U.S. patent application number 14/793252 was filed with the patent office on 2016-02-04 for systems and methods for diesel oxidation catalyst with decreased so3 emissions.
The applicant listed for this patent is Clean Diesel Technologies, Inc.. Invention is credited to Randal L. Hatfield.
Application Number | 20160030885 14/793252 |
Document ID | / |
Family ID | 51654598 |
Filed Date | 2016-02-04 |
United States Patent
Application |
20160030885 |
Kind Code |
A1 |
Hatfield; Randal L. |
February 4, 2016 |
SYSTEMS AND METHODS FOR DIESEL OXIDATION CATALYST WITH DECREASED
SO3 EMISSIONS
Abstract
A diesel oxidation catalyst (DOC) catalytic converter for at
least the conversion of carbon monoxide and hydrocarbons, removal
of a fraction of particulate matter, and decrease of sulfur
trioxide emissions within exhaust gases from an engine and
consequently of sulfuric acid, is disclosed. The DOC may include
any suitable configuration including at least a substrate and a
washcoat, where the substrate has a plurality of channels, suitable
porosity, offers a three-dimensional support for the washcoat, and
is made of any suitable material. The washcoat may be deposited on
the substrate by any suitable method, and may include a mixture of
at least one or more carrier material oxides and one or more
catalysts. Suitable materials for the carrier material oxides may
include titanium dioxide, tin dioxide, and zirconium dioxide, among
others, excluding aluminum oxide (Al.sub.2O.sub.3), which may serve
for a decrease of sulfur trioxide emissions and consequently of
sulfuric acid mist. Suitable catalysts within the washcoat may
include platinum, palladium, rhodium, and iridium, among
others.
Inventors: |
Hatfield; Randal L.; (Port
Hueneme, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Clean Diesel Technologies, Inc. |
Oxnard |
CA |
US |
|
|
Family ID: |
51654598 |
Appl. No.: |
14/793252 |
Filed: |
July 7, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13861432 |
Apr 12, 2013 |
9076094 |
|
|
14793252 |
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Current U.S.
Class: |
423/213.2 |
Current CPC
Class: |
B01D 2255/1021 20130101;
Y02A 50/20 20180101; B01D 2255/2094 20130101; B01D 2258/012
20130101; B01D 2255/1025 20130101; B01D 53/8609 20130101; B01D
2255/1028 20130101; B01D 2255/2092 20130101; B01D 53/944 20130101;
B01D 2255/20715 20130101; B01D 2255/20707 20130101; B01D 2255/915
20130101; B01D 2255/1023 20130101; Y02A 50/2341 20180101; B01D
2257/302 20130101 |
International
Class: |
B01D 53/86 20060101
B01D053/86; B01D 53/94 20060101 B01D053/94 |
Claims
1. A method for reducing emissions from a diesel engine having
associated therewith an exhaust system, the method providing a
catalyst system for a catalytic reaction, the method further
comprising the steps of: providing a substrate; and depositing on
said substrate a washcoat suitable for deposition on the substrate
and comprising at least one carrier material oxide, at least one
catalyst, or mixtures thereof, wherein the at least one carrier
material oxide is selected from the group consisting of titanium
oxide, tin dioxide, zirconium dioxide and aluminum oxide, and
wherein the catalyst comprises platinum and palladium; and wherein
at least one carbon monoxide and at least one hydrocarbon is
oxidized by the catalyst system, and wherein oxidation of sulfur
dioxide also occurs and is at a lower percentage than that
achievable without the at least one carrier material oxide.
2. The method of claim 1, wherein the substrate is selected from
the group consisting of a refractive material, a ceramic substrate,
a honeycomb structure, a metallic substrate, a ceramic foam, a
metallic foam, a reticulated foam, and mixtures thereof.
3. The method of claim 1, wherein the substrate comprises a
plurality of channels.
4. The method of claim 1, wherein the substrate comprises at least
one of the group consisting of alumina, silica alumina, silica,
titania, sillimanite, zirconia, petalite, lithium aluminum
silicate, magnesium silicates, mullite, alumina, cordierite,
silicon carbide, silicon nitride, and aluminum nitride.
5. The method of claim 1, where the washcoat is formed by
deposition of a slurry.
6. The method of claim 5, wherein the deposition of the slurry is
by dip coating or spray coating.
