U.S. patent application number 14/785417 was filed with the patent office on 2016-03-24 for carrier for exhaust gas purification catalyst, catalyst for exhaust gas purification, and catalyst structure for exhaust gas purification.
The applicant listed for this patent is KUMAMOTO UNIVERSITY, MITSUI MINING & SMELTING CO., LTD.. Invention is credited to Ohki HOUSHITO, Hironori IWAKURA, Masato MACHIDA, Yuki NAGAO, Yunosuke NAKAHARA.
Application Number | 20160082419 14/785417 |
Document ID | / |
Family ID | 51791916 |
Filed Date | 2016-03-24 |
United States Patent
Application |
20160082419 |
Kind Code |
A1 |
NAKAHARA; Yunosuke ; et
al. |
March 24, 2016 |
CARRIER FOR EXHAUST GAS PURIFICATION CATALYST, CATALYST FOR EXHAUST
GAS PURIFICATION, AND CATALYST STRUCTURE FOR EXHAUST GAS
PURIFICATION
Abstract
The disclosed exhaust gas purification catalyst carrier includes
a modified aluminum borate which contains aluminum borate and at
least one addition element selected from the group consisting of a
rare earth element and an alkaline earth metal and which has an
electronegativity of 2.732 or lower.
Inventors: |
NAKAHARA; Yunosuke;
(Saitama, JP) ; HOUSHITO; Ohki; (Saitama, JP)
; IWAKURA; Hironori; (Saitama, JP) ; NAGAO;
Yuki; (Saitama, JP) ; MACHIDA; Masato;
(Kumamoto, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MITSUI MINING & SMELTING CO., LTD.
KUMAMOTO UNIVERSITY |
Tokyo
Kumamoto |
|
JP
JP |
|
|
Family ID: |
51791916 |
Appl. No.: |
14/785417 |
Filed: |
April 23, 2014 |
PCT Filed: |
April 23, 2014 |
PCT NO: |
PCT/JP2014/061470 |
371 Date: |
October 19, 2015 |
Current U.S.
Class: |
502/207 ;
502/439 |
Current CPC
Class: |
F01N 3/106 20130101;
B01D 2255/204 20130101; B01D 2255/70 20130101; B01D 2255/2066
20130101; B01D 53/945 20130101; B01D 2255/2065 20130101; B01J 23/58
20130101; B01J 23/10 20130101; B01D 2255/2068 20130101; B01J 35/002
20130101; F01N 2570/10 20130101; B01J 23/63 20130101; B01D
2255/2063 20130101; B01J 23/44 20130101; Y02T 10/12 20130101; Y02T
10/22 20130101; F01N 3/101 20130101; B01D 2255/2042 20130101; B01D
2255/2092 20130101; B01J 21/02 20130101; B01D 2255/1023 20130101;
B01J 2523/00 20130101; B01D 2255/2045 20130101; B01J 2523/00
20130101; B01J 2523/24 20130101; B01J 2523/305 20130101; B01J
2523/31 20130101; B01J 2523/3706 20130101; B01J 2523/00 20130101;
B01J 2523/305 20130101; B01J 2523/31 20130101; B01J 2523/3706
20130101; B01J 2523/3718 20130101; B01J 2523/00 20130101; B01J
2523/23 20130101; B01J 2523/305 20130101; B01J 2523/31 20130101;
B01J 2523/3706 20130101; B01J 2523/00 20130101; B01J 2523/305
20130101; B01J 2523/31 20130101; B01J 2523/3706 20130101; B01J
2523/3725 20130101; B01J 2523/00 20130101; B01J 2523/305 20130101;
B01J 2523/31 20130101; B01J 2523/3706 20130101; B01J 2523/3712
20130101 |
International
Class: |
B01J 23/63 20060101
B01J023/63; B01J 23/10 20060101 B01J023/10 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 26, 2013 |
JP |
2013-094197 |
Claims
1-6. (canceled)
7. An exhaust gas purification catalyst carrier, comprising a
modified aluminum borate which contains aluminum borate and at
least one addition element selected from the group consisting of a
rare earth element and an alkaline earth metal and which has an
electronegativity of 2.732 or lower.
8. An exhaust gas purification catalyst carrier, comprising a
modified aluminum borate which contains aluminum borate and at
least one addition element selected from the group consisting of a
rare earth element and an alkaline earth metal, in an amount of 6
mass % or more as an oxide thereof.
9. An exhaust gas purification catalyst carrier according to claim
7, wherein the addition element contains two or more elements.
10. An exhaust gas purification catalyst carrier according to claim
8, wherein the addition element contains two or more elements.
11. An exhaust gas purification catalyst carrier according to claim
7, wherein the addition element is an element selected from the
group consisting of Ca, Sr, Ba, La, Pr, Nd, and Ce.
12. An exhaust gas purification catalyst carrier according to claim
8, wherein the addition element is an element selected from the
group consisting of Ca, Sr, Ba, La, Pr, Nd, and Ce.
13. An exhaust gas purification catalyst carrier according to claim
9, wherein the addition element is an element selected from the
group consisting of Ca, Sr, Ba, La, Pr, Nd, and Ce.
14. An exhaust gas purification catalyst carrier according to claim
10, wherein the addition element is an element selected from the
group consisting of Ca, Sr, Ba, La, Pr, Nd, and Ce.
15. An exhaust gas purification catalyst, comprising an exhaust gas
purification catalyst carrier as recited in claim 7, and Pd
supported on the carrier.
16. An exhaust gas purification catalyst, comprising an exhaust gas
purification catalyst carrier as recited in claim 8, and Pd
supported on the carrier.
17. An exhaust gas purification catalyst, comprising an exhaust gas
purification catalyst carrier as recited in claim 9, and Pd
supported on the carrier.
18. An exhaust gas purification catalyst, comprising an exhaust gas
purification catalyst carrier as recited in claim 10, and Pd
supported on the carrier.
19. An exhaust gas purification catalyst, comprising an exhaust gas
purification catalyst carrier as recited in claim 11, and Pd
supported on the carrier.
20. An exhaust gas purification catalyst, comprising an exhaust gas
purification catalyst carrier as recited in claim 12, and Pd
supported on the carrier.
