U.S. patent application number 15/252862 was filed with the patent office on 2016-12-22 for exhaust gas purifier.
This patent application is currently assigned to N.E. CHEMCAT CORPORATION. The applicant listed for this patent is N.E. CHEMCAT CORPORATION. Invention is credited to Makoto Nagata, Toshinori Okajima.
Application Number | 20160367943 15/252862 |
Document ID | / |
Family ID | 49583544 |
Filed Date | 2016-12-22 |
United States Patent
Application |
20160367943 |
Kind Code |
A1 |
Okajima; Toshinori ; et
al. |
December 22, 2016 |
EXHAUST GAS PURIFIER
Abstract
An exhaust gas purification catalyst apparatus, which is
superior in oxidation performance of, in particular, nitrogen
monoxide, among hydrocarbons, carbon monoxide, nitrogen oxides and
particulate components such as soot, included in exhaust gas from a
lean burn engine, and combustion performance of light oil. The
exhaust gas purification apparatus arranged with an oxidation
catalyst (DOC) comprising a noble metal component for oxidizing
carbon monoxide, hydrocarbons, in particular, nitrogen monoxide
among nitrogen oxides, and for combusting light oil, a catalyzed
soot filter (CSF) including a noble metal component for collecting
a particulate component such as soot and removing by combustion
(oxidation). The oxidation catalyst (DOC) has a catalyst layer
where platinum (Pt), palladium (Pd) and barium oxide (BaO) are
supported on alumina (Al.sub.2O.sub.3) having a pore size of 12 to
120 nm, and ratio of platinum and palladium is 1:1 to 11:2 in
weight equivalent.
Inventors: |
Okajima; Toshinori;
(Shizuoka, JP) ; Nagata; Makoto; (Shizuoka,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
N.E. CHEMCAT CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
N.E. CHEMCAT CORPORATION
Tokyo
JP
|
Family ID: |
49583544 |
Appl. No.: |
15/252862 |
Filed: |
August 31, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14396234 |
Oct 22, 2014 |
9480948 |
|
|
PCT/JP2013/060669 |
Apr 9, 2013 |
|
|
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15252862 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J 23/44 20130101;
B01D 2255/2042 20130101; B01J 37/0248 20130101; F01N 2570/10
20130101; F01N 2570/12 20130101; B01D 2255/2092 20130101; B01J
23/58 20130101; B01D 53/944 20130101; B01D 2255/902 20130101; F01N
3/103 20130101; F01N 3/2066 20130101; F01N 2570/14 20130101; F01N
3/106 20130101; Y02T 10/12 20130101; B01D 53/9418 20130101; B01J
37/0244 20130101; B01D 2258/012 20130101; B01J 29/7615 20130101;
B01J 37/0219 20130101; B01D 2255/9202 20130101; B01J 29/06
20130101; B01J 35/04 20130101; F01N 2370/02 20130101; B01D
2255/1023 20130101; F01N 3/206 20130101; B01D 2257/406 20130101;
B01J 35/1061 20130101; B01D 2255/1021 20130101; F01N 3/035
20130101; F01N 2250/02 20130101; B01J 35/0006 20130101; Y02T 10/24
20130101; F01N 2610/02 20130101; F01N 13/0097 20140603; Y02A
50/2341 20180101; B01J 21/04 20130101; F01N 13/009 20140601; B01J
35/1066 20130101; F01N 2510/06 20130101; B01D 53/9477 20130101;
Y02A 50/20 20180101 |
International
Class: |
B01D 53/94 20060101
B01D053/94; B01J 21/04 20060101 B01J021/04; F01N 3/10 20060101
F01N003/10; B01J 35/10 20060101 B01J035/10; F01N 3/035 20060101
F01N003/035; F01N 3/20 20060101 F01N003/20; B01J 23/44 20060101
B01J023/44; B01J 35/00 20060101 B01J035/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 14, 2012 |
JP |
2012-110519 |
Claims
1. An exhaust gas purification apparatus, comprising: a first
oxidation catalyst (DOC) comprising a noble metal component for
oxidizing, in particular, nitrogen monoxide, among carbon monoxide,
hydrocarbons, nitrogen oxides, and for combusting light oil, a
catalyzed soot filter (CSF) comprising a noble metal component for
collecting a particulate component such as soot and removing by
combustion (oxidation), a second oxidation catalyst (DOC), a
reducing agent spraying means for supplying a reducing agent
selected from a urea component or an ammonia component, and a
selective reduction catalyst (SCR) for removing by reduction of
nitrogen oxides by contacting with the reducing agent, wherein the
first oxidation catalyst (DOC), the catalyzed soot filter (CSF),
the second oxidation catalyst (DOC), the reducing agent spraying
means, and the selective reduction catalyst (SCR) are arranged in
this order from the upstream side of an exhaust gas passage, in
order to purify carbon monoxide, hydrocarbons, nitrogen oxides, and
particulate components such as soot, in exhaust gas discharged from
a diesel engine, the first oxidation catalyst (DOC) and the second
oxidation catalyst (DOC) have a catalyst layer where platinum (Pt)
and palladium (Pd) are supported on alumina (Al.sub.2O.sub.3)
having a pore size of 12 to 120 nm, and ratio of platinum and
palladium is 1:1 to 11:2 in weight equivalent, and the catalyzed
combustion filter (CSF) has a catalyst layer, where platinum (Pt)
and palladium (Pd) are supported on alumina having a pore size of
12 to 120 nm, or a mixture of two or more kinds of alumina having
different pore size within its range, and ratio of platinum and
palladium is 1:1 to 11:4 in weight equivalent.
2. The exhaust gas purification apparatus according to claim 1,
wherein the catalyst layer is coated onto an integral
structure-type substrate, in one or more layers.
3. The exhaust gas purification apparatus according to claim 1,
wherein the catalyst layer has a base layer composed of alumina, at
the lower layer thereof.
4. The exhaust gas purification apparatus according to claim 1,
wherein the alumina having the pore size of 12 to 120 nm is a
mixture of two or more kinds of alumina having different pore
size.
5. The exhaust gas purification apparatus according to claim 1,
wherein barium oxide is included in the first oxidation catalyst
(DOC) is in an amount of 0.5 to 4.0 g/L.
6. The exhaust gas purification apparatus according to claim 1,
wherein the first oxidation catalyst (DOC) or the second oxidation
catalyst (DOC) includes a coated amount of the catalyst layer of 50
to 300 g/L.
7. The exhaust gas purification apparatus according to claim 1,
wherein the first oxidation catalyst (DOC) or the second oxidation
catalyst (DOC) includes a total supported amount of the noble
metals of 0.5 to 4.0 g/L in metal equivalent per volume.
8. The exhaust gas purification apparatus according to claim 1,
wherein the catalyzed soot filter (CSF) includes a coated amount of
the catalyst layer of 4 to 100 g/L.
9. The exhaust gas purification apparatus according to claim 1,
wherein the catalyzed soot filter (CSF) includes a total supported
amount of the noble metals of 0.05 to 2.0 g/L in metal equivalent
per volume.
10. The exhaust gas purification apparatus according to claim 1,
further comprising an ammonia oxidation catalyst (AMOX) arranged
after the selective reduction catalyst (SCR).
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a divisional of U.S. application Ser. No. 14/396,234
filed on Oct. 22, 2014, which is a 371 of PCT/JP2013/060669 filed
on Apr. 9, 2013, which claims priority to Japanese Application No.
2012-110519 filed May 14, 2012, the entire contents of which is
incorporated herein by reference.
TECHNICAL FIELD
[0002] The present invention relates to an exhaust gas purification
apparatus, and in more detail, the present invention relates to an
exhaust gas purification catalyst apparatus combined an diesel
oxidation catalyst (DOC) and a catalyzed soot filter (CSF), which
are superior in oxidation performance of, in particular, nitrogen
monoxide (NO), among hydrocarbons (HC), carbon monoxide (CO),
nitrogen oxides (NO.sub.x) and particulate components such as soot,
included in exhaust gas from a lean burn engine, and combustion
performance of unburned fuel such as light oil.
BACKGROUND ART
[0003] In exhaust gas discharged from a lean burn engine such as a
boiler, a gas turbine, a lean burn-type gasoline engine or a diesel
engine, various harmful substances derived from fuel or combustion
air are included. Such harmful substances include a hydrocarbon
(HC), a soluble organic fraction (it may also be called SOF), soot,
carbon monoxide (CO), nitrogen oxides (NO.sub.x) and the like, and
regulations on discharge amount of these harmful components have
been strengthening year by year. As a purification method of these
harmful components, there has been practically used a method for
purifying exhaust gas by making it contacted with a catalyst.
[0004] In such a lean burn engine, there has also been investigated
on suppression of generation amount of harmful substances by
controlling kinds, supply amount and supply timing of fuel, amount
of air or the like. However, satisfactory purification of exhaust
gas has not been attained by a conventional catalyst or a control
method. In particular, in a lean burn engine, nitrogen oxides are
easily discharged, in addition, regulation thereof has been
strengthening more and more, however, by conventional NO.sub.x
purification technology, in the case of a diesel engine mounted on
an automobile, it is difficult to suppress discharge of the harmful
substances by conventional NO.sub.x purification technology,
because operation condition thereof is always changing.
[0005] Further, in recent year, regulation of discharge amount of
carbon dioxide (CO.sub.2) has been strengthened, as the greenhouse
effect gas. Because discharge amount of CO.sub.2 is proportional to
fuel amount used in engine operation, it has been desired that, in
a combustion engine, used amount of fuel is small and fuel
efficiency is good. A diesel engine is a combustion engine having
good fuel efficiency and small discharge amount of CO.sub.2,
however, includes a large quantity of NO.sub.x in exhaust gas.
[0006] To suppress discharge of NO.sub.x from a diesel engine, it
is considered to make air/fuel ratio small mechanically, and supply
to an engine a large quantity of fuel, which is also a reducing
agent, however, it incurs deterioration of fuel efficiency, and
also increases discharge of CO.sub.2. In addition, such a
combustion control cannot utilize advantage of a diesel engine,
that is, good fuel efficiency.
[0007] As a method for purify NO.sub.x in exhaust gas discharged
from a lean burn engine such as a diesel engine, there has been
known technology for denitration by reduction, where exhaust gas
including NO.sub.x (NO and NO.sub.2) contacts with a selective
reduction catalyst consists of titanium oxide, vanadium oxide,
zeolite and the like as main components, under presence of ammonia
(NH.sub.3) component arising by decomposition of urea, and it is
referred to as a selective reduction method or a Selective
Catalytic Reduction (hereafter it may be referred to as SCR)
method.
[0008] In the SCR, where this NH.sub.3 component is used as a
reducing agent, NO.sub.x is finally reduced to N.sub.2 mainly by
the following reaction formulas (1) to (3):
4NO+4NH.sub.3+O.sub.2.fwdarw.4N.sub.2+6H.sub.2O (1)
6NO.sub.2+8NH.sub.3.fwdarw.7N.sub.2+12H.sub.2O (2)
NO+NO.sub.2+2NH.sub.3.fwdarw.2N.sub.2+3H.sub.2O (3)
[0009] In practice, in NO.sub.x purification by the NH.sub.3
component, the reaction is promoted under atmosphere including NO
and NO.sub.2 each nearly half as in the expression (3) (refer to
NON PATENT LITERATURE 1). However, most of NO.sub.x components
discharged from a lean burn engine is nitrogen monoxide (refer to
PATENT LITERATURE 1), therefore, in order to purify NO.sub.x
efficiently, so as to increase concentration of the NO.sub.2
component in exhaust gas, there has been proposed an arrangement of
an NO oxidation means at an exhaust gas passage (refer to PATENT
LITERATURE 2). Specifically, platinum (Pt) having high oxidation
capability of NO is used as an oxidation catalyst.
[0010] There has also been proposed a method for purifying harmful
particulate components, NO.sub.x, in one catalyst system
simultaneously, by utilizing such an NO oxidation means. One of
them is the one for purifying NO.sub.x by arranging the oxidation
catalyst in exhaust gas passage, arranging a filter at the latter
part thereof, spraying the ammonia component at the latter part
thereof, and using the selective reduction catalyst (SCR) arranged
at the latter part thereof (refer to PATENT LITERATURE 3).
[0011] By such a catalyst arrangement, it is possible to perform a
means for oxidizing NO in exhaust gas to NO.sub.2, by an oxidation
catalyst, and removing by combustion of particulate components, and
purifying by reduction of NO.sub.x, simultaneously, using a single
catalyst system. And, it has been known that a platinum component
is effective as this oxidation catalyst component of NO (refer to
PATENT LITERATURE 4 and NON PATENT LITERATURE 2).
[0012] In this way, there have been proposed a purification of
NO.sub.x and a purification means of the particulate components,
however, any cases thereof is the one aiming at increasing
purification efficiency of NO.sub.x in SCR, by increasing
concentration of NO.sub.2 in exhaust gas, by arranging DOC in front
of SCR.
[0013] In addition, purification technology of soot or SOF (they
may hereafter be referred to collectively as a "particulate
component" or PM: Particulate Matter) influences also on fuel
efficiency enhancement of a diesel engine. As for the particulate
component, there has practically been used a method for arranging a
heat resistant filter (DPF: Diesel Particulate Filter) in exhaust
gas passage, and filtering off the particulate component with this
filter. The particulate component thus filtered off deposits on the
filter, and continued deposition of the particulate component on
the filter incurs decrease in output of an engine caused by
pressure increase accompanied with clogging of the filter.
Accordingly, there has been investigated regeneration of the filter
by combustion removal of the particulate component deposited on the
filter (PATENT LITERATURE 3, PATENT LITERATURE 4).
[0014] In the system of PATENT LITERATURE 3 and PATENT LITERATURE
4, by arranging DPF at the latter part of DOC, the particulate
component deposited on the filter is removed by combustion
utilizing NO.sub.2 in addition to oxygen. Utilization of NO.sub.2,
because of enabling to initiate combustion of the particulate
component from low temperature, not only promotes removal by
combustion of the particulate component but also enables to
lengthen interval to regeneration of the filter by suppression of
increase in pressure drop. Among the filters for capturing and
removing by combustion the particulate component in this way, DPF
coated with a catalyst component is also referred to as CSF
(Catalyzed Soot Filter).