7. The method of claim 1, wherein the washcoat further comprises at
least one oxide solid.
8. The method of claim 1, wherein the at least one catalyst
consists of platinum and palladium.
9. The method of claim 1, wherein the ratio of platinum to
palladium is selected from the group consisting of about 18:1,
about 15:1, about 10:1, about 5:1, about 3:1, about 2.5:1, and
about 1:1.
10. The method of claim 1, wherein the washcoat further comprises
at least one second catalyst, wherein the at least one second
catalyst comprises rhodium and iridium.
11. The method of claim 10, wherein the ratio of rhodium to iridium
is selected from the group consisting of about 18:1, about 15:1,
about 10:1, about 5:1, about 3:1, about 2.5:1, and about 1:1.
12. The method of claim 1, wherein the at least one carrier
material oxide is titanium oxide and the oxidation of sulfur
dioxide is reduced by about 50%.
13. The method of claim 1, wherein the at least one carrier
material oxide is titanium oxide and the oxidation of sulfur
dioxide is reduced by about 80%.
14. The method of claim 1, wherein the at least one carrier
material oxide is tin dioxide and the oxidation of sulfur dioxide
is reduced by about 50%.
15. The method of claim 1, further comprising depositing on said
substrate of an overcoat comprising the at least one catalyst.
16. The method of claim 1, further comprising depositing on said
substrate of an overcoat comprising at least one second catalyst.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation application of U.S.
patent application Ser. No. 13/861,432, filed Apr. 4, 2013,
entitled Systems and Methods for Diesel Oxidation Catalyst with
Decreased SO.sub.3 Emissions, the entirety of which is incorporated
by reference herein.
BACKGROUND
[0002] 1. Field of the Disclosure
[0003] The present disclosure relates generally to catalytic
converters, and more particularly to a diesel oxidation catalyst
for decreasing sulfur trioxide emissions and consequently sulfuric
acid mist.
[0004] 2. Background Information
[0005] One problem faced in the treatment of diesel engine exhaust
is presented by the presence of sulfur in diesel fuel. Upon
combustion, sulfur forms sulfur dioxide (SO.sub.2), which a diesel
oxidation catalyst (DOC) catalyzes to sulfur trioxide (SO.sub.3)
with subsequent formation of condensable acidic sulfur compounds,
such as sulfuric acid, which condense upon and thereby add to the
mass of particulates. Additionally, sulfuric acid can cause
corrosion of the downstream exhaust system leading to perforation
and damage to components. DOCs are also generally used for burning
(oxidizing) HC and CO as well as some of the soluble organic
compounds that are adsorbed on soot particles. Additionally, DOCs
may be used for oxidizing nitrous oxides (N.sub.2O) to nitrogen
dioxide (NO.sub.2). Under certain conditions, presence of NO.sub.2
may not be favorable, such as in mining or other underground
conditions, because the NO.sub.2 may be toxic. On the other hand,
in other conditions, especially when a DPF is located after the
DOC, NO.sub.2 formation may be favorable because it may oxidize
soot which may help to regenerate the DPF.
[0006] Typical DOCs include a coating of one or more carrier
material oxides, such as aluminum oxide, silicon dioxide, titanium
dioxide, and cerium oxide, as well as mixtures thereof; one or more
zeolites for absorbing HCs; and platinum, in addition to small
amounts of palladium, in ratios of about 15:1, 10:1, 5:1, 3:1,
2.5:1, and 1:1, employed as a catalytically active component on a
ceramic or metal substrate. The employed carrier material oxides
have a large surface area of about 150 m.sup.2/g to about 300
m.sup.2/g and may generally remain stable up to exhaust gas
temperatures of about 800.degree. C. In order to achieve a high
degree of catalytic activity, the catalysts are distributed very
finely on the carrier material oxides, producing high amounts of
SO.sub.3. Deterioration in activity of the oxidation catalyst
caused by sulfur from SO.sub.3, as well as contamination and
corrosion from sulfuric acid mist, are a major concern.
SUMMARY
[0007] The present disclosure relates to a diesel oxidation
catalyst (DOC) catalytic converter that uses oxygen for converting
at least carbon monoxide (CO) to carbon dioxide (CO.sub.2) and
hydrocarbons (HC) to water and CO.sub.2, while suppressing the
formation of sulfur trioxide (SO.sub.3) and consequently of
sulfuric acid (H.sub.2SO.sub.4) mist within exhaust gases from an
engine. Additionally, the present DOC may be used for removal of a
fraction of particulate matter (PM). The DOC may include at least a
substrate and a washcoat, although other suitable configurations
may be utilized.
