nd2O3 3

BaO/SrO 2

NiO 1.5

Pt/Pd/Rh 0.5

Gandhi 2004

substrate

wall inner

layer

outer

layer

substrate

wall

substrate

wall

substrate

wall

Sept 29, 2011 6

What Are Precious Metals vs Base Metals?

Precious

Metals

Platinum Group Metals (PGM)

Transition

Metals

Base metals are non-precious,

i.e., oxidize or corrode easily.

www.wpclipart.com

Sept 29, 2011 7

PCV

System

Spark

Control,

PVS,

etc.

EGR

valves

Therm-

actor

Technologies Deployed to Meet

Increasing Stringent

Emission Standards

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Oxidation

Catalysts,

some

electronics,

some

feedback

carb

(EEC I &

EEC II)

More

Electronics

(S/D)

More F/B

(EE III & V)

Pt/Rh TWC

Throttle

Body

Injection

Port

Injection

(S/D)

(EEC IV)

High-tech

TWC

Mass

Air

(EEC V)

Pd/Rh TWC

Pd-only TWC

Adv. Washcoat

Fore/Aft O2

sensor

OBD II

Adapt. fuel

Misfire

Detection

Sealed

Fuel Vapor

System

Zone-coat TWC

High cell density

TWC

NOx Trap

PTEC

Controller

Gandhi 2003/2004

• Base metals, Ag & Au: low activity and/or durability

• Ru, Ir, and Os: form volatile oxides

• Pt and Pd: suitable for oxidation catalysts

• Rh added for NOx control

• Oxygen storage components added (Ce)

• Stabilized alumina (Ba, La)

• Pd enabled by unleaded fuel

• Layers & metal segregation

• Stabilized cerium oxides

• More effective PGM use

Sept 29, 2011 8

Supply Chain for Automotive Catalysts

Partially derived from

Platinum 2011

Substrate

Manufacturers

Catalyst

Coaters Canners

Automotive

Assemblers

Catalytic

Promoter

Suppliers

Raw

Material

Suppliers

Customers

PGM

Market

“open loop”

recycled

PGM

PGM

mining

Jewelry Electrical Industrial

Catalysts

PGM

Refining PGM

Recycling

PGM

Recycling

Sept 29, 2011 9

PGM Supply and Demand

Platinum 2011

• Main use for Rh is autocatalysts

• Pt & Pd are also used in jewelry, industrial

catalysts, and investment

• Recently the demand for Pt and Pd is higher than

the supply

• Recycled PGM can help offset this deficit

Sept 29, 2011 10

PGM Price Volatility Pt, Pd, and Rh prices since 1992

• Catalyst design with PGM is made

more difficult by price volatility

• Metal type is kept varied to offer

several TWC design options, i.e.,

Pt/Rh vs Pd/Rh vs Pd only

• Base metals such as copper are

far less expensive

www.kitco.com

Sept 29, 2011 11

Base Metal TWC Research (1980 Assessment)

1) PGM less affected by sulfur <500C

2) PGMs have higher specific activity

3) PGM is more thermally resistant to loss of low temperature activity

Kummer, 1980

Sept 29, 2011 12

Base Metal TWC Performance Example of Cu TWC on Modern Gas Engine

• Cu and Cu/Cr tested in lab

and on engine

• 4wt%Cu/2wt%Cr provided

highest net NOx conversion

• A rich bias was required,

lowering fuel economy

• Copper catalysts must be

close-coupled to the engine

(hotter location) to avoid

sulfur poisoning and

increase activity

rich

bias

Theis, SAE 922251

Sept 29, 2011 13

Summary of 30+ Years of TWC • Base metals, Ag & Au not active or durable enough

• Ru, Ir, and Os all form volatile oxides

• Pt and Pd were left for the oxidation catalysts

• Rh added for NOx control

• Oxygen storage components added (Ce); later stabilized with Zr

• Stabilized alumina with Ba, La

• Pd/Rh and Pd-only options enabled by Pb-free fuel

• Cu and Cu/Cr retested on modern gas engine; found rich bias required and sulfur still an issue

Sept 29, 2011 14

Diesel Fraction of New U.S. Vehicle Sales

Year

1990 1995 2000 2005 2010

% D

iese

l M

ark

et

Sh

are

0.1

1

10

100

Cars

Class 1 + Class 2 trucks

Class 2b + Class 3 trucks

Class 2b trucks

Class 2b trucks (Ford+GM+Chrysler)

Class 3 trucks (Ford+GM+Chrysler)

Wallington et al., in review

Trucks

Class 1: < 6,000 lbs

Class 2: 6,001-10,000 lbs

Trucks

Class 3: 10,001-14,000 lbs

Class 2b: 8,501-10,000 lbs

Cars

Sept 29, 2011 15

A Brief History of U.S. Diesel Aftertreatment

Model Year

1990 1995 2000 2005 2010 2015

Em

issio

n s

tandard

s a

pplic

able

fo

r m

ediu

m-d

uty

die

sels

(g/[

bhp h

r])

0.01

0.1

1

10

NOx

PM

Evolution of emissions standards for NOx and PM.