[0015] In this way, in DOC, the noble metal component such as
platinum (Pt) or palladium (Pd) is used aiming at removing by
oxidation of HC or CO in exhaust gas, or in CSF, aiming at
purifying by oxidation of soot or SOF in exhaust gas, respectively,
however, DOC also has action of oxidation of NO in exhaust gas to
NO.sub.2, as described above. Exhaust gas having increased amount
of NO.sub.2 promotes reduction purification of NO.sub.x in SCR at
the backward, and combustion of the particulate component at DPF or
CSF.
[0016] In addition, increase in temperature of exhaust gas by
utilization of HC in exhaust gas at DOC is effective to promote
removal by combustion of the particulate component deposited onto
DPF or CSF arranged at the backward of DOC. Therefore, in an
exhaust gas purification system of a diesel engine, there may be
the case where HC components are combusted (oxidized) by supplying
the HC components to DOC. As a means for using the HC components to
increase temperature of exhaust gas in this way, there is a method
for supplying relatively more amount of fuel to an engine and
generating unburned HC and supplying it to DOC; or a method for
supplying fuel by spraying in the piping from an engine to DOC.
[0017] In this way, there have been proposed various methods of
purification of NO.sub.x and a purification means of the
particulate components, however, with strengthening of exhaust gas
regulations in recent years, there has been tendency of not only
increasing number of catalysts to be used in the exhaust gas
purification system corresponding to exhaust gas from a lean burn
engine, but also requiring to attain higher function of an
individual catalyst. Therefore, there has been increasing tendency
of amount of high price noble metals to be used in DOC or CSF.
[0018] Under such circumstances, there has been required a way to
solve two conflicting problems for DOC or CDF containing a noble
metal such as Pt or Pd, that is, enhancement of removing
performance by oxidation of CO, HC, soot or the like, oxidation
performance of NO, and combustibility of unburned fuel such as
light oil, and simultaneously decreasing use amount of the noble
metal.
[0019] Accordingly, the present inventor has proposed an exhaust
gas purification method characterized by arranging an oxidation
means, a spraying means of a urea aqueous solution and a specific
selective reduction catalyst, in this order in a passage of an
exhaust gas discharged from a diesel engine, including a platinum
component or a palladium component, as a noble metal component,
which is said oxidation means, and after increasing concentration
of nitrogen dioxide with oxidation of hydrocarbon components,
carbon monoxide, nitrogen monoxide, and nitrous oxide in exhaust
gas, by an oxidation catalyst, where amount of this noble metal
component is 0.1 to 3 g/L in metal equivalent, and amount of
platinum in the noble metal component is 50 to 100% by weigh in
metal equivalent, and then spray supplying the urea aqueous
solution from the spraying means of the urea aqueous solution to
the selective reduction catalyst, to decompose nitrogen oxides to
nitrogen and water, with generated ammonia by contacting the SCR at
150 to 600.degree. C. (refer to PATENT LITERATURE 5). By this
method, it has become possible to purify NO.sub.x with using urea
water, which is standardized and easily available, by a simple
configuration without performing hydrolysis of urea outside the
catalyst system.
[0020] However, this is not the one relating to improvement of the
oxidation catalyst, and thus it cannot be said that use amount of
the noble metal was decreased sufficiently.
CITATION LIST
Patent Literature
[0021] PATENT LITERATURE 1: JP-A-05-38420 (Claim 1, paragraphs
0012, 0013, 0014) [0022] PATENT LITERATURE 2: JP-A-08-103636 (Claim
1, paragraphs 0002, 0012) [0023] PATENT LITERATURE 3:
JP-A-01-318715 [0024] PATENT LITERATURE 4: JP-A-2002-502927 (Claim
1, paragraphs 0007, 0008) [0025] PATENT LITERATURE 5:
JP-A-2009-262098 (Claim 12, paragraph 0015)
Non Patent Literature
[0025] [0026] NON PATENT LITERATURE 1: Catalysis Today 114 (2006)
3-12 (Page 2, left column) [0027] NON PATENT LITERATURE 2:
Influence of Support Materials and Aging on NO Oxidation
Performance of Pt Catalysts under an Oxidative Atmosphere at Low
Temperature, JOURNAL OF CHEMICAL ENGINEERING OF JAPAN, Vol. 40
(2007) No. 9 pp. 741-748
SUMMARY OF INVENTION
Technical Problem
[0028] In view of the above conventional technical problems, it is
an object of the present invention to provide the exhaust gas
purification catalyst apparatus, using in combination of the
oxidation catalyst (DOC) and the catalyzed soot filter (CSF), which
are superior in oxidation performance of, in particular, nitrogen
monoxide (NO), among hydrocarbons (HC), carbon monoxide (CO),
nitrogen oxides (NO.sub.x) and particulate components such as soot,
included in exhaust gas from a lean burn engine, and combustion
performance of unburned fuel such as light oil.
Solution to Problem
[0029] The present inventors have intensively studied a way to
solve the above conventional technical problems and found, as a
result, that oxidation activity of, in particular, NO, and
combustibility of unburned fuel such as light oil are promoted, in
an exhaust gas purification apparatus arranged with the catalysts
in the order of DOC, CSF and SCR, and arranged with the supply
means of an ammonia component as a reducing agent, between DOC and
SCR catalysts, when the DOC supports Pt and Pd of the noble metal
component, onto one or more kinds of alumina having a pore size of
12 to 120 nm, and in this case, Pt and Pd are set at 1:1 to 11:2,
in weight ratio, and has a catalyst layer added with barium oxide,
and have thus completed the present invention.
[0030] That is, according to a first aspect of the present
invention, there is provided an exhaust gas purification apparatus
arranged with an oxidation catalyst (DOC) including a noble metal
component for oxidizing, in particular, nitrogen monoxide, among
carbon monoxide, hydrocarbons, nitrogen oxides, and for combusting
light oil, a catalyzed soot filter (CSF) including a noble metal
component for collecting a particulate component such as soot and
removing it by combustion (oxidation), a reducing agent spraying
means for supplying a reducing agent selected from a urea component
or an ammonia component, and a selective reduction catalyst (SCR)
for removing by reduction of nitrogen oxides by contacting with the
reducing agent, in this order from the upstream side of an exhaust
gas passage, in order to purify carbon monoxide, hydrocarbons,
nitrogen oxides, and particulate components such as soot, in
exhaust gas discharged from a diesel engine, characterized in that
the oxidation catalyst (DOC) has a catalyst layer where platinum
(Pt), palladium (Pd) and barium oxide (BaO) are supported on
alumina (Al.sub.2O.sub.3) having a pore size of 12 to 120 nm, and
ratio of platinum and palladium is 1:1 to 11:2 in weight
equivalent
[0031] In addition, according to a second aspect of the present
invention, in the first aspect, there is provided the exhaust gas
purification apparatus, characterized in that the catalyst layer is
coated onto an integral structure-type substrate, in one or more
layers.
[0032] In addition, according to a third aspect of the present
invention, in the first aspect, there is provided the exhaust gas
purification apparatus, characterized in that the catalyst layer
has a base layer composed of alumina, at the lower layer
thereof.
[0033] In addition, according to a fourth aspect of the present
invention, in the first aspect, there is provided the exhaust gas
purification apparatus, characterized that the alumina having the
pore size of 12 to 120 nm is a mixture of two or more kinds of
alumina having different pore size.
[0034] In addition, according to a fifth aspect of the present
invention, in the first aspects, there is provided the exhaust gas
purification apparatus, characterized in that the oxidation
catalyst (DOC) is further installed also between the catalyzed soot
filter (CSF) and the reducing agent spraying means.
[0035] In addition, according to a sixth aspect of the present
invention, in the first aspect, there is provided the exhaust gas
purification apparatus, characterized in that amount of barium
oxide in the oxidation catalyst (DOC) is 0.5 to 4.0 g/L.
[0036] In addition, according to a seventh aspect of the present
invention, in the first aspect, there is provided the exhaust gas
purification apparatus, characterized in that coated amount of the
catalyst layer in the oxidation catalyst (DOC) is 50 to 300
g/L.
[0037] In addition, according to an eighth aspect of the present
invention, in the first aspect, there is provided the exhaust gas
purification apparatus, characterized in that total supported
amount of the noble metals in the oxidation catalyst (DOC) is 0.5
to 4.0 g/L in metal equivalent per volume.
[0038] In addition, according to a ninth aspect of the present
invention, in the first or the fifth aspect, there is provided the
exhaust gas purification apparatus, characterized in that the
catalyzed soot filter (CSF) has a catalyst layer, where platinum
(Pt) and palladium (Pd) are supported on alumina having a pore size
of 12 to 120 nm, or a mixture of two or more kinds of alumina
having different pore size within this range, and ratio of platinum
and palladium is 1:1 to 11:4 in weight equivalent.
[0039] In addition, according to a tenth aspect of the present
invention, in the ninth aspect, there is provided the exhaust gas
purification apparatus, characterized in that coated amount of the
catalyst layer in the catalyzed soot filter (CSF) is 4 to 100
g/L.
[0040] In addition, according to an eleventh aspect of the present
invention, in the ninth or the tenth aspect, there is provided the
exhaust gas purification apparatus, characterized in that total
supported amount of the noble metals in the catalyzed soot filter
(CSF) is 0.05 to 2.0 g/L in metal equivalent per volume.
[0041] Further, according to a twelfth aspect of the present
invention, in the first aspect, there is provided the exhaust gas
purification apparatus, characterized in that an ammonia oxidation
catalyst (AMOX) is further arranged after the selective reduction
catalyst (SCR).
Advantageous Effects of Invention
[0042] The exhaust gas purification apparatus of the present
invention is superior in oxidation activity of NO, and
combustibility of unburned fuel such as light oil, and is superior
in oxidation performance of, in particular, NO, among HC, CO,
NO.sub.x and particulate components such as soot, discharged from a
lean burn engine such as a diesel engine, and combustion
performance of unburned fuel such as light oil.
[0043] Further, the exhaust gas purification apparatus of the
present invention can be manufactured in low cost, because of
saving of use amount of the high price noble metals, and can
manufacture and supply stably the exhaust gas purification
apparatus.
BRIEF DESCRIPTION OF DRAWINGS
[0044] FIG. 1 is an explanation drawing showing schematically a
configuration, where an oxidation catalyst (DOC), a catalyzed soot
filter (CSF), a supplying means of a reducing component, and a
selective reduction catalyst (SCR) are arranged in this order, in
an exhaust gas purification catalyst apparatus of the present
invention.
[0045] FIG. 2 is an explanation drawing showing schematically a
configuration, where an oxidation catalyst (DOC), a catalyzed soot
filter (CSF), a oxidation catalyst (DOC), a supplying means of a
reducing component, and a selective reduction catalyst (SCR) are
arranged in this order, in an exhaust gas purification catalyst
apparatus of the present invention.
[0046] FIG. 3 is a graph showing oxidation performances of NO, CO
and HC in a model gas evaluation test using an oxidation catalyst
(DOC).
[0047] FIG. 4 is a graph showing oxidation activity of NO in an
exhaust gas purification test by a diesel engine on a mount using
an oxidation catalyst (DOC).
[0048] FIG. 5 is a graph showing combustibility of light oil in an
exhaust gas purification test by a diesel engine bench using an
oxidation catalyst (DOC).
[0049] FIG. 6 is a graph showing oxidation activities of NO, CO and
HC in an exhaust gas purification test by a diesel engine bench
using an oxidation catalyst (DOC) and a catalyzed soot filter
(CSF).
[0050] FIG. 7 is a graph showing oxidation activities of NO, CO and
HC in an exhaust gas purification test by a diesel engine bench,
where two oxidation catalysts (DOC) and a catalyzed soot filter
(CSF) are aligned in series.
REFERENCE SIGNS LIST
[0051] 1 diesel engine [0052] 2 exhaust gas passage [0053] 3
reducing agent spraying means [0054] 4 oxidation catalyst (DOC)
[0055] 5 catalyzed soot filter (CSF) [0056] 6 selective reduction
catalyst (SCR)
DESCRIPTION OF EMBODIMENTS
[0057] Description will be given below in detail mainly on the case
of applying the exhaust gas purification apparatus of the present
invention to a diesel automobile application, however, it is not
without saying that the present invention is also effective to a
diesel engine to be used in various power sources such as power
generation.
1. [Exhaust Gas Purification Apparatus (DOC+CSF+SCR)]
[0058] The present invention is the exhaust gas purification
apparatus arranged with the specified oxidation catalyst (DOC)
including the noble metal component for oxidizing nitrogen oxides
(NO) in exhaust gas discharged from a diesel engine, the catalyzed
soot filter (CSF) including the noble metal component for
collecting and removing by combustion (oxidation) of particulate
matter (PM) in exhaust gas, the reducing agent spraying means for
supplying the reducing agent selected from a urea component or an
ammonia component, and the selective reduction catalyst (SCR) not
including the noble metal component for removing by reduction of
nitrogen oxides (NO.sub.x), by contacting with the reducing agent,
in this order from the upstream side of an exhaust gas passage, and
this exhaust gas purification catalyst apparatus (DOC+CSF+SCR) may
also be referred to as a catalyst apparatus I.
[0059] That is, as shown in FIG. 1, the catalyst apparatus I of the
present invention is an exhaust gas purification catalyst apparatus
installed with a spraying means of a reducing agent 3 at the
backward of an oxidation catalyst (DOC) 4 and the catalyzed soot
filter (CSF) 5 in passage of exhaust gas 2 from a diesel engine 1,
and arranged with a selective reduction catalyst (SCR) 6 at the
backward of this injection means 3.
[0060] In the catalyst apparatus I of the present invention, by
oxidation of NO to NO.sub.2 by DOC and CSF, an NO.sub.x reduction
reaction, using a urea aqueous solution or an ammonia aqueous
solution (hereafter, it may be referred to as an ammonia component
or a NH.sub.3 component) in SCR arranged backward thereof, is
promoted.
[0061] In addition, by combusting unburned light oil at DOC to
raise exhaust gas temperature, by periodically spraying unburned
light oil to the inside of a cylinder of a diesel engine, or to the
inside of a piping of the middle part of the diesel engine and DOC,
soot accumulated in CSF is combusted using combustion heat
thereof.
