U.S. patent application number 11/858203 was filed with the patent office on 2008-03-27 for treatment systems and methods for internal combustion engine exhaust streams.
Invention is credited to Sanath V. Kumar.
Application Number | 20080072578 11/858203 |
Document ID | / |
Family ID | 39092158 |
Filed Date | 2008-03-27 |
United States Patent
Application |
20080072578 |
Kind Code |
A1 |
Kumar; Sanath V. |
March 27, 2008 |
Treatment Systems and Methods for Internal Combustion Engine
Exhaust Streams
Abstract
Emissions treatment systems and methods are disclosed, which
reduce the carbon monoxide, unburned hydrocarbons, and nitrogen
oxides content in the exhaust stream of an internal combustion
engine adjusted to a rich combustion ratio. One embodiment of a
system comprises an ammonia oxidation catalyst, a supplemental air
supply for providing a lean combustion ratio, and at least one
three-way catalyst. Another embodiment further comprises a second
three-way catalyst located in the exhaust stream.
Inventors: |
Kumar; Sanath V.; (North
Brunswick, NJ) |
Correspondence
Address: |
BASF CATALYSTS LLC
100 CAMPUS DRIVE
FLORHAM PARK
NJ
07932
US
|
Family ID: |
39092158 |
Appl. No.: |
11/858203 |
Filed: |
September 20, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60826487 |
Sep 21, 2006 |
|
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Current U.S.
Class: |
60/299 ; 422/222;
60/274 |
Current CPC
Class: |
F01N 3/281 20130101;
F01N 2610/02 20130101; F01N 3/206 20130101; F01N 3/2835 20130101;
Y02T 10/22 20130101; B01D 2251/2062 20130101; B01D 2255/9022
20130101; B01D 53/9477 20130101; B01D 2255/20738 20130101; F01N
3/22 20130101; B01D 2255/504 20130101; B01D 2255/50 20130101; F01N
3/2832 20130101; B01D 53/945 20130101; Y02T 10/12 20130101; B01D
2255/407 20130101; F01N 3/30 20130101; F01N 3/0814 20130101 |
Class at
Publication: |
60/299 ; 422/222;
60/274 |
International
Class: |
F01N 3/20 20060101
F01N003/20; F01N 3/10 20060101 F01N003/10 |
Claims
1. An emissions treatment system for reducing carbon monoxide,
unburned hydrocarbons, and nitrogen oxides content in an exhaust
gas stream of an internal combustion engine adjusted to a rich
combustion ratio comprising: an ammonia oxidation catalyst; a
supplemental air source for supplying supplemental air upstream of
the ammonia oxidation catalyst; and a first three-way catalyst
located to receive and pass the exhaust gas from the engine through
the first three-way catalyst, wherein the internal combustion
engine is adjusted to the rich combustion ratio.
2. The emissions treatment system of claim 1, wherein the first
three-way catalyst is located upstream of the supplemental air
source.
3. The emissions treatment system of claim 1, wherein the first
three-way catalyst is located downstream from the ammonia oxidation
catalyst, and the supplemental air source is upstream of the
ammonia oxidation catalyst.
4. The emissions treatment system of claim 2 further comprising a
second three-way catalyst located downstream from the ammonia
oxidation catalyst.
5. The emissions treatment system of claim 4 wherein: the first
three-way catalyst comprises a precious metal component and a rare
earth oxide deposited on a substrate; the ammonia oxide catalyst
comprises a precious metal component; a zeolite component
containing a base metal oxide selected from the group consisting of
oxides of chromium, manganese, iron, cobalt, nickel, copper,
vanadium, titanium, zinc, and combinations thereof and a silica
component; deposited on a substrate; and the second three-way
catalyst comprises a precious metal component and a rare earth
oxide deposited on a substrate.
6. The emissions treatment system of claim 1 wherein the first
three-way catalyst comprises a precious metal component selected
from the group consisting of platinum, palladium, rhodium, and
combinations thereof; and a rare earth oxide selected from the
group consisting of ceria, lanthana, praseodymia, neodymia, and
combinations thereof.
7. The emissions treatment system of claim 1 wherein the first
three-way catalyst comprises: a first catalytic layer deposited on
a substrate comprising a platinum component in an amount in the
range of about 12.5 to about 100 g/ft.sup.3, an alumina support in
an amount in the range of about 0.2 to about 2.0 g/in.sup.3, a
ceria-zirconia composite in an amount in the range of about 0.2 to
about 1.0 g/in.sup.3, a zirconium component in an amount in the
range of about 0.03 to about 0.15 g/in.sup.3, and a barium
component in an amount in the range of about 0.03 to about 0.15
g/in.sup.3; and a second catalytic layer deposited on the first
catalytic layer comprising a rhodium component in an amount of
about 12.5 to about 100 g/ft.sup.3, an alumina support in an amount
in the range of about 0.2 to about 2.0 g/in.sup.3, a ceria-zirconia
composite in an amount in the range of about 0.2 to about 1.0
g/in.sup.3, and a zirconium component in an amount in the range of
about 0.03 to about 0.15 g/in.sup.3.
8. The emissions treatment system of claim 1 wherein the ammonia
oxidation catalyst comprises a layer deposited on a substrate
comprising a platinum component in an amount in the range of about
1 to about 25 g/ft.sup.3, a zeolite component in an amount in the
range of about 0.5 to about 2.5 g/in.sup.3, wherein the zeolite
component contains iron, and a silica component in an amount in the
range of about 0.1 to about 1.5 g/in.sup.3.
9. The emissions treatment system of claim 4 wherein the second
three-way catalyst comprises a precious metal component selected
from the group consisting of platinum, palladium, rhodium, and
combinations thereof; and a rare earth oxide selected from the
group consisting of ceria, lanthana, praseodymia, neodymia, and
combinations thereof.