• mid-1990s: Diesel oxidation catalysts (DOCs)

with ceria and alumina for PM oxidation

• 2007:

• ultra-low sulfur diesel,

• particulate filters for PM control

• high precious metal DOCs

• lean NOx control (NOx traps)

• 2010:

• lean NOx control (urea SCR)

Wallington et al., in review

Sept 29, 2011 16

An Example of U.S. Diesel Aftertreatment 2011 MY Ford Diesel Super Duty

Cu/zeolite Pd-rich Pt/Pd

Aqueous urea tank

(refilled at oil change)

HC + O2 CO2

CO + O2 CO2

NH3 + NOx N2 C + O2 CO2

media.ford.com

Sept 29, 2011 17

-700

-600

-500

-400

-300

-200

-100

0

100

200

300

400

500

600

700

0 200 400 600 800 1000 1200

Test Time (s)

Tem

pera

ture

(C

)

0

20

40

60

80

100

120

Veh

icle

sp

eed

(m

ph

)

Ford 2011MY Diesel (9500 lbs)

Ford 3.5L GTDI (5250 lbs)

Exhaust Gas Temperatures

λ = intake air / theoretical air req.

Chassis FTP-75 Cycle

Sept 29, 2011 18

Exhaust Gas Oxygen Content

-40

-30

-20

-10

0

10

20

30

40

50

0 200 400 600 800 1000 1200

Test Time (s)

Lam

bd

a

0

20

40

60

80

100

120

140

160

180

veh

icle

sp

eed

(m

ph

)

Ford 2011MY Diesel (9500 lbs)

Ford 3.5L GTDI (5250 lbs)

λ = intake air / theoretical air req.

Chassis FTP-75 Cycle

Sept 29, 2011 19

Diesel Lean NOx Control Options

• HC SCR using Pt

• Lean NOx Trap with Pt, Pd and Rh

• EtOH SCR using Ag

• Urea SCR with Cu/zeolite SAE 2004-01-1292

SAE 2005-01-1082

Sept 29, 2011 20

Basics of Urea SCR

• Urea is injected into the exhaust pipe upstream of the catalyst as an aqueous solution at 32.5 wt% (eutectic)

• Non-toxic, commodity chemical that forms ammonia

• Tradename in U.S. is “Diesel Exhaust Fluid” – DEF

• SCR needs oxygen for high conversions

H2N NH2

C

O

HNCO NH3+

CO2 NH3+H2O

heat

heat

urea decomposition:

NOx reduction:

4NO O2+ 4NH3 + 4N2 6H2O+

2NH3 NO NO2+ + 2N2 3H2O+

6NO2+ 8NH3 7N2 12H2O+

urea

Sept 29, 2011 21

SCR Catalyst Options

0

10

20

30

40

50

60

70

80

90

100

100 150 200 250 300 350 400 450 500 550 600 650

Inlet Gas Temperature (ºC)

Gro

ss

NO

x c

on

ve

rsio

n (

%)

Cu-Based SCR

Fe- Based SCR

Vanadium Based SCR

FTP US06

• Cu/zeolites are best

at low temperatures

• Fe/zeolites perform

well at high

temperatures

• Vanadium based

SCRs are not

appropriate for US

Diesels with Filters

SAE 2007-01-1575

Sept 29, 2011 22

What are Zeolites? • Zeolites are composed of aluminum oxide and silicon

oxide in a crystalline structure

• Some zeolites are found in nature but most are

synthesized for high purity

• Zeolites are in widespread use as water softeners,

absorbents, dessicants, oil refining

• Also called “molecular sieves” due to varying cage sizes

on the angstrom scale

Beta (BEA) Chabazite (CHA)

www.iza-structure.org/databases/

Sept 29, 2011 23

Small Pore Zeolites Enabled

Use of Cu Automotive Catalyst

• Cu/CHA development enabled Cu/zeolite for automotive use • Related patents and publications:

– Zones “Zeolite SSZ-13 and its method of preparation” US4544538, 1985

– Bull et al., “Copper CHA zeolite catalysts”, US7601662, 2009

– Kwak et al., “Excellent activity and selectivity of Cu-SSZ-13 in the selective catalytic reduction of NOx with NH3”, J. Catal. 275 (2010) 187-190

– McEwen et al., “Integrated operando X-ray and DFT characterization of Cu-SSZ-13 exchange sites during the selective catalytic reduction of NOx with NH3”, Catal. Today, in press.