1. [DOC: Oxidation Catalyst]
[0062] DOC to be used in the present invention is an oxidation
catalyst including the noble metal component for oxidizing NO, HC
or CO in exhaust gas and unburned fuel such as light oil, and
contains at least a platinum component and a palladium component as
the noble metal component.
(Noble Metal Component)
[0063] In the oxidation catalyst, as described above, the platinum
component is generally used as the noble metal component, and the
palladium component may also be used in some cases. However, it is
difficult to obtain sufficient NO oxidation activity only by the Pd
component. In addition, the Pd component may be poisoned easily by
a sulfur component in light oil or heavy oil, which is fuel of a
diesel engine, thus may be deactivated during use for a long period
of time.
[0064] Although Pd has such a problem, because it is far
inexpensive in price as compared with Pt, or it may exhibit higher
oxidation activity than Pt, depending on HC species or atmosphere
of exhaust gas, by suitable distribution of supporting ratio of Pt
and Pd, optimum condition in view of performance and price can be
found out.
[0065] In the present invention, in consideration of the above,
ratio of Pt and Pd is preferably 1:1 to 11:2, and more preferably
3:2 to 11:2. The ratio below 1:1 largely decreases oxidation
activity of HC, CO, NO or the like, accompanied with decrease in
content of platinum, and largely decreases heat generation
capability of exhaust gas by combustion of unburned fuel light oil
or the like, while the ratio over 11:2 could lose merit in view of
price.
[0066] In addition, in the present invention, supported amount of
the noble metal component of DOC is preferably 0.5 to 4.0 g/L, and
more preferably 0.8 to 3.0 g/L in metal equivalent per volume of an
integral structure-type substrate. Too low amount of the noble
metal component does not sufficiently provide removal performance
by oxidation of HC or CO, oxidation performance of NO, and
combustibility of unburned fuel such as light oil, while too high
amount of the noble metal component could lose merit in view of
price.
[0067] Further, in the present invention, coated amount of the
catalyst layer of the oxidation catalyst (DOC) is preferably 50 to
300 g/L, and more preferably 70 to 250 g/L. The coated amount of
the catalyst layer below 50 g/L decreases oxidation activity by
deterioration of dispersion property of the noble metals such as
platinum to be supported, while the amount over 300 g/L increases
pressure drop by narrowing inside the cell, and thus not
preferable.
(Promoter Component)
[0068] In the oxidation catalyst (DOC) in the exhaust gas
purification apparatus of the present invention, barium (Ba) is
used as a promoter. Ba is one of the elements having high
ionization tendency, and gives an electron to the noble metals such
as Pt or Pd to promote reduction of the noble metals. In
particular, Ba has good compatibility with Pd and has function to
promote activity of Pd.
[0069] As a starting salt of Ba, a water-soluble salt is
preferable, due to providing high dispersion on alumina, and barium
acetate, barium chloride, barium nitrate, barium hydroxide, and
barium oxide (it is converted to barium hydroxide when dissolved in
water) are used.
[0070] Among them, barium acetate or barium hydroxide (barium
oxide) is preferable, because of having high solubility to water,
and being easily oxidized at relatively low temperature, when
converted to an oxide by heat treatment under air atmosphere inside
an electric furnace.
[0071] In the present invention, supported amount of Ba is
preferably 0.5 to 4.0 g/L, and more preferably 0.5 to 3.0 g/L in
barium oxide equivalent. The supported amount in barium oxide
equivalent less than 0.5 g/L could become inferior in electron
donating property to Pt or Pd. On the other hand, the supported
amount in barium oxide equivalent over 4.0 g/L could increase the
capability to discharge as NO, due to storage of NO.sub.2 oxidized
by Pt.
(Inorganic Base Material)
[0072] The above noble metal component or the promoter is supported
onto an inorganic oxide (an inorganic base material), and mixed
with other catalyst components, as needed, and coated onto the
structure-type substrate as a catalyst composition. As the
inorganic oxide as the base material for supporting the noble metal
component in this way, a known catalyst material for exhaust gas
purification can be used. Such an inorganic material is preferably
a porous inorganic oxide, due to having high heat resistance, large
specific surface area, thus being capable of providing stable and
high dispersion of the noble metal component.
[0073] As one example of the inorganic oxide (inorganic base
material) for supporting the noble metals or the promoter, alumina
is included. As a material of alumina, there are included
.gamma.-alumina, .beta.-alumina, .delta.-alumina, .eta.-alumina,
and .theta.-alumina, and among them, .gamma.-alumina is preferable.
In addition, it is preferable that lanthanum oxide, zirconia, ceria
or the like is added to .gamma.-alumina. In particular,
.gamma.-alumina added with lanthanum oxide is superior in heat
resistance, and in the case that the noble metal component such as
the platinum component or the palladium component is supported, it
is possible to maintain the high catalytic activity, even at high
temperature (JP-A-2004-290827).
[0074] In the present invention, it is preferable that alumina has
a pore size (mode diameter, the same shall apply hereafter) of 12
to 120 nm, more preferably 12 to 80 nm, and still more preferably
12 to 60 nm. The pore size of alumina smaller than 12 nm not only
delays diffusion of gas inside the pore, but also could clog the
pores by soot or the like. On the other hand, the pore size larger
than 120 nm decreases relatively BET specific surface area and
deteriorates dispersion of the noble metals or the promoter, and
thus it is not preferable.
[0075] In addition, BET specific surface area value (based on a BET
method, the same shall apply hereafter) of alumina is preferably 80
to 250 m.sup.2/g, and still more preferably 100 to 200 m.sup.2/g.
The BET specific surface area of alumina larger than 250 m.sup.2/g
decreases relatively the pore size, and thus could deteriorate gas
diffusion or clog the pores. On the other hand, BET specific
surface area smaller than 80 m.sup.2/g could deteriorate dispersion
of the noble metals or the promoter.
[0076] In the present invention, alumina having a pore size of 12
to 120 nm may be one kind, however, it is preferable to be a
mixture of two or more kinds having different pore size. Reason for
this is that it is considered that for gas species having the
smaller molecular weight, a base material having the smaller pore
size becomes preferable in view of contact probability between gas
and active species, while on the contrary for gas species having
the larger molecular weight, a base material having the larger pore
size becomes preferable in view of gas diffusion inside the pore.
For example, for long chain HC having large molecular weight,
alumina having relatively large pore size is preferable, because of
difficulty in entering inside the pore, unless the pore size is as
large as 20 to 120 nm, while for CO or NO having small molecule
weight, alumina having relatively small pore size is not
necessarily preferable, because of easy entering inside the pore
and thus making a reaction easy, even when the pore size is as
small as 12 to 20 nm.
(Backing Material)
[0077] In the present invention, as a substrate of DOC, a
flow-through-type honeycomb structure of an integral structure is
used, where through holes having both ends opened accumulate to
provide a honeycomb shape, as will be described later. Usually, as
this honeycomb structure, the one having specifications of
quadrangular prism cell is used, therefore by coating catalyst
slurry, the catalyst becomes easily accumulated at the four corners
by surface tension. Therefore, the catalyst layer becomes thick
only at the four corners of the quadrangular prism cell, and on the
contrary, the catalyst layer at the other parts becomes relatively
thin. The thick catalyst layer requires longer time when gas
diffuses from the surface to the bottom of the catalyst layer,
resulting in no effective use of the noble metals at the bottom
part, in a portion having thick catalyst layer. To avoid this, it
is preferable that the four corners are filled up by coating the
backing material to become the bottom layer, in advance.
[0078] As such a material, alumina, silica, zeolite or the like can
be used. These materials are not especially limited in view of
property thereof, however, such one is preferable as having a
certain level of BET specific surface area, and being
inexpensive.
[0079] It should be noted that the coated amount of the backing
material is preferably 20 to 130 g/L, and more preferably 30 to 100
g/L. The coated amount of the backing material below 20 g/L could
provide inferior effect of filling up the four corners of the
quadrangular prism cell. On the other hand, the amount over 130 g/L
increases pressure drop due to narrowing inside the cell, and thus
it is not preferable.
(Starting Salt of Noble Metal and Combustible Substance)
[0080] In order to support platinum of a noble metal onto the above
inorganic base material by making composite with palladium, as a
starting salt of platinum, an ethanolamine solution of
hexahydroxoplatinic(IV) acid, tetraammineplatinum(II) acetate,
tetraammineplatinum(II) carbonate, tetraammineplatinum(II) nitrate,
a nitric acid solution of hexahydroxoplatinic(IV) acid, platinum
nitrate, diamminedinitroplatinum nitrate, hexachloroplatinic(IV)
acid or the like can be used. In addition, as a starting salt of
palladium, tetraamminepalladium(II) acetate,
tetraamminepalladium(II) carbonate, tetraamminepalladium(II)
nitrate, diamminedinitropalladium, palladium nitrate, palladium
chloride or the like can be used. The preferable one as the
starting salt of platinum is the ethanolamine solution of
hexahydroxoplatinic(IV) acid, platinum nitrate, diammine
dinitroplatinum nitrate, tetraammineplatinum (II) nitrate, or the
like, and the one where components other the noble metal easily
volatilizes by heat treatment in catalyst preparation is
preferable.
[0081] It should be noted that the case of using a chloride as the
starting salt could give adverse influence on catalytic activity
due to remaining of chlorine, depending on a production method.
[0082] After mixing an aqueous solution of such a metal salt and
the inorganic base material, drying and calcining thereof can be
performed by a known method, as appropriate.
[0083] Platinum and palladium may be supported each separately in
supporting, however, in the present invention, in order to make
platinum and palladium close as much as possible, in expectation of
synergy effect, it is preferable to match property (acidity,
alkalinity) of aqueous solution of each starting salt of platinum
and palladium. For example, there is included a combination of
tetraammineplatinum(II) acetate-tetraamminepalladium(II) acetate
(both are alkaline); an ethanolamine solution of
hexahydroxoplatinic(IV) acid-tetraamminepalladium(II) acetate (the
same as above); platinum nitrate-palladium nitrate (both are
acidic); diamminedinitroplatinum nitrate-palladium nitrate (the
same as above); hexachloroplatinic(IV) acid-palladium chloride (the
same as above) or the like.
[0084] By making property of the aqueous solutions of each of the
starting salts of platinum and palladium the same, a uniform
solution state can be maintained as it is, without generation of a
precipitate even in mixing both aqueous solutions, therefore the
platinum particle and the palladium particle are present each in a
mixed state, and it becomes easy for each to come close, even after
making supported onto the inorganic base material.
[0085] In addition, in the present invention, it is preferable to
add a combustible substance, in producing slurry by adding a
catalyst component, in advance. It is because, in calcining after
coating the slurry onto a substrate having an integral structure,
the combustible substance is calcined to generate heat, and
generates high temperature, and thereby the catalyst components are
sintered onto the substrate, as well as the noble metal components
such as platinum are fixed onto the inorganic base material, and
therefore temperature requiring for calcining can be decreased
[0086] Further, in using a combustible substance, because the
combustible substance combusts (oxidizes) at the vicinity of
catalyst surface and consumes oxygen in air, catalyst surface is
possible to become a reduced state, therefore the noble metals such
as platinum becomes a reducing atmosphere at high temperature,
which gives expectation of particle growth, while the noble metals
such as platinum maintain a metal state.
[0087] As the combustible substance, an inexpensive material
containing carbon is preferable, and includes, for example, in
addition to refined sugar, monosaccharides such as fructose,
glucose, brain sugar; disaccharides such as sucrose, maltose,
lactose.
[0088] These combustible substances have characteristics of being
safe as materials, and superior also in solubility, and not only
sufficiently combust under condition in calcining, by coating the
catalyst component onto the honeycomb structure, such as at an
ignition temperature of 350.degree. C., but also provide complete
combustion easily and remain little residue such as soot, because
of having less carbon atoms of 6 to 12 for forming a molecule.
[0089] This DOC may be used only one inside the apparatus, however,
it may be made an apparatus of (DOC+DOC+CSF+SCR) by using two
sets.
2. [Substrate Having Integral-Type Structure]
[0090] In the present invention, as DOC, in order to support the
noble metal component in a good dispersion state, the substrate
having an integral-type structure, that is, the honeycomb structure
(hereafter it may also be referred to as a honeycomb substrate) is
used. The honeycomb structure is a structure with a honeycomb shape
where many through-holes are concentrated. As a material of such a
honeycomb structure, stainless steel, silica, alumina, silicon
carbide, cordierite or the like may be used, however, in the
present invention, the honeycomb structure made of any of these
materials may also be used.
[0091] As such a honeycomb structure, it is desirable to use a
flow-through-type honeycomb structure having through holes, opened
at both ends, integrated in a honeycomb shape, in applications not
only for DOC but also SCR to be described later. On the other hand,
in DPF and CSF to be described later, it is desirable to use a
wall-flow-type honeycomb structure having through holes integrated
in a honeycomb shape, which is open at one of the opening part of
the through hole and is closed at the other end. In such a
honeycomb structure-type catalyst, a catalyst composition dedicated
for each honeycomb structure-type catalyst may be coated on one
honeycomb structure.
[0092] Such a honeycomb substrate is selectable from known
honeycomb structure-type substrates, and whole shape thereof is
arbitrary and may be selected as appropriate from column-type,
square pole-type, hexagonal cylinder-type or the like, in response
to a structure of an exhaust system to be applied.
[0093] Further, as for pore number of the opening part, a suitable
pore number may be determined in consideration of kind of exhaust
gas to be treated, gas flow rate, pressure drop or removal
efficiency or the like, however, usually about 100 to 1500 pieces
per one square inch (6.45 cm.sup.2) is preferable, and 100 to 900
pieces is more preferable for application of exhaust gas
purification of a diesel automobile. The cell density per one
inch.sup.2 (6.45 cm.sup.2) of 100 pieces or more is capable of
securing contact area between exhaust gas and the catalyst, and
provides sufficient exhaust gas purification function, while the
cell density per one inch.sup.2 (6.45 cm.sup.2) of 1500 pieces or
less does not lead to significant pressure drop of exhaust gas, and
does not impair performance of an internal combustion engine.
