August 5, 2009 1

Tailored Acicular Mullite Substrates for Multifunctional Diesel Particulate Filters

Michael Malanga*, Steven J. Martin, Robin Ziebarth, Alek Pyzik, Chan Han

* Dow Automotive, Auburn Hills, Michigan Emissions Control Technologies

August 5, 2009

2

Emerging Multifunctional Diesel Particulate Filters

• The promise of multifunctional diesel particulate filters:• Reduced volume and weight• Reduced system cost

* Fewer cans, canning operations, materials, etc.• Reduced total system pressure drop• Higher working temperatures for improved catalytic activity

• Key limitation for substrates to practical implementation:• Excessive filter pressure drop with high catalyst loads

DOC LNT CDPF DOC LNT + CDPF DOC + LNT +CDPF

DOC CDPF SCR DOC CDPF + SCR DOC + CDPF + SCR

Urea Urea Urea

August 5, 2009 3

0

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0 10 20 30 40 50 60

Total soot (g)

Pres

sure

dro

p (m

bar)

9x8 ACM uncoated 1000m3/hr9X9 Cordierite Coated 1000m3/hr8x12 SiC Coated 1000m3/hr

DPF Based on Acicular Mullite (ACM): Low Pressure Drop and Linear PD vs Soot Mass

ACM microstructure provides unique combination of gas permeability, catalyst coatability, and

substrate strength

8.34 lACM 9x8

9.38 lCordierite 9x9

9.88 lSiC 8x12

8.34 lACM 9x8

9.38 lCordierite 9x9

9.88 lSiC 8x12ACM

Cordierite

4

No Increase in Pressure Drop with Catalyst CoatingStandard CDPF Applications

ACM microstructure and enables high catalyst coating capacity

9X6.5 Pressure drop comparison: Coated vs uncoated

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0 10 20 30 40 50 60 70

Total soot (g)

Pres

sure

dro

p (m

bar)

1000m3/hr1500 m3/hr2000 m3/hr1000m3/hr coated1500m3/hr coated2000m3/hr coated

9/8/2009 5

Catalyzed ACM DPF Microstructure

ACM DPFwas coated with 80g/l or 2264g/cu.ftcatalyst

(200x SEM)

SEM analysis showed that ACM DPF can be coated with relatively high catalyst washcoat without significantly affecting the porosity or pore size Therefore, it maintains a low back pressure performance at very high catalyst

August 5, 2009 6

ACM SynthesisMullite Precursor

Alumina + Clay

(~1.7Al2O3·SiO2)

+ SiF4

~700C

- SiF4

~1100CFluorotopaz(Al2SiO4F2)

Acicular mullite(~1.7Al2O3

·SiO2)

After calcination, prior to conversion to Topaz

Honeycomb macrostructure created by extrusion, drying, and calcination

Porous microstructure created by reaction conversion to acicular mullite

August 5, 2009 7

Controlled ACM Microstructure Allows Tailored Catalyst + DPF Substrate

ACM Process allows control over pore size

and

porosityThrough control of free volume and morphology of microstructure in the walls

9 micron

30 micron

50 %

80 %

AveragePoreSize

Average %Porosity

August 5, 2009 8

Typical Pore Size Distribution in ACMAverage Pore Size is controlled with relatively narrow distribution through control of The morphology and any added porogens.

August 5, 2009 9

“Tailored”

Filter Substrate Evaluation

Simulated “Wash Coat”

Loading

•

Uniform coating of the

microstructure vs. layer on channel surface

•

Reproducible process using common catalyst material

•

Ability to apply multiple coats to assess pressure drop dependence on loading

Coating Procedure •

Filter was immersed in 20 wt% colloidal alumina

•

Excess removed by forcing air through the filter

•

Gas flow used to dry the filter•

Calcine

125 g/l Al2

O3

Prepare a Series of Pore Sizes and Porosities for ACM

• Microstructures with pore size from 9-23 um(64% average porosity)