21. An exhaust gas purification catalyst, comprising an exhaust gas
purification catalyst carrier as recited in claim 13, and Pd
supported on the carrier.
22. An exhaust gas purification catalyst, comprising an exhaust gas
purification catalyst carrier as recited in claim 14, and Pd
supported on the carrier.
23. An exhaust gas purification catalyst product, comprising a
catalyst support formed of a ceramic or metallic material, and a
layer of an exhaust gas purification catalyst as recited in claim
15, the layer being supported on the catalyst support.
24. An exhaust gas purification catalyst product, comprising a
catalyst support formed of a ceramic or metallic material, and a
layer of an exhaust gas purification catalyst as recited in claim
16, the layer being supported on the catalyst support.
25. An exhaust gas purification catalyst product, comprising a
catalyst support formed of a ceramic or metallic material, and a
layer of an exhaust gas purification catalyst as recited in claim
17, the layer being supported on the catalyst support.
26. An exhaust gas purification catalyst product, comprising a
catalyst support formed of a ceramic or metallic material, and a
layer of an exhaust gas purification catalyst as recited in claim
18, the layer being supported on the catalyst support.
Description
TECHNICAL FIELD
[0001] The present invention relates to a carrier for an exhaust
gas purification catalyst (hereinafter referred to as an exhaust
gas purification catalyst carrier), to an exhaust gas purification
catalyst, and to an exhaust gas purification catalyst product. More
particularly, the invention relates to an exhaust gas purification
catalyst carrier, to an exhaust gas purification catalyst, and to
an exhaust gas purification catalyst product, which exhibit
excellent exhaust gas purification performance, (in particular CO
removal performance), in a fuel-rich region (hereinafter referred
to simply as a "rich region"), even after long-term use thereof
under high-temperature conditions.
BACKGROUND ART
[0002] Exhaust gas discharged from an internal combustion engine
of, for example, an automobile contains toxic components such as
hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides
(NO.sub.x). Hitherto, three-way catalysts have been used for
removing such toxic components for detoxifying the exhaust gas.
[0003] Such three-way catalysts include a noble metal (e.g., Pt,
Pd, or Rh) serving as a catalytically active component; a material
such as alumina, ceria, zirconia, or oxygen-occluding
ceria-zirconia composite oxide, serving as a carrier; and a
catalyst support made of a ceramic or metallic material and having
a shape of honeycomb, plate, pellet, etc.
[0004] Recently, the regulation of automobile exhaust gas has
become more strict, and the demand and prices of Pt and Rh, which
are noble metals serving as a main catalytically active component
of internal combustion engine exhaust gas purification catalysts,
have risen. Since a rise in Rh price is a critical issue, efforts
have been made on reduction of exhaust gas purification catalyst
production cost by use of inexpensive Pd as a catalytically active
component, and various means therefor have been proposed (see, for
example, Patent Documents 1, 2, and 3). Meanwhile, there are some
cases where a catalyst carrier made of aluminum borate is used. In
one case of such a catalyst, a catalyst component is deposited on a
powder compact which is covered with aluminum borate whiskers and
which includes voids therein, whereby gas diffusivity is enhanced
(see Patent Document 4).
[0005] However, it has been reported that Pd causes impairment in
exhaust gas purification performance by sintering thereof at high
temperature in a reducing atmosphere. Thus, suppression of Pd
sintering is an inevitable issue for designing coming catalysts of
a noble-metal saving format. Also, aluminum borate whiskers, having
an acicular shape, have a small specific surface area, which causes
cohesion of noble metal elements after long-term use of the
relevant catalyst under high-temperature conditions. That is,
durability of the catalyst is unsatisfactory.
[0006] In order to solve such problems, the present applicant
previously developed an exhaust gas purification catalyst which
exhibits excellent NO.sub.x purification performance, particularly
in a rich region. The catalyst includes a carrier containing a
substituted aluminum borate in which 2.5 to 11.5 at. % aluminum
atoms are substituted by Fe, Co, Ga, or Ni atoms, and Pd supported
on the carrier (see Patent Document 5).
PRIOR ART DOCUMENTS
Patent Documents
[0007] Patent Document 1: Japanese Patent Application Laid-Open
(kokai) No. Hei 06-099069 Patent Document 2: Japanese Patent
Application Laid-Open (kokai) No. Hei 07-171392 Patent Document 3:
Japanese Patent Application Laid-Open (kokai) No. Hei 08-281071
Patent Document 4: Japanese Patent Application Laid-Open (kokai)
No. 2002-370035
Patent Document 5: WO 2012/005375
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0008] However, the exhaust gas purification catalyst disclosed in
Patent Document 5, employing a substituted aluminum borate,
exhibits somewhat lower purification performance after long-term
use thereof in a rich region, although the catalyst exhibits
excellent purification performance after long-term use thereof
under a fuel-lean or a stoichiometric condition.
[0009] In the meantime, the exhaust gas purification catalyst for
automobiles is designed in accordance with the type of automobile.
Specifically, automobiles mainly employing a combustion mode in a
lean condition (at high air-fuel ratio) are provided with an
exhaust gas purification catalyst which is durable in a lean
condition, while automobiles mainly employing a combustion mode in
a rich region (at low air-fuel ratio) are provided with an exhaust
gas purification catalyst which is durable in a rich region.
[0010] Thus, an object of the present invention is to provide an
exhaust gas purification catalyst carrier, an exhaust gas
purification catalyst, and an exhaust gas purification catalyst
product, which exhibit excellent exhaust gas purification
performance, (in particular CO removal performance), in a rich
region, even after long-term use thereof under high-temperature
conditions.
Means for Solving the Problems
[0011] The present inventors have conducted extensive studies in
order to attain the aforementioned object, and have found that the
electronegativity of a catalyst carrier made of a modified aluminum
borate to which an alkaline earth element or a rare earth element
has been added can be reduced, to thereby promote electron supply
from noble metal elements to the carrier, whereby the noble metal
elements are immobilized on the carrier even in a rich region, to
thereby attain excellent Pd dispersion degree and catalytic
activity, even after long-term use thereof in a rich region. The
present invention has been accomplished on the basis of this
finding.