[0094] In addition, thickness of the cell wall of the honeycomb
substrate is preferably 2 to 12 mil (milli inch) (0.05 to 0.3 mm),
and more preferably 3 to 8 mil (0.076 to 0.2 mm).
(Catalyst Preparation Method)
[0095] In order to prepare a catalyst such as DOC from the
honeycomb substrate to be used in the present invention, a washcoat
method is generally used.
[0096] Firstly the catalyst material and the honeycomb substrate
are provided. The catalyst material is prepared, together with
additives such as a binder or a surfactant, as needed, by mixing
with water or a solvent, where a water-soluble organic solvent is
added to water, to make a slurry-like mixture, and by coating it
onto the honeycomb substrate, and then by drying and calcining.
That is, the catalyst material is mixed with water or a solvent,
where a water-soluble organic solvent is added to water, (hereafter
it may also be referred to as an aqueous medium), in specified
ratio, to obtain the slurry-like mixture. In the present invention,
the aqueous medium may be enough to be used in amount which is
capable of dispersing each catalyst component uniformly in the
slurry.
[0097] The catalyst material includes the noble metal component
including at least platinum, as the inorganic base material. The
noble metal component may be supported, in advance, onto the
inorganic base material. The metal catalyst component and the
inorganic base material are mixed in the aqueous medium, in
advance, to prepare the slurry.
[0098] In preparing the catalyst material, in the case where the
noble metal is supported on the inorganic base material, in
advance, a known method may be adopted, as appropriate.
[0099] One example thereof is shown below, firstly, as a raw
material of the noble metal component, a compound such as a
nitrate, a carbonate, an acetate, a chloride, specifically, an
ethanolamine solution of hexahydroxoplatinic(IV) acid,
tetraammineplatinum(II) acetate, tetraammineplatinum(II) carbonate,
tetraammineplatinum(II) nitrate, a nitric acid solution of
hexahydroxoplatinic(IV) acid, platinum nitrate,
diamminedinitroplatinum nitrate, hexachloroplatinic(IV) acid or the
like, and as a starting salt of palladium, tetraamminepalladium(II)
acetate, tetraamminepalladium(II) carbonate,
tetraamminepalladium(II) nitrate, diamminedinitropalladium,
palladium nitrate, palladium chloride or the like is prepared. By
selecting any one from them and dissolving it in an organic
solvent, a solution of the noble metal component is provided.
[0100] Then, the solution of this noble metal component is mixed
with the inorganic base material, together with the aqueous medium,
then it is dried at 50 to 200.degree. C. to remove the solvent, and
then it is calcined at 300 to 1,200.degree. C. It should be noted
that other than the above components, known catalyst materials may
be blended, as a binder and the like. As such a known catalyst
materials, there are included alumina, silica, titania, zirconia,
silica-alumina, ceria, an alkali metal material, an alkaline earth
metal material, a transition metal material, a rare earth metal
material, silver, a silver salt and the like, and a dispersing
agent, and a pH adjuster can be used in combination, as needed.
[0101] In order to cover the catalyst composition onto the
honeycomb substrate, the catalyst composition is coated as the
slurry-like mixture. The catalyst composition may be coated as one
layer, or so as to become two or more layers. After coating the
catalyst composition, drying and calcining are performed. It should
be noted that drying temperature is preferably 100 to 300.degree.
C., and more preferably 100 to 200.degree. C. In addition,
calcining temperature is preferably 300 to 600.degree. C., and
particularly preferably 400 to 600.degree. C. Drying time is
preferably 0.5 to 2 hours and calcining time is preferably 1 to 3
hours. Heating may be performed using a known heating means such as
an electric furnace, or a gas furnace.
(Function of DOC)
[0102] Major component of NO.sub.x included in exhaust gas from an
engine is NO. In a conventional exhaust gas purification catalyst
apparatus, it has been said desirable that NO and NO.sub.2 are set
in suitable ratio to promote NO.sub.x purification in the SCR
catalyst. This NO:NO.sub.2 ratio is set at about 1:1, in the SCR
catalyst having zeolite such as Fe-.beta. or MFI, as a major
component.
[0103] Also in the exhaust gas purification apparatus of the
present invention, DOC is arranged at the forward of the SCR
catalyst to oxidize NO to NO.sub.2, and increase NO.sub.2
concentration in NO.sub.x. As for such NO oxidation performance,
the noble metal component has higher performance as compared with a
transition metal, and the Pt component is superior to the Pd
component (JP-A-2009-167844: paragraph [0021], JP-A-2008-526509:
paragraph [0005], JP-A-2008-155204: paragraph [0006], NON PATENT
LITERATURE 4 (JOURNAL OF CHEMICAL ENGINEERING OF JAPAN, Vol. 40
(2007) No. 9 pp. 741-748, or the like)).
[0104] In addition, at the latter part of DOC, a means for removing
by combustion of the particulates such as soot trapped at the
wall-flow-type honeycomb structure is arranged. In addition, in
order to combust unburned fuel light oil by periodically spraying
unburned fuel light oil to the inside of a cylinder of a diesel
engine or to the inside of a piping of the middle part of the
diesel engine and DOC, exhaust gas temperature is raised, and
particulates such as soot are combusted using combustion heat
thereof. As a means for removing by combustion of the particulates,
a wall-flow-type honeycomb structure alone (DPF) or a catalyzed
wall-flow-type honeycomb structure (CSF) is used. Use of the
catalyzed wall-flow-type honeycomb structure (CSF) is general,
because saving of fuel required for combustion, and decrease in
initiation temperature for combusting the particulates such as soot
are possible.
3. [CSF: Catalyzed Soot Filter]
[0105] In the present invention, the catalyzed soot filter (CSF) is
a catalyzed soot filter including the noble metal component for
capturing, and removing by combustion (oxidation) of the
particulate matter (PM) in exhaust gas discharged from a diesel
engine. It is preferable that the catalyzed soot filter (CSF) has a
catalyst layer where platinum (Pt) and palladium (Pd) are supported
onto one kind of alumina having a pore size of 12 to 60 nm, or a
mixture of two or more kinds of alumina having different pore size
within this range, and ratio of platinum and palladium is 1:1 to
11.4 in weight equivalent.
[0106] In the catalyst apparatus I of the present invention, it may
be good that CSF is a bag filter having high heat resistance,
however, it is desirable to catalyze and use the wall-flow-type
honeycomb structure obtained by making a sintered compact of an
inorganic oxide such as silica, alumina, silicon carbide,
cordierite porous.
[0107] CSF contains at least the platinum component and the
palladium component as the noble metal component. Containment of
the Pt component is capable of enhancing NO.sub.x reduction
purification performance in the SCR catalyst at the latter part of
CSF, by exerting NO oxidation performance also at even CSF, and by
increasing NO.sub.2 concentration in exhaust gas.
[0108] In addition, addition of the Pd component to the Pt
component is expected to suppress volatilization of the Pt
component. The catalyzed soot filter (CSF) has a ratio of platinum
and palladium of preferably 1:1 to 11:4, and more preferably 3:2 to
11:4, in weight equivalent. Outside of this range is not preferable
similarly as in the case of the above-described DOC. It is because,
the ratio below 1:1 largely decreases oxidation activity of HC, CO,
NO or the like accompanied with decrease in content rate of
platinum, while the ratio over 11:4 increases decrease in
denitration performance of SCR caused by the noble metal such as
platinum volatilized, even under coexistence with palladium. And,
the catalyzed soot filter (CSF) has a supported amount of platinum
of preferably 0.05 to 2.0 g/L, and more preferably 0.1 to 1.5 g/L,
in metal equivalent.
[0109] Further, in the present invention, a coated amount of an
oxidizing component, which composes a catalyst layer of the
catalyzed soot filter (CSF), is preferably 4 to 100 g/L, and more
preferably 5 to 50 g/L. The coated amount of the oxidizing
component below 4 g/L deteriorates dispersibility of the noble
metal such as platinum to be supported, thus causing decrease in
oxidation activity, while the amount over 100 g/L narrows pores
opened countlessly at the filter cell wall, causing increase in
pressure drop, and thus is not preferable.
[0110] Such CSF, in the present invention, may be said "a structure
covered with the oxidation catalyst composition" similarly as DOC.
Therefore, as for the inorganic base material, all of the porous
inorganic oxides described in detail in the item of DOC can be
used. In addition, as for the starting salt of the noble metals
such as platinum, all of the raw materials described in detail in
the item of DOC can be used.
[0111] Similarly as the above-described DOC, the honeycomb
structure is used also for CSF. In particular, it is desirable to
use a wall-flow-type substrate having through holes, integrated in
a honeycomb shape, which are open at one of the opening part of the
through hole and are closed at the other end. In the wall-flow-type
substrate, wall of the through hole is composed of a porous
material, and the particulate matter enters into the through hole
together with exhaust gas from the through hole opening part, and
exhaust gas passes through the porous hole of the through hole wall
and is discharged backward, and the particulate component deposits
in the through hole closed. By combustion removal of the
particulate component deposited in this way, as described above,
CSF is regenerated and becomes possible again to capture the
particulate component from exhaust gas.
[0112] However, different from the flow-through-type honeycomb
structure to be used in DOC, because the wall-flow-type honeycomb
structure having function as a filter is used, the catalyst
component to be used as CSF is required to have also different
function from DOC, while having the same function as DOC.
[0113] In fact, coating of the same amount of the catalyst
component on the wall-flow-type honeycomb structure, as on the
flow-through-type honeycomb structure, increases pressure drop
abnormally, thus significantly decreasing output of an engine,
although the through hole wall is made of a porous material.
Therefore, in the case of coating the catalyst component on the
wall-flow-type honeycomb structure, amount of the catalyst
component is preferably set to half or less, as compared with on
the flow-through-type honeycomb structure.
(Function of CSF)
[0114] Major role of CSF is to remove by oxidation of particulate
components such as soot trapped at the wall-flow-type honeycomb
structure, and function of the catalyst component where the noble
metals are supported, is to decrease initiation temperature for
removing by oxidation of the particulate components such as soot.
Furthermore, because CSF has oxidation catalyst function, and thus
it enables to combust floating particulate matter such as soot and
SOF attached in CSF from relatively low temperature, therefore it
enables to decrease consumption of fuel for combustion such as
soot. In addition, in the case of high level discharge amount of
NO, NO is not oxidized sufficiently to NO.sub.2 by only DOC,
however, CSF is also capable of further oxidizing NO, which is not
oxidized sufficiently by DOC, to NO.sub.2.
4. [SCR Catalyst: Selective Reduction Catalyst]
[0115] In the catalyst apparatus I of the present invention, SCR
catalyst (selective reduction catalyst) is arranged at the latter
part of DOC and CSF. By this structure, high purification
performances are exerted not only for HC, CO and NO.sub.x, but also
soot and SOF.
[0116] The SCR catalyst to be used in the exhaust gas purification
apparatus of the present invention is the one for purifying by
reduction NO.sub.x in exhaust gas using the ammonia component as
the reducing agent. The SCR catalyst material includes, other than
zeolite or a zeolite-like compound (crystal metal aluminophosphate)
to be described later, various inorganic materials of a transition
metal oxide such as vanadium oxide, titania, zirconia, or tungsten
oxide; a rare earth oxide such as ceria, lanthanum oxide,
praseodymium oxide, samarium oxide, gadolinium oxide, or neodymium
oxide; a base metal oxide such as gallium oxide or tin oxide; or a
composite oxide thereof, and the like. In addition, alumina or
silica, and a mixture or a composite of alumina or silica modified
with a rare earth, an alkali metal, an alkaline earth group and the
like, with the above oxide, and the like are also included.
However, it is desirable in an automotive application not to
include a harmful heavy metal such as vanadium.
[0117] In the present invention, it is preferable that the SCR
catalyst includes zeolite or crystal metal aluminophosphate. In
addition, in the present invention, it is preferable that the noble
metal component such as Pt or Pd is not included, because of
generating NO.sub.x by oxidation of the ammonia component.
[0118] Zeolite is a generic name of an aluminosilicate having
micropores in a crystal, and is capable of selectively taking in a
molecule inside the pore thereof, and promoting a reaction. Such a
zeolite or the above inorganic material has superior NO.sub.x
reduction purification performance as an SCR material, however, it
significantly decreases NO.sub.x reduction purification performance
when contaminated with a noble metal. On the other hand, according
to the present invention, because Pt, which is the noble metal
component in DOC, is supported on a honeycomb structure in a state
difficult to be scattered even when exposed at high temperature,
contamination of zeolite or the above inorganic material can be
prevented, and superior NO.sub.x reduction purification performance
as the SCR catalyst can be exerted stably for a long period of
time.
[0119] The SCR catalyst is preferably an integral structure-type
substrate, such as a flow-through-type honeycomb structure or a
wall-flow-type honeycomb structure.
(Zeolite and Zeolite-Like Compound)
[0120] In the present invention, zeolite is not especially limited,
however, it may be selected as appropriate from a Y-type,
.beta.-type, MFI-type, CHA-type, USY-type, SUZ-type, MCM-type,
PSH-type, SSZ-type, ERB-type, ITQ-type, mordenite, and ferrierite.
In addition, it is included a crystal metal aluminophosphate,
having a similar layer-like structure as zeolite (JP-A-60-86011).
As such a crystal metal aluminophosphate, there has been known a
crystalline aluminophosphate (ALPO) or a crystalline
silicoaluminophosphate (SAPO), and they have been investigated as
the SCR catalyst materials (US 2008/0241060). Such zeolite and the
zeolite-like compound may be used alone or two or more kinds of the
materials by mixing, or multiple materials may be coated in
multilayer on the surface of the structure-type substrate. In
addition, zeolite and the zeolite-like compound may be the ion
exchanged one at the cation site thereof with a transition metal
component such as iron, copper, or a rare earth such as cerium or
lanthanum.
[0121] Among such zeolite and the zeolite-like compound, use of
.beta.-type zeolite is preferable in the present invention, as the
SCR catalyst material. .beta.-Type zeolite has a relatively complex
3D pore structure consisting of linear pore having relatively large
diameter and aligned in one direction, and a curved pore crossing
with them, and provides easy diffusion of a cation in ion exchange
and easy diffusion of a gas molecule such as NH.sub.3, as well as
has property superior in reactivity and durability.