[0008] According to aspects of the present disclosure, the
substrate may be a refractive material, a ceramic substrate, a
honeycomb structure, a metallic substrate, a ceramic foam, a
metallic foam, a reticulated foam, or suitable combinations, where
the substrate may have a plurality of channels and a suitable
porosity and offers a three-dimensional support for the washcoat.
Suitable materials for the substrate may include alumina, silica
alumina, silica, titania, sillimanite, zirconia, petalite,
spodumene (lithium aluminum silicate), magnesium silicates,
mullite, alumina, cordierite, other alumino-silicate materials,
silicon carbide, silicon nitride, aluminum nitride, and
combinations thereof.
[0009] The washcoat material may be deposited on the substrate by
suspending oxide solids in water to form an aqueous slurry and
depositing the aqueous slurry on the substrate. Other components
may optionally be added to the aqueous slurry to adjust rheology of
the slurry and/or enhance binding of the washcoat to the substrate.
The slurry may be placed on the substrate in any suitable manner,
such as dip coating or spray coating.
[0010] The washcoat material may include oxide solids with a
mixture of at least one or more carrier material oxides and one or
more catalysts. Suitable carrier material oxides within the
washcoat may include titanium dioxide, tin oxide, and zirconium
dioxide, among others. Additional aspects of the present disclosure
may involve excluding conventionally used aluminum oxide
(Al.sub.2O.sub.3) as a carrier material oxide. Excluding
Al.sub.2O.sub.3 may serve for decreasing amounts of SO.sub.3,
produced when sulfur in the exhaust gas makes contact with the
catalyst in the washcoat. Excluding Al.sub.2O.sub.3 may further
permit decreasing SO.sub.3 by about 10 times or more, and may
inhibit formation of corrosive H.sub.2SO.sub.4 mist.
[0011] Finally, suitable catalysts in the washcoat for oxidation of
CO and HC may include platinum and palladium in ratios of about
18:1, 15:1, 10:1, 5:1, 3:1, 2.5:1, and 1:1, although other suitable
catalysts, such as rhodium and iridium, may be employed at other
suitable ratios. The DOC of the present disclosure may be suitable
for the oxidative purification of exhaust gases from diesel engines
running on high-sulfur diesel because of a high decrease of
SO.sub.3 production and consequently of lower levels of
H.sub.2SO.sub.4 mist.
LIST OF FIGURES
[0012] Embodiments of the present disclosure are described by way
of example with reference to the accompanying figures, which are
schematic and are not intended to be drawn to scale. Unless
indicated as representing prior art, the figures represent aspects
of the present disclosure.
[0013] FIG. 1 depicts a diesel oxidation catalyst (DOC)
configuration including a substrate and a washcoat, according to an
embodiment.
[0014] FIG. 2 depicts the DOC from the present disclosure employed
in an exhaust cleaning system of a diesel vehicle, according to an
embodiment.
DETAILED DESCRIPTION
Definitions
[0015] As used herein, the following terms have the following
definitions:
[0016] "SO.sub.3 decrease" refers to inhibiting formation of sulfur
trioxide by catalytic reactions of materials included in oxide
solids in a diesel oxidation catalyst.
[0017] "H.sub.2SO.sub.4 decrease" refers to inhibiting formation of
vapor sulfuric acid as a result of SO.sub.3 decrease.
[0018] "Oxide solids" refers to materials including those selected
from the group of at least a carrier material oxide, a catalyst,
and/or a mixture thereof.
[0019] "Carrier material oxides" refers to support materials used
for providing a surface for at least one catalyst.
[0020] "Catalysts" refers to materials employed for conversion of
at least hydrocarbons and carbon monoxide from exhaust gases.
DESCRIPTION OF THE DRAWINGS
[0021] Various example embodiments of the present disclosure are
described more fully with reference to the accompanying drawings in
which some example embodiments of the present disclosure are shown.
