impact of biodiesel-based na on the selective catalytic ... · field pennycress, jatropha, etc. –...

Impact of Biodiesel-Based Na

on the Selective Catalytic Reduction (SCR) of NOx Using

Cu-zeolite D. William Brookshear1,

Todd J. Toops2, William Rohr1, Ke Nguyen1, and Bruce G. Bunting2

1-University of Tennessee - Knoxville

2-Oak Ridge National Laboratory

2011 DEER Conference

October 5, 2011

2 Managed by UT-Battelle for the U.S. Department of Energy

Motivation to introduce higher levels of biodiesel tempered by the unknown • Biodiesel: alkyl ester combusts similar to diesel fuel

• Domestic renewable energy source synthesized from

vegetable oil or animal fat – Vegetable: Soybean (~90%), rapeseed,

field pennycress, jatropha, etc. – Animal sources: Only waste or by-products being

converted at this time – Currently focus is on waste/excess oil

• Barrier to implementation is the unknowns associated

with a new fuel – Combusts like diesel, but unknown impact on

emissions control devices – Trace elements are primary cause of concern in

emissions control…particularly Na and K


Concerns associated with Na and K are mechanical and chemical

• NaOH or KOH is a liquid-phase catalyst used in biodiesel synthesis – NaOH and KOH difficult to separate

completely from products – Specification set at 5 ppm Na+K in

B100

• Potential Na/K emissions control effects – Ash accumulation in DPF – Alkali absorption into monolith walls

• possible weakening of monolith – Catalyst poisoning/fouling

• Na-exchanged zeolite is commercial catalyst

Migration into cordierite

Increased ash accumulation

NaOH or

KOH biodiesel

Vegetable oil +

methanol


Recent research illustrates potential Na impact on SCR and DPF cordierite walls • Cavataio et al. (SAE 2009-01-2823) • Aqueous addition of Na to SCR and

DOC using incipient wetness technique – Investigated Na and K – Multiple DOC and SCR formulations

• Dramatic deactivation observed • Na and K accelerated zeolite structure

collapse

• Williams et al. (SAE 2011-01-1136) • Accelerated full-size engine approach

– DOCDPFSCR approach – Both Na and K added to fuel – 150k and 435k mile equivalent

• Na+K penetrate wall of DPF • Small but significant decrease in NOx

performance


Accelerated aging targets Na-impact

• Introduce high levels of Na to B20

• Two configurations evaluated – DOCSCRDPF

• “light duty” configuration • with and without Na (control)

– DOCDPFSCR • “heavy duty” configuration

• Levels elevated to achieve 435,000 mile Na exposure

– Dioctyl sulfo-succinate sodium salt with Na:S = 1 – 5000+ ppm Na in B20 – Periodic soot regeneration performed at 700°C – Measure performance in bench-core reactor

• First 3” of catalysts studied • Employ portions of the CLEERS SCR protocol • SV = 30,000 h-1, NH3/NO = 0.8-1.0, NO2:NO = 0 or 1

DOC

Mix

erSCRDP

F

DOC

Mix

erSCRDP

F


DOC-SCR-DPF (LIGHT-DUTY)

Na ACCELERATED-AGING


Na observed after accelerated aging throughout SCR washcoat • Na throughout washcoat

– In bulk ~0.2%wt • Elevated Na levels also

observed at surface – 0.3-0.6%wt

• Concentration of Na axially

uniform

• Low sulfur levels detected in SCR washcoat – Near detection limit – Increased level at

surface ~0.1%wt – Na:S ≠ 1

Accelerated Na-Aged SCR (from DOCSCRDPF) Inlet (center) Inlet (near edge) Middle

Na

200 μm

EPMA line scans

0.00.10.20.30.40.50.6

0% 20% 40% 60% 80% 100%Fraction from monolith to surface

Ato

mic

Wei

gh

t % Na in Front Na in Middle

S in Front S in Middle

120 μm

20

0


A version of the CLEERS transient SCR protocol utilized to probe behavior

cool

0 20 40 60 80 100 120 140 160

time (minutes)

T

O2

NH3

NO

NO2

Ti

0%

350

0

350

0

350

0

14%

NH3 uptake

NO+NO2 SCR

NO SCR α = 0.9 0.8 1.0

NO oxidation cool


Standard SCR reaction significantly inhibited with Na addition • Some aging observed for both the control and Na addition

– Illustrates some thermal effects on this model Cu zeolite SCR catalyst • SCR with Na has significantly less activity for the standard SCR reaction

0102030405060708090

100

150 250 350 450 550

NO

xCo

nver

sion

(%)

Temperature (°C)

Standard Reaction (NO2:NO = 0:1)

Fresh

Control (w/o Na)

