U.S. patent application number 12/520950 was filed with the patent office on 2010-03-11 for exhaust emission control apparatus for internal combustion engine.
This patent application is currently assigned to Toyota Jidosha Kabushiki Kaisha. Invention is credited to Hirohito Hirata, Masaya Ibe, Masaya Kamada, Mayuko Osaki.
Application Number | 20100058742 12/520950 |
Document ID | / |
Family ID | 39588422 |
Filed Date | 2010-03-11 |
United States Patent
Application |
20100058742 |
Kind Code |
A1 |
Hirata; Hirohito ; et
al. |
March 11, 2010 |
EXHAUST EMISSION CONTROL APPARATUS FOR INTERNAL COMBUSTION
ENGINE
Abstract
One object of the present invention is to provide an exhaust
emission control apparatus for an internal combustion engine that
is capable of improving the NOx purification performance. An
exhaust emission control apparatus being placed in an exhaust path
of an internal combustion engine, comprising: an NOx retention
material; ozone injection means for injecting ozone into an exhaust
gas being positioned upstream from the NOx retention material; an
HC adsorbent adsorbing HC contained in the exhaust gas; and a
catalyst being placed in a region where desorbed NOx and desorbed
HC contact each other. The HC adsorbent is prepared so as to desorb
adsorbed HC at the same time as NOx being stored in the NOx
retention material is desorbed.
Inventors: |
Hirata; Hirohito; (
Aichi-ken, JP) ; Ibe; Masaya; (Aichi-ken, JP)
; Osaki; Mayuko; (Aichi-ken, JP) ; Kamada;
Masaya; (Aichi-ken, JP) |
Correspondence
Address: |
GIFFORD, KRASS, SPRINKLE,ANDERSON & CITKOWSKI, P.C
PO BOX 7021
TROY
MI
48007-7021
US
|
Assignee: |
Toyota Jidosha Kabushiki
Kaisha
Toyota-Shi, Aichi-Ken
JP
|
Family ID: |
39588422 |
Appl. No.: |
12/520950 |
Filed: |
December 20, 2007 |
PCT Filed: |
December 20, 2007 |
PCT NO: |
PCT/JP2007/074539 |
371 Date: |
October 23, 2009 |
Current U.S.
Class: |
60/286 ;
60/297 |
Current CPC
Class: |
B01J 23/58 20130101;
B01D 2257/702 20130101; Y02T 10/12 20130101; B01D 2255/1021
20130101; F01N 3/0835 20130101; Y02A 50/20 20180101; B01D 2255/2042
20130101; Y02A 50/2344 20180101; F01N 2240/38 20130101; B01D
2251/104 20130101; F01N 13/009 20140601; B01J 37/0246 20130101;
F01N 3/029 20130101; B01D 2257/404 20130101; F01N 2240/28 20130101;
B01J 23/42 20130101; F01N 2570/14 20130101; B01D 53/9454 20130101;
B01D 2255/912 20130101; F01N 3/0842 20130101; B01D 2255/2092
20130101; F01N 3/206 20130101; F01N 2610/146 20130101; B01D 2255/91
20130101; B01J 29/44 20130101; F01N 3/24 20130101; B01J 35/0006
20130101; Y02T 10/22 20130101; F01N 2570/12 20130101; B01J 37/0248
20130101 |
Class at
Publication: |
60/286 ;
60/297 |
International
Class: |
F01N 9/00 20060101
F01N009/00; F01N 3/035 20060101 F01N003/035 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2006 |
JP |
2006-355741 |
Claims
1. An exhaust emission control apparatus being placed in an exhaust
path of an internal combustion engine, comprising: an NOx retention
material; ozone injection means for injecting ozone into an exhaust
gas being positioned upstream from the NOx retention material; an
HC adsorbent adsorbing HC contained in the exhaust gas; and a
catalyst being placed in a region where desorbed NOx and desorbed
HC contact each other; wherein, said HC adsorbent is prepared so as
to desorb adsorbed HC at the same time as NOx being stored in the
NOx retention material is desorbed.
2. The exhaust emission control apparatus according to claim 1,
wherein the HC adsorbent and the NOx retention material are
integrated with the catalyst.
3. The exhaust emission control apparatus according to claim 1,
wherein the NOx retention material is separated from the HC
adsorbent, wherein the HC adsorbent is positioned upstream from the
NOx retention material, and wherein the ozone injection means
injects ozone into the exhaust gas being positioned downstream from
the NOx retention material.
4. The exhaust emission control apparatus according to claim 3,
wherein the NOx retention material is separated from the catalyst,
and wherein the NOx retention material is positioned upstream from
the catalyst.
5. The exhaust emission control apparatus according to claim 3,
wherein the NOx retention material is combined with the
catalyst.
6. The exhaust emission control apparatus according to claim 1,
further comprising: control means for controlling the ozone
injection means so that a molar quantity of ozone to be injected
into the exhaust gas becomes greater than a molar quantity of
nitrogen monoxide contained in the exhaust gas.
7. The exhaust emission control apparatus according to claim 6,
wherein the control means controls the ozone injection means so
that the molar quantity of ozone to be injected into the exhaust
gas becomes at least two times the molar quantity of nitrogen
monoxide contained in the exhaust gas.
8. An exhaust emission control apparatus being placed in an exhaust
path of an internal combustion engine, comprising: an NOx retention
material; ozone injection device for injecting ozone into an
exhaust gas being positioned upstream from the NOx retention
material; an HC adsorbent adsorbing HC contained in the exhaust
gas; and a catalyst being placed in a region where desorbed NOx and
desorbed HC contact each other; wherein, said HC adsorbent is
prepared so as to desorb adsorbed HC at the same time as NOx being
stored in the NOx retention material is desorbed.
Description
TECHNICAL FIELD
[0001] The present invention relates to an exhaust emission control
apparatus for an internal combustion engine.