[0012] Notably, characteristics, its production method, etc. of
aluminum borate are disclosed in, for example, Siba P. Ray,
"Preparation and Characterization of Aluminum Borate", J. Am.
Ceram. Soc., 75[9], p. 2605-2609 (1992).
[0013] Conventionally, aluminum borate is represented by a formula
9Al.sub.2O.sub.3.2B.sub.2O.sub.3 (Al.sub.18B.sub.4O.sub.33),
obtained through chemical analysis. However, a thesis (Martin et
al., "Crystal-chemistry of mullite-type aluminoborates
Al.sub.18B.sub.4O.sub.33 and Al.sub.5BO.sub.9: A stoichiometry
puzzle", Journal of Solid State Chemistry 184(2011) p. 70 to 80),
discloses crystal structure analyses revealing that aluminum borate
is represented by Al.sub.5BO.sub.9
(5Al.sub.2O.sub.3:B.sub.2O.sub.3, Al.sub.20B.sub.4O.sub.36); i.e.,
formula 10Al.sub.2O.sub.3.2B.sub.2O.sub.3. The thesis also
discloses that aluminum borate may be represented by either formula
9Al.sub.2O.sub.3.2B.sub.2O.sub.3 (Al.sub.18B.sub.4O.sub.33) or
Al.sub.5BO.sub.9 (5Al.sub.2O.sub.3:B.sub.2O.sub.3,
Al.sub.20B.sub.4O.sub.36), meaning that the two formulas represent
a unique substance.
[0014] Thus, as used herein, the term "aluminum borate" encompasses
aluminum borate represented by formula
10Al.sub.2O.sub.3.2B.sub.2O.sub.3 (5Al.sub.2O.sub.3:B.sub.2O.sub.3,
Al.sub.20B.sub.4O.sub.36) and aluminum borate represented by
formula 9Al.sub.2O.sub.3.2B.sub.2O.sub.3
(Al.sub.18B.sub.4O.sub.33).
[0015] Accordingly, a characteristic feature of the exhaust gas
purification catalyst carrier of the present invention resides in
that the catalyst carrier comprises a modified aluminum borate
which contains aluminum borate (in particularly aluminum borate
having a cage structure) and at least one addition element selected
from the group consisting of a rare earth element and an alkaline
earth metal and which has an electronegativity of 2.732 or lower.
Another characteristic feature resides in that the catalyst carrier
comprises a modified aluminum borate which contains aluminum borate
and at least one addition element selected from the group
consisting of a rare earth element and an alkaline earth metal, in
an amount of 6 mass % or more as an oxide thereof. The aluminum
borate employed in the present invention encompasses aluminum
borate species having an aluminum oxide to boron oxide ratio of
10:2 to 9:2; i.e., an aluminum borate represented by formula
10Al.sub.2O.sub.3.2B.sub.2O.sub.3 (5Al.sub.2O.sub.3:B.sub.2O.sub.3,
Al.sub.20B.sub.4O.sub.36) and an aluminum borate represented by
formula 9Al.sub.2O.sub.3.2B.sub.2O.sub.3
(Al.sub.18B.sub.4O.sub.33). The aluminum borate employed in the
present invention can be identified as an aluminum borate
represented by formula 10Al.sub.2O.sub.3.2B.sub.2O.sub.3 through
X-ray diffractometry. However, since the formula
9Al.sub.2O.sub.3.2B.sub.2O.sub.3 (Al.sub.18B.sub.4O.sub.33) is also
given in an X-ray diffraction standard chart, the aluminum borate
can also be identified as an aluminum borate represented by formula
9Al.sub.2O.sub.3.2B.sub.2O.sub.3 (Al.sub.48B.sub.4O.sub.33).
[0016] The aforementioned addition element preferably contains two
or more such elements. The addition element is particularly
preferably an element selected from the group consisting of Ca, Sr,
Ba, La, Pr, Nd, and Ce.
[0017] The exhaust gas purification catalyst of the present
invention includes the aforementioned exhaust gas purification
catalyst carrier, and Pd supported on the carrier.
[0018] The exhaust gas purification catalyst product of the present
invention includes a catalyst support formed of a ceramic or
metallic material, and a layer of the aforementioned exhaust gas
purification catalyst, the layer being supported on the catalyst
support.
Effects of the Invention
[0019] The exhaust gas purification catalyst carrier, the exhaust
gas purification catalyst, and the exhaust gas purification
catalyst product according to the present invention exhibit
excellent exhaust gas purification performance (in particular, CO
removal performance) in a rich region, after long-term use thereof
under high-temperature conditions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] An XRD pattern of aluminum borate produced in Referential
Example 1.
MODES FOR CARRYING OUT THE INVENTION
[0021] The carrier employed in the exhaust gas purification
catalyst of the present invention comprises a modified aluminum
borate which contains at least one addition element selected from
the group consisting of a rare earth element and an alkaline earth
metal and has an electronegativity of 2.732 or lower.
Alternatively, the catalyst carrier comprises a modified aluminum
borate which contains aluminum borate and at least one addition
element selected from the group consisting of a rare earth element
and an alkaline earth metal, in an amount of 6 mass % or more as an
oxide thereof, preferably 7 mass % or more. When such a modified
aluminum borate is employed, an exhaust gas purification catalyst
containing Pd supported on the carrier exhibits excellent Pd
dispersion degree and catalytic activity in a rich region after
long-term use of the catalyst under high-temperature
conditions.
[0022] Preferably, the addition element contained in the modified
aluminum borate of the present invention is not a partial
substitution element with respect to boron or aluminum of aluminum
borate, but is supported on aluminum borate or modifies aluminum
borate. In the preferred case, the addition element is present as
an oxide or the like of the addition element such as a crystal
grain boundary. When such an addition element is analyzed through
XRD, no substantial shift is observed for the peak attributed to
aluminum borate, but a peak attributed to the addition element is
observed as, for example, a corresponding oxide peak.
[0023] Hereinafter, such aluminum borate species may also be
referred to collectively as modified aluminum borate.