DOC-SCR-DPF w/ Na


Minimal impact when feeding equimolar NO2:NO (fast SCR reaction) • Minimal effects when feeding both NO2 and NO

– However, the catalyst most affected is the SCR with Na addition

0

20

40

60

80

100

150 250 350 450 550

NO

xCo

nver

sion

(%)

Temperature (°C)

Fast SCR reaction NO:NO2 = 1:1

Fresh

Control (w/o Na)

DOC-SCR-DPF w/ Na


NH3 storage decreases with aging; control and Na-aged show similar impact

• Significant impact on NH3 storage for both aged samples – Similar impact suggests thermal effect is more responsible than Na

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

150 250 350 450 550

NH

3 St

orag

e (m

mol

/gca

t)

Temperature (°C)

NH3 Storage

Fresh

Control (w/o Na)

DOC-SCR-DPF w/ Na


NH3 oxidation decreases with aging • NH3 oxidation reduced above 400°C in both aged samples

– Oxidation associated with Cu sites – Significant difference between control and Na-aged SCR suggests Na effect

0

10

20

30

40

50

60

70

80

150 250 350 450 550

Oxi

dati

on -

%

Temperature (°C)

NH3 Oxidation

Fresh

Control (w/o Na)

DOC-SCR-DPF w/ Na


Further evidence of Na impact on Cu-sites with decreased NO oxidation • Na-aged samples show less oxidation of NO to NO2 over entire

temperature range • Fresh and control show similar, albeit low reactivity

0

1

2

3

4

5

6

150 250 350 450 550

%N

O O

xidi

zed

to N

O2

Temperature (°C)

NO Oxidation

Fresh

Control (w/o Na)

DOC-SCR-DPF w/ Na


Increasing NH3 does not improve performance on Na-aged SCR • Indicates NH3 oxidation does not limit

performance – NH3 breakthrough observed

• Further illustrates NO to NO2 oxidation is limiting performance in Na-aged sample – Oxidation sites are most impacted

• Impact on control is less pronounced

0 10 20 30 40 50 60 70 80 90

100

150 250 350 450 550

NO

x Co

nver

sion

(%)

Temperature ( C)

Na-addition, NO2:NO = 0:1

Alpha = 1.0

Alpha = 0.9

Alpha = 0.8

0 10 20 30 40 50 60 70 80 90

100

150 250 350 450 550

NO

x Co

nver

sion

(%)

Temperature ( C)

Control (w/o Na), NO2:NO = 0:1

Alpha = 1.0

Alpha = 0.9

Alpha = 0.8

0 10 20 30 40 50 60 70 80 90

100

150 250 350 450 550

NO

x Co

nver

sion

(%)

Temperature ( C)

Fresh, NO2:NO = 0:1

Alpha = 1.0

Alpha = 0.9

Alpha = 0.8


Control-SCR and Na-aged SCR have similar BET profiles


DOC DPF SCR

(HEAVY-DUTY) Na ACCELERATED-AGING


Minimal Na Contamination SCR when placed after DPF


When DPF is in front of SCR, catalyst is protected from Na and its effects • No significant effect from accelerated Na-aging if DPF is in front of SCR

– Some protection from thermal effects also gained with DPF upstream of SCR

0102030405060708090

100

150 250 350 450 550

NO

xCo

nver

sion

(%)

Temperature (°C)


FreshControl (w/o Na)DOC-SCR-DPF w/ NaDOC-DPF-SCR w/ Na


Similar good behavior observed with fast SCR conditions

0

20

40

60

80

100

150 250 350 450 550

NO

xCo

nver

sion

(%)

Temperature (°C)




NH3 storage similar to that of fresh SCR • No aging or Na contamination impact on NH3 storage capability of catalyst

– DPF upstream of SCR preserves storage capability of catalyst

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

150 250 350 450 550

NH

3 St

orag

e (m

mol

/gca

t)

Temperature (°C)

NH3 Storage

Fresh

Control (w/o Na)

DOC-SCR-DPF w/ Na

DOC-DPF-SCR w/ Na


NO and NH3 oxidation were similarly less affected

• NH3 oxidation only slightly lower than that of fresh SCR • NO to NO2 oxidation shows moderately higher oxidation activity

0

10

20

30

40

50

60

70

80

150 250 350 450 550

Oxi

dati

on -

%

Temperature (°C)

NH3 Oxidation


0

1

2

3

4

5

6

7

150 250 350 450 550

%N

O O

xidi

zed

to N

O2

Temperature (°C)

NO Oxidation



BET Surface Area Analysis of SCRs • SCR from DOC-SCR-DPF configuration shows highest surface area

reduction, while SCR from DOC-DPF-SCR configuration is unaffected


Future Directions • Does ASTM specification need to be lowered? If so what level?