[0122] In addition, zeolite has an acid site which is capable of
adsorbing a basic compound such as NH.sub.3, and number of the acid
site differs depending on Si/Al ratio thereof. Generally, zeolite
having low Si/Al ratio has more number of the acid site, and has
larger degree of degradation in durability under co-presence of
steam, while on the contrary, zeolite having high Si/Al ratio is
superior in heat resistance but has less acid site. In the NH.sub.3
selective reduction catalyst, because NH.sub.3 adsorbs at the acid
site of zeolite, which becomes an active site to reduce and remove
nitrogen oxides such as NO.sub.2, the one having more acid sites
(the one having lower Si/Al ratio) is advantageous for the
denitration reaction. In this way, as for the Si/Al ratio,
durability and activity are in a trade off relation, and in
consideration of this, the Si/Al ratio of zeolite is preferably 5
to 500, more preferably 10 to 100, and still more preferably 15 to
50. Both the .beta.-type zeolite and the MFI-type zeolite suitable
for the SCR catalyst similarly have such characteristics.
(.beta.-Type Zeolite)
[0123] It is preferable that, as the SCR catalyst material in the
present invention, .beta.-type zeolite, which is ion exchanged with
an iron element at a cation site of zeolite, is used. In addition,
this zeolite, which is ion exchanged with an iron element, may
include an iron oxide as the iron component. In this way, because
zeolite including the iron element has high adsorption-desorption
rate of NH.sub.3, and also high activity as SCR, it is preferable
to be included as a main component. Here the main component means
that it is 50% by weight or more in total zeolite amount to be used
in the catalyst composition to be covered on a substrate of the SCR
catalyst.
[0124] .beta.-Type zeolite has a 3D pore structure as described
above, and provides easy diffusion of cation in ion exchange and
diffusion of a gas molecule such as NH.sub.3. In addition, because
such a structure is a unique structure and a complicated pore
structure, as compared with mordenite, faujasite or the like having
only linear pore aligned in one direction, .beta.-type zeolite is
an effective material for an automotive catalyst, due to little
arising structural collapse caused by heat, and having high
stability.
(.beta.-Type Zeolite Added with Iron Element)
[0125] Generally, in zeolite, as a solid acid site, a cation is
present as a counter ion. As the cation, an ammonium ion or a
proton is general, however, the .beta.-type zeolite added with an
iron element as the cation species is preferable (hereafter, it may
be referred to as "Fe-.beta." in some cases).
[0126] It is preferable that ratio for .beta.-type zeolite to be
ion exchanged with the iron element is expressed by the following
expression (9), based on the fact that one iron element (ion) and
two [AlO.sub.4/2] units, which is a monovalent ion exchange site in
zeolite, form an ion pair.
[Mole number of the iron element included by ion exchange in unit
weight of zeolite/{(mole number of Al.sub.2O.sub.3 present in unit
weight of zeolite).times.(1/2)}].times.100 (9)
[0127] Ion exchange ratio is preferably 10 to 100%, more preferably
12 to 92%, and still more preferably 30 to 70%. The ion exchange
ratio of 92% or lower further stabilizes a skeleton structure of
zeolite, enhances heat resistance of a catalyst and hence lifetime
of the catalyst, and is capable of providing more stabilized
catalytic activity. However, the too low ion exchange ratio below
10% may not provide sufficient denitration performance in some
cases. It should be noted that in the case where the
above-described ion exchange ratio is 100%, it means that all of
the cation species in zeolite is ion exchanged with the iron
element. In this way, ion exchanged zeolite exerts superior
purification capability.
(Various Kinds of Inorganic Materials)
[0128] In the present invention, the inorganic material may be
selected as appropriate from a transition metal oxide such as
titania, zirconia, or tungsten oxide; a rare earth oxide such as
ceria, lanthanum oxide, praseodymium oxide, samarium oxide,
gadolinium oxide, or neodymium oxide; a base metal oxide such as
gallium oxide or tin oxide; or a composite oxide thereof, or the
like. In addition to the above, because alumina or silica, and
alumina or silica modified with a rare earth, an alkali metal, an
alkaline earth group or the like, are superior in heat resistance
and has larger specific surface area as compared with the above
oxide, by mixing or making composite with the above oxide, specific
surface area of the above oxide itself can be increased, and thus
is more preferable.
[0129] Among them, ceria has been known as an NO.sub.x adsorption
function material, and also in the present invention, by promoting
adsorption of NO.sub.x, it has function enabling to promote the SCR
reaction between NH.sub.3 and NO.sub.x. In addition, zirconia can
be expected to have effect as a dispersion maintaining material for
highly dispersing other components in a thermally stable state.
Additionally, a tungsten oxide has strong acidity and has strong
adsorption force of urea or ammonia, which is an alkaline
component, therefore, use of the tungsten oxide can be expected to
have effect of enhancing denitration performance, therefore it is
preferable to use these oxides alone or by mixing or composite
making.
[0130] These oxides and composite oxides thereof are not especially
limited, as for a composition, a structure and a preparation
thereof. For example, there may be adopted a method for calcining a
solid material obtained by dissolving a starting raw material
having a form of a nitrate, a sulfate, a carbonate, an acetate, a
chloride or the like, including the above element, into an aqueous
solution, then mixing and precipitating as a precipitate, by pH
adjustment or the like, or by evaporation to dryness; a method for
performing the above treatment by solubilizing these multiple metal
salts all at once, in mixing and making composite; or a method for
performing the above treatment for single or multiple metal salts
to form an oxide, and then supporting residual metal salts all at
once or sequentially.
5. [Reducing Agent Spraying Means]
[0131] In the exhaust gas purification catalyst apparatus of the
present invention, the reducing agent spraying means (Injector) is
the one for supplying the reducing agent selected from the urea
component or the ammonia component, and usually composed of a
storage tank of the reducing agent, a piping and a spraying nozzle
attached at the tip thereof.
[0132] Position of the reducing agent spraying means is set at a
position backward of catalyzed soot filter (CSF), and forward of
the selective reduction catalyst (SCR) for contacting nitrogen
oxides (NO.sub.X) with the reducing agent to reduce. Further, in
the case where the second oxidation catalyst (DOC) is set between
CSF and SCR, it is preferable that it is set at the backward of the
second oxidation catalyst (DOC).
[0133] Kind of the reducing component is selected from the urea
component or the ammonia component. As the urea component, an
aqueous solution of urea, having a specified concentration of 31.8
to 33.3% by weight, for example, a trade name of "Adblue", and as
the ammonia component, ammonia gas may be used other than ammonia
water. However, because NH.sub.3, which is the reducing agent,
itself has harmfulness such as irritating odor, it is a preferable
system that NH.sub.3 is generated by thermal decomposition or
hydrolysis by adding an aqueous solution of urea from the upstream
of the denitration catalyst, and which is acted as the reducing
agent, as compared with use of the NH.sub.3 component as it is, as
the reducing agent.
6. [AMOX: Ammonia Oxidation Catalyst]
[0134] In the exhaust gas purification apparatus of the present
invention, the ammonia oxidation catalyst (AMOX) can be arranged,
further after SCR, as needed. In a practical way, in the case where
NO.sub.X or NH.sub.3 cannot be purified completely down to
regulated value or lower by SCR, AMOX is used additionally.
[0135] Accordingly, AMOX includes also a catalyst component having
NO.sub.x purification function, other than a catalyst having
NH.sub.3 oxidation function. As a catalyst having NH.sub.3
oxidation function, it is preferable to support one or more
elements selected from platinum, palladium, or rhodium and the
like, as noble metal component, on one or more kinds of inorganic
materials consisting of alumina, silica, titania, zirconia and the
like. In addition, it is also preferable to use an inorganic
material having heat resistance enhanced by adding a promoter such
as a rare earth, an alkali metal, or an alkaline earth group.
Platinum and palladium as the noble metals exert superior oxidation
activity. By supporting this on the inorganic material having large
specific surface area and also high heat resistance, sintering of
the noble metal component becomes difficult, and by maintaining
specific surface area of the noble metal high, active site
increases and high activity can be exerted.
[0136] On the other hand, as the catalyst having NO.sub.x
purification function, all of the zeolite and oxides described at
the SCR section can be used.
[0137] These two kinds of catalysts are mixed uniformly and may be
coated onto an integrated-type honeycomb structure, however, the
catalyst having NH.sub.3 oxidation function may also be coated onto
the lower layer, and the catalyst having NO.sub.x purification
function may also be coated onto the upper layer.
II. [Exhaust Gas Purification Apparatus (DOC+CSF+DOC+SCR)]
[0138] In the present invention, another DOC is arranged at the
latter part of CSF, relative to the above exhaust gas purification
apparatus (DOC+CSF+SCR), and carbon monoxide (CO), hydrocarbons
(HC) and nitric oxide (NO) in exhaust gas discharged from a diesel
engine, are oxidized at the first DOC, and particulate matter (PM)
in exhaust gas is captured at the next CSF, and removed by
combustion (oxidation), and further oxidation function of unburned
CO, HC and NO is enhanced at the next DOC, and after supplying the
reducing agent selected from a urea component or an ammonia
component into this apparatus, nitrogen oxides (NO.sub.x) are
removed by reduction by contacting with the reducing agent at SCF.
Hereafter, this exhaust gas purification catalyst apparatus
(DOC+CSF+DOC+SCR) is also referred to as a catalyst apparatus
II.
[0139] That is, the catalyst apparatus II of the present invention
is, as shown in FIG. 2, an exhaust gas purification catalyst
apparatus, where the oxidation catalysts (DOC) 4 is sandwiched at
the both sides of the catalyzed soot filter (CSF) 5, as well as the
reducing agent spraying means 3 is installed at the backward
thereof, and the selective reduction catalyst (SCR) 6 is arranged
at the backward of this injection means 3, in an exhaust gas
passage 2 from a diesel engine 1.
[0140] In this way, in the catalyst apparatus II, by setting DOC in
front of or at the backward of CSF, and placing a part of the noble
metals of the front stage DOC to the latter part DOC, oxidation
performance of NO can be enhanced, while decreasing total use
amount of the noble metals, although volume as a catalyst system
increases, and an NO.sub.x reduction reaction, using the urea
aqueous solution or the ammonia aqueous solution (NH.sub.3
component) in SCR arranged backward thereof is promoted.
EXAMPLES
[0141] Characteristics of the present invention will be made more
clearly below, by showing Examples and Comparative Examples,
however, the present invention should not be limited to the aspects
of these Examples.
[0142] It should be noted that pore size of alumina to be used in
the oxidation catalyst (DOC) and the catalyzed soot filter (CSF),
to be used in the present Example as well as Comparative Example,
was measured by a method shown below.
<Pore Distribution Measurement>
[0143] Pore distribution of alumina was measured by a mercury
intrusion method, using PASCAL140-440, manufactured by Thermo Co.,
Ltd., after drying 0.3 g of various kinds of alumina powder (mode
diameter was adopted as pore size).
[0144] In addition, evaluation tests by durability specifications
and an engine, where the oxidation catalyst (DOC) and the catalyzed
soot filter (CSF) were used alone or in combination, were performed
by methods shown below.
<Durability Test of Catalyst>
[0145] The oxidation catalyst (DOC) and the catalyzed soot filter
(CSF) obtained by the following Examples and Comparative Examples
were heat treated under air atmosphere inside an electric furnace,
under condition of 750.degree. C. for 50 hours, and 750.degree. C.
for 100 hours, as for the catalyst for a model gas evaluation test
and as for the catalyst for engine evaluation test,
respectively.
<Model Gas Evaluation Test of Catalyst>
[0146] The oxidation catalyst (DOC) obtained by the following
Examples 1 and 2, and Comparative Example 1 was cut out to a size
(a diameter of 24 mm.times.a length of 66 mm, 30 mL) of catalyst
for model gas evaluation, using a core drill and a diamond cutter,
and after heat treatment thereof at 750.degree. C. for 50 hours
using an electric furnace, it was subjected to a temperature rising
and temperature lowering light off test, using a model gas
evaluation apparatus.
1. Temperature Rising Light Off Test
[0147] After mounting the catalyst for the model gas evaluation
onto a holder of the model gas evaluation apparatus, while flowing
gas components shown in Table 1 in GHSV (Gas Hourly Space Velocity:
space velocity at gas; inflow velocity of reaction gas per unit
volume of the catalyst) of 40,000/hr, temperature thereof was
raised from room temperature up to 400.degree. C. in a rate of
30.degree. C./minute. In this case, temperature at the catalyst bed
of catalyst was measured, when oxidation rate of NO, CO or HC
reached to each numerical value. It should be noted that NOT30
represents catalyst bed temperature of catalyst, when 30% of NO was
oxidized, COT75 represents catalyst bed temperature of catalyst,
when 75% of CO was oxidized, and HCT75 represents catalyst bed
temperature of catalyst, when 75% of HC was oxidized.
TABLE-US-00001 TABLE 1 Flow rate 20 L/min GHSV 40,000/hr Components
C.sub.3H.sub.6 300 ppmC CO 300 ppm NO 300 ppm O.sub.2 6.0% CO.sub.2
6.0% H.sub.2O 6.0% N.sub.2 Remainder
<Engine Evaluation Test of a Catalyst>
[0148] After performing heat treatment at 750.degree. C. for 100
hours, using an electric furnace, the oxidation catalyst (DOC) and
the catalyzed soot filter (CSF) of the following Examples 3 to 7,
and Comparative Examples 1 to 4 were stored into a converter, each
alone or in combination thereof, and then the converter was mounted
at the discharge port of a 5 L diesel engine to perform two kinds
of evaluation tests, that is, a steady state test and a temperature
rising and temperature lowering light off test, by the following
procedure.