Schneider, CLEERS Telecon, Sept 2011

Chabazite (CHA)

www.iza-structure.org/databases/

Sept 29, 2011 24

A Few Challenges Faced During Commercial

Urea SCR System Development

• Stabilization of Pt

• Stabilization of Cu/zeolite

• HC poisoning/coking of Cu/zeolite

• Sulfur effects on Cu/zeolite

• Urea specifications and refill

Sept 29, 2011 25

Thermal Stability of DOC

0

0.2

0.4

0.6

0.8

1

100 150 200 250 300

Convers

ion E

ffic

iency

Temperature (Deg C)

HC Light-Off Conversion2-Mode 100 hrs / 300 ppm S + 20 mgP/gal

20:1

2:1

1:4

Pt only

0%

10%

20%

30%

40%

50%

150 200 250 300 350 400 450 500 550

% N

O2

of

To

tal N

Ox

Temperature (C)

NO2:NOx

Pt only20:1

2:1

1:4

• Addition of Pd to Pt has a

stabilizing effect for HC oxidation

during cold-start

• Pd also stabilizes Pt for NO

oxidation but has no inherent

activity itself

Sept 29, 2011 26

Precious Metal Poisoning of SCR

• Pt from upstream DOC can volatilize and interfere with SCR function

• Prime indicators are increased NH3 oxidation and N2O production

• Front section of catalyst most affected and can be regenerated

• Pt DOC may be stabilized with addition of Pd and lower exotherm Ts

EVALUATION of DYNAMOMETER

AGED FeSCR CATALYST

Lab flow reactor Pt poisoning of Cu

SCR by upstream DOC

-50

-25

0

25

50

75

100

100 150 200 250 300 350 400 450 500 550 600

Inlet Gas Temperature (ºC)

NO

x C

on

ve

rsio

n (

%)

Non - Contaminated

Contaminated

0

10

20

30

40

50

60

70

80

90

100

100 150 200 250 300 350 400 450 500 550 600

Catalyst Temperature (ºC)

NO

x C

on

ve

rsio

n (

%)

1st Inch (Inlet)

2nd Inch

3rd Inch

4th Inch

5th Inch

6th Inch (Outlet)

SAE 2008-01-2488

SAE 2009-01-0627

Sept 29, 2011 27

Thermal Stability of SCR Catalyst

• Thermal stability of

Cu/zeolite recently

improved from 750 to

900 C (Cu/beta

Cu/CHA)

• NO2 no longer needed for

low temp conversion

• Lower cost aftertreatment

now possible

SAE 2008-01-1025

4NH3 + 4NO + O2 4N2 + 6H2O

Sept 29, 2011 28

HC Poisoning/Coking of Zeolitic SCR

0

10

20

30

40

50

60

70

80

90

100

NO

x C

on

vers

ion

(%

)

0

2

4

6

8

10

12

14

16

18

20

Cu

mu

lati

ve H

Cs (

g/l

cata

lyst)

% NOx Conv.

Cum. HC's

Degreened

Activity

(250°C,

20% NO2

in feed)

Start HC

Addition

500°C,

10 min

Activity

Regained

End HC

Addition

SCR Catalyst Durability: HC

• HC poisoning is reversible after 500°C, lean

HC Inhibition HC Storage/Exotherm

Both issues were resolved by transition from Cu/beta to Cu/CHA

DEER 2004

Sept 29, 2011 29

Sulfur Effects on Cu/zeolite

0

10

20

30

40

50

60

70

80

90

100

150 200 250 300 350 400 450 500 550 600 650

Catalyst Temperature (°C)

NO

x c

on

vers

ion

(%

)

degreened

120k mi sulfated

after regen at 650°C

• Sulfur affects NOx activity below 300C

• Sulfur can be removed by lean filter regeneration conditions >650C

• Amount adsorbed between regens can be tolerated based on 15 ppm-

wt S in diesel fuel

Effect of 20ppm SO2 at 200°C

(Calculated miles based on 15ppm fuel sulfur)

0

10

20

30

40

50

60

70

80

90

100

160 180 200 220 240 260 280 300

Temperature(°C)%

NO

x C

on

vers

ion

0 miles

500miles

Effect of 120K mi at 15ppm fuel sulfur

DEER 2004

Sept 29, 2011 30

Urea Specifications and Refill

• OEMs and suppliers formed

USCAR working group to define

specifications

• Aqueous urea is sold as “Diesel

Exhaust Fluid” or “DEF”

• Current refill uses bottles, drums,

totes, and bulk dispensers

• ~ $2.79/gal in bulk

• ~ $4.65/gal in bottles http://www.dieselexhaustfluid.com/

Mattina, 16th Annual Fleet Fueling Conference, Sept

2010.

