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
20
40
60
80
100
120
140
160
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
0
50
100
150
200
250
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350
400
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
August 5, 2009 10
0
5
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25
30
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
40.00
50.00
60.00
70.00
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
15
20
25
30
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
10
20
30
40
50
60
70
80
30 40 50 60 70 80 90
Porosity (%)
Stre
ngth
(MPa
)
100
150
200
250
300
350
400
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.