1. Steady State Test
1-1. Oxidation Performance of NO
[0149] Number of revolutions of the diesel engine was set at 1,800
rpm, and catalyst bed temperature was fixed at 250.degree. C. and
300.degree. C., and then a part of exhaust gas was suctioned from
the catalyst entrance and catalyst exit by a suction tube to
measure NO concentration using an NO meter to calculate NO
oxidation ratio from difference thereof, by the following
expression:
NO oxidation ratio (%)=100.times.{(NO concentration at the
entrance)-(NO concentration at the exit)}/(NO concentration at the
entrance)
1-2. Combustibility of Light Oil
[0150] Number of revolutions of the diesel engine was set at 1,800
rpm, and catalyst bed temperature was fixed at 250.degree. C. and
300.degree. C., and then light oil was ON/OFF sprayed in 20 ml/min
(250.degree. C.) or 30 ml/min (300.degree. C.) in an interval of 5
minutes, from a spray tube installed in front of the catalyst
entrance, to measure temperature of exhaust gas using a
thermocouple installed at the backward of the catalyst exit, and
the result was adopted as temperature increment (the following
.DELTA.T (.degree. C.)) of exhaust gas in light oil spray ON/OFF.
The higher .DELTA.T exhibits the more heat generation by combustion
of light oil, thus showing superior combustibility.
.DELTA.T(.degree. C.)=(exhaust gas temperature at the catalyst exit
when light oil spray is ON)-(exhaust gas temperature at the
catalyst exit when light oil spray is OFF)
2. Temperature Rising and Temperature Lowering Light Off Test
[0151] Number of revolutions of the diesel engine was set at 1,800
rpm, and catalyst bed temperature was fixed at 150.degree. C., and
then temperature was raised up to 400.degree. C. in a rate of
10.degree. C./min, and then temperature was lowered down to
150.degree. C. in a rate of 10.degree. C./min. In this temperature
rising, catalyst bed temperature at the first stage oxidation
catalyst (DOC) was measured, when oxidation rate of NO, CO or HC
reached to each numerical value.
[0152] It should be noted that NOT30 represents catalyst bed
temperature at the first stage oxidation catalyst (DOC), when 30%
of NO was oxidized, COT75 represents catalyst bed temperature at
the first stage oxidation catalyst (DOC), when 75% of CO was
oxidized, and HCT75 represents catalyst bed temperature at the
first stage oxidation catalyst (DOC), when 75% of HC was
oxidized.
Example 1
Production of Oxidation Catalyst (DOC) (1)
=Lower Layer=
[0153] 1 kg of .gamma.-alumina powder A having a BET specific
surface area of 150 m.sup.2/g and a pore size of 9 nm, and water
were put into a ball mill and milled till predetermined particle
size is attained to obtain slurry .alpha..
[0154] Subsequently, an integral structure-type substrate, that is,
a honeycomb flow-through-type cordierite substrate {300
cell/inch.sup.2 (465 k/m.sup.2)/8 mil (0.2 mm), a diameter of 7.5
inch (190.5 mm).times.a length of 3.3 inch (83.8 mm), 2.39 L}, was
immersed into this slurry, and coated by a wash-coat method, so as
to attain an alumina supported amount of 65 g/L per unit volume.
After that it was dried at 150.degree. C. for 1 hour and calcined
at 500.degree. C. for 2 hours under atmospheric environment to
obtain a product already coated with the lower layer of DOC
(1).
=Upper Layer=
[0155] An aqueous solution of platinum nitrate and an aqueous
solution of palladium nitrate were mixed, as raw materials of the
noble metal component, to obtain a Pt--Pd mixed solution. Here,
ratio of platinum and palladium was set at 5:1, in weight
ratio.
[0156] Next, onto 1 kg of .gamma.-alumina powder B having a BET
specific surface area of 150 m.sup.2/g and a pore size of 23 nm,
the Pt--Pd mixed solution was impregnated, so as to attain 1.292%
by weight (Pt/Pd=5/1) in noble metal equivalent, to obtain Pt--Pd
supported alumina powder a. 1114.4 g of this Pt--Pd supported
alumina powder a, 8 g of barium hydroxide, in barium oxide
equivalent, 45 g of refined sugar and water were put into a ball
mill and milled till predetermined particle size is attained to
obtain slurry .beta..
[0157] Subsequently, the product already coated with the lower
layer was immersed into this slurry, and coated by a wash-coat
method, so as to attain a catalyst supported amount of 112.24 g/L
per unit volume. After that it was dried at 150.degree. C. for 1
hour and calcined at 500.degree. C. for 2 hours under atmospheric
environment to obtain DOC (1) (Pt=1.2 g/L, Pd=0.24 g/L, BaO=0.8
g/L, amount of catalyst=112.24 g/L, amount of lower layer alumina:
65 g/L).
<Production of Catalyzed Soot Filter CSF (1)>
[0158] An aqueous solution of platinum nitrate and an aqueous
solution of palladium nitrate were mixed, as raw materials of the
noble metal component, to obtain a Pt--Pd mixed solution. Here,
ratio of platinum and palladium was set at 2:1, in weight
ratio.
[0159] Next, onto 600 g of .gamma.-alumina powder B, 400 g of
.gamma.-alumina powder C having a BET specific surface area of 165
m.sup.2/g and a pore size of 14 nm, the Pt--Pd mixed solution was
impregnated and supported, so as to attain 2.43% by weight in noble
metal equivalent, to obtain Pt--Pd supported alumina powder b.
[0160] Then, 543.2 g of Pt--Pd supported alumina powder b, 30 g of
silica gel in silica equivalent and water were put into a ball mill
and milled till predetermined particle size is attained to obtain
slurry .gamma.. Subsequently, an integral structure-type substrate,
that is, a honeycomb wall-flow-type cordierite substrate {300
cell/inch.sup.2 (465 k/m.sup.2)/12 mil (0.3 mm), a diameter of 7.5
inch (190.5 mm).times.a length of 6.7 inch (170.2 mm), 4.85 L}, was
immersed into this slurry, and coated by a wash-coat method, so as
to attain a catalyst supported amount of 28.66 g/L per unit volume.
After that it was dried at 150.degree. C. for 1 hour and calcined
at 500.degree. C. for 2 hours under atmospheric environment to
obtain CSF (1) (Pt=0.44 g/L, Pd=0.22 g/L, amount of catalyst=28.66
g/L).
<Apparatus Configuration>
[0161] A catalyst for model gas evaluation was cut out from the
above oxidation catalyst DOC (1), to a size of (a diameter of 24
mm.times.a length of 66 mm, 30 mL), using a core drill and a
diamond cutter, and after heat treatment thereof at 750.degree. C.
for 50 hours, the model gas evaluation test was performed using the
above oxidation catalyst DOC (1). Results of oxidation activities
of NO, CO and HC are shown in FIG. 3. It should be noted that
components of the oxidation catalyst DOC (1) and amount of the
noble metals are shown in Tables 2 and 3.
[0162] After that, by arranging the oxidation catalyst DOC (1) {a
diameter of 7.5 inch (190.5 mm).times.a length of 3.3 inch (83.8
mm), 2.39 L}, after heat treatment at 750.degree. C. for 100 hours,
at the front stage inside a catalyst converter, placing the CSF
(1), after heat treatment under the same condition, at the rear
stage thereof, arranging a selective reduction catalyst (SCR, refer
to JP-A-2009-26098) which was heat treated at 650.degree. C. for
100 hours, in air stream containing 10% steam, at a different
catalyst converter at the rear side thereof, and connecting these
in series, an apparatus of the present invention shown in FIG. 1
was configured. Good performance of exhaust gas purification was
confirmed by using this apparatus.
Example 2
Production of Oxidation Catalyst (DOC) (2)
=Lower Layer=
[0163] A product already coated with the lower layer of DOC (2) was
obtained similarly by a preparation method of the lower layer of
Example 1.
=Upper Layer=
[0164] Onto 1 kg of .gamma.-alumina powder B, the Pt--Pd mixed
solution was impregnated, so as to attain 0.777% by weight
(Pt/Pd=5/1) in noble metal equivalent, to obtain Pt--Pd supported
alumina powder c. In addition, onto 200 g of .gamma.-alumina powder
C, the Pt--Pd mixed solution was impregnated, so as to attain 3.85%
by weight (Pt/Pd=5/1) in noble metal equivalent, to obtain Pt--Pd
supported alumina powder d.
[0165] And, 927.2 g of the Pt--Pd supported alumina powder c, 187.2
g of the Pt--Pd supported alumina powder d, 8 g of barium
hydroxide, in barium oxide equivalent, 45 g of refined sugar and
water were put into a ball mill and milled till predetermined
particle size is attained to obtain slurry .delta..
[0166] Subsequently, the product already coated with the lower
layer was immersed into this slurry, and coated by a wash-coat
method, so as to attain a catalyst supported amount of 112.24 g/L
per unit volume. After that it was dried at 150.degree. C. for 1
hour and calcined at 500.degree. C. for 2 hours under atmospheric
environment to obtain DOC (2) (Pt=1.2 g/L, Pd=0.24 g/L, BaO=0.8
g/L, amount of catalyst=112.24 g/L, amount of lower layer alumina:
65 g/L).
<Apparatus Configuration>
[0167] A catalyst for model gas evaluation was cut out from the
above oxidation catalyst DOC (2), to a size of (a diameter of 24
mm.times.a length of 66 mm, 30 mL), using a core drill and a
diamond cutter, and after heat treatment thereof at 750.degree. C.
for 50 hours, the model gas evaluation test was performed using the
above oxidation catalyst DOC (2). Results of oxidation activities
of NO, CO and HC are shown in FIG. 3. It should be noted that
components of the oxidation catalyst DOC (2) and amount of the
noble metals are shown in Tables 2 and 3.
[0168] After that, by arranging the oxidation catalyst DOC (2) {a
diameter of 7.5 inch (190.5 mm).times.a length of 3.3 inch (83.8
mm), 2.39 L}, after heat treatment at 750.degree. C. for 100 hours,
at the front stage inside a catalyst converter, and connecting the
heat treated products of CSF and SCR in series using the catalyst
converter, an apparatus of the present invention shown in FIG. 1
was configured. Good performance of exhaust gas purification was
confirmed by using this apparatus.
Comparative Example 1
Production of Oxidation Catalyst (DOC) (3)
=Lower Layer=
[0169] Onto 341 g of .gamma.-alumina powder A, 506 g of
.gamma.-alumina powder D having a BET specific surface area of 220
m.sup.2/g and a pore size of 8 nm, and 253 g of .gamma.-alumina
powder E having a BET specific surface area of 160 m.sup.2/g and a
pore size of 10 nm, the Pt--Pd mixed solution was impregnated, so
as to attain 0.614% by weight (Pt/Pd=5/1) in noble metal
equivalent, to obtain Pt--Pd supported alumina powder e. 1106.8 g
of this Pt--Pd supported alumina powder e, 111 g of refined sugar
and water were put into a ball mill and milled till predetermined
particle size is attained to obtain slurry .epsilon..
[0170] Subsequently, a honeycomb flow-through-type cordierite
substrate, similar to the one as in Example 1, was immersed into
this slurry, and coated by a wash-coat method, so as to attain a
catalyst supported amount of 110.68 g/L per unit volume. After that
it was dried at 150.degree. C. for 1 hour and calcined at
500.degree. C. for 2 hours under atmospheric environment to obtain
a product already coated with the lower layer of DOC (3).
=Upper Layer=
[0171] Onto 279 g of .gamma.-alumina powder A, 414 g of
.gamma.-alumina powder D, and 207 g of .gamma.-alumina powder E,
the Pt--Pd mixed solution was impregnated, so as to attain 1.25% by
weight (Pt/Pd=5/1) in noble metal equivalent, to obtain Pt--Pd
supported alumina powder f.
[0172] Next, 911.4 g of the Pt--Pd supported alumina powder f, 91 g
of refined sugar and water were put into a ball mill and milled
till predetermined particle size is attained to obtain slurry
.zeta..
[0173] Subsequently, the product already coated with the lower
layer was immersed into this slurry, and coated by a wash-coat
method, so as to attain a catalyst supported amount of 91.14 g/L
per unit volume. After that it was dried at 150.degree. C. for 1
hour and calcined at 500.degree. C. for 2 hours under atmospheric
environment to obtain DOC (3) (Pt=1.52 g/L, Pd=0.30 g/L, total
amount of catalyst=201.82 g/L).
<Apparatus Configuration>
[0174] A catalyst for model gas evaluation was cut out from the
above oxidation catalyst DOC (3), to a size of (a diameter of 24
mm.times.a length of 66 mm, 30 mL), using a core drill and a
diamond cutter, and after heat treatment thereof at 750.degree. C.
for 50 hours, the model gas evaluation test was performed using the
above oxidation catalyst DOC (3). Results of oxidation activities
of NO, CO and HC are shown in FIG. 3. It should be noted that
components of the oxidation catalyst DOC (3) and amount of the
noble metals are shown in Tables 2 and 3.
[0175] After that, by arranging the oxidation catalyst DOC (3) {a
diameter of 7.5 inch (190.5 mm).times.a length of 3.3 inch (83.8
mm), 2.39 L}, after heat treatment at 750.degree. C. for 100 hours,
at the front stage inside a catalyst converter, and connecting the
heat treated products of CSF and SCR in series using the catalyst
converter, an apparatus of the present invention shown in FIG. 1
was configured. Good performance of exhaust gas purification was
not obtained even by using this apparatus.
TABLE-US-00002 TABLE 2 Example 1 Example 2 Comparative Example 1
DOC(1) Alumina B DOC(2) Alumina B DOC(3) Alumina A BaO Alumina C
Alumina D -- BaO Alumina E
TABLE-US-00003 TABLE 3 Noble metal Example 1 Example 2 Comparative
Example 1 DOC Pt (g) 2.87 2.87 3.63 Pd (g) 0.57 0.57 0.72 Ratio Pt
(%) 100 100 126 Pd (%) 100 100 126 Footnote: Pt amount and Pd
amount were calculated based on the catalyst of Example 1 as
100%.
[Evaluation 1]
[0176] From FIG. 3 summarizing the model gas evaluation test by the
catalysts after heat treatment at 750.degree. C. for 50 hours, and
Tables 2 and 3 showing catalyst components and amount of the noble
metals, it is understood the followings on oxidation activities of
NO, CO and HC, in the case of single oxidation catalyst (DOC).
