U.S. patent application number 14/317740 was filed with the patent office on 2014-10-16 for exhaust purification system.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. The applicant listed for this patent is Hirohito HIRATA, Muriel LEPAGE, Mayuko OSAKI. Invention is credited to Hirohito HIRATA, Muriel LEPAGE, Mayuko OSAKI.
Application Number | 20140305105 14/317740 |
Document ID | / |
Family ID | 44627902 |
Filed Date | 2014-10-16 |
United States Patent
Application |
20140305105 |
Kind Code |
A1 |
OSAKI; Mayuko ; et
al. |
October 16, 2014 |
EXHAUST PURIFICATION SYSTEM
Abstract
An exhaust gas purification system provided with an NO.sub.X
purification catalyst reducing the amount of use of precious metals
and/or able to exhibit an NO.sub.X purification performance at a
low temperature and/or in an oxidizing atmosphere and having an
NO.sub.X purification performance even for an exhaust gas
composition containing hydrocarbons and oxygen together with a low
temperature and/or oxidizing atmosphere, that is, an exhaust gas
purification system provided with an NO.sub.X purification catalyst
provided in an exhaust gas passage and comprised of carrier
particles on which nanoparticles in which gold atoms and nickel
atoms are included in a state in close proximity are carried and an
oxidation catalyst oxidizing hydrocarbons in exhaust gas at a
position at an upstream side of the NO.sub.X purification
catalyst.
Inventors: |
OSAKI; Mayuko; (Toyota-shi,
JP) ; HIRATA; Hirohito; (Toyota-shi, JP) ;
LEPAGE; Muriel; (Brussels, BE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
OSAKI; Mayuko
HIRATA; Hirohito
LEPAGE; Muriel |
Toyota-shi
Toyota-shi
Brussels |
|
JP
JP
BE |
|
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi
JP
|
Family ID: |
44627902 |
Appl. No.: |
14/317740 |
Filed: |
June 27, 2014 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
14118430 |
|
|
|
|
PCT/JP2011/062315 |
May 24, 2011 |
|
|
|
14317740 |
|
|
|
|
Current U.S.
Class: |
60/299 |
Current CPC
Class: |
B01D 53/9413 20130101;
Y02T 10/12 20130101; B01J 23/892 20130101; B01D 53/9459 20130101;
Y02A 50/20 20180101; B01D 53/9486 20130101; F01N 3/103 20130101;
B01D 53/944 20130101; B01D 2255/106 20130101; Y02T 10/20 20130101;
F01N 2570/14 20130101; B01J 35/006 20130101; F01N 3/0835 20130101;
B01J 35/0013 20130101; B01D 53/9477 20130101; B01D 2255/9202
20130101; F01N 3/2066 20130101; Y02A 50/2344 20180101; B01D 53/945
20130101; B01D 2255/20753 20130101; B01J 37/0211 20130101; Y02T
10/22 20130101 |
Class at
Publication: |
60/299 |
International
Class: |
F01N 3/20 20060101
F01N003/20 |
Claims
1-5. (canceled)
6. A exhaust purification system provided with an NO.sub.x
purification catalyst provided in an exhaust gas passage and
comprised of carrier particles on which nanoparticles of an alloy
of gold atoms and nickel atoms in a state in close proximity are
carried and an