10. The emissions treatment system of claim 4 wherein a monolithic
substrate comprises a first discrete portion including a coating of
the ammonia oxidation catalyst, and a second discrete portion
including a coating of the second three-way catalyst.
11. The emissions treatment system of claim 10 wherein the
monolithic substrate selected from the group consisting of a
ceramic material with a multiplicity of passageways therethrough, a
metallic material being in the form of an expanded matrix, and a
metallic material being in the form of a flat or corrugated metal
foil configured in a multiplicity of layers.
12. The emissions treatment system of claim 3 wherein: the ammonia
oxidation catalyst comprises a platinum component in an amount in
the range of about 1 to about 25 g/ft.sup.3, and is effective to
selectively oxidize at least about 99% of ammonia formed in the
first three-way catalyst to nitrogen and water, and to selectively
reduce the nitrogen oxides to nitrogen; and the first three-way
catalyst comprises a precious metal component, a base metal oxide
selected from the group consisting of oxides of chromium,
manganese, iron, cobalt, nickel, copper, vanadium, titanium, zinc,
and combinations thereof, and a rare earth oxide deposited on a
substrate, and is effective to oxidize at least about 99% of the
unburned hydrocarbon to carbon dioxide and water, oxidize at least
about 99% of the carbon monoxide to carbon dioxide.
13. The emissions treatment system of claim 12 wherein the ammonia
oxidation catalyst comprises a zeolite component in an amount in
the range of about 0.5 to about 2.5 g/in.sup.3, wherein the zeolite
of contains iron or a copper-oxide copper-nitrate composite in an
amount in the range of about 0.1 to about 0.5 g/in.sup.3 and a
silica component in an amount in the range of about 0.1 to about
1.5 g/in.sup.3.
14. The emissions treatment system of claim 12 wherein the first
three-way catalyst comprises a first catalytic layer deposited on
the substrate comprising a platinum component in an amount in the
range of about 12.5 to about 100 g/ft.sup.3, an alumina support in
an amount in the range of about 0.2 to about 2.0 g/in.sup.3, a
ceria-zirconia composite in an amount in the range of about 0.2 to
about 1.0 g/in.sup.3, a zirconium component in the range of about
0.03 to about 0.15 g/in.sup.3, and a barium component in an amount
in the range of about 0.03 to about 0.15 g/in.sup.3; and a second
catalytic layer deposited on the first catalytic layer, the second
catalytic layer comprising a rhodium component in the range of
about 12.5 to about 100 g/ft.sup.3, an alumina support in an amount
in the range of about 0.2 to about 2.0 g/in.sup.3, a ceria-zirconia
composite in the range of about 0.2 to about 1.0 g/in.sup.3, and a
zirconium component in the range of about 0.03 to about 0.15
g/in.sup.3.
15. A method for reducing carbon monoxide, unburned hydrocarbons,
and nitrogen oxides in an exhaust stream of an internal combustion
engine comprising: providing the internal combustion engine
adjusted to a rich combustion ratio; passing the exhaust stream
through a first three-way catalyst; adding sufficient air to the
exhaust stream, upstream of an ammonia oxidation catalyst, to
provide a lean combustion ratio; and passing the exhaust stream
through the ammonia oxidation catalyst.
16. The method of claim 15, wherein passing the exhaust stream
through the ammonia oxidation catalyst occurs after passing the
exhaust stream through the first three-way catalyst.
17. The method of claim 16, further comprising passing the exhaust
stream exiting the ammonia oxidation catalyst through a second
three-way catalyst.
18. The method of claim 15 further comprising providing a
sufficient amount of the first three-way catalyst to oxidize at
least about 50% of the carbon monoxide to carbon dioxide, and to
oxidize at least about 50% of the unburned hydrocarbons to carbon
dioxide and water, and providing a sufficient amount of the ammonia
oxidation catalyst to selectively oxidize at least about 99% of
ammonia formed in the first three-way catalyst to nitrogen and
water.
19. The method of claim 17 further comprising providing a
sufficient amount of the second three-way catalyst to oxidize at
least about 99% of the unburned hydrocarbons entering the second
three-way catalyst to carbon dioxide and water, and about 99% of
the carbon monoxide entering the second three-way catalyst to
carbon dioxide.