• Porosity from 64-80% (18 um average pore size)

Example of Coated Substrate

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0 20 40 60 80 100 120

Flow, lpm

Cor

rect

ed d

p, in

. H2O

18-1, 0g/L Al2O318-3, 74g/L Al2O318-1, 128g/L Al2O318-2, 170g/L Al2O3

Pressure Drop Dependence on Coating for 64% Porosity ACM DPF

CDPF Applications•Catalyst loadings 20-40g/L•No PD increase on ACM at 64% porosity

NOx Control Systems•Catalyst loading determines NOx storage capacity or NOx reduction efficiency and time between regenerations•Catalysts loadings100-200g/L•PD increase at 64% porosity

128 g/l

74 g/l0 g/l

170 g/l

CatalystLoading

August 5, 2009 11

0.00

10.00

20.00

30.00

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80.00

0 50 100 150 200 250 300

Coating Concentration, g/l

PD a

t 30

lpm

, "H

2O

0107031 (9 micron)1607080 (17 micron)0809005 (23 micron)

0809011 (23 micron)

9 micron17 micron23 micron

model

Pressure Drop vs Alumina Wash Coat Loading for a Series of Pore SizesACM, 200 cpsi, 0.355 mm wall thickness, 64% porosity

23 um

17 um

9 um

August 5, 2009 12

ACM DPF Pressure Drop Dependence on Porosity at 125g/L Al2

O3 Loading

0

2

4

6

8

10

12

0 20 40 60 80 100

Flow , lpm

Pres

sure

Dro

p, in

H2O

T rap 1 - 64%Trap 2 - 70%Trap 3 - 75%Trap 4 - 80%

80%

75%

70%

64%Porosity

August 5, 2009 13

0

5

10

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20

25

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0 20 40 60 80 100 120

Flow , lpm

Cor

rect

ed d

p, in

. H2O

18-1, 0g/L Al2O 3

18-3, 74g/L Al2O 3

18-2, 170g/L Al2O 3

75-2, 170g/L Al2O 3

Increased Porosity Reduces P at HighAl2

O3 LoadingAn increase of porosity from 64% to 75% allows a doubling of the

catalyst loading (75 to 150g/L alumina) with small increase in pressure drop. (constant pore size)

0 g/l, 64%

170 g/l, 64%

170 g/l, 75%

August 5, 2009 14

Strength and MTSF Dependence on Pore Volume Fraction in ACM Honeycombs

Failure stress was determined using the method outlined in ASTM C 1674-08 “Flexural Strength of Advanced Ceramics with Engineered Porosity (Honeycomb Cellular Channels) at Ambient Temperatures”. (4-point bend test)

Elastic modulus was tested following the method outlined in ASTM C 1259-94, “Standard Test Method for Dynamic Young’s Modulus, Shear Modulus, and Poisson’s Ratio for Advanced Ceramics by Impulse Excitation of Vibration”.

Cordierite data:

G.A. Merkel, et al., “New Cordierite Diesel Particulate Filters for Catalyzed and Non-Catalyzed Applications,”

Proceedings of the 9th Diesel Engine Emissions Reduction Conference August 24-28, 2003, Newport, Rhode Island

E

MTSF

Honeycomb Comparison

0

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30 40 50 60 70 80 90

Porosity (%)

Stre

ngth

(MPa

)

100

150

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450

500

MTS

F (°

C)

ACM cordierite MTSF

August 5, 2009 15

Tailored Acicular Mullite Substrates for Multifunctional Diesel Particulate

•

ACM microstructure and morphology allows for unique control of pore sizes and porosity.

•

Larger pore sizes allow high catalyst loads with significantly lower back pressures.

•

High porosity enable high catalyst loads with minimal pressure drop increase

•

Optimization of these parameters along with wall thickness and CPSI can create a catalyst/DPF substrate with improved multifunctional

capability.