[0024] The aforementioned aluminum borate species may be produced
through, for example, the following method.
<Solid-Phase Method>
[0025] Boric acid was weighed in such an amount that the
compositional proportions of a target compound, aluminum borate
(formula: Al.sub.20B.sub.4O.sub.36), were attained, and dissolved
in ion-exchange water. Subsequently, the solution was mixed with a
specifically weighed boehmite acetate sol, and the resultant
mixture was heated under stirring. The thus-formed gel was dried at
about 120.degree. C. for 12 hours or longer. After completion of
drying, the dried product was fired at about 300.degree. C. for
about one hour and then at about 1,000.degree. C. for about 5
hours, to thereby yield the target aluminum borate.
[0026] More specifically, boric acid was weighed in such an amount
that the compositional proportions of the target aluminum borate
(formula: Al.sub.20B.sub.4O.sub.36) were attained, and dissolved in
ion-exchange water. Subsequently, the solution was mixed with a
specifically weighed boehmite acetate sol, and the resultant
mixture was heated under stirring. The thus-formed gel was dried at
120.degree. C. for 12 hours or longer. After completion of drying,
the dried product was fired at 300.degree. C. for one hour and then
at 1,000.degree. C. for 5 hours, to thereby yield the target
aluminum borate.
<Reverse Co-Precipitation Method>
[0027] Boric acid was weighed in such an amount that the
compositional proportions of a target compound, aluminum borate
(formula: Al.sub.20B.sub.4O.sub.36), were attained, and dissolved
in hot pure water. Subsequently, the solution was mixed with a
specifically weighed aluminum nitrate, to thereby prepare a
solution. The solution was added dropwise to aqueous ammonium
carbonate. The thus-formed precipitates were washed with pure water
with filtration, and the solid was dried overnight at about
120.degree. C. and fired in air at about 300.degree. C. for about
one hour. Thereafter, the dried product was fired at about
1,000.degree. C. for about 5 hours, to thereby yield the target
aluminum borate.
[0028] More specifically, boric acid was weighed in such an amount
that the compositional proportions of the target aluminum borate
(formula: Al.sub.20B.sub.4O.sub.36) were attained, and dissolved in
ion-exchange water. Subsequently, the solution was mixed with a
specifically weighed aluminum nitrate nanohydrate, to thereby
prepare a solution. The solution was added dropwise to aqueous
ammonium carbonate. The thus-formed precipitates were washed with
pure water with filtration, and the solid was dried at 120.degree.
C. for 12 hours or longer and fired in air at 300.degree. C. for
one hour. Thereafter, the dried product was fired in air at
1,000.degree. C. for 5 hours, to thereby yield the target aluminum
borate. No significant difference was observed between the aluminum
borate prepared through the above reverse co-precipitation and that
prepared through the aforementioned solid-phase method.
[0029] The carrier of the exhaust gas purification catalyst of the
present invention contains a modified aluminum borate prepared by
modifying (or depositing) at least one element selected from the
group consisting of a rare earth element and an alkaline earth
metal with (or on) the above-produced aluminum borate.
[0030] In one mode of the method of producing such a modified
aluminum borate, aluminum borate was immersed in a solution
containing a specific amount of a compound of additional element
(e.g., a nitrate salt, a sulfate salt, or an acetate salt),
subjecting the mixture to evaporation to dryness, and firing the
solid at a specific temperature (e.g., 400 to 1,000.degree. C.)
[0031] The addition element content, reduced to the corresponding
oxide content; i.e., the ratio (amount of addition element
oxide)/(sum of amount of aluminum borate+amount of addition element
oxide) selected in the present invention, is 0.1 to 20 mass %,
preferably 3 to 15 mass %, more preferably 6 to 13 mass %, still
more preferably 7 to 13 mass %.
[0032] The modified aluminum borate has an electronegativity of
2.732 or lower, or contains at least one element selected from the
group consisting of a rare earth element and an alkaline earth
metal, in an amount of 6 mass % or more as an oxide thereof,
preferably 7 mass % or more. When the electronegativity is higher
than the above upper limit, the supported Pd component tends to be
undesirably stable PdO, whereby the catalyst becomes inert to
reduction of NOx or the like, which is not preferred. No particular
limitation is imposed on the lower limit of the electronegativity,
but the practical value thereof is conceivably about 2.700. Also,
when said at least one element selected from the group consisting
of a rare earth element and an alkaline earth metal is added as an
oxide in an amount of 7 mass % or more, electrons are sufficiently
supplied from noble metal elements to the carrier, whereby the
noble metal elements are immobilized on the carrier even in a rich
region, to thereby attain excellent Pd dispersion degree and
catalytic activity, even after long-term use thereof in a rich
region.
[0033] The exhaust gas purification catalyst of the present
invention contains Pd supported on a carrier containing the
aforementioned modified aluminum borate. By virtue of employing Pd
supported on the modified aluminum borate, the exhaust gas
purification catalyst exhibits excellent exhaust gas purification
performance (in particular, CO removal performance) in a rich
region, after long-term use thereof under high-temperature
conditions. The amount of Pd supported on the carrier is preferably
0.05 to 5 mass %, based on the mass of the carrier, more preferably
0.4 to 3 mass %. When the amount of supported Pd based on the mass
of the carrier is 0.05 mass % or more, durability of the catalyst
increases, and when the amount is 5 mass % or less, Pd can be
consistently supported in a highly dispersed state. In contrast,
when the amount of supported Pd based on the mass of the carrier is
less than 0.05 mass %, durability is poor due to a small absolute
amount of noble metal, and when the amount is in excess of 5 mass
%, supporting of Pd in a highly dispersion state may fail to be
attained due to an excess amount of noble metal. In the present
specification, the amount of supported Pd is reduced to the mass of
metallic Pd.