20. An exhaust system for reducing the carbon monoxide, unburned
hydrocarbons, and nitrogen oxides content in an exhaust stream of
an internal combustion engine adjusted to a rich stoichiometric
ratio comprising: an exhaust conduit located to receive exhaust
from the engine; a first three-way catalyst located to receive and
pass the exhaust gas through the first three-way catalyst, the
first three-way catalyst comprising a first catalytic layer
deposited on a first substrate comprising a platinum component in
an amount in the range of about 12.5 to about 100 g/ft.sup.3, an
alumina support in an amount in the range of about 0.2 to about 2.0
g/in.sup.3, a ceria-zirconia composite in an amount in the range of
about 0.2 to about 1.0 g/in.sup.3, a zirconium component in the
range of about 0.03 to about 0.15 g/in.sup.3, and a barium
component in an amount in the range of about 0.03 to about 0.15
g/in.sup.3; and a second catalytic layer deposited on the first
catalytic layer, the second catalytic layer comprising a rhodium
component in the range of about 12.5 to about 100 g/ft.sup.3, an
alumina support in an amount in the range of about 0.2 to about 2.0
g/in.sup.3, a ceria-zirconia composite in the range of about 0.2 to
about 1.0 g/in.sup.3, and a zirconium component in the range of
about 0.03 to about 0.15 g/in.sup.3, wherein the first substrate
comprises a metallic foil substrate comprising a multiplicity of
layers, each having the first three-way catalyst deposited thereon;
an air source having an inlet to the exhaust downstream from the
first three-way catalyst for introducing sufficient air into the
exhaust stream to provide a lean combustion ratio; an ammonia
oxidation catalyst downstream from the air source comprising a
layer deposited on a second substrate comprising a platinum
component in an amount in the range of about 1 to about 25
g/ft.sup.3, a zeolite component in an amount in the range of about
0.5 to about 2.5 g/in.sup.3, wherein the zeolite of contains iron
or a copper-oxide copper-nitrate composite in an amount in the
range of about 0.1 to about 0.5 g/in.sup.3 and a silica component
in an amount in the range of about 0.1 to about 1.5 g/in.sup.3,
wherein the second substrate comprises a metallic foil substrate
comprising a multiplicity of layers, each having the ammonia
oxidation catalyst deposited thereon; and a second three-way
catalyst downstream from the ammonia oxidation catalyst comprising
a comprising a first catalytic layer deposited on a third substrate
comprising a platinum component in an amount in the range of about
12.5 to about 100 g/ft.sup.3, an alumina support in an amount in
the range of about 0.2 to about 2.0 g/in.sup.3, a ceria-zirconia
composite in an amount in the range of about 0.2 to about 1.0
g/in.sup.3, a zirconium component in an amount in the range of
about 0.03 to about 0.15 g/in.sup.3, and a barium component in an
amount in the range of about 0.03 to about 0.15 g/in.sup.3; and a
second catalytic layer deposited on the first catalytic layer
comprising a rhodium component in an amount of about 12.5 to about
100 g/ft.sup.3, an alumina support in an amount in the range of
about 0.2 to about 2.0 g/in.sup.3, a ceria-zirconia composite in an
amount in the range of about 0.2 to about 1.0 g/in.sup.3, and a
zirconium component in an amount in the range of about 0.03 to
about 0.15 g/in.sup.3, wherein the third substrate comprises a
metallic foil substrate comprising a multiplicity of layers, each
having the second three-way catalyst deposited thereon.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to U.S. Provisional
Application No. 60/826,487, filed Sep. 21, 2006, which is hereby
incorporated by reference in its entirety.
FIELD OF INVENTION
[0002] Embodiments of the present invention are generally related
to processes and systems for reduction of atmospheric pollutants
present in internal combustion engine exhaust streams. More
particularly, embodiments of the present invention are directed to
reduction of undesirable components of exhaust from engines that do
not have complex engine management systems.
BACKGROUND
[0003] Internal combustion engines have evolved into the backbone
of the world's individual transportation system. In most highly
developed countries, this individual transportation system is
dominated by automobiles having digital processor-based engine
control systems that continually adjust combustion parameters such
as fuel supply, intake air temperature, spark timing and duration,
and the like. These complex systems minimize output of potential
atmospheric pollutants such as carbon monoxide, unburned
hydrocarbons and oxides of nitrogen. The pollutant content of the
exhaust stream is further reduced by exhaust gas recirculation,
secondary air injection, and catalysts in the exhaust system. Even
a simple example of one of these engine management systems
including microprocessor controllers, sensors, catalysts and the
like can easily add hundreds of dollars to the cost of the
automobile.
[0004] In developing countries, individual transportation is making
a transition from bicycles to internal combustion engine-powered
scooters, motorcycles, and small cars. The small displacement
two-stroke or four-stroke engines powering these transports are
necessarily simple and low-cost, and as a result do not have
complex engine management systems. These engines are typically
open-loop-carbureted or fuel-injected. Additionally, the small
inexpensive vehicles often do not receive much maintenance. In many
of these developing countries, atmospheric pollution has become a
problem. These small displacement engines are substantial sources
of the pollution.
[0005] Internal combustion engines used in automobiles typically
include relatively complex engine management systems for reducing
pollutants from an engine exhaust stream. Representative early work
on complex engine emission management systems is described in U.S.
Pat. No. 3,943,709. This patent discloses an exhaust treatment
system that includes an air duct with a choke valve, means for
controlling the choke valve, a first stage catalytic converter, a
secondary air supply, an air pump, means for controlling the
secondary air supply and a secondary catalytic converter. More
recently, U.S. Pat. No. 6,634,169 discloses a catalyst system that
includes a programmable engine management system, a plurality of
sensors communicative with the engine management system, a
secondary air supply system communicative with the engine
management system, a fuel injection system and at least two
catalytic converters. Both of these patents suggest a complex and
costly addition to the vehicle's basic cost.
[0006] In simple low displacement engines such as those used in
scooters, motorcycles and simple, small cars, the addition of a
complex engine management system could easily raise the cost of
such vehicles to the point where they would not be accessible to
those desiring them. Such engines can be adjusted to maintain a
"rich", i.e., from about 8 to about 14.7 parts air to 1 part fuel,
combustion ratio. An approach for reducing emissions in a scooter
or motorcycle is disclosed in U.S. Patent Application Pub. No.
2006/0101813, which discloses a muffler device divided into three
chambers by partition boards, the muffler device includes a front
reduction catalyst within a front exhaust pipe, a rear exhaust pipe
with a secondary air inlet behind the reduction catalyst for
introducing secondary air into the exhaust stream so as to raise
the combustion ratio above the stoichiometric ratio to greater than
14.7 (lean) before passing the exhaust stream into an oxidation
catalyst. However, this combination may result in ammonia being
produced in the reducing catalyst and subsequently being oxidized
to NO.sub.x in the oxidation catalyst, resulting in a net increase
in NO.sub.x emissions.
[0007] There is a need to provide simple and effective systems for
reducing potential pollutants in the exhaust of low cost vehicles
that do not possess sensors and digital controls. In addition,
there is a continuing need to provide improved systems and methods
for the treatment of exhaust gas streams from internal combustion
engines.