In the drawings, the thicknesses of layers and regions may be
exaggerated for clarity. Detailed illustrative embodiments of the
present disclosure are disclosed herein. However, specific
structural and functional details disclosed herein are merely
representative for purposes of describing example embodiments of
the present disclosure. This disclosure however, may be embodied in
many alternate forms and should not be construed as limited to only
the embodiments set forth herein.
[0022] The present disclosure describes a diesel oxidation catalyst
(DOC) that includes at least a substrate and a washcoat that may be
treated and deposited on the substrate. The DOC of the present
disclosure may permit decreasing sulfur trioxide (SO.sub.3) by
about 10 times or more, and consequently a decrease of sulfuric
acid (H.sub.2SO.sub.4) mist.
[0023] Substrate Composition
[0024] FIG. 1 shows a DOC 100 that may generally be mounted before
a diesel particulate filter (DPF) in an exhaust pipe of an engine,
and which may be used at least to oxidize hydrocarbons (HC) and
carbon monoxide (CO), remove parts of particulate matter (PM), and
decrease SO.sub.3 and consequently H.sub.2SO.sub.4 within an
Exhaust Gas 102. DOC 100 may generally be set in different
configurations that may include at least a Substrate 104 and a
Washcoat 106, although other configurations may be employed.
[0025] Substrate 104 may be a refractive material, a ceramic
substrate, a honeycomb structure, a metallic substrate, a ceramic
foam, a metallic foam, a reticulated foam, or suitable
combinations, where Substrate 104 may have a plurality of channels
and a suitable porosity. Substrate 104, either metallic or ceramic,
may offer a three-dimensional support structure.
[0026] According to an embodiment, Substrate 104 may be in the form
of beads or pellets, or any suitable form. Substrate 104 may be
formed from any suitable material, including alumina, silica
alumina, silica, titania, and mixtures thereof. In another
embodiment, Substrate 104 may be a ceramic honeycomb Substrate 104
or a metal honeycomb Substrate 104. The ceramic honeycomb Substrate
104 may be formed from any suitable material, including
sillimanite, zirconia, petalite, spodumene (lithium aluminum
silicate), magnesium silicates, mullite, alumina, cordierite (e.g.
Mg2A14Si5O18), other alumino-silicate materials, silicon carbide,
silicon nitride, aluminum nitride, and combinations thereof. The
metal honeycomb Substrate 104 may be formed from a heat-resistant
base metal alloy, particularly an alloy that includes iron.
[0027] According to an embodiment, Substrate 104 may be a
monolithic carrier having a plurality of fine, parallel flow
passages extending through the monolith. The passages can be of any
suitable cross-sectional shape and/or size. The passages may be of
any suitable shape, including trapezoidal, rectangular, square,
sinusoidal, hexagonal, oval, and circular. The monolith may contain
from about 9 to about 1200 or more gas inlet openings or passages
per square inch of cross section, although fewer passages may be
used.
[0028] Washcoat Preparation and Deposition Method
[0029] According to an embodiment, Washcoat 106 may be formed on
Substrate 104 by suspending oxide solids in water to form an
aqueous slurry and depositing the aqueous slurry on Substrate 104.
Other components may optionally be added to the aqueous slurry to
adjust rheology of the slurry and/or enhance binding of Washcoat
106 to Substrate 104. These other components may include acid or
base solutions or various salts or organic compounds, such as
ammonium hydroxide, aluminum hydroxide, acetic acid, citric acid,
tetraethylammonium hydroxide, other tetraalkylammonium salts,
ammonium acetate, ammonium citrate, glycerol, commercial polymers
such as polyethylene glycol, polyvinyl alcohol and other suitable
polymers.
[0030] The slurry may be placed on Substrate 104 in any suitable
manner. For example, Substrate 104 may be dipped into the slurry,
or the slurry may be sprayed on Substrate 104. If Substrate 104 is
a monolithic carrier with parallel flow passages, Washcoat 106 may
be formed on the walls of the passages. Exhaust Gas 102 flowing
through the flow passages can contact Washcoat 106 on the walls of
the passages as well as materials that are supported on Washcoat
106.
[0031] Washcoat Composition
[0032] Suitable carrier material oxides within oxide solids in
Washcoat 106 may include thermally stable and very high surface
area materials. Surface area of carrier material oxides may range
from 150 m.sup.2/g to about 350 m.sup.2/g, and may generally be
stable at temperatures of about 700.degree. C. to about
1000.degree. C., with 800.degree. C. being preferred.