[0034] In one mode of production, the exhaust gas purification
catalyst of the present invention may be produced by mixing the
modified aluminum borate with a solution of a Pd compound (a
soluble Pd compound; e.g., Pd nitrate, Pd chloride, or Pd sulfate)
so that the amount of supported Pd based on the mass of the carrier
is adjusted to 0.2 to 3 mass %, and then subjecting the mixture to
evaporation to dryness and firing the dried product at 450 to
650.degree. C. Notably, in the specification and other attachments,
no particular limitation is imposed on the solvent for forming the
"solution," so long as the solvent can form the solution, and water
is generally used. Notably, so long as the effects of the present
invention are not impaired, the modified aluminum borate may be
used in combination with an additional carrier, such as a porous
body of a compound selected from the group consisting of silica,
ceria, ceria-zirconia, alumina, and titania.
[0035] The exhaust gas purification catalyst product of the present
invention includes a catalyst support formed of a ceramic or
metallic material, and a layer of the aforementioned exhaust gas
purification catalyst of the present invention, the layer being
formed and supported on the catalyst support. In such an exhaust
gas purification catalyst product, no particular limitation is
imposed on the shape of the catalyst support formed of a ceramic or
metallic material, and the support is generally in the form of
honeycomb, plate, pellet, etc. In the case of a honeycomb shape
support, the amount of exhaust gas purification catalyst supported
is preferably 70 to 300 g/L, more preferably 100 to 200 g/L. When
the catalyst amount is less than 70 g/L, durability of the catalyst
tends to decrease due to an insufficient catalyst amount. Examples
of the material of the catalyst support include ceramic materials
such as alumina (Al.sub.2O.sub.3), mullite
(3Al.sub.2O.sub.3-2SiO.sub.2), and cordierite
(2MgO-2Al.sub.2O.sub.3-5SiO.sub.2), and metallic materials such as
stainless steel.
[0036] The exhaust gas purification catalyst product of the present
invention may be produced through the following method. A modified
aluminum borate (50 to 70 parts by mass, preferably 50 to 60 parts
by mass), La-stabilized alumina (20 to 40 parts by mass, preferably
20 to 30 parts by mass), barium hydroxide (0 to 3 parts by mass,
preferably 1 to 3 parts by mass), and an alumina-bases binder (5 to
10 parts by mass) are mixed with a Pd compound solution, and the
mixture is pulverized under wet conditions, to thereby prepare a
slurry. The thus-prepared slurry is applied onto, through a widely
known technique, a catalyst support formed of a ceramic or metallic
material, preferably a honeycomb-shape catalyst support. The
resultant structure is dried and then fired at 450 to 650.degree.
C., to thereby produce an exhaust gas purification catalyst product
which includes a catalyst support, and a layer of the exhaust gas
purification catalyst, the layer being supported on the catalyst
support.
[0037] The present invention will next be described in detail by
way of Referential Examples, Examples, and Comparative Examples.
Notably, the addition element content is derived as the ratio of
amount of addition element oxide/total amount of aluminum borate
and addition element oxide. In Tables 1 to 3, 10A2B denotes
10Al.sub.2O.sub.3.2B.sub.2O.sub.3.
Referential Example 1
[0038] An aluminum borate (Al.sub.20B.sub.4O.sub.36) was prepared
through the following solid-phase method. Specifically, boric acid
was weighed in such an amount that the compositional proportions of
a target compound were attained, and dissolved in ion-exchange
water. Subsequently, the solution was mixed with a specifically
weighed boehmite acetate sol, and the resultant mixture was heated
under stirring. The thus-formed gel was dried at 120.degree. C. for
12 hours or longer. After completion of drying, the dried product
was fired in air at 300.degree. C. for one hour and then at
1,000.degree. C. for 5 hours, to thereby yield the aluminum borate
of interest. The aluminum borate was found to have an XRD pattern
shown in FIG. 1. As is clear from FIG. 1, the aluminum borate was
identified as an aluminum borate represented by formula
10Al.sub.2O.sub.3.2B.sub.2O.sub.3, through X-ray diffraction
analysis.
[0039] Notably, since the formula 9Al.sub.2O.sub.3.2B.sub.2O.sub.3
(Al.sub.18B.sub.4O.sub.33) is also given in an X-ray diffraction
standard chart, the yielded product was also identified as an
aluminum borate represented by formula
9Al.sub.2O.sub.3.2B.sub.2O.sub.3 (Al.sub.18B.sub.4O.sub.33).
Referential Example 2
[0040] An aluminum borate (Al.sub.20B.sub.4O.sub.36) was prepared
through a reverse co-precipitation method. Specifically, boric acid
was weighed in such an amount that the compositional proportions of
a target compound were attained, and dissolved in ion-exchange
water. Subsequently, the solution was mixed with a specifically
weighed aluminum nitrate nanohydrate, to thereby prepare a
solution. Then, the solution was added dropwise to aqueous ammonium
carbonate, to thereby form precipitates. The precipitates were
washed with pure water with filtration, and dried at 120.degree. C.
for 12 hours or longer, followed by firing in air at 300.degree. C.
for one hour and further in air at 1,000.degree. C. for 5 hours, to
thereby yield the aluminum borate of interest. No significant
difference was observed between the aluminum borate prepared
through the above co-precipitation and that prepared through the
solid-phase method of Referential Example 1.
Aluminum Borate Production Example 1
[0041] To a three-neck flask dipped in a hot water bath at
50.degree. C., 2-propanol (1.5 L), aluminum isopropoxide (200 g)
pulverized by means of an agate mortar, and boron n-propoxide (40.9
g) were added, and the mixture was stirred under a flow of nitrogen
gas. After complete dissolution of aluminum isopropoxide
(confirmation of transparency of the solution), a mixture (24.6 g)
of 2-propanol:water=1:1 was gradually added dropwise to the
solution for hydrolysis, to thereby form a white gel substance. The
thus-formed precipitates were washed sequentially with ethanol and
pure water, followed by filtration. Thereafter, the solid was dried
overnight (for about 15 hours) at 120.degree. C., and fired in air
at 300.degree. C. for 3 hours and further in air at 1,000.degree.
C. for 5 hours, to thereby yield an aluminum borate as a white
product. Through X-ray diffractometry, this aluminum borate was
identified as an aluminum borate represented by formula
10Al.sub.2O.sub.3.2B.sub.2O.sub.3.