SUMMARY
[0008] In an embodiment of the invention, an emissions treatment
system for engines that do not possess complex engine management
systems is provided. According to one or more embodiments, an
emissions treatment system for reducing the carbon monoxide,
unburned hydrocarbons, and nitrogen oxides content in the exhaust
gas stream of an internal combustion engine adjusted to a rich
stoichiometric ratio includes at least one three-way catalyst, a
supplemental air supply, and. an ammonia oxidation catalyst. The
supplemental air source supplies supplemental air upstream of the
ammonia oxidation catalyst. A first three-way catalyst is located
to receive and pass the exhaust gas from the engine through the
first three-way catalyst.
[0009] In one embodiment, the first three-way catalyst is located
upstream of the supplemental air source. In another embodiment, the
first three-way catalyst is located downstream from the ammonia
oxidation catalyst, and the supplemental air source is upstream of
the ammonia oxidation catalyst. In a further embodiment, a second
three-way catalyst is located downstream from the ammonia oxidation
catalyst.
[0010] In an embodiment, the first three-way catalyst comprises a
precious metal component and a rare earth oxide deposited on a
substrate. In one or more embodiments, the first three-way catalyst
comprises a precious metal component selected from the group
consisting of platinum, palladium, rhodium, and combinations
thereof; and a rare earth oxide selected from the group consisting
of ceria, zirconia, lanthana, praseodymia, neodymia, and
combinations thereof. A detailed embodiment provides a two-layered
three-way catalyst deposited on a substrate, wherein a first
catalytic layer comprises a platinum component in an amount in the
range of about 12.5 to about 100 g/ft.sup.3, an alumina support in
an amount in the range of about 0.2 to about 2.0 g/in.sup.3, a
ceria-zirconia composite in an amount in the range of about 0.2 to
about 1.0 g/in.sup.3, a zirconia component in an amount in the
range of about 0.03 to about 0.15 g/in.sup.3, and a barium
component in an amount in the range of about 0.03 to about 0.15
g/in.sup.3. A second layer deposited on the first layer comprises a
rhodium component in an amount of about 12.5 to about 100
g/ft.sup.3, an alumina support in an amount in the range of about
0.2 to about 2.0 g/in.sup.3, a ceria-zirconia composite in an
amount in the range of about 0.2 to about 1.0 g/in.sup.3, and a
zirconia component in an amount in the range of about 0.03 to about
0.15 g/in.sup.3.
[0011] In one or more embodiments, the ammonia oxide catalyst
comprises a precious metal component; a zeolite component
containing a base metal oxide selected from the group consisting of
oxides of chromium, manganese, iron, cobalt, nickel, copper,
vanadium, titanium, zinc, and combinations thereof; and a silica
component deposited on a substrate. A detailed embodiment provides
that the ammonia oxidation catalyst comprises a layer deposited on
a substrate, comprising a platinum component in an amount in the
range of about 1 to about 25 g/ft.sup.3, a zeolite component in an
amount in the range of about 0.5 to about 2.5 g/in.sup.3, wherein
the zeolite component contains iron, and a silica component in an
amount in the range of about 0.1 to about 0.5 g/in.sup.3. In
another detailed embodiment, the zeolite component further
comprises a copper-oxide copper-nitrate composite in an amount in
the range of about 0.1 to about 0.5 g/in.sup.3, and a silica
component in an amount in the range of about 0.1 to about 1.5
g/in.sup.3.
[0012] In one or more embodiments, the second three-way catalyst
comprises a precious metal component and a rare earth oxide
deposited on a substrate. In a detailed embodiment, the second
three-way catalyst comprises a precious metal component selected
from the group consisting of platinum, palladium, rhodium, and
combinations thereof; and a rare earth oxide selected from the
group consisting of ceria, lanthana, praseodymia, neodymia, and
combinations thereof.
[0013] One embodiment provides that a monolithic substrate
comprises a first discrete portion including a coating of the
ammonia oxidation catalyst, and a second discrete portion including
a coating of the second three-way catalyst. A detailed embodiment
provides that the monolithic substrate is selected from the group
consisting of a ceramic material with a multiplicity of passageways
therethrough, a metallic material being in the form of an expanded
matrix, and a metallic material being in the form of a flat or
corrugated metal foil configured in a multiplicity of layers.
[0014] In certain embodiments, the ammonia oxidation catalyst is
effective to selectively oxidize at least about 99% of ammonia
formed in the first three-way catalyst to nitrogen and water, and
to selectively reduce the nitrogen oxides to nitrogen; and the
first three-way catalyst is effective to selectively oxidize at
least about 99% of the unburned hydrocarbon to carbon dioxide and
water, oxidize at least about 99% of the carbon monoxide to carbon
dioxide.
[0015] Another aspect provides methods for reducing carbon
monoxide, unburned hydrocarbons, and nitrogen oxides in an exhaust
stream of an internal combustion engine. The methods comprise:
providing the internal combustion engine adjusted to a rich
combustion ratio; passing the exhaust stream through a first
three-way catalyst; adding sufficient air to the exhaust stream,
upstream of an ammonia oxidation catalyst, to provide a lean
combustion ratio; and passing the exhaust stream through the
ammonia oxidation catalyst.
[0016] In one embodiment, passing the exhaust stream through the
ammonia oxidation catalyst occurs after passing the exhaust stream
through the first three-way catalyst. The method can further
comprising passing the exhaust stream exiting the ammonia oxidation
catalyst through a second three-way catalyst.
[0017] In a detailed embodiment, the method further comprises
providing a sufficient amount of the first three-way catalyst to
oxidize at least about 50% of the carbon monoxide to carbon
dioxide, and to oxidize at least about 50% of the unburned
hydrocarbons to carbon dioxide and water, and providing an ammonia
oxidation catalyst to oxidize at least about 99% of ammonia formed
in the first three-way catalyst selectively to nitrogen and
water.
[0018] Another detailed embodiment provides that the method further
comprises providing a sufficient amount of a second three-way
catalyst to oxidize at least about 99% of the unburned hydrocarbons
entering the second three-way catalyst to carbon dioxide and water,
and about 99% of the carbon monoxide entering the second three-way
catalyst to carbon dioxide.