• Websites offer DEF locations

http://www.factsaboutscr.com

Sept 29, 2011 31

Diesel MDV Impact on Sustainability

Year

1995 2000 2005 2010 2015

CO

2 (

g/k

Wh)

at P

eak T

orq

ue

600

700

800

900

1000

Gasoline

Diesel

Comparison of Class 2b / Class 3 peak torque brake specific

CO2 for medium-duty vehicles 1998 - 2011 calendar years.

• Data from EPA HD database.

• Figure from Wallington, et al., in review.

• At light/moderate loads the CO2 advantage for SCR-equipped diesel will be > 10%.

Urea SCR

used on

majority of

diesels in

2010+.

Sept 29, 2011 32

0.00

5.00

10.00

15.00

20.00

25.00

2004 2005 2006 2007 2008 2009 2010 2011 2012

Pre

cio

us

Me

tal

Us

ag

e

Total PGM Pt Equiv

Diesel MDV Impact on Sustainability Precious Metal Usage on Ford Super Duty Trucks

2011MY J1

DOC+SCR+CDPF

2011MY J2

DOC+SCR+CDPF

DOC only

DOC +CDPF

2011MY

TWC

Increasing

Emission

Stringency

Pd-rich

Diesel-

Gasoline

PGM Gap

Sept 29, 2011 33

Potential Use of Base Metal Catalysts: Addition of SCR to TWC or LNT System

TWC+SCR

LNT+SCR

SAE 2009-01-0285

• SCR may enable lower PGM usage • SCR may be a key enabler for lean burn

Li et al., 2009

• Use of SCR depends on lean burn gasoline dev.& LD diesel usage

• Advanced lean aftertreatment depends on availability of low sulfur fuel

Sept 29, 2011 34

Potential Use of Base Metal Catalysts: NO NO2 Oxidation Function

Pd BMO DOCs Pt-free Perovskite LNTs

US2011/0165046

• Low temperature NO oxidation benefits lean NOx reduction.

• Base metals can replace a portion of the precious metals.

• Pd needed for HC oxidation

~ LaMnO3 (Qi, DEER 2010)

• PGM needed for HC and NOx reduction

Sept 29, 2011 35

Summary • TWC is limited to Pt, Pd and Rh after 30+ years of

research and development

• Diesel aftertreatment content has seen rapid growth in last 5 years from DOCs to filters to lean NOx control

• Pd-rich DOCs and Cu/zeolite lean NOx aftertreatment are now in production on medium duty diesel trucks

• Other potential uses of base metals are now in research stages and depend greatly on lean burn engine development

• The availability of lower sulfur fuel enables high efficiency lean NOx aftertreatment

Sept 29, 2011 36

Acknowledgements

• Jeff Hepburn, Robert McCabe, Douglas

Dobson, Carolyn Hubbard, Dominic

Dicicco, Tim Wallington, Kevin Guo (Ford)

• Martyn Twigg (retired Johnson Matthey)

Sept 29, 2011 37

References • Heck and Farrauto, Appl. Catal. A: Gen. 221 (2001) 443-457

• Shelef and McCabe, Catalysis Today 62 (2000) 35-50

• Gandhi and McCabe, ChemCon, Mumbai, 2004

• Gandhi, et al., Journal of Catalysis, Vol. 216, Issues 1-2, 2003, pp. 433-442

• www.wpclipart.com

• Platinum 2011, Johnson Matthey, May 2011

• www.kitco.com

• J.T. Kummer, Prog. Energy Combust. Sci. Vol. 6, pp. 177-199, 1980

• Theis and Labarge, SAE 922251

• media.ford.com

• T.J. Wallington, C.K. Lambert, W.C. Ruona, Energy Policy, in review

• Lambert et al., SAE 2004-01-1292

• Thomas et al., SAE 2005-01-1082

• Jen et al., SAE 2008-01-2488

• Cavataio et al., SAE 2009-01-0627

• Cavataio et al., SAE 2007-01-1575

• www.iza-structure.org/databases

• Cavataio et al., SAE 2008-01-1025

• Lambert et al., DEER 2004

• Xu et al., SAE 2009-01-0285

• W. Li et al., 12th CLEERS Workshop, 2009

• Drews et al., US 2011/0165046 A1

• Qi et al., DEER 2010 Conference