[0033] Carrier material oxides generally used in the art include
beta zeolites, MFI, ZSM-5, ferrierite, and SAPO's, and other
zeolites, with a ratio of silica (SiO.sub.2) to aluminum oxide
(Al.sub.2O.sub.3) of about 8:200. Other suitable materials used in
the art may generally include oxygen storage materials, doped
aluminum oxide, spinel, delafossite, lyonsite, garnet, perovksite,
pyrochlore, doped ceria, fluorite, zirconium oxide, doped zirconia,
titanium oxide, tin oxide, silicon dioxide, zeolite, and mixtures
thereof.
[0034] According to an aspect of the present disclosure, suitable
Carrier Material Oxides 108 in Washcoat 106 may include titanium
dioxide (TiO.sub.2), tin dioxide (SnO.sub.2), and zirconium dioxide
(ZrO.sub.2), amongst others. Additional aspects of the present
disclosure may involve excluding Al.sub.2O.sub.3 as a carrier
material oxide in Washcoat 106, which may serve for decreasing
SO.sub.3, produced when sulfur in Exhaust Gas 102 makes contact
with the catalyst within Washcoat 106. SO.sub.3 may plug filters
and corrode parts of a vehicle's exhaust system, and may lead to
formation of H.sub.2SO.sub.4 mist, which is a highly corrosive
contaminant. Excluding aluminum oxide may permit decreasing
SO.sub.3 by about 10 times or more.
[0035] Finally, suitable Catalysts 110 in Washcoat 106 for
oxidation of CO and HC may include platinum/palladium in ratios of
about 18:1, 15:1, 10:1, 5:1, 3:1, 2.5:1, and 1:1, although other
suitable Catalysts 110, such as rhodium and iridium, may be
employed at other suitable ratios. The Catalysts 110 from DOC 100
use O.sub.2 (oxygen) in Exhaust Gas 102 to convert at least CO to
CO.sub.2 (carbon dioxide) and HC to H.sub.2O (water) and
CO.sub.2.
[0036] Table 1 shows a comparison of SO.sub.3 production performed
by a standard 18/1/0 (Pt, Pd, and Rh in g/ft.sup.3) DOC and an
18/1/0 DOC 100 on TiO.sub.2. As may be appreciated, the production
of SO.sub.3 by a standard DOC is defined as 100%, while the
relative production by 18/1/0 DOC 100 on TiO.sub.2 is of about 12%.
Additional data shown on Table 1 are the CO and HC conversion by
each of these DOCs. For the CO and HC conversion, measurements were
performed after the catalysts were aged at about 750.degree. C. for
about 5 hours and then exposed to SO.sub.2 poisoning for about 100
ppm SO.sub.2 at about 300.degree. C. for about 100 hours, plus
about 50 minutes of about 30 ppm of SO.sub.2 at about 300.degree.
C. The SO.sub.3 production was measured on fresh catalysts.
TABLE-US-00001 TABLE 1 Sample Description 18/1/0 Standard DOC
18/1/0 on TiO.sub.2 Relative SO.sub.3 100% 12% Production % CO
Conversion % 99.23% 99.15% HC Conversion % 98.12% 94.86%
[0037] Table 2 shows the production of SO.sub.3 and conversion of
CO and HC by DOCs at 3/3/0. As may be appreciated, the production
of SO.sub.3 by a standard CS-570 DOC at 3/3/0 is defined as 100%.
At these conditions, the relative SO.sub.3 production by a DOC 100
on TiO.sub.2 is of about 20%; the relative SO.sub.3 production by a
DOC on (69% ZrO2, 29% SnO.sub.2, 1.4% CaO) is of about 100.01%; and
the relative SO.sub.3 production by a DOC on SnO.sub.2 is of about
50%. Additional data shown on Table 2 are the CO and HC conversion
by each of these DOCs. For the CO and HC conversions, measurements
were performed after the catalysts were aged at about 750.degree.
C. for about 5 hours and then exposed to SO.sub.2 poisoning for
about 100 ppm SO.sub.2 at about 300.degree. C. for about 100 hours,
plus about 50 minutes of about 30 ppm of SO.sub.2 at about
300.degree. C. The SO.sub.3 production was measured on fresh
catalysts.