[0019] Other aspects include providing exhaust systems having an
exhaust conduit, a first three-way catalyst deposited on a metallic
foil substrate; an air source having an inlet to the exhaust
downstream from the first three-way catalyst for introducing
sufficient air into the exhaust stream to provide a lean combustion
ratio; an ammonia oxidation catalyst downstream from the air source
deposited on a metallic foil substrate; and a second three-way
catalyst downstream from the ammonia oxidation catalyst deposited
on a metallic foil substrate.
[0020] In one or more embodiments, the three-way catalysts are
three-layered, having an undercoat layer below the first layer.
Other embodiments provide that one or more of the first three-way
catalyst, the second three-way catalyst, the air inlet, and the
ammonia oxidation catalyst are contained in a housing comprising a
muffler.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1A is a schematic representation of an embodiment of
exhaust system;
[0022] FIG. 1B is a block diagram of an embodiment of an exhaust
treatment system;
[0023] FIG. 1C is a block diagram of another embodiment of an
exhaust treatment system;
[0024] FIGS. 2A, 2B, 2C and 2D are schematic representations of
several embodiments of substrates useful in exhaust systems;
[0025] FIG. 3 is a cut-away schematic representation of a catalyst
useful in an embodiment of the invention;
[0026] FIG. 4 is a graphical representation of concentrations of a
model exhaust stream passing through an exhaust treatment system
without an ammonia oxidation catalyst; and
[0027] FIG. 5 is a graphical representation of concentrations of a
model exhaust stream, substantially identical to that represented
in FIG. 3 passing through a specific embodiment of the exhaust
treatment system of the invention.
DETAILED DESCRIPTION
[0028] Before describing several exemplary embodiments of the
invention, it is to be understood that the invention is not limited
to the details of construction or process steps set forth in the
following description. The invention is capable of other
embodiments and of being practiced or being carried out in various
ways.
[0029] Embodiments of the exhaust system and method of the present
invention are particularly well-suited for open loop low
displacement engines that do not have sophisticated engine
management systems. In a simple low displacement engine, the
addition of a complex engine management system could easily raise
the cost of a simple low-cost vehicle using the engine to the point
where it would not be accessible to those desiring such a vehicle.
Such an engine can be adjusted to maintain a "rich" combustion
ratio. Such systems and methods are disclosed hereinbelow.
[0030] In this disclosure, the term NO.sub.x is used. The term
refers to oxides of nitrogen, primarily NO and NO.sub.2, but also
refers to other nitrogen oxides which may be formed as combustion
products of internal combustion engines fueled by hydrocarbon
fuels.
[0031] Reference is also made to internal combustion engines being
adjusted to a "rich combustion ratio" in this disclosure. In this
disclosure, the term "rich" is intended to include a combustion
ratio that is less than 14.7 parts of air to one part of fuel to
about 8 parts of air to about one part of fuel. Such a "rich"
mixture generally includes the normal hydrocarbon combustion
products of carbon dioxide and water as well as unburned
hydrocarbons, carbon monoxide and various oxides of nitrogen.
Generally, this stoichiometric, or ideal combustion ratio of 14.7
applies to hydrocarbon fuels referred to in the United States as
"gasoline". Other fuels, such as two-cycle blends including
lubricants and the like, may have a stoichiometric ratio different
than 14.7. Fuels that are oxygenated, i.e., that have oxygen
containing components generally will have a stoichiometric ratio of
less than 14.7. For particular applications, a stoichiometric ratio
may differ and is considered to be within the scope of this
disclosure. Thus, the term rich as used herein should not be
limited to a particular type of fuel or stoichiometric ratio.
[0032] Referring to FIG. 1A, an embodiment of the exhaust system 10
of the present invention is provided that is useful for reducing
the carbon monoxide, unburned hydrocarbons, and nitrogen oxides
content in the exhaust stream of an internal combustion engine 12
adjusted to a rich combustion ratio and, optionally, the sound
produced by the engine. Exhaust system 10 includes an exhaust
manifold or conduit 14 that is situated to receive substantially
all the exhaust gas from engine 12.
[0033] System 10 has a first three-way catalyst 16 located to
receive and pass the exhaust gas from engine 12 therethrough.
According to one or more embodiments, the first three-way catalyst
16 generally includes sufficient amounts of a precious metal
component, one or more base metal oxides, and a rare earth oxide
deposited on a surface 17A of a suitable substrate 18 to oxidize at
least about 50% of the unburned hydrocarbon to CO.sub.2 and
H.sub.2O, oxidize at least about 50% of the carbon monoxide to
CO.sub.2, and reduce about 90% of the nitrogen oxides to NH.sub.3,
N.sub.2 and H.sub.2O. The precious metal components can include
platinum, palladium, rhodium, ruthenium, and iridium. The base
metal oxides include, but are not limited to, base metal oxides
such as oxides of chromium, manganese, iron, cobalt, nickel,
barium, copper, vanadium titanium and zinc. The rare earth oxides
may include cerium, lanthanum, neodymium, praseodymium, etc., and
combinations thereof. Suitable supports include activated compounds
selected from the group consisting of alumina, silica,
silica-alumina, alumino-silicates, alumina-zirconia,
alumina-chromia, and alumina-ceria. Useful three-way catalysts are
disclosed in U.S. Pat. Nos. 5,254,519 and 5,597,771, the entire
contents of which are incorporated herein by reference.
[0034] Still referring to FIG. 1A, system 10 further includes a
source 20 for supplying supplemental air into the exhaust stream
downstream from the first three-way catalyst 16. Suitable sources
for supplying supplemental air include, but are not limited to, an
electrically-or an engine-powered air pump capable of supplying air
into the system, or in another embodiment, a reed valve opening and
closing in synchronization with the engine exhaust pulses that
alternately opens and closes to admit atmospheric air into the
system. Source 20 includes an inlet 21 that allows the supplemental
air to be admitted into the system at a preselected location. The
addition of the supplemental air serves to provide a lean
combustion ratio by raising the air to fuel ratio above the
stoichiometric value. As discussed above, depending upon the fuel
being used, the stoichiometric value may differ from 14.7.