[0177] Firstly, as is clear from the results of oxidation activity
test of NO of FIG. 3, the oxidation catalyst DOC (1) (Pt/Pd=5/1)
(weight ratio, the same shall apply hereafter) of Example 1 of the
present invention, because of using alumina B having a pore size of
23 nm, as a base material to support the noble metals, although
total amount of platinum and palladium is as high as 26% by weight,
exerted superior oxidation activity of NOX to the oxidation
catalyst DOC (3) of Comparative Example 1 (refer to Table 3), where
three kinds of alumina A, D and E, having a pore size of 10 nm or
smaller, as a base material to support the noble metals, were used.
Further, the oxidation catalyst DOC (2) of Example 2, where alumina
C having a pore size of 14 nm was added to alumina B having a pore
size of 23 nm, as abase material to support the noble metals,
exerted far higher oxidation activity of NO as compared with the
oxidation catalyst DOC (1) of Example 1, where only alumina B
having a pore size of 23 nm was used in the upper layer containing
noble metals.
[0178] However, there was observed no difference in oxidation
activity of CO or HC, between the oxidation catalysts DOC (1) and
DOC (2) of Examples 1 and 2, and the oxidation catalyst DOC (3) of
Comparative Example 1.
[0179] These results show that use of alumina having a pore size of
12 nm or larger, as the base material of the noble metal of Pt or
Pd, is effective to enhance oxidation activity of NO, and in
addition, multiple use of alumina having a pore size of 12 nm or
larger is effective to further enhance oxidation activity of
NO.
Example 3
Production of Oxidation Catalyst (DOC) (4)
=Lower Layer=
[0180] Onto 1 kg of .gamma.-alumina powder B, the Pt--Pd mixed
solution was impregnated, so as to attain 0.293% by weight
(Pt/Pd=5/1) in noble metal equivalent, and then an aqueous solution
of barium hydroxide was impregnated, so as to attain 0.065% by
weight in barium oxide equivalent to obtain Pt--Pd--Ba supported
alumina powder g.
[0181] Similarly, onto 200 g of .gamma.-alumina powder C, the
Pt--Pd mixed solution was impregnated and supported, so as to
attain 1.45% by weight (Pt/Pd=5/1) in noble metal equivalent, and
then an aqueous solution of barium hydroxide was impregnated, so as
to attain 0.323% by weight in barium oxide equivalent to obtain
Pt--Pd--Ba supported alumina powder h.
[0182] And, 920.3 g of Pt--Pd--Ba supported alumina powder g, 186.3
g of Pt--Pd--Ba supported alumina powder h, 5.8 g of barium
hydroxide in barium oxide equivalent, 111 g of refined sugar, and
water were put into a ball mill and milled till predetermined
particle size is attained to obtain slurry .eta..
[0183] Subsequently, a honeycomb flow-through-type cordierite
substrate, the similar one as in Example 1, was immersed into this
slurry, and coated by a wash-coat method, so as to attain an
catalyst supported amount of 111.24 g/L per unit volume. After that
it was dried at 150.degree. C. for 1 hour and calcined at
500.degree. C. for 2 hours under atmospheric environment to obtain
a product already coated with the lower layer of DOC (4).
=Upper Layer=
[0184] Onto 1 kg of .gamma.-alumina powder B, the Pt--Pd mixed
solution was impregnated and supported, so as to attain 0.595% by
weight (Pt/Pd=5/1) in noble metal equivalent, and barium hydroxide,
so as to attain 0.172% by weight in barium oxide equivalent to
obtain Pt--Pd--Ba supported alumina powder i. In addition, onto 200
g of .gamma.-alumina powder C, the Pt--Pd mixed solution was
impregnated and supported, so as to attain 2.89% by weight
(Pt/Pd=5/1) in noble metal equivalent, and barium hydroxide, so as
to attain 0.834% by weight in barium oxide equivalent to obtain
Pt--Pd--Ba supported alumina powder j.
[0185] Then 755.8 g of Pt--Pd--Ba supported alumina powder i, 155.8
g of Pt--Pd--Ba supported alumina powder j, 10.4 g of barium
hydroxide, in barium oxide equivalent, 92 g of refined sugar and
water were put into a ball mill and milled till predetermined
particle size is attained to obtain slurry .theta..
[0186] Subsequently, the product already coated with the lower
layer was immersed into this slurry, and coated by a wash-coat
method, so as to attain a catalyst supported amount of 92.2 g/L per
unit volume. After that it was dried at 150.degree. C. for 1 hour
and calcined at 500.degree. C. for 2 hours under atmospheric
environment to obtain DOC (4) (Pt=1.2 g/L, Pd=0.24 g/L, BaO=2.0
g/L, total amount of catalyst=203.44 g/L).
<Apparatus Configuration>
[0187] An engine evaluation test above oxidation catalyst DOC (4)
after heat treatment at 750.degree. C. for 100 hours was performed
using the above oxidation catalyst DOC (4). Results of oxidation
activity of NO are shown in FIG. 4 and results of light oil
combustion performance are shown in FIG. 5. It should be noted that
components of the oxidation catalyst DOC (4) and amount of the
noble metals are shown in Tables 4 and 5.
[0188] After that, by arranging the above oxidation catalyst DOC
(4) at the front stage inside a catalyst converter, and connecting
the heat treated products of CSF and SCR in series using the
catalyst converter, at the backward thereof, similarly as in
Example 1, an apparatus of the present invention shown in FIG. 1
was configured. Good performance of exhaust gas purification was
confirmed by using this apparatus.
Comparative Example 2
Production of Oxidation Catalyst (DOC) (5)
[0189] DOC (5) (Pt=1.20 g/L, Pd=0.24 g/L, total amount of
catalyst=201.44 g/L) was obtained by the same catalyst preparation
method as in DOC (3), except in that Pt--Pd supported amount of all
Pt--Pd supported alumina powder was decreased by 21% by weight
uniformly, in the oxidation catalyst DOC (3) of Comparative Example
1.
<Apparatus Configuration>
[0190] The engine evaluation test using the oxidation catalyst DOC
(5) after heat treatment at 750.degree. C. for 100 hours was
performed using the oxidation catalyst DOC (5). Results of
oxidation activity of NO are shown in FIG. 4 and results of light
oil combustion performance are shown in FIG. 5. It should be noted
that components of the oxidation catalyst DOC (5) and amount of the
noble metals are shown in Tables 4 and 5.
[0191] After that, by arranging the oxidation catalyst DOC (5) at
the front stage inside a catalyst converter, and connecting the
heat treated products of CSF and SCR in series using the catalyst
converter, at the backward thereof, similarly as in Example 1, an
apparatus for Comparative Example shown in FIG. 1 was configured.
Good performance of exhaust gas purification was not obtained even
by using this apparatus.
TABLE-US-00004 TABLE 4 Comparative Example 3 Example 2 Comparative
Example 1 DOC(4) Alumina B DOC(5) Alumina A DOC(3) Alumina A
Alumina C Alumina D Alumina D BaO Alumina E Alumina E
TABLE-US-00005 TABLE 5 Comparative Example 3 Example 2 Comparative
Example 1 DOC Pt (g) 2.87 2.87 3.63 Pd (g) 0.57 0.57 0.72 BaO(g)
4.78 0.00 0.00 Alumina (g) 478 478 478 Ratio Pt (%) 100 100 126 Pd
(%) 100 100 126 (Footnote) Pt amount and Pd amount were calculated
based on the catalyst of Example 3 as 100%.
[Evaluation 2]
[0192] From FIGS. 4 and 5 summarizing an engine steady state
evaluation test by the catalysts after heat treatment at
750.degree. C. for 100 hours, and Tables 4 and 5 showing catalyst
components and amount of the noble metals, it is understood the
following on oxidation activity of NO and light oil combustibility,
in the case of single oxidation catalyst (DOC).
[0193] Firstly, as is clear from the results of oxidation activity
test of NO of FIG. 4, the oxidation catalyst DOC (4) (Pt/Pd=5/1) of
Example 3 of the present invention exerted superior oxidation
activity of NO, in particular, at low temperature (250.degree. C.),
to the oxidation catalyst DOC (5) of Comparative Example 2 (refer
to Table 5), where amount of platinum and palladium was the same.
Further, the oxidation catalyst DOC (4) of Example 3 exerted higher
oxidation activity of NO as compared with the oxidation catalyst
DOC (3) of Comparative Example 1, where amount of platinum and
palladium was increased each by a little less than 30% by weight
(refer to Table 5), and effect thereof was significant at low
temperature (250.degree. C.).
[0194] In addition, as is clear from the results of light oil
combustibility test of FIG. 5, the oxidation catalyst DOC (4) of
Example 3 of the present invention showed higher temperature
increase by heat generation accompanied with light oil combustion,
as compared with the oxidation catalyst DOC (5) of Comparative
Example 2, where amount of platinum and palladium was the same, and
effect thereof was significant at low temperature (250.degree. C.).
Still more, the oxidation catalyst DOC (4) of Example 3 showed also
higher temperature increase of heat generation by light oil
combustion, as compared with the oxidation catalyst DOC (3) of
Comparative Example 1, where amount of platinum and palladium was
increased each by a little less than 30% by weight. These results
show that the oxidation catalyst DOC (4) of Example 3, which
contains barium oxide (BaO), and where pore size of two kinds of
alumina is 12 nm to 40 nm {in practice, 23 nm (alumina B) and 14 nm
(alumina C) (refer to Table 4)}, is superior in oxidation activity
of NO as well as light oil combustibility, to the oxidation
catalyst DOC (3) and DOC (5) of Comparative Examples 1 and 2, which
do not contain barium oxide, and where pore size of alumina is also
10 nm or smaller {in practice, 9 nm (alumina A), 8 nm (alumina D)
and 10 nm (alumina E), (refer to Table 4)}.
Example 4
Apparatus Configuration
[0195] An engine evaluation test was performed, after heat
treatment of each of DOC (4) of the Example 3 and CSF (1) of the
Example 1 at 750.degree. C. for 100 hours, by connecting them in
series inside the catalyst converter. Results of oxidation
activities of NO, CO and HC are shown in FIG. 6. It should be noted
that components of DOC (4)+CSF (1) and amount of the noble metals
are shown in Tables 6 and 7.
[0196] By connecting the heat treated product of SCR in series
using the catalyst converter, at the latter part of the catalyst
converter of the {DOC (4)+CSF (1)}, similarly as in Example 1, an
apparatus of the present invention shown in FIG. 1 was configured.
Good performance of exhaust gas purification was confirmed using
this apparatus.
Example 5
Production of Catalyzed Soot Filter CSF (2)
[0197] Onto 1 kg of .gamma.-alumina powder F having a BET specific
surface area of 95 m.sup.2/g and a pore size of 10 nm, the Pt--Pd
mixed solution (Pt/Pd=2/1) was impregnated and supported, so as to
attain 2.43% by weight in noble metal equivalent, to obtain Pt--Pd
supported alumina powder k.
[0198] And, 543.2 g of the Pt--Pd supported alumina powder k, 30 g
of alumina sol in alumina equivalent and water were put into a ball
mill and milled till predetermined particle size is attained to
obtain slurry .tau.. Subsequently, a honeycomb wall-flow-type
cordierite substrate, similar to the one as in Example 1, was
immersed into this slurry, and coated by a wash-coat method, so as
to attain a catalyst supported amount of 28.66 g/L per unit volume.
After that it was dried at 150.degree. C. for 1 hour and calcined
at 500.degree. C. for 2 hours under atmospheric environment to
obtain CSF (2) (Pt=0.44 g/L, Pd=0.22 g/L, amount of catalyst=28.66
g/L).
<Apparatus Configuration>
[0199] An engine evaluation test was performed, after heat
treatment of each of DOC (4) of the Example 3 and the CSF (2) at
750.degree. C. for 100 hours, by connecting them in series inside
the catalyst converter. Results of oxidation activities of NO, CO
and HC are shown in FIG. 6. It should be noted that components of
DOC (4)+CSF (2) and amount of the noble metals are shown in Tables
6 and 7.
[0200] By connecting the heat treated product of SCR in series
using the catalyst converter, at the latter part of the catalyst
converter of the above {DOC (4)+CSF (2)}, similarly as in Example
1, an apparatus of the present invention shown in FIG. 1 was
configured. Relatively good performance of exhaust gas purification
was confirmed using this apparatus.
Comparative Example 3
Production of Catalyzed Soot Filter CSF (3)
[0201] CSF (3) (Pt=0.58 g/L, Pd=0.29 g/L, amount of catalyst=28.87
g/L) was obtained by the same catalyst preparation method as in the
catalyzed soot filter CSF (2) of Example 5, except in that Pt--Pd
supported amount of Pt--Pd supported alumina powder, was increased
by 32% by weight uniformly.
<Apparatus Configuration>
[0202] An engine evaluation test was performed, after heat
treatment of each of DOC (3) of the Comparative Example 1 and the
CSF (3) at 750.degree. C. for 100 hours, by connecting them in
series inside the catalyst converter. Results of oxidation
activities of NO, CO and HC are shown in FIG. 6. It should be noted
that components of DOC (3)+CSF (3) and amount of the noble metals
are shown in Tables 6 and 7.
[0203] By connecting the heat treated product of SCR in series
using the catalyst converter, at the latter part of the catalyst
converter of the above {DOC (3)+CSF (3)}, similarly as in Example
1, an apparatus for comparison shown in FIG. 1 was configured.
Relatively good performance of exhaust gas purification was not
obtained even by using this apparatus.
TABLE-US-00006 TABLE 6 Example 4 Example 5 Comparative Example 3
DOC(4) Alumina B DOC(4) Alumina B DOC(3) Alumina A Alumina C
Alumina C Alumina D BaO BaO Alumina E CSF(1) Alumina B CSF(2)
Alumina F CSF(3) Alumina F Alumina C -- --
TABLE-US-00007 TABLE 7 Noble metal Example 4 Example 5 Comparative
Example 3 DOC Pt (g) 2.87 2.87 3.63 Pd (g) 0.57 0.57 0.72 CSF Pt
(g) 2.13 2.13 2.81 Pd (g) 1.07 1.07 1.41 Total Pt (g) 5.00 5.00
6.44 Pd (g) 1.64 1.64 2.13 Ratio Pt (%) 100 100 129 Pd (%) 100 100
130 (Footnote) Pt amount and Pd amount were calculated based on the
catalyst of Example 4 as 100%.