Example 1
[0042] The aluminum borate produced in Production Example 1 was
immersed in aqueous lanthanum nitrate and in aqueous strontium
nitrate. The amount of lanthanum nitrate in the aqueous solution
and that of the strontium nitrate in the aqueous solution were
adjusted such that the La.sub.2O.sub.3 content and the SrO content
of the aluminum borate represented by
10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified with target
La.sub.2O.sub.3 and SrO were attained as 5 mass % and 5 mass %,
respectively. Thereafter, the mixture was dried overnight (for
about 15 hours) at 120.degree. C. to dryness, and then fired in air
at 600.degree. C. for 3 hours, to thereby yield an aluminum borate
represented by 10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified with
La.sub.2O.sub.3 and SrO at 5 mass % and 5 mass %, respectively.
[0043] To the aluminum borate (99 parts by mass) represented by
10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified with La.sub.2O.sub.3 and
SrO at 5 mass % and 5 mass %, and palladium nitrate (1 part by
mass, as reduced to Pd metal), an appropriate amount of
ion-exchange water was added, and the resultant slurry was stirred,
dried, and fired at 500.degree. C. for one hour.
Example 2
[0044] The aluminum borate produced in Production Example 1 was
immersed in aqueous lanthanum nitrate and in aqueous praseodymium
nitrate. The amount of lanthanum nitrate in the aqueous solution
thereof and that of praseodymium nitrate in its aqueous solution
were adjusted such that the La.sub.2O.sub.3 content and the
Pr.sub.6O.sub.11 content of the aluminum borate represented by
10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified with target
La.sub.2O.sub.3 and Pr.sub.6O.sub.11 were attained as 5 mass % and
5 mass %, respectively. Thereafter, the mixture was dried overnight
(for about 15 hours) at 120.degree. C. to dryness, and then fired
in air at 600.degree. C. for 3 hours, to thereby yield an aluminum
borate represented by 10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified
with La.sub.2O.sub.3 and Pr.sub.6O.sub.11 at 5 mass % and 5 mass %,
respectively.
[0045] To the aluminum borate (99 parts by mass) represented by
10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified with La.sub.2O.sub.3 and
Pr.sub.6O.sub.11 at 5 mass % and 5 mass %, and palladium nitrate (1
part by mass, as reduced to Pd metal), an appropriate amount of
ion-exchange water was added, and the resultant slurry was stirred,
dried, and fired at 500.degree. C. for one hour.
Example 3
[0046] The aluminum borate produced in Production Example 1 was
immersed in aqueous lanthanum nitrate and in aqueous calcium
nitrate. The amount of lanthanum nitrate in the aqueous solution
and that of the calcium nitrate in its aqueous solution were
adjusted such that the La.sub.2O.sub.3 content and the CaO content
of the aluminum borate represented by
10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified with target
La.sub.2O.sub.3 and CaO were attained as 5 mass % and 5 mass %,
respectively. Thereafter, the mixture was dried overnight (for
about 15 hours) at 120.degree. C. to dryness, and then fired in air
at 600.degree. C. for 3 hours, to thereby yield an aluminum borate
represented by 10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified with
La.sub.2O.sub.3 and CaO at 5 mass % and 5 mass %, respectively. To
the aluminum borate (99 parts by mass) represented by
10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified with La.sub.2O.sub.3 and
CaO at 5 mass % and 5 mass %, and palladium nitrate (1 part by
mass, as reduced to Pd metal), an appropriate amount of
ion-exchange water was added, and the resultant slurry was stirred,
dried, and fired at 500.degree. C. for one hour.
Example 4
[0047] The aluminum borate produced in Production Example 1 was
immersed in aqueous lanthanum nitrate and in aqueous barium
nitrate. The amount of lanthanum nitrate in the aqueous solution
and that of the barium nitrate in its aqueous solution were
adjusted such that the La.sub.2O.sub.3 content and the BaO content
of the aluminum borate represented by
10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified with La.sub.2O.sub.3 and
BaO were attained as 5 mass % and 5 mass %, respectively.
Thereafter, the mixture was dried overnight (for about 15 hours) at
120.degree. C. to dryness, and then fired in air at 600.degree. C.
for 3 hours, to thereby yield an aluminum borate represented by
10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified with La.sub.2O.sub.3 and
BaO at 5 mass % and 5 mass %, respectively.
[0048] To the aluminum borate (99 parts by mass) represented by
10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified with La.sub.2O.sub.3 and
BaO at 5 mass % and 5 mass %, and palladium nitrate (1 part by
mass, as reduced to Pd metal), an appropriate amount of
ion-exchange water was added, and the resultant slurry was stirred,
dried, and fired at 500.degree. C. for one hour.
Example 5
[0049] The aluminum borate produced in Production Example 1 was
immersed in aqueous lanthanum nitrate and in aqueous neodymium
nitrate. The amount of lanthanum nitrate in the aqueous solution
and that of the neodymium nitrate in its aqueous solution were
adjusted such that the La.sub.2O.sub.3 content and the
Nd.sub.2O.sub.3 content of the aluminum borate represented by
10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified with target
La.sub.2O.sub.3 and Nd.sub.2O.sub.3 were attained as 5 mass % and 5
mass %, respectively. Thereafter, the mixture was dried overnight
(for about 15 hours) at 120.degree. C. to dryness, and then fired
in air at 600.degree. C. for 3 hours, to thereby yield an aluminum
borate represented by 10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified
with La.sub.2O.sub.3 and Nd.sub.2O.sub.3 at 5 mass % and 5 mass %,
respectively.
[0050] To the aluminum borate (99 parts by mass) represented by
10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified with La.sub.2O.sub.3 and
Nd.sub.2O.sub.3 at 5 mass % and 5 mass %, and palladium nitrate (1
part by mass, as reduced to Pd metal), an appropriate amount of
ion-exchange water was added, and the resultant slurry was stirred,
dried, and fired at 500.degree. C. for one hour.