[0035] System 10 then includes an ammonia oxidation catalyst 22
located to receive and pass the exhaust gas from, i.e., downstream
from, the first three-way catalyst 16 therethrough. In one or more
embodiments, the ammonia oxidation catalyst 22 includes a
sufficient amount of a catalytic material on a surface 17B of
suitable substrate 18B to oxidize at least about 90% of the ammonia
formed in first three-way catalyst to N.sub.2 and H.sub.2O.
According to one or more embodiments, the ammonia oxidation
catalyst is designed to achieve selectivity in converting ammonia
to nitrogen in the exhaust gas stream of an internal combustion
engine adjusted to a rich combustion ratio. Thus, as used herein,
the phrase "ammonia oxidation catalyst" refers to a catalyst that
effectively and selectively converts ammonia to nitrogen (N.sub.2)
and H.sub.2O with minimal NO.sub.x formation. For example,
according to one embodiment, an ammonia oxidation catalyst
selectively converts ammonia to at least about 40% nitrogen,
specifically, to at least about 50% nitrogen, and more specifically
to at least about 60% nitrogen. In a particular embodiment, the
ammonia oxidation catalyst converts ammonia to at least about 85%
nitrogen, for example, greater than about 90%. A useful,
non-limiting example of an ammonia oxidation catalyst includes a
zeolite component selected from the group including ZSM-5, beta-
and y-zeolites, and the like that includes a base metal oxide
selected from the group including, but not limited to, oxides of
chromium, manganese, iron, cobalt, nickel, copper, vanadium,
titanium, zinc and the like. Said ammonia oxidation catalyst
further comprising a platinum group metal component (i.e.,
platinum, palladium, rhodium, and iridium components, and
combinations thereof) dispersed on a refractory metal oxide, for
example, alumina, and, optionally, further including a cerium
component such as ceria. An example of such an ammonia oxidation
catalyst is disclosed in U.S. Pat. No. 5,462,907, the entire
content of which is incorporated herein by reference.
[0036] In the system shown in FIG. 1A, a second three-way catalyst
30 is located to receive and pass the exhaust gas from, i.e.,
downstream from, ammonia oxidation catalyst 22 therethrough. In one
or more embodiments, the second three-way catalyst 30 includes
sufficient amounts of a precious metal, a base metal oxide, and a
rare earth oxide deposited on a surface 17C of suitable substrate
18C to oxidize at least about 80% of the remaining unburned
hydrocarbon to CO.sub.2 and H.sub.2O, oxidize at least about 99% of
the remaining carbon monoxide to CO.sub.2. Suitable materials
useful in the second three-way catalyst 30 include, but are not
limited to, the group consisting of platinum, palladium, rhodium,
and combinations thereof; oxides of chromium, manganese, iron,
cobalt, nickel, copper, vanadium, titanium, zinc and the like;
oxides of aluminum, oxides of cerium; and compatible combinations
thereof. Useful three-way catalysts are disclosed in U.S. Pat. Nos.
5,254,519 and 5,597,771, the entire contents of which are
incorporated herein by reference.
[0037] Optionally, system 10 includes a muffler 40 for reducing the
sound produced by engine 12. In one embodiment, the components of
system 10 are substantially contained in a housing 60 that is
formed from a metallic material. Suitable materials include mild
steel or mild steel having a corrosion-resistant metallic plating,
such as a chromium plating. In another embodiment, housing 60 may
be formed from stainless steel.
[0038] It will be appreciated that the system 10 shown in FIG. 1A
is exemplary only. According to one or more embodiments, the system
may be modified. For example, as shown in FIG. 1B system 10B to
comprises an air source 20 and an inlet 21 upstream of an ammonia
oxidation catalyst 22 and a three-way catalyst 16, all being
downstream from engine 12. In another embodiment shown in FIG. 1C,
the system 10C has the three-way catalyst 16 placed upstream of the
air source 20 and inlet 21 so that the air source 20 is situated
between the three-way catalyst and the ammonia oxidation catalyst
22, all of which are located downstream from engine 12. This
embodiment can further be modified to provide a second three-way
catalyst located downstream from the ammonia oxidation catalyst
similar to the embodiment shown in FIG. 1A.
[0039] Referring to FIGS. 2A, 2B, 2C and 2D, suitable materials for
forming substrates 18A, B and C include, but are not limited to,
materials resistant to thermal shock and that are mechanically
strong. In one embodiment, each of catalysts 16, 22, and 30 are
deposited on individual discrete portions of a substrate. For
particular applications, the substrate materials may be the same or
different. Examples of suitable materials include, but are not
limited to, ceramic materials having different physical forms,
i.e., a monolithic cylinder 70 having a multiplicity of small
passageways 72 therethrough (as show in FIG. 2A), a multiplicity of
beads 80 (as shown in FIG. 2B), either formed from a suitable
ceramic or metal material and the like, or a metal matrix 90 (as
shown in FIG. 2C. FIG. 2D shows an embodiment in which a suitable
metal matrix is formed from a multiplicity of thin layers 94 of a
flat or corrugated foil 92 formed from a stainless steel alloy
including chromium and aluminum. One suitable alloy is produced by
Sanvik Materials Technology, Benton Harbor, Mich. The alloy is
formed into sheets having a thickness from about 50 to 60
micrometers. In one embodiment, these sheets are assembled into a
form suitable for use as a catalyst substrate by Emitec, Auburn
Hills, Mich. The surface of the substrate typically has coatings of
the selected catalytic material applied thereto in one or more
layers. Generally speaking, the coatings include one or more
catalytic materials on support materials in amounts ranging from
about 0.0001 to about 1000 grams per cubic foot of catalyst, more
commonly from about 0.20 to about 80 grams per cubic foot. Various
aluminas are suitable as support materials. However, for particular
applications greater or lesser amounts may be selected.