BACKGROUND ART
[0002] It is known that a conventional exhaust emission control
apparatus disclosed, for instance, in JPA-2002-89246 includes an
NOx Storage-Reduction catalyst (hereinafter referred to as an "NSR
catalyst"). More specifically, the NSR catalyst comprises a
catalyst function which purifies nitrogen oxide (NOx) and
hydrocarbons (HC) contained in the combustion gas exhausted in the
internal combustion engine, and a storage function which stores NOx
in the catalyst. Before the catalyst activates, such as when there
is a cold startup of the internal combustion engine, or while the
exhaust gas is lean, and when the reducing agent is in short
supply, NOx may be emitted into the atmosphere without being
purified in the catalyst. NSR catalyst is capable of storing NOx in
the catalyst, and performing a purifying treatment by reacting the
stored NOx and reducing agents such as HC under a situation where
the catalyst has been activated and rich or stoichiometric driving
is performed.
[0003] Moreover, during a cold startup operation of the internal
combustion engine in which the NSR catalyst does not reach its
activation temperature, the above mentioned storage reaction may
not occur with a high degree of efficiency because oxidation
reaction of NOx is not activated. In the above described
conventional system, therefore, it is decided to add ozone to
exhaust gas. NOx reacts with ozone in the gas-phase. Therefore, the
system can effectively oxidize NOx even before the catalyst is
fully activated so as to increase the NOx storage amount.
[0004] Patent Document 1: JP-A-2002-89246
[0005] Patent Document 2: JP-A-6-185343
[0006] Patent Document 3: JP-A-10-169434
DISCLOSURE OF INVENTION
Problem to be Solved by the Invention
[0007] NOx stored in the catalyst is decomposed to N.sub.2,
H.sub.2O, CO.sub.2, and others by reducing agents in the exhaust
gas such as HC or CO. During stoichiometric operation, therefore,
the reducing agent for reducing the stored NOx may be in short
supply, thereby NOx purification may not be performed
effectively.
[0008] The present invention has been made to solve the above
problem. One object of the present invention is to provide an
exhaust emission control apparatus for an internal combustion
engine that is capable of improving the NOx purification
performance.
Means for Solving the Problem
[0009] First aspect of the present invention is an exhaust emission
control apparatus being placed in an exhaust path of an internal
combustion engine, comprising:
[0010] an NOx retention material;
[0011] ozone injection means for injecting ozone into an exhaust
gas being positioned upstream from the NOx retention material;
[0012] an HC adsorbent adsorbing HC contained in the exhaust gas;
and
[0013] a catalyst being placed in a region where desorbed NOx and
desorbed HC contact each other;
[0014] wherein, said HC adsorbent is prepared so as to desorb
adsorbed HC at the same time as NOx being stored in the NOx
retention material is desorbed.
[0015] Second aspect of the present invention is the exhaust
emission control apparatus according to the first aspect, wherein
the HC adsorbent and the NOx retention material are integrated with
the catalyst.
[0016] Third aspect of the present invention is the exhaust
emission control apparatus according to the first aspect, wherein
the NOx retention material is separated from the HC adsorbent,
[0017] wherein the HC adsorbent is positioned upstream from the NOx
retention material, and
[0018] wherein the ozone injection means injects ozone into the
exhaust gas being positioned downstream from the NOx retention
material.
[0019] Fourth aspect of the present invention is the exhaust
emission control apparatus according to the third aspect, wherein
the NOx retention material is separated from the catalyst, and
[0020] wherein the NOx retention material is positioned upstream
from the catalyst.
[0021] Fifth aspect of the present invention is the exhaust
emission control apparatus according to the third aspect, wherein
the NOx retention material is combined with the catalyst.
[0022] Sixth aspect of the present invention is the exhaust
emission control apparatus according to any one of the first to the
fifth aspects, further comprising:
[0023] control means for controlling the ozone injection means so
that a molar quantity of ozone to be injected into the exhaust gas
becomes greater than a molar quantity of nitrogen monoxide
contained in the exhaust gas.
[0024] Seventh aspect of the present invention is the exhaust
emission control apparatus according to the sixth aspect, wherein
the control means controls the ozone injection means so that the
molar quantity of ozone to be injected into the exhaust gas becomes
at least two times the molar quantity of nitrogen monoxide
contained in the exhaust gas.
ADVANTAGES OF THE INVENTION
[0025] According to the first aspect of the present invention, an
HC adsorbent which adsorbs HC is placed in an exhaust path of an
internal combustion engine. The HC adsorbent is prepared so that
the adsorbed HC might be desorbed when the NOx being stored by the
NOx retention material reaches its desorbed temperature. Therefore,
the present invention can make the NOx desorbed from the NOx
retention material along with the HC desorbed from the HC adsorbent
to react with the catalyst so as to be purified, thereby preventing
the reducing agents from being in short so as to improve the NOx
purification performance.
[0026] According to the second aspect of the present invention, it
is possible to make the desorbed HC and the desorbed NOx react in
the catalyst with a high degree of efficiency since the HC
adsorbent and the NOx retention material are integrated with the
catalyst. Further, it is possible to hold down production costs
since the number of parts is reduced by the integration.
[0027] According to the third aspect of the present invention,
ozone is introduced into downstream from the NOx retention
material. Therefore, the present invention makes it possible to
prevent ozone from reacting with HC which is adsorbed into the HC
adsorbent, thereby improving the oxidation efficiency of NOx.
[0028] It is thought that the storage element which is supported by
the NOx retention material could be a catalyst poison for a noble
metal of the catalyst. According to the forth aspect of the present
invention, since the NOx retention material is separated from the
catalyst, it is possible to enhance the activation of the catalyst.