[Evaluation 3]
[0204] From FIG. 6 summarizing a engine steady state evaluation
test by the above catalysts after heat treatment at 750.degree. C.
for 100 hours, and Tables 6 and 7 showing catalyst configuration
and components and amount of the noble metals, it is understood the
following on oxidation activities of NO, CO and HC, in the case
where the oxidation catalyst (DOC) and the catalyzed soot filter
(CSF) are combined.
[0205] As is clear from the oxidation activity test of NO, CO and
HC of FIG. 6, Example 4 of the present invention, which is the case
where the catalyzed soot filter CSF (1) using two kinds of alumina
having a pore size of 12 to 120 nm, is arranged at the latter part
of the oxidation catalyst DOC (4), exerted superior oxidation
activities of all of NO, CO and HC.
[0206] In addition, Example 5 of the present invention, which is
the case where the catalyzed soot filter CSF (2) using alone
alumina having a pore size of 10 nm, is arranged at the latter part
of the oxidation catalyst DOC (4), exerted oxidation activities of
all of NO, CO and HC.
[0207] On the other hand, the catalyst of Comparative Example 3 {a
combination of DOC (3) and CSF (3)}, exerted low oxidation
activities of all of NO, CO and HC, although supported amount of
the noble metals was increased by about 30% by weight as compared
with Examples 4 and 5, in both of the oxidation catalyst and the
catalyzed soot filter.
[0208] The above results suggest that contribution of combination
of DOC+CSF on oxidation activities of NO, CO and HC is larger in
the front stage DOC than in the latter part CSF, because there is
not so much difference in total amount of the noble metals (total
amount of Pt+Pd) of DOC and CSF used in Examples 4 and 5, and
reduction of the noble metals is considered effective to CSF than
to DOC.
Example 6
Production of Oxidation Catalyst DOC (6)
=Lower Layer=
[0209] Onto 1,000 g of .gamma.-alumina powder B, the Pt--Pd mixed
solution (Pt/Pd=2/1) was impregnated, so as to attain 0.336% by
weight (Pt/Pd=2/1) in noble metal equivalent, and then an aqueous
solution of barium hydroxide was impregnated, so as to attain
0.054% by weight in barium oxide equivalent to obtain Pt--Pd--Ba
supported alumina powder l.
[0210] Similarly, onto 200 g of .gamma.-alumina powder C, the same
Pt--Pd mixed solution was impregnated and supported, so as to
attain 1.66% by weight (Pt/Pd=2/1) in noble metal equivalent, and
then an aqueous solution of barium hydroxide was impregnated, so as
to attain 0.268% by weight in barium oxide equivalent to obtain
Pt--Pd--Ba supported alumina powder m.
[0211] And, 920.6 g of Pt--Pd--Ba supported alumina powder l, 186.6
g of Pt--Pd--Ba supported alumina powder m, 3 g of barium hydroxide
in barium oxide equivalent, 111 g of refined sugar, and water were
put into a ball mill and milled till predetermined particle size is
attained to obtain slurry .kappa..
[0212] Subsequently, an integral structure-type substrate, that is,
a honeycomb flow-through-type cordierite substrate {300
cell/inch.sup.2 (465 k/m.sup.2)/8 mil (0.2 mm), a diameter of 7.5
inch (190.5 mm).times.a length of 2.64 inch (67.1 mm), 1.91 L}, was
immersed into this slurry, and coated by a wash-coat method, so as
to attain a catalyst supported amount of 111.02 g/L per unit
volume. After that it was dried at 150.degree. C. for 1 hour and
calcined at 500.degree. C. for 2 hours under atmospheric
environment to obtain a catalyst already coated with the lower
layer of DOC (6).
=Upper Layer=
[0213] Onto 1 kg of .gamma.-alumina powder B, the Pt--Pd mixed
solution was impregnated and supported, so as to attain 0.682% by
weight (Pt/Pd=2/1) in noble metal equivalent, and barium hydroxide,
so as to attain 0.099% by weight in barium oxide equivalent to
obtain Pt--Pd--Ba supported alumina powder n. In addition, onto 200
g of .gamma.-alumina powder C, the Pt--Pd mixed solution was
impregnated and supported, so as to attain 3.31% by weight
(Pt/Pd=2/1) in noble metal equivalent, and barium hydroxide, so as
to attain 0.481% by weight in barium oxide equivalent to obtain
Pt--Pd--Ba supported alumina powder o.
[0214] And, 755.9 g of Pt--Pd--Ba supported alumina powder n, 155.9
g of Pt--Pd--Ba supported alumina powder o, 4.5 g of barium
hydroxide, in barium oxide equivalent, 92 g of refined sugar and
water were put into a ball mill and milled till predetermined
particle size is attained to obtain slurry .lamda..
[0215] Subsequently, the catalyst already coated with the lower
layer was immersed into this slurry, and coated by a wash-coat
method, so as to attain a catalyst supported amount of 91.63 g/L
per unit volume. After that it was dried at 150.degree. C. for 1
hour and calcined at 500.degree. C. for 2 hours under atmospheric
environment to obtain DOC (6) (Pt=1.1 g/L, Pd=0.55 g/L, BaO=1.0
g/L, total amount of catalyst=202.65 g/L).
<Production of Oxidation Catalyst DOC (7)>
[0216] DOC (7) (Pt=1.2 g/L, Pd=0.24 g/L, BaO=2.0 g/L, total amount
of catalyst=203.44 g/L) was obtained by the same catalyst
preparation method as in DOC (4) of Example 3, except in that size
of the honeycomb flow-through-type cordierite substrate was changed
to {300 cell/inch.sup.2 (465 k/m.sup.2)/8 mil (0.2 mm), a diameter
of 7.5 inch (190.5 mm).times.a length of 2.64 inch (67.1 mm), 1.91
L}, in production of DOC (4) of Example 3.
<Production of Catalyzed Soot Filter CSF (4)>
[0217] Onto 600 g of .gamma.-alumina powder B and 400 g of
.gamma.-alumina powder C, the Pt--Pd mixed solution (Pt/Pd=2/1) was
impregnated and supported, so as to attain 2.39% by weight in noble
metal equivalent, to obtain alumina powder p, which supports
Pt--Pd. And, 130.3 g of the alumina powder p, which supports
Pt--Pd, 7.2 g of silica sol in silica equivalent and water were put
into a ball mill and milled till predetermined particle size is
attained to obtain slurry .mu.. Subsequently, a honeycomb
wall-flow-type cordierite substrate, similar to the one as in
Example 1, was immersed into this slurry, and coated by a wash-coat
method, so as to attain a catalyst supported amount of 6.876 g/L
per unit volume. After that it was dried at 150.degree. C. for 1
hour and calcined at 500.degree. C. for 2 hours under atmospheric
environment to obtain CSF (4) (Pt=0.104 g/L, Pd=0.052 g/L, amount
of catalyst=6.876 g/L).
<Apparatus Configuration>
[0218] By connecting the above DOC (6), DOC (7) and CSF (4) in
series inside the catalyst converter, in this order, an apparatus
of the present invention was configured. An engine temperature
rising evaluation test was performed using this, and results of
oxidation activities of NO, CO and HC are shown in FIG. 7. It
should be noted that components of DOC (6), DOC (7) and CSF (4),
and amount of the noble metals are shown in Tables 8 and 9.
[0219] By arranging heat treated product of SCR, similarly as in
Example 1, at the latter part of CSF (4) of the Example 6, an
apparatus of the present invention shown in FIG. 1 was configured
(it is different from apparatuses of Examples 1 to 5, in that DOC
is installed divided into two). Good performance of exhaust gas
purification was confirmed using this apparatus.
Example 7
Apparatus Configuration
[0220] By using the DOC (6), DOC (7) and CSF (4) of the above
Example 6, and connecting in series inside the catalyst converter,
in the order of DOC+CSF+DOC, an apparatus of the present invention
was configured. An engine temperature rising evaluation test was
performed using this, and results of oxidation activities of NO, CO
and HC are shown in FIG. 7. It should be noted that components of
DOC (6), CSF (4) and DOC (7), and amount of the noble metals are
shown in Tables 8 and 9.
[0221] By arranging heat treated product of SCR, similarly as in
Example 1, at the latter part of DOC (7) of the Example 7, an
apparatus of the present invention shown in FIG. 2 was configured.
Good performance of exhaust gas purification was confirmed using
this apparatus.
Example 8
[0222] DOC (8) (Pt=0.91 g/L, Pd=0.18 g/L, BaO=2.0 g/L, total amount
of catalyst=203.09 g/L) was obtained by the same catalyst
preparation method as Example 3, except in that Pt--Pd supported
amount of all Pt--Pd supported alumina powder, was decreased by 24%
by weight uniformly, in the oxidation catalyst DOC (4) of Example
3.
<Apparatus Configuration>
[0223] By using the DOC (6) and CSF (4) of the Example 6 and the
DOC (8), and connecting in series inside the catalyst converter, in
the order of DOC+CSF+DOC, an apparatus of the present invention was
configured. An engine temperature rising evaluation test was
performed using this, and results of oxidation activities of NO, CO
and HC are shown in FIG. 7. It should be noted that components of
CSF (4) and amount of the noble metals are shown in Tables 8 and
9.
[0224] By arranging heat treated product of SCR, similarly as in
Example 1, at the latter part of DOC (8) of the Example 8, an
apparatus of the present invention shown in FIG. 2 was configured.
Good performance of exhaust gas purification was confirmed using
this apparatus.
TABLE-US-00008 TABLE 8 Comparative Example 4 Example 6 Example 7
Example 8 Example 3 DOC(4) Alumina B DOC(6) Alumina B DOC(6)
Alumina B DOC(6) Alumina B DOC(3) Alumina A Alumina C Alumina C
Alumina C Alumina C Alumina D BaO BaO BaO BaO Alumina E CSF(1)
Alumina B DOC(7) Alumina B CSF(4) Alumina B CSF(4) Alumina B CSF(3)
Alumina F Alumina C Alumina C Alumina C Alumina C -- BaO DOC(7)
Alumina B DOC(8) Alumina B CSF(4) Alumina B Alumina C Alumina C
Alumina C BaO BaO
TABLE-US-00009 TABLE 9 Noble Exam- Exam- Exam- Exam- Comparative
ordering metal ple 4 ple 6 ple 7 ple 8 Example 3 DOC Pt (g) 2.87
2.10 2.10 2.10 3.63 Pd (g) 0.57 1.05 1.05 1.05 0.72 DOC Pt (g) --
2.29 -- -- -- Pd (g) -- 0.46 -- -- -- CSF Pt (g) 2.13 0.50 0.50
0.50 2.81 Pd (g) 1.07 0.25 0.25 0.25 1.41 DOC Pt (g) -- -- 2.29
1.74 -- Pd (g) -- -- 0.46 0.35 -- Total Pt (g) 5.00 4.89 4.89 4.34
6.44 Pd (g) 1.64 1.76 1.76 1.65 2.13 Ratio Pt (%) 100 98 98 87 129
Pd (%) 100 107 107 101 130 (Footnote) Pt amount and Pd amount were
calculated based on the catalyst of Example 4 as 100%.
[Evaluation 4]
[0225] From FIG. 7 summarizing the engine temperature rising
evaluation test by the catalysts (DOC+CSF, DOC+DOC+CSF, or
DOC+CSF+DOC) after heat treatment at 750.degree. C. for 100 hours,
and Tables 8 and 9 showing catalyst configuration, components and
noble metal amount, the following is understood.
[0226] Example 6, in which oxidation catalyst DOC (6)(Pt/Pd=2/1),
where supported amount of the noble metals was concentrated to DOC
based on knowledge obtained by evaluation 3, oxidation catalyst DOC
(7)(Pt/Pd=2/1) of the present invention, and catalyzed soot filter
CSF (4), where supported amount of the noble metals of CSF was
decreased drastically, were arranged in series, exerted far
superior oxidation activities of CO and HC to Example 4, but a
little inferior oxidation activity of NO, although total supported
amount of both Pt and Pd is nearly the same as in the Example 4
(refer to Table 9). However, even so, oxidation activity of NO was
superior to that of Comparative Example 3 where total supported
amount of the noble metals is over by a little less than 30% by
weight. Reason for this is considered that an oxidation reaction of
CO or HC occurs more preferentially than an oxidation reaction of
NO, by concentrated support of the noble metals on DOC, and it is
considered that it is suitable to oxidation of CO or HC, but it is
a little not preferable combination to oxidation of NO.
[0227] Further, Example 7, in which DOC(6), CSF(4) and DOC(7) were
arranged in series in this order, so as to sandwich catalyzed soot
filter CSF (4) of the present invention, exerted NO oxidation
activity far superior to Example 4, although total supported amount
of both Pt and Pd is nearly the same as in the Example 4 (refer to
Table 9). In addition, Example 7 also showed nearly the same
oxidation activities of CO and HC as in Example 4, and also
superior to Comparative Example 3, where total supported amount of
the noble metals is over by a little less than 30% by weight.
[0228] In addition, Example 8, in which oxidation catalyst DOC (6)
of the present invention, catalyzed combustion filter CSF (4), and
oxidation catalyst DOC (8), where supported amount of the noble
metals (Pt/Pd=5/1) was further decreased, were arranged in series,
was superior to Comparative Example 3 in oxidation activities of NO
and CO, although a little inferior in oxidation activity of HC,
irrespective of decrease in total supported amount of both Pt and
Pd still more about 10% by weight as compared with Example 7, and
decrease as much as by nearly 30% by weight as compared with
Comparative Example 3 (refer to Table 9).
[0229] In this way, the present invention contributes to enhance
oxidation activities of NO, CO and HC by the addition of BaO,
optimization of specifications of alumina fine pores, optimization
of arrangement of DOC and the like, while decreasing supported
amount of high price noble metals (Pt and Pd) by as much as about
20 to 30% by weight. In particular, the present invention exerts
significant effect in enhancement of oxidation activity of NO.
INDUSTRIAL APPLICABILITY
[0230] The exhaust gas purification apparatus of the present
invention can be used in purification technology of NO.sub.x
generating by lean combustion, for example, in applications for a
mobile body including a diesel automobile and also a gasoline
automobile, a ship or the like, or for a fixed applications such as
a power generator, and in particular, useful for a diesel
automobile.
* * * * *