[0040] Suitable catalytic materials for three-way catalysts
include, but are not limited to, precious metals such as platinum,
palladium, rhodium, and the like, either singly or in combinations.
Other materials useful in these type catalysts include rare earth
metal oxide/zirconia composites, one suitable material being a
ceria-zirconia composite; and base metal oxides such as oxides of
chromium, manganese, iron, cobalt, nickel, copper, vanadium,
titanium, zinc and the like. Other materials include, but are not
limited to, zirconium components, barium components, and nickel
components.
[0041] The catalytic materials may be mixed into aqueous slurry,
also known as a washcoat, with one or more refractory oxides of
aluminum, titanium, silica or zirconium as nitrate or acetate
salts. The slurry is then applied to the substrate material, dried,
and then calcined, generally by heating in a controlled atmosphere.
The calcination step forms a porous, substantially permanent
coating having the catalytic material therein on the substrate. In
the embodiments of the present invention, as shown in FIG. 3, there
generally is more than one coating layer applied sequentially to
the substrate.
[0042] Generally, the catalytic layers also contain at least a
portion of a material known as an oxygen storage component. The
oxygen storage component may be selected from any known material in
the art, but generally is an oxide of a rare earth element such as
cerium, praseodymium, lanthanum, neodymium, and combinations
thereof or one or more of these elements combined with zirconia.
Cerium oxide is generally preferred. Additionally, for particular
applications, one or more of catalysts 16, 22, and 30 may be
deposited on different zones on a monolithic substrate or contained
in separate portions of housing 60 as separate catalysts 16, 22,
and 30.
[0043] In one embodiment of the present invention, a method for
reducing the amount of CO, NO.sub.x, and HC in the exhaust stream
of an internal combustion engine adjusted to a rich stoichiometric
ratio of includes passing the exhaust stream from internal
combustion engine 12 adjusted to a rich combustion ratio, i.e.,
generally from about 8 to about 14.7 parts of air to about one part
of fuel, containing unburned hydrocarbons, nitrogen oxides and
carbon monoxide through a first three-way catalyst 16. The method
according to an embodiment of the invention then includes adding
sufficient air to the exhaust stream from first three-way catalyst
16 at inlet 21 to provide a lean combustion ratio by raising the
air fuel ratio above about 14.7 and passing the exhaust stream from
the first three-way catalyst 16 through the ammonia oxidation
catalyst 30 located downstream from air inlet 21. An optional
further step in the method according to this embodiment of the
invention includes passing the exhaust gas from ammonia oxidation
catalyst 30 through second three-way catalyst 30. For particular
applications, the method may also include passing the exhaust
stream through muffler 40 or silencer to substantially reduce the
sound produced by the engine. In other embodiments, the method may
first include passing the exhaust stream through a three-way
catalyst prior to addition of the air.
[0044] In one embodiment, there is provided a sufficient amount of
first three-way catalyst 16 to oxidize at least about 50% of the
carbon monoxide to CO.sub.2, reduce about 90% of the nitrogen
oxides to NH.sub.3, N.sub.2 and H.sub.2O and oxidize at least about
50% of the unburned hydrocarbon to CO.sub.2 and H.sub.2O.
Additionally, the method further includes providing a sufficient
amount of ammonia oxidation catalyst 22 to selectively oxidize at
least about 99% of the ammonia formed in the first three-way
catalyst to N.sub.2 and H.sub.2O; and providing a sufficient amount
of second three-way catalyst 30 to oxidize at least about 99% of
the remaining unburned hydrocarbon to CO.sub.2 and H.sub.2O and
about 99% of the remaining CO to CO.sub.2.
[0045] In one embodiment, as seen in FIG. 3, three-way catalyst 16
is in the form of one or more porous layers 17 of catalytic
materials 18 applied to surface of multi-layer metallic foil
substrate 94. An exemplary first layer includes, but is not limited
to, a platinum component in an amount in the range of about 12.5 to
about 100 g/ft.sup.3, or 25 g/ft.sup.3 in one embodiment; an
alumina support in an amount in the range of about 0.2 to about 2.0
g/in.sup.3, or 1.0 g/in.sup.3 in a specific embodiment; a rare
earth metal oxide-zirconia composite in an amount in the range of
about 0.03 to about 0.15 g/in.sup.3, or in a specific embodiment, a
ceria-zirconia composite in an amount in the range of about 0.2 to
about 1.0 g/in.sup.3, or in a specific example, 0.3 g/in.sup.3; a
zirconium component in an amount in the range of about 0.03 to
about 0.15 g/in.sup.3, or in a specific embodiment, 0.08
g/in.sup.3; and a barium component in an amount in the range of
about 0.03 to about 0.15 g/in.sup.3, or in a specific embodiment,
0.1 g/in.sup.3.
[0046] An exemplary second catalytic layer deposited on the first
catalytic layer includes, but is not limited to, a rhodium
component in an amount of about 12.5 to about 100 g/ft.sup.3, or in
a specific embodiment, 25 g/ft.sup.3; an alumina support in an
amount in the range of about 0.2 to about 2.0 g/in.sup.3, or 1.0
g/in.sup.3 in a specific embodiment; a rare earth metal
oxide-zirconia composite in an amount in the range of about 0.2 to
about 1.0 g/in , or in a specific embodiment, 0.7 g/in.sup.3 of a
ceria-zirconia composite, which functions as an oxygen storage
component; and a zirconium component in an amount in the range of
about 0.2 to about 2.0 g/in.sup.3; or specifically 0.03 to about
0.15 g/in.sup.3; or even 0.08 g/in.sup.3.