Furthermore, since the catalyst is positioned downstream from the
NOx retention material, it is possible to purify NOx, which has not
been stored by the NOx retention material, in the catalyst after a
certain level of catalyst activation has been reached. Therefore,
this makes it possible to improve the NOx purification
performance.
[0029] According to the fifth aspect of the present invention, the
NOx retention material is combined with the catalyst. Therefore,
this makes it possible to make the desorbed NOx react in the
catalyst with a high degree of efficiency. Furthermore, the number
of parts is reduced by combining them into a single unit.
Therefore, this makes it possible to save on production costs.
BRIEF DESCRIPTION OF DRAWINGS
[0030] FIG. 1 is a diagram illustrating the hardware configuration
of a first embodiment of the present invention.
[0031] FIG. 2 is a diagram showing an NOx storage reaction.
[0032] FIG. 3 is a diagram showing an NOx reduction reaction.
[0033] FIG. 4 is a diagram illustrating the hardware configuration
of the experiment of the present evaluation test.
[0034] FIG. 5 is a cross-section diagram illustrating the inside of
the catalyst test piece 200 of the present experiment.
[0035] FIG. 6 is a graph illustrating the purification efficiencies
for a few kinds of components in the first and the second
experiments.
[0036] FIG. 7 is a diagram illustrating the hardware configuration
of the second embodiment of the present invention.
[0037] FIG. 8 is a diagram illustrating an internal configuration
of an exhaust purification catalyst 60 which is able to be applied
as modifications of the exhaust purification catalyst 42.
[0038] FIG. 9 is a diagram illustrating the hardware configuration
of the experiment of the present evaluation test.
[0039] FIG. 10 is a cross-section diagram illustrating the inside
of the catalyst test pieces 300, 310 of the present experiment.
[0040] FIG. 11 is a graph illustrating the purification
efficiencies for a few kinds of components according to the first
and the second experiments.
DESCRIPTION OF REFERENCE CHARACTERS
[0041] 10 exhaust emission control apparatus [0042] 12 internal
combustion engine (engine) [0043] 14 exhaust path [0044] 20 exhaust
purification catalyst [0045] 30 ozone supply device [0046] 32 air
inlet [0047] 34 ozone injection orifice [0048] 40 exhaust emission
control apparatus [0049] 42 exhaust purification catalyst [0050] 44
NSR catalyst [0051] 46 HC adsorbent [0052] 50 ECU (Electronic
Control Unit) [0053] 60 exhaust purification catalyst [0054] 62 HC
adsorbent [0055] 64 NOx retention material [0056] 66 three-way
catalyst [0057] 100 model gas generator [0058] 102 gas cylinders
[0059] 110,112 exhaust gas analyzer [0060] 114 ozone analyzer
[0061] 120 ozone generator [0062] 122 oxygen cylinder [0063]
124,128,130 flow rate control unit [0064] 126 ozone analyzer [0065]
200 catalyst test piece [0066] 202 quartz tube [0067] 204,206
catalyst sample [0068] 300,310 catalyst test piece [0069] 302,312
quartz tube [0070] 304,314,316 catalyst sample
BEST MODE FOR CARRYING OUT THE INVENTION
[0071] Embodiments of the present invention will now be described
with reference to the accompanying drawings. Like elements in the
drawings are designated by the same reference numerals and will not
be redundantly described. It should be understood that the present
invention is not limited to the embodiments described below.
First Embodiment
Configuration of First Embodiment
[0072] FIG. 1 is a diagram illustrating the hardware configuration
of a first embodiment of the present invention. As shown in FIG. 1,
an exhaust emission control apparatus 10 of the present embodiment
is installed in an internal combustion engine (hereinafter referred
to as an "engine") 12.
[0073] An exhaust path 14 is attached to an exhaust side of the
engine 12. An exhaust purification catalyst 20 is installed in the
exhaust path 14. The exhaust purification catalyst 20 supports
platinum (Pt) that is a noble metal and barium carbonate
(BaCO.sub.3) on a ceramic carrier. Pt functions as an active site
that activates the oxidation reaction of CO, HC, and others or the
reduction reaction of NOx. Further, BaCO.sub.3 functions as an NOx
storage substance which stores NOx in the form of nitrate salt.
[0074] Zeolite based ZSM-5 is supported by a ceramic carrier of the
exhaust purification catalyst 20. ZSM-5 functions as an HC
adsorbent that adsorbs HC. The following explanation assumes that
the terms "catalyst" refers to a portion of the carrier that
supports Pt. Further, it is also assumed that the term "NOx
retention material" refers to a portion of the carrier that
supports BaCO.sub.3. Furthermore, it is also assumed that the term
"HC adsorbent" refers to a portion of the carrier that supports
ZSM-5.
[0075] The exhaust emission control apparatus 10 according to the
first embodiment includes an ozone supply device 30. The ozone
supply device 30 includes a system that generates ozone by
performing a creeping discharge into oxygen taken from an air inlet
32. The configuration, function, and other characteristics of the
ozone supply device 30 will not be described in detail because they
are not main parts of the present invention and are well-known.
[0076] The ozone supply device 30 includes an ozone injection
orifice 34 that injects ozone toward the exhaust purification
catalyst 20. The ozone injection orifice 34 is placed so that the
injected ozone might be uniformly mixed with the exhaust gas which
is streamed into the exhaust purification catalyst 20.
[0077] As shown in FIG. 1, the exhaust emission control apparatus
10 according to the present embodiment includes an ECU (Electronic
Control Unit) 50. An output section of the ECU 50 is connected to
the ozone supply device 30 described above. An input section of the
ECU 50 is connected to various sensors which detect an operating
condition and the operating status of the engine 12. In accordance
with the various input information, the ECU 50 calculates an
injection timing and an injection quantity for ozone and controls
the ozone supply device 30.