TABLE-US-00002 TABLE 2 Standard 3/3/0 on (69% ZrO.sub.2, Sample
CS-570 DOC 3/3/0 on 29% SnO.sub.2, 3/3/0 on Description (3/3/0)
TiO.sub.2 1.4% CaO) SnO.sub.2 Relative SO.sub.3 100% 20% 100.01%
50% Production % CO 96.77% 94.79% 97.89% 96.16% Conversion % HC
98.30% 89.16% 94.54% 94.80% Conversion %
[0038] Table 3 shows the production of SO.sub.3 and conversion of
CO and HC by DOCs at 0/20/0 being compared to the standard CS-570
DOC at 3/3/0, defined as 100%. As may be appreciated, the relative
SO.sub.3 production by a DOC 100 on TiO.sub.2 at these conditions
is of about 44%, and the relative SO.sub.3 production by a DOC on
(69% ZrO2, 29% SnO.sub.2, 1.4% CaO) is of about 23%. Comparing DOC
(69% ZrO2, 29% SnO.sub.2, and 1.4% CaO) at 3/3/0 (100.01%) and at
0/20/0 (23%), a large reduction of SO.sub.3 production may be
appreciated when using only Pd as a catalyst 110 within Washcoat
106. Additional data shown on Table 3 are the CO and HC conversion
by each of these DOCs. For the CO and HC conversions, measurements
were performed after the catalysts were aged at 750.degree. C. for
about 5 hours and then exposed to SO.sub.2 poisoning for about 100
ppm SO.sub.2 at about 300.degree. C. for about 100 hours, plus
about 50 minutes of about 30 ppm of SO.sub.2 at about 300.degree.
C. The SO.sub.3 conversion was measured on fresh catalysts.
TABLE-US-00003 TABLE 3 Standard Sample CS-570 DOC 0/20/0 on (69%
ZrO.sub.2, Description (3/3/0) 0/20/0 on TiO.sub.2 29% SnO.sub.2,
1.4% CaO) Relative SO.sub.3 100% 44% 23% Production % CO 96.77%
91.84% 93.90% Conversion % HC 98.30% 94.54% 96.35% Conversion %
[0039] FIG. 2 shows an Exhaust Cleaning System 200 that includes a
DOC 100 for oxidizing HC and CO, eliminating a fraction of PM, and
decreasing SO.sub.3 emissions and consequently production of
H.sub.2SO.sub.4 mist, according to an embodiment. FIG. 2 includes
Exhaust Gas 102, a DOC 100, a diesel particulate filter (DPF 202),
Urea 206, a selective catalytic reduction (SCR 204), and a Cleaned
Exhaust Gas 208.
Examples
[0040] Example #1 is an embodiment of an Exhaust Cleaning System
200. Initially, DOC 100 oxidizes CO to CO.sub.2 and HC to H.sub.2O
(water) and CO.sub.2 from incoming Exhaust Gas 102, while removing
a fraction of PM (up to 90%) and decreasing SO.sub.3 emissions by
about 10 times or more and consequently formation of
H.sub.2SO.sub.4 mist. Subsequently, Exhaust Gas 102 passes through
DPF 202, which is a soot trap for removing remaining PM and soot
from Exhaust Gas 102. DPF 202 may include a cordierite or silicon
carbide substrate with a geometry that forces Exhaust Gas 102 to
flow through the substrate walls. Other suitable materials may be
employed in DPF 202, such as rare metals including palladium,
silver, or platinum, for providing higher efficiency. Finally, Urea
206 may be injected before SCR 204 for thermal decomposition and
hydrolysis to form ammonia, which reduces NO.sub.x into nitrogen,
resulting in a Cleaned Exhaust Gas 208. Urea 206 may be
commercially available as AdBlue, although other commercially
available Urea 206 may be employed.
[0041] Example #2 is a second DOC configuration for oxidizing HC
and CO and decreasing SO.sub.3 emissions. The second DOC
configuration includes a substrate, a washcoat including at least
one catalyst and carrier oxide materials, and an overcoat including
at least one catalyst material.
[0042] Example #3 is a third DOC configuration for oxidizing HC and
CO and decreasing SO.sub.3. The third DOC configuration includes a
substrate, a washcoat including carrier oxide materials but no
catalyst materials, and an overcoat including catalyst
materials.
* * * * *