[0047] The second three-way catalyst 30 may have the same or
different washcoat slurries as the first three-way catalyst 16. In
a specific embodiment, catalyst 16 and catalyst 30 are formed from
substantially the same materials in the same concentrations.
[0048] An additional embodiment of either or both three-way
catalysts 16 and 30 for particular applications may include an
undercoat layer 19 applied to surface 17a of substrate 92 prior to
the application of the first and second coating layers described
above. In one embodiment, the undercoat 19 layer includes, but is
not limited to, an undercoat alumina support in an amount in the
range of about 0.5 to about 1.5 g/in.sup.3, or 0.9 g/in.sup.3 in a
specific embodiment; an undercoat zirconium component in an amount
in the range of about 0.05 to about 0.15 g/in.sup.3, or in a
specific embodiment, 0.10 g/in.sup.3.
[0049] In an embodiment of the invention, ammonia oxidation
catalyst 22 is formed from one or more porous layers applied to the
surface of a substrate formed from a multi-layer metallic foil
substrate. The layer includes, but is not limited to, a platinum
component in an amount in the range of about 1 to about 25
g/ft.sup.3, or in a specific embodiment, about 5.0 g/ft.sup.3; a
beta-zeolite component in an amount in the range of about 0.5 to
about 2.5 g/in.sup.3, wherein the betazeolite component contains
iron, or in a specific embodiment about 1.5 g/ft.sup.3; and a
silica component in an amount in the range of about 0.1 to about
1.5 g/in.sup.3, or in a specific embodiment, 0.6 g/in.sup.3.
Optionally, the zeolite component also includes a copper-nitrate
copper-oxide composite in an amount in the range of about 0.1 to
about 0.5 g/in, or in a specific embodiment, about 0.16
g/in.sup.3.
Specific Embodiments of Catalysts
[0050] A specific embodiment of a three-way catalyst useful in the
system of the invention includes a first catalytic layer deposited
on the substrate comprising about 25 g/ft.sup.3 of a platinum
component; about 1 g/in.sup.3 of an alumina support; about 0.3
g/in.sup.3 of a rare earth metal oxide-zirconia component; about
0.08 g/in.sup.3 of a zirconium component; and about 0.1 g/in.sup.3
of a barium component. The specific embodiment of a three-way
catalyst also includes a second catalytic layer deposited on the
first catalytic layer comprising about 25 g/ft.sup.3 of a rhodium
component; about 1.0 g/in.sup.3 of an alumina support; about 0.7
g/in.sup.3 of a rare earth metal oxide-zirconia composite,
preferably a ceria-zirconia composite; and about 0.08 g/in.sup.3 of
a second zirconium component. In the system of the invention, the
first three-way catalyst and the second three-way catalyst may have
the same or different composition, in this specific embodiment,
both the first and the second three-way catalysts have the same
composition as given above. A specific embodiment of an ammonia
oxidation catalyst useful in the system of the invention includes
about 5 g/ft.sup.3 of a platinum component; about 1.5 g/in.sup.3 of
a zeolite component containing iron; about 0.16 g/in.sup.3 of a
base metal oxide composite, preferably copper nitrate; and about
0.6 g/in.sup.3 of a silica.
[0051] In a further specific embodiment, the three-way catalysts of
the invention may utilize an additional undercoat catalytic layer
deposited directly on the substrate surface beneath the first
catalytic layer. The undercoat layer includes about 0.9 g/in.sup.3
of an undercoat alumina support; about 0.1 g/in.sup.3 of an
undercoat zirconium component.
[0052] Referring to FIGS. 4 and 5, the graphical representations
show a model exhaust stream including hydrocarbons, about 1500 ppm,
(THC), nitrogen oxides, about 2500 ppm, (NO.sub.x) and carbon
monoxide, about 1600 ppm, (CO), about 10,000 ppm water vapor with
the balance being nitrogen. In FIG. 4, a model exhaust system that
includes two three-way (TWC) catalysts made in accordance with the
specific embodiments referred to above, a first three-way catalyst
and a second three-way catalyst, and a blank chamber is
illustrated. At the first position, represented by (FG), the
initial concentrations of the model exhaust stream are seen. At the
mid-bed (MB) location the concentration of the several components
of the model stream are shown after passage through the first
three-way catalyst. At the tail-pipe (TP) position, the
concentrations of the several components of the model exhaust
stream are seen after passage through the second three-way
catalyst. A person skilled in the art of exhaust stream catalysis
will recognize that the concentration of the NO.sub.x component is
increased by passage through the second three-way catalyst in this
embodiment.
[0053] Referring now to FIG. 5, a model exhaust stream similar to
that of FIG. 4 is passed through an embodiment of the system of the
present invention which includes the first three-way catalyst made
in accordance with the specific embodiment discussed above, a
supplemental air supply, an ammonia oxidation catalyst made in
accordance with the specific embodiment discussed above and the
second three-way catalyst made in accordance with the specific
embodiment described above. At the TP position, one skilled in the
art of exhaust stream catalysis will recognize that by
incorporation of the ammonia oxidation catalyst of the invention,
substantially all of the ammonia produced by passing the model
exhaust stream through the first three-way catalyst is converted in
the ammonia oxidation catalyst to nitrogen and water. Thus, there
are very little residual nitrogen compounds that are re-oxidized to
nitrogen oxides in the second three-way catalyst, thereby
substantially reducing the NO.sub.x concentration in the TP
position when compared to the TP position of FIG. 4 without the
ammonia oxidation catalyst.
[0054] It will be apparent to those skilled in the art that various
modifications and variations can be made to the present invention
without departing from the spirit or scope of the invention. Thus,
it is intended that the present invention cover modifications and
variations of this invention provided they come within the scope of
the appended claims and their equivalents.
* * * * *