Example 6
[0051] The aluminum borate produced in Production Example 1 was
immersed in aqueous lanthanum nitrate and in aqueous cerium
nitrate. The amount of lanthanum nitrate in the aqueous solution
and that of the cerium nitrate in its aqueous solution were
adjusted such that the La.sub.2O.sub.3 content and the CeO.sub.2
content of the aluminum borate represented by
10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified with target
La.sub.2O.sub.3 and CeO.sub.2 were attained as 5 mass % and 5 mass
%, respectively. Thereafter, the mixture was dried overnight (for
about 15 hours) at 120.degree. C. to dryness, and then fired in air
at 600.degree. C. for 3 hours, to thereby yield an aluminum borate
represented by 10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified with
La.sub.2O.sub.3 and CeO.sub.2 at 5 mass % and 5 mass %,
respectively.
[0052] To the aluminum borate (99 parts by mass) represented by
10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified with La.sub.2O.sub.3 and
CeO.sub.2 at 5 mass % and 5 mass %, and palladium nitrate (1 part
by mass, as reduced to Pd metal), an appropriate amount of
ion-exchange water was added, and the resultant slurry was stirred,
dried, and fired at 500.degree. C. for one hour.
Comparative Example 1
[0053] .gamma.-Al.sub.2O.sub.3 (99 parts by mass) and palladium
nitrate (1 part by mass, as reduced to metallic Pd) were added to
an appropriate amount of ion-exchange water, and the resultant
slurry was stirred. Then, the slurry was dried and fired at
500.degree. C. for one hour.
Comparative Example 2
[0054] The aluminum borate produced in Production Example 1 was
immersed in aqueous lanthanum nitrate. The amount of lanthanum
nitrate in the aqueous solution was adjusted such that the
La.sub.2O.sub.3 content of the aluminum borate represented by
10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified with target
La.sub.2O.sub.3 was attained as 5 mass %. Thereafter, the mixture
was dried overnight (for about 15 hours) at 120.degree. C. to
dryness, and then fired in air at 600.degree. C. for 3 hours, to
thereby yield an aluminum borate represented by
10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified with La.sub.2O.sub.3 at
5 mass %.
[0055] To the aluminum borate (99 parts by mass) represented by
10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified with La.sub.2O.sub.3 at
5 mass %, and palladium nitrate (1 part by mass, as reduced to Pd
metal), an appropriate amount of ion-exchange water was added, and
the resultant slurry was stirred, dried, and fired at 500.degree.
C. for one hour.
Comparative Example 3
[0056] The aluminum borate produced in Production Example 1 was
immersed in aqueous lanthanum nitrate and in aqueous barium
nitrate. The amount of lanthanum nitrate in the aqueous solution
thereof and that of the barium nitrate in its aqueous solution were
adjusted such that the La.sub.2O.sub.3 content and the BaO content
of the aluminum borate represented by
10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified with target
La.sub.2O.sub.3 and BaO were attained as 1 mass % and 2 mass %,
respectively. Thereafter, the mixture was dried overnight (for
about 15 hours) at 120.degree. C. to dryness, and then fired in air
at 600.degree. C. for 3 hours, to thereby yield an aluminum borate
represented by 10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified with
La.sub.2O.sub.3 and BaO at 1 mass % and 2 mass %, respectively.
[0057] To the aluminum borate (99 parts by mass) represented by
10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified with La.sub.2O.sub.3 and
BaO at 1 mass % and 2 mass %, and palladium nitrate (1 part by
mass, as reduced to Pd metal), an appropriate amount of
ion-exchange water was added, and the resultant slurry was stirred,
dried, and fired at 500.degree. C. for one hour.
<Catalytic Performance Evaluation Method>
[0058] Each of the samples produced in the Examples and Comparative
Examples was assessed in terms of purification performance with
respect to a simulated exhaust gas, by means of an immobilized bed
flow-type reactor. Each catalyst powder (50 mg) was placed in the
reactor tube, and a gas which simulated a complete combustion gas
and which was composed of NO (.05%), CO (.39%), C.sub.3H.sub.6
(1,200 ppmC), O.sub.2 (.4%), H.sub.2 (.1%), and H.sub.2O (10%), the
balance being N.sub.2, was fed to the catalyst powder at a total
flow rate of 1,000 cc/min. The reactor tube was heated to
500.degree. C. at a temperature elevation rate of 10.degree.
C./min, and maintained at 500.degree. C. for 10 minutes, for
carrying out a preliminary treatment. Subsequently, the reactor
tube was cooled, and heated again from 100.degree. C. to
500.degree. C. at 10.degree. C./min.
[0059] The outlet gas composition was determined by means of a
CO/NO analyzer (model: PG240, product of Horiba) and an HC analyzer
(model: VMF-1000F, product of Shimadzu Corporation).
[0060] Each catalyst was aged at 900.degree. C. and 25H in a rich
region of A/F=14.0 (H.sub.2O=10%).
<Pd Dispersion Degree Evaluation Method>
[0061] The degree of Pd dispersion was measured according to the CO
pulse adsorption method (i.e., a known technique) (T. Takeguchi, S.
Manabe, R. Kikuchi, K. Eguchi, T. Kanazawa, S. Matsumoto, Applied
Catalysis A: 293 (2005) 91). The degree of Pd dispersion was
calculated by the following formula: degree of Pd dispersion=the
amount (by mole) of Pd corresponding to the amount of CO
adsorbed/the total amount (by mole) of Pd contained in the catalyst
of interest.
<Catalytic Performance Evaluation Results>
[0062] Table 1 shows the values of the temperature (T50) at which
50% removal of NO and HC was completed in the presence of each
catalyst after aging, and the temperature (T70) at which 70%
removal of CO was completed in the presence of the catalyst. As is
clear from Table 1, the catalyst samples of the Examples exhibited
more excellent low-temperature catalytic activity, as compared with
those of the Comparative Examples. Among three components, CO
removal performance was remarkably excellent.
TABLE-US-00001 TABLE 1 Carrier composition NO-T50 HC-T50 CO-T70
Comp. .gamma.-Al.sub.2O.sub.3 392.2 360.2 374.1 Ex. 1 Comp. 5 wt. %
La.sub.2O.sub.3/10A2B 375.5 355.5 373.1 Ex. 2 Comp. (1 wt. %
La.sub.2O.sub.3 + 371.5 353.7 372.1 Ex. 3 2 wt. % BaO)/10A2B Ex. 1
(5 wt. % La.sub.2O.sub.3 + 371.3 352.9 365.8 5 wt. % SrO)/10A2B Ex.