– NREL lead collaboration • Focus of NREL/MECA/Ford/ORNL/NBB collaboration

– Ford F250 with full emissions control system – 150,00 mile equivalent with ULSD, Na, K, and Ca – Light Duty (DOC-SCR-DPF) results forthcoming

• Systematic study of Na impact on mechanical strength of DPF walls – Funded through the Advanced Propulsions Materials Program (Jerry Gibbs) – Collaboration with Michael Lance and Andy Wereszczak

• ORNL – Materials Science and Technology Division • Strength testing technique discussed at poster Tuesday night (P-15)

– Long term aging approach with overnight operation


Summary • Na can significantly impact the chemistry

of SCR catalysis

• When placed behind a DPF the impact is significantly muted

• Impact of both thermal and Na

contamination less severe when feeding equimolar amounts of NO and NO2

• Results discussed in bonus slides – Na contamination in accelerated aged

samples mimics that seen in long-term engine aged catalysts

– Na penetrates cordierite walls of DPF

• Manuscript submitted to Catalysis Today (under review)

Na 16

0 200 μm

0102030405060708090

100

150 250 350 450 550

NO

xCo

nver

sion

(%)

Temperature (°C)



0

20

40

60

80

100

150 250 350 450 550

NO

xCo

nver

sion

(%)

Temperature (°C)




Acknowledgements

• Funding provided by DOE – Vehicles Technology Program – Kevin Stork: Fuels & Lubricants – Non-Petroleum Based Fuels

• Long-term aged emissions control parts

– General Motors – Umicore, MECA

• Discussions and project development

– Bob McCormick, Matt Thornton, Aaron Williams – NREL – Rasto Brezny – MECA


Additional slides


COMPARISON OF ACCELERATED APPROACH

TO LONG-TERM AGING


Long-term engine-aged systems used for comparison when possible

B20 DOC DPF • Obtained from GM

– Pt/Al2O3-based DOC – SiC-based DPF

• Field-aged system with B20 – 120,000 mile equivalent

• Minimal knowledge about aging details – Na content was below specification

• Exact value unknown – Temperature history unknown

• Unfortunately unable to secure any B20-

aged SCR catalysts

DPF section

DOC


Biodiesel and lube oil components observed in DOC; accelerated- and engine-aged results similar

• Na, S and P observed in DOC – Inlet cross-sections shown with EPMA

• Long–term aged – S throughout washcoat – P at surface of washcoat – Na observed at surface

• Primarily at inlet of DOC • Accelerated aged

– S throughout washcoat – Minimal lube oil phosphorous detected – Na observed throughout DOC

• Equally in inlet and exit of DOC

Long-term aged DOC Accelerated-aged DOC 10

0 200 μm

S

15

0

P

200 μm

Na 16

0 200 μm

Long-term Aging Accelerated Aging

Average Maximum Penetration Average Maximum Penetration

S 0.70% 1.00% throughout 0.40% 0.60% throughout

P n/a 8% 30 μm n/a <0.1% <10 μm

Na n/a 0.40% 30 μm n/a 0.40% 30 μm

15

15

45


DOC minimally affected; similar effects shown for both accelerated- and engine-aged devices

• Both aged samples show slight decrease between 225°C and 300°C – Conversion decreases by <12%

• Oxidation of NO to NO2 is as much as

12% higher in engine-aged DOC samples than in fresh – This effect is possibly due to

increased Pt particle size from thermal aging, which can improve NO to NO2 oxidation

0102030405060708090

100

100 200 300 400

NO

Oxi

dati

on -

%

Temperature - C

NO to NO2 Oxidation in DOC

FreshAccelerated Na-AgedEngine-Aged

0102030405060708090

100

100 200 300 400

Ethy

lene

Con

vers

ion

-%

Temperature - C

Ethylene Conversion in DOC

FreshAccelerated Na-AgedEngine-Aged


EPMA ANALYSIS OF DPF SAMPLES


• DOC-SCR-DPF: penetration is observed; not deep

Back of DPF Middle of DPF Front of DPF

Na found in walls of cordierite DPFs N

a EP

MA

Ba

ck S

catt

er Im

ages


Back of DPF Middle of DPF Front of DPF N

a EP

MA

Ba

ck S

catt

er Im

ages

Na found in walls of cordierite DPFs • DOC-DPF-SCR: penetration is more severe; closer to DOC exotherm


Ash in long-term GM-aged DPFs (SiC) • Ash plugs apparent in rear of DPF • 20x more Ca than Na detected in

ash – Ca associated with standard

lube oil • Na not detected in wall of SiC DPF

FLOW FLOW

Ash plugs in exposed DPF channels

Ca Na

P S

EPMA of ash plugs in DPF

impact of biodiesel-based na on the selective catalytic ... · field pennycress, jatropha, etc. –...

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