Operation of First Embodiment
(NOx Storage Operation Using Ozone)
[0078] An operation of the present embodiment will now be described
with reference to FIGS. 2 and 3. In the exhaust purification
catalyst 20, NOx is decomposed to N.sub.2, H.sub.2O, CO.sub.2, and
others by reacting with HC or CO. As a result, the NOx contained in
the exhaust gas is purified effectively. However, during a cold
startup of the engine 12 in which the exhaust purification catalyst
20 is not warmed up until its activation temperature, the NOx
contained in the exhaust gas is not purified in the exhaust
purification catalyst 20 because it has not activated enough.
[0079] In view of the above circumstances, the present embodiment
prevents the unpurified NOx from being emitted into the atmosphere
by storing them into the exhaust purification catalyst 20. Ozone is
injected into the exhaust gas as a means for storing the NOx in the
exhaust purification catalyst 20. More specifically, the ozone
generated by the ozone supply device 30 is injected from the ozone
injection orifice 34 toward the exhaust purification catalyst
20.
[0080] FIG. 2 is a diagram showing an NOx storage reaction. More
specifically, FIG. 2 is an enlarged view showing the exhaust
purification catalyst 20. As shown in FIG. 2, NOx is oxidized by
being reacted with ozone in the gas-phase before the exhaust
purification catalyst 20 is fully activated, i.e., the catalyst is
at a low temperature. More specifically, the following reactions
occur.
NO+O.sub.3.fwdarw.NO.sub.2+O.sub.2 (1)
NO.sub.2+O.sub.3.fwdarw.NO.sub.3+O.sub.2 (2)
NO.sub.2+NO.sub.3.fwdarw.N.sub.2O.sub.5 (3)
(NO.sub.2+NO.sub.3.rarw.N.sub.2O.sub.5)
[0081] The NOx oxidized to NO.sub.2, NO.sub.3, or N.sub.2O.sub.5 is
stored in the NOx retention material in the form of nitrate such as
Ba(NO.sub.3).sub.2. Thereby, it is possible to store the NOx
effectively. Therefore, it is possible to effectively prevent the
NOx from being emitted into the atmosphere, even when the exhaust
purification catalyst 20 is not fully activated.
[0082] Moreover, according to the gas-phase reaction of ozone as
shown in the above formulas (1) and (2), the region in which NOx is
oxidized is not limited to a region on catalyst. Therefore, for
instance, it is possible to support the NOx storage substance and
noble metal separately in the exhaust purification catalyst 20.
Therefore, the NOx storage substance which could be a catalyst
poison for the noble metal can be separated from the noble metal,
thus improving the purification efficiency of the catalyst.
[0083] According to the aforementioned NOx storage reaction, the
forms of NO.sub.2, NO.sub.3, N.sub.2O.sub.5, or HNO.sub.3 which is
generated when the former nitrogen oxides react with water can be
stored. However, there is a limitation of NOx storage amount as for
the form of NO.sub.2. Therefore, it is possible to dramatically
increase the storage amount of NOx if the reaction as shown in the
above formula (2) occurs actively so as to convert large amounts of
NO.sub.2 into NO.sub.3.
[0084] However, the activation energy necessary to take place the
reaction as shown in the above formula (2) is higher than the
energy required in the reaction as shown in the above formula (1).
Therefore, the reaction of the above formula (1) takes priority
over the reaction of the above formula (2). Therefore, all
reactions occurring are just the reactions of the above formula (1)
so that the final form of oxidized NO becomes NO.sub.2 when the
molar quantity of ozone contained in the exhaust gas is smaller
than the molar quantity of NO.
[0085] In view of the above circumstances, the injection quantity
of ozone is controlled so that the molar quantity of ozone to be
injected into the exhaust gas might be greater than the molar
quantity of NO contained in the exhaust gas. This make it possible
to be oxidized from NO.sub.2 to NO.sub.3. Therefore, it is possible
to increase the storage amount of NOx.
[0086] Further, it is preferred that the injection quantity of
ozone is controlled so that the molar quantity of ozone to be
injected into the exhaust gas might be more than twice the molar
quantity of NO contained in the exhaust gas. This makes it possible
for most of the NO to be oxidized to NO.sub.3. Therefore, it is
possible to increase the storage amount of NOx dramatically.
(Reduction Operation of the Stored Nox)
[0087] As described above, according to the present embodiment, the
ozone is injected toward the exhaust purification catalyst 20. This
makes it possible to store the NOx, which is exhausted with a cold
startup of the engine 12, effectively. Therefore, it is possible to
prevent the NOx from being emitted into the atmosphere.
[0088] After the exhaust purification catalyst 20 activates, the
stored NOx is purified by reacting with a reducing agent such as HC
contained in the exhaust gas. FIG. 3 is a diagram showing an NOx
reduction reaction. Specifically, FIG. 3 is an enlarged view
showing the exhaust purification catalyst 20. As shown in FIG. 3,
the stored NOx is decomposed to N.sub.2, H.sub.2O, CO.sub.2, and
others by being reduced with a reducing agent such as HC contained
in the exhaust gas after the catalyst activates. Therefore, if the
NOx reduction reaction could take place with a high degree of
efficiency, this makes it possible to purify the NOx which is
stored before the catalyst activates.
[0089] However, NOx may be emitted into the atmosphere without
being purified in the catalyst during a stoichiometric operation of
the internal combustion engine 12 since the reducing agent for
purifying the desorbed NOx may be in short supply. In view of the
above circumstances, an HC adsorbent is placed into the exhaust
purification catalyst 20 in the present embodiment. The HC
adsorbent is configured by making the carrier support a zeolite
based adsorbent that adsorbs HC at low temperatures and desorbs the
HC at high temperatures. Desorption temperature characteristics of
the adsorbed HC vary depending on the substance of the adsorbent.
According to the present embodiment, the HC adsorbent is prepared
so that the desorption start temperature of HC might coincide with
the desorption start temperature of NOx which is stored in the
exhaust purification catalyst 20.
[0090] The HC contained in the exhaust gas is adsorbed by the HC
adsorbent during a cold startup of the engine 12. The adsorbed HC
is desorbed at the time when desorption of the stored NOx is
started after a rise in the temperature of the exhaust purification
catalyst 20. Therefore, it is possible to reliably purify the NOx
stored before the catalyst activation by additionally supplying HC
that functions as a reducing agent during the desorption period of
NOx when reducing agents are apt to be in short supply.
[0091] The first embodiment, which has been described above,
assumes that ozone is generated by the ozone supply device 30 and
injected toward the exhaust purification catalyst 20 from ozone
injection orifice 34. However, the configuration of the ozone
supply device 30 is not limited to the above-described one. That
is, an ozone generation device may be installed in the exhaust path
14 or the ozone supply device 30 may inject ozone into the exhaust
path 14 upstream from the exhaust purification catalyst 20, as long
as ozone can be added to the exhaust gas introduced into the
exhaust purification catalyst 20.
[0092] Furthermore, although BaCO.sub.3 is used as an NOx storage
substance in the above described first embodiment, the material is
not limited to this. For example, alkali metals such as Na, K, Cs
and Rb, alkali earth metals such as Ba, Ca and Sr, and rare earth
elements such as Y, Ce, La and Pr may be used as needed. Also, the
material of the catalyst is not limited to Pt. For example, noble
metals such as Rh and Pd may be used as needed. Furthermore, the
material of the HC adsorbent is not limited to ZSM-5. For example,
various publicly known HC adsorbent may be used as needed.
[0093] In the first embodiment, which has been described above, the
ozone supply device 30 corresponds to the "ozone supply means"
according to the first aspect of the present invention; and the
exhaust purification catalyst 20 corresponds to the "catalyst"
according to the first aspect of the present invention.
Evaluation Test for First Embodiment
[Configuration of Experiment]
[0094] Next, evaluation test for confirming the advantage of the
invention showing the first embodiment will now be described with
reference to FIGS. 4 to 7. FIG. 4 is a diagram illustrating the
hardware configuration of the experiment of the present evaluation
test. As shown in FIG. 4, the present experiment includes a model
gas generator 100. The model gas generator 100 is able to mix the
gases which are supplied in a plurality of gas cylinders 102 to
create the simulant gas which represents the exhaust gas of the
internal combustion engine.
[0095] A catalyst test piece 200 is installed a path which is
placed downstream from the model gas generator 100. An electric
furnace, which controls the temperature of the catalyst test piece
200 to a desired temperature, is installed around the catalyst test
piece 200. The configuration of the catalyst test piece 200 will be
described in detail below.
[0096] Exhaust gas analyzers 110, 112 and an ozone analyzer 114 are
attached a path which is placed downstream from the catalyst test
piece 200. The simulant gas which is generated by the model gas
generator 100 is gone through inside of the catalyst test piece 200
and then it is analyzed its gas components by these analyzers.
[0097] Further, the experiment shown in FIG. 4 includes a system in
order to inject an injection gas containing ozone. More
specifically, the present experiment includes an oxygen cylinder
122. An ozone generator 120 is connected downstream from the oxygen
cylinder 122 via a flow rate control unit 124. The ozone generator
is a device in order to generate ozone from oxygen which is
supplied in the oxygen cylinder 122. The ozone generator 120 is
connected upstream from the catalyst test piece 200 via an ozone
analyzer 126 and a flow rate control unit 128. Further, the oxygen
cylinder 122 is connected upstream from the ozone analyzer 126
directly via a flow rate control unit 130 which is placed
separately. According to the aforementioned configuration, it is
possible to control the ozone amount and the oxygen amount
contained in the injection gas separately.
[0098] Following measuring instruments are used for the present
evaluation test. [0099] Ozone generator 120; Iwasaki Electric,
OP100W [0100] Ozone analyzer 126; Ebara Jitsugyo, EG600 [0101]
Ozone analyzer 114; Ebara Jitsugyo, EG2001B [0102] Exhaust gas
analyzer 110; Horiba, MEXA9100D (HC/CO/NOx measurement) [0103]
Exhaust gas analyzer 112; Horiba, VAI-510 (CO.sub.2
measurement)
[0104] Next, a specific configuration of the catalyst test piece
200 will now be described in detail. FIG. 5 is a cross-sectional
view illustrating the inside of the catalyst test piece 200 of the
present experiment. According to the present evaluation test, a
catalyst test piece 200a was used as the catalyst test piece 200 in
a first experiment, and a catalyst test piece 200b was used as the
catalyst test piece 200 in a second experiment. FIG. 5(a) is a
cross-sectional view illustrating the inside of the catalyst test
piece 200a being used in the first experiment. As shown in FIG.
5(a), the catalyst test piece 200a includes a catalyst sample 204,
which comprises an HC adsorbing function, an NOx storage function,
and a catalyst function, inside of a quartz tube 202. The catalyst
sample 204 was created by performing the procedure described
below.
(Creating Procedure of Catalyst Sample 206)
[0105] First, .gamma.-Al.sub.2O.sub.3 was dispersed in ion-exchange
water. An aqueous solution of barium acetate was then added in it.
The resulting mixture heated to remove water from it, dried at 120
degrees Celsius, and pulverized to powder. The powder was then
burned for two hours at 500 degrees Celsius. After burning, the
burnt powder was immersed in a solution containing ammonium
hydrogen carbonate, and then dried at 250 degree Celsius. As a
result of that, barium-supported catalyst was obtained.
[0106] Next, the barium-supported catalyst was dispersed in
ion-exchange water. An aqueous solution containing dinitro-diammine
platinum was then added to support Pt. The resulting mixture was
dried, pulverized, and burned for one hour at 450 degrees Celsius.
According to this catalyst, the supported quantity of barium was
0.1 mole per 120 g of .gamma.-Al.sub.2O.sub.3, and the supported
quantity of Pt was 2 g.
[0107] H.sup.+ ion of ZSM-5 type zeolite (Si/Al ratio=40, H-type)
was exchanged ion using silver nitrate, dried, and then burned at
450 degrees Celsius to prepare Ag ion-exchange ZSM-5. The Ag
ion-exchange ZSM-5 was mixed with .gamma.-Al.sub.2O.sub.3 being
supported Pt and Ba to obtain a catalyst. The mixture ratio (ZSM-5:
Al.sub.2O.sub.3) was 5:12.
[0108] A 30 mm diameter, 50 mm long, 4 mil/400 cpsi cordierite
honeycomb was coated with the catalyst being prepared earlier and
burned for one hour at 450 degrees Celsius. The coating amount was
such that Al.sub.2O.sub.3 was coated at a rate of 120 g/L.
Therefore, the Ag ion-exchange ZSM-5 would be coated at a rate of
50 g/L.
[0109] Meanwhile, FIG. 5(b) is a cross-sectional view illustrating
the inside of the catalyst test piece 200b being used in the second
experiment. As shown in FIG. 5(b), the catalyst test piece 200b
includes a catalyst sample 206, which comprises an NOx storage
function and a catalyst function, inside a quartz tube 202. The
catalyst sample 206 was created by performing the procedure
described below.
(Creating Procedure of Catalyst Sample 204)
[0110] First, .gamma.-Al.sub.2O.sub.3 was dispersed in ion-exchange
water. An aqueous solution of barium acetate was then added in it.
The resulting mixture heated to remove water from it, dried at 120
degrees Celsius, and pulverized to powder. The powder was then
burned for two hours at 500 degrees Celsius. After firing, the
burnt powder was immersed in a solution containing ammonium
hydrogen carbonate, and then dried at 250 degree Celsius. As a
result of that, barium-supported catalyst was obtained.
[0111] Next, the barium-supported catalyst was dispersed in
ion-exchange water. An aqueous solution containing dinitro-diammine
platinum was then added to support Pt. The resulting mixture was
dried, pulverized, and burned for one hour at 450 degrees Celsius.
According to this catalyst, the supported quantity of barium was
0.1 mole per 120 g of .gamma.-Al.sub.2O.sub.3, and the supported
quantity of Pt was 2 g.
[0112] A 30 mm diameter, 50 mm long, 4 mil/400 cpsi cordierite
honeycomb was coated with the catalyst being prepared earlier and
burned for one hour at 450 degrees Celsius. The coating amount was
such that Al.sub.2O.sub.3 was coated at a rate of 120 g/L.
[Experiment Conditions]
[0113] Following experiment conditions are used for the present
evaluation test.
[0114] Temperature: control a temperature in the range 30 degrees
Celsius-500 degrees Celsius
[0115] Temperature rise rate: 10 degrees Celsius/min.
[0116] Simulant gas compositions: [0117] stoichiometric
compositions [0118] C.sub.3H.sub.6 (1000 ppm=3000 ppmC) [0119] CO
(6500 ppm) [0120] NO (1500 ppm) [0121] O.sub.2 (7000 ppm) [0122]
CO.sub.2 (10%) [0123] H.sub.20 (3%) [0124] Remainder N.sub.2
[0125] Simulant gas flow rate: 30 L/Min.
[0126] Injection gas compositions: [0127] O3 (30000 ppm) [0128]
Remainder N.sub.2
[0129] Injection gas flow rate: 6 L/min.
[Test Method]
[0130] The electrical furnace being placed around the catalyst test
piece 200 was controlled so that its temperature might be raised
from low-temperature side. The injection gas was injected when the
temperature was in the range of 30 degrees Celsius-300 degrees
Celsius. Moreover, when the temperature was 300 degrees or higher,
only simulant gas was injected without supplying the injection gas.
The experiments was performed both the first experiment being used
the catalyst sample 204 and the second experiment being used the
catalyst sample 206. An exhaust gas purification efficiency was
calculated as a percentage by subtracting the amount of NOx being
emitted into downstream from the catalyst test piece 200
(hereinafter referred to as an "NOx outlet flow") from the amount
of NOx being introduced into the catalyst test piece 200
(hereinafter referred to as an "NOx inlet flow") within the test
time and then being divided by the NOx inlet flow within the test
time.
NOx inlet flow=NOx concentration of simulant gas.times.simulant gas
flow rate.times.test time (4)
NOx outlet flow=NOx concentration of downstream from the catalyst
200.times.gas flow rate (simulant gas and injection gas).times.test
time (5)
purification efficiency=(NOx inlet flow-NOx outet flow)/NOx inlet
flow.times.100 (6)
[Results of Test]
[0131] FIG. 6 is a graph illustrating the purification efficiencies
for a few kinds of components in the first and the second
experiments. As shown in FIG. 6, it indicates that the catalyst
test piece being used for the first experiment exhibited higher
purification efficiencies for NOx, HC, and CO. The aforementioned
results indicate an advantage by adding the HC adsorbent to the NSR
catalyst.
Second Embodiment
Characteristic Configuration of Second Embodiment
[0132] Next, the second Embodiment of the present invention will
now be described with reference to FIG. 7. FIG. 7 is a diagram
illustrating the hardware configuration of the second embodiment of
the present invention. Elements in the exhaust emission control
apparatus 40 shown in FIG. 7 that are common with those in the
exhaust emission control apparatus 10 shown in FIG. 1 are
designated by the same reference numerals, and redundant
description thereof will be omitted.
[0133] As shown in FIG. 7, an exhaust purification apparatus 40 of
the present embodiment includes an exhaust purification catalyst 42
which is installed in the exhaust path 14. An NSR catalyst 44, in
which platinum (Pt) as noble metal and barium carbonate
(BaCO.sub.3) are supported by the ceramic carrier, is placed in the
exhaust purification catalyst 42. Pt functions as an active site
which activates the oxidation reaction of CO, HC and others or the
reduction reaction of NOx. Further, BaCO.sub.3 functions as an NOx
storage substance which stores NOx in the form of nitrate.
[0134] An HC adsorbent 46, in which zeolite based ZSM-5 is
supported by a ceramic carrier, is placed in the exhaust
purification catalyst 42 upstream from the NSR catalyst 44. The
ZSM-5 functions as an HC adsorbent which adsorbs HC.
[0135] The exhaust emission control apparatus 40 according to the
second embodiment includes an ozone supply device 30. The ozone
supply device 30 includes an ozone injection orifice 34. The ozone
injection orifice 34 is placed upstream from the NSR catalyst 44
and downstream from the HC adsorbent 46, and injecting ozone toward
the NSR catalyst 44.
Characteristic Operation of Second Embodiment
[0136] In the exhaust emission control apparatus 10 according to
the above described first embodiment, it is assumed that the
exhaust purification catalyst 20 in which the HC adsorbent, the NOx
storage substance and the noble metal are supported on the common
carrier is provided so that the NOx exhausted during a cold startup
of the engine 12 is effectively stored in order to be prevented
from being emitted into the atmosphere. However, according to the
aforementioned configurations, the ozone is also injected into the
HC adsorbent which is placed inside of the exhaust purification
catalyst 20. Therefore, the injected ozone may react not only with
the NOx but also with the HC adsorbed in the HC adsorbent, thereby
decreasing an oxidized rate of NOx.
[0137] In view of the above circumstances, the second embodiment
uses the exhaust purification catalyst 42, in which the HC
adsorbent is separated from the NOx retention material. In the
exhaust purification catalyst 42, the introduced ozone is
effectively prevented from reacting with the HC adsorbed in the HC
adsorbent 46 since the HC adsorbent 46 is positioned upstream from
the ozone injection orifice as shown in FIG. 7. Therefore, the HC
adsorbed in the HC adsorbent 46 can be certainly supplied to the
NSR catalyst 44, thereby efficiently improving the NOx purification
capability.
[0138] Further, according to the exhaust purification catalyst 42,
since the NSR catalyst 44 is positioned downstream from the ozone
injection orifice 34, all of the injected ozone is used for
reacting with NOx. Therefore, it is possible to improve the
oxidation rate of NOx and increase the storage amount of NOx.
[0139] Although the NSR catalyst 44 in which the noble metal Pt and
BaCO.sub.3 functioning as an NOx storage substance are supported by
the common ceramic carrier is used in the second embodiment, the
configuration of the NSR catalyst 44 is not limited to this. For
example, according to the gas-phase reaction of the above formulas
(1) and (2), the region for oxidizing the NOx is not limited to a
region on catalyst. Thus, it becomes possible, for instance, to
support the NOx storage substance and noble metal separately in the
NSR catalyst 44. More concretely, the NOx storage substance and the
noble metal may be supported separately, for instance, at the
upstream side and the downstream side of the carrier,
respectively.
[0140] FIG. 8 is a diagram illustrating an internal configuration
of an exhaust purification catalyst 60 which is able to be applied
as modifications of the exhaust purification catalyst 42. As shown
in FIG. 8, an HC adsorbent 62 is installed inside of an exhaust
purification catalyst 60. Further, an NOx retention material 64 is
installed downstream from the HC adsorbent 62. Furthermore, a
three-way catalyst 66 is installed downstream from the NOx
retention material. Furthermore, the ozone injection orifice 34 is
installed upstream from the NOx retention material 64 and
downstream from the HC adsorbent 62. The ozone injection orifice 34
injects the ozone toward the NOx retention material 64.
[0141] According to the aforementioned configurations, it is
possible to improve the purification performance of the catalyst
since the three-way catalyst in which the noble metal is supported
and the NOx retention material 64 in which the NOx storage
substance that can be a catalyst poison is supported are installed
separately. Further, the NOx that is not stored by the NOx
retention material 64 can be purified in the three-way catalyst 66
after the catalyst is activated for some extent since the three-way
catalyst 66 is positioned downstream from the NOx retention
material 64, whereby the NOx purification performance is
improved.
[0142] Further, the interior configuration of the NSR catalyst 44
is not limited to the configuration in which the NOx storage
substance and the noble metal are supported separately at the
upstream side and the downstream side of the carrier; a
configuration in which an upper layer side and a lower layer side
are used for supporting them separately can be also used as the
interior configuration. It should be noted that, in a case where
the layered configuration is employed, it is preferable that the
noble metal is arranged as the upper layer on the NOx storage
substance so that the NOx desorbed from the NOx storage substance
is reduced by the noble metal.
[0143] Although the exhaust purification catalyst 42 that has the
HC adsorbent 46 and the NSR catalyst 44 therein is used in the
above described second embodiment, the configuration of the
catalyst is not limited to this. For example, the HC adsorbent 46
and the NSR catalyst 44 may be installed into the exhaust path 14
respectively without combining them into a single unit. Further, in
this case, the various kinds of configurations can be taken as the
ozone supply device 30. For instance, in order to add ozone to the
exhaust gas which is flown into the NSR catalyst 44, an ozone
generation device may be installed in the exhaust path 14 or the
ozone may be injected from the ozone supply device 30 into a
certain part of the exhaust path 14 which is positioned downstream
from the HC adsorbent 46 and upstream from the NSR catalyst 44.
[0144] Further, although BaCO.sub.3 is used as the NOx storage
substance in the second embodiment, the material of the NOx storage
substance is not limited to this. For example, alkali metals, such
as Na, K, Cs and Rb, alkali earth metals such as Ba, Ca and Sr, and
rare earth elements such as Y, Ce, La and Pr may be used as needed.
Further, the material of the catalyst is not limited to Pt. For
example, noble metals such as Rh and Pd may be used as needed.
Furthermore, the material of the HC adsorbent is not limited to
ZSM-5. For example, various publicly known substances for adsorbing
HC may be used as needed.
[0145] It should be noted that in the above described second
embodiment, the ozone supply device 30 corresponds to the "ozone
supply means" according to the first aspect of the present
invention; and the exhaust purification catalyst 42 corresponds to
the "catalyst" according to the first aspect of the present
invention.
Evaluation Test for Second Embodiment
[Configuration of Experiment]
[0146] Next, evaluation test for confirming the advantage of the
invention showing the second embodiment will now be described with
reference to FIGS. 9 to 11. FIG. 9 is a diagram illustrating the
hardware configuration of the experiment of the present evaluation
test. Like elements between the experiment shown in FIG. 9 and the
experiment shown in FIG. 4 are designated by the same reference
numerals and will not be redundantly described.
[0147] As shown in FIG. 9, a catalyst test piece 300 is installed
downstream from the model gas generator 100. Further, a catalyst
test piece 310 is installed downstream from the catalyst test piece
300. The ozone generator 120 is installed upstream from the
catalyst test piece 300 and downstream from the catalyst test piece
310 via the ozone analyzer 126 and the flow rate control unit
128.
[0148] Next, concrete configurations of the catalyst test pieces
300, 310 will now be described in detail. FIG. 10 is a
cross-sectional view illustrating the inside of the catalyst test
pieces 300, 310 of the present experiment. According to the present
evaluation test, the catalyst test pieces 300a and 310b were used
in a first experiment, and the catalyst test pieces 300b and 310b
were used in a second experiment. FIG. 10(a) is cross-section
diagrams illustrating the inside of the catalyst test pieces 300a
and 310a being used in the first experiment. As shown in FIG. 9(a),
the catalyst test piece 300a includes a catalyst sample 304
comprising an HC adsorbing function inside of a quartz tube 302.
Further, the catalyst test piece 310a includes a catalyst sample
314 comprising an HC adsorbing function inside of a quartz tube
312. The catalyst samples 304 and 314 were created by performing
the procedure described below.
(Creating Procedure of Catalyst Sample 306)
[0149] First, H.sup.+ ion of ZSM-5 type zeolite (Si/Al ratio=40,
H-type) was exchanged ion using silver nitrate, dried, and then
burned at 450 degrees Celsius to prepare Ag ion-exchange ZSM-5.
Next, A 30 mm diameter, 50 mm long, 4 mil/400 cpsi cordierite
honeycomb was coated with the catalyst being prepared earlier and
burned for one hour at 450 degrees Celsius. The coating amount was
50 g/L.
(Creating Procedure of Catalyst Sample 314)
[0150] First, .gamma.-Al.sub.2O.sub.3 was dispersed in ion-exchange
water. An aqueous solution of barium acetate was then added in it.
The resulting mixture heated to remove water from it, dried at 120
degrees Celsius, and pulverized to powder. The powder was then
burned for two hours at 500 degrees Celsius. After burning, the
burnt powder was immersed in a solution containing ammonium
hydrogen carbonate, and then dried at 250 degree Celsius. As a
result of that, barium-supported catalyst was obtained.
[0151] Next, the barium-supported catalyst was dispersed in
ion-exchange water. An aqueous solution containing dinitro-diammine
platinum was then added to support Pt. The resulting mixture was
dried, pulverized, and burned for one hour at 450 degrees Celsius.
According to this catalyst, the supported quantity of barium was
0.1 mole per 120 g of .gamma.-Al.sub.2O.sub.3, and the supported
quantity of Pt was 2 g.
[0152] A 30 mm diameter, 50 mm long, 4 mil/400 cpsi cordierite
honeycomb was coated with the catalyst being prepared earlier and
burned for one hour at 450 degrees Celsius. The coating amount of
Al.sub.2O.sub.3 was 120 g/L.
[Experiment Conditions]
[0153] Following experiment conditions are used for the present
evaluation test.
[0154] Temperature: control a temperature in the range 30 degrees
Celsius-500 degrees Celsius
[0155] Temperature rise rate: 10 degrees Celsius/min.
[0156] Simulant gas compositions: [0157] stoichiometric
compositions [0158] C.sub.3H.sub.6 (1000 ppm=3000 ppmC) [0159] CO
(6500 ppm) [0160] NO (1500 ppm) [0161] O.sub.2 (7000 ppm) [0162]
CO.sub.2 (10%) [0163] H.sub.20 (3%) [0164] Remainder N.sub.2
[0165] Simulant gas flow rate: 30 L/Min.
[0166] Injection gas compositions: [0167] O3 (30000 ppm) [0168]
Remainder N.sub.2
[0169] Injection gas flow rate: 6 L/min.
[Test Method]
[0170] The electrical furnaces which are placed around the catalyst
test pieces 300 and 310 were controlled so that its temperature
might be raised from low-temperature side. The injection gas was
injected when the temperature was in the range of 30 degrees
Celsius-300 degrees Celsius. Moreover, when the temperature was 300
degrees or higher, only simulant gas was injected without supplying
the injection gas. The experiments were performed both the first
experiment being used the catalyst samples 304, 314 and the second
experiment being used the catalyst sample 306. An exhaust gas
purification efficiency was calculated by using above formula
(5).
[Results of Test]
[0171] FIG. 11 is a graph illustrating the purification
efficiencies for a few kinds of components according to the first
and the second experiments. As shown in FIG. 11, it indicates that
the catalyst test piece being used for the first experiment
exhibited higher purification efficiencies for NOx, HC, and CO. The
aforementioned results indicate an advantage by installing the HC
adsorbent upstream from ozone injection orifice.
* * * * *