2 (5 wt. % La.sub.2O.sub.3 + 357.6 336.1 347.3 5 wt. %
Pr.sub.6O.sub.11)/10A2B Ex. 3 (5 wt. % La.sub.2O.sub.3 + 365.2
344.3 357.3 5 wt. % CaO)/10A2B Ex. 4 (5 wt. % La.sub.2O.sub.3 +
371.3 353.8 365.9 5 wt. % BaO)/10A2B Ex. 5 (5 wt. % La.sub.2O.sub.3
+ 371.3 352.5 365.5 5 wt. % Nd.sub.2O.sub.3)/10A2B Ex. 6 (5 wt. %
La.sub.2O.sub.3 + 362.5 341.0 353.2 5 wt. % CeO.sub.2)/10A2B
[0063] Table 2 shows Pd dispersion degrees of the tested catalyst
after aging. As is clear from Table 2, Pd dispersion degree of the
catalysts of the Examples was higher than that of the Comparative
Examples.
TABLE-US-00002 TABLE 2 Pd dispersion Carrier composition degree
Comp. Ex. 1 .gamma.-Al.sub.2O.sub.3 2.79% Comp. Ex. 2 5 wt. %
La.sub.2O.sub.3/10A2B 3.24% Comp. Ex. 3 (1 wt. % La.sub.2O.sub.3 +
2 wt. % BaO)/10A2B 3.44% Ex. 1 (5 wt. % La.sub.2O.sub.3 + 5 wt. %
SrO)/10A2B 3.68% Ex. 2 (5 wt. % La.sub.2O.sub.3 + 5 wt. %
Pr.sub.6O.sub.11)/10A2B 4.77% Ex. 3 (5 wt. % La.sub.2O.sub.3 + 5
wt. % CaO)/10A2B 4.56% Ex. 4 (5 wt. % La.sub.2O.sub.3 + 5 wt. %
BaO)/10A2B 3.80% Ex. 5 (5 wt. % La.sub.2O.sub.3 + 5 wt. %
Nd.sub.2O.sub.3)/10A2B 5.04% Ex. 6 (5 wt. % La.sub.2O.sub.3 + 5 wt.
% CeO.sub.2)/10A2B 5.11%
[0064] Table 3 shows electronegativity values of the carriers. The
electronegativity was a weighted average of the electronegativity
(Pauling's electronegativity) of a metal or metals forming the
corresponding metal oxide and that of oxygen, based on the
compositional proportions of the elements contained in the metal
oxide. As shown in Table 3, aluminum borate serves as an acidic
carrier having an electronegativity higher than that of
Al.sub.2O.sub.3. In the case where aluminum borate is modified with
an electron-accepting element such as an alkaline earth metal
element or a rare earth metal element, conceivably, electrons are
supplied from noble metal elements to the carrier, whereby the
noble metal elements are immobilized on the carrier even in a rich
region. Also, presumably, the electronegativity of the carrier
decreases to be almost a neutral electronegativity, which is
equivalent to that of Al.sub.2O.sub.3, to thereby attain excellent
reactivity (e.g., inhibition of adsorption of exhaust gas
components). Thus, as is clear from Tables 1 and 2, Pd dispersion
degree and component (in particular, CO) removal reactivity at low
temperature are conceivably enhanced, by virtue of the above
effects. The electronegativity of the carrier was found to be
preferably 2.732 or lower. Also, when the amount of an oxide
modifying aluminum borate is adjusted to 7 mass % or more,
purification performance and Pd dispersibility can be enhanced. In
comparison of Comparative Example 2 with Example 6, even though the
electronegativity values of two carriers are almost the same,
catalytic activity is remarkably higher in Example 6. Thus,
aluminum borate is preferably modified with two or more
elements.
[0065] Notably, electronegativity can be derived through the
following calculation.
[0066] In the case of Comparative Example 2, the ratio by mass of
La.sub.2O.sub.3:10Al.sub.2O.sub.3.2B.sub.2O.sub.3 in
10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified with 5 mass %
La.sub.2O.sub.3 is 5:95. When 5 mass % La.sub.2O.sub.3 is reduced
to the corresponding mol % value, the value is 18.72 mol % with
respect to that of 10Al.sub.2O.sub.3.2B.sub.2O.sub.3 taken as 100
mol %. Pauling's electronegativity values of the elements forming
the oxide are as follows: La=1.1, O=3.44, B=2.04, and Al=1.61.
Thus, the weighted average is as follows:
{18.72%.times.(2.times.1.1+3.times.3.44)+(20.times.1.61+4.times.2.04+36.t-
imes.3.44)}/(18.72%.times.5+60)=2.733.
TABLE-US-00003 TABLE 3 Electronegativity Material of carrier Comp.
Ex. 1 Al.sub.2O.sub.3 2.708 -- 10A2B 2.737 Comp. Ex. 2 5 wt. %
La.sub.2O.sub.3/10A2B 2.733 Comp. Ex. 3 (1 wt. % La.sub.2O.sub.3 +
2 wt. % BaO)/10A2B 2.733 Ex. 1 (5 wt. % La.sub.2O.sub.3 + 5 wt. %
SrO)/10A2B 2.722 Ex. 2 (5 wt. % La.sub.2O.sub.3 + 5 wt. %
Pr.sub.6O.sub.11)/10A2B 2.731 Ex. 3 (5 wt. % La.sub.2O.sub.3 + 5
wt. % CaO)/10A2B 2.714 Ex. 4 (5 wt. % La.sub.2O.sub.3 + 5 wt. %
BaO)/10A2B 2.725 Ex. 5 (5 wt. % La.sub.2O.sub.3 + 5 wt. %
Nd.sub.2O.sub.3)/10A2B 2.730 Ex. 6 (5 wt. % La.sub.2O.sub.3 + 5 wt.
% CeO.sub.2)/10A2B 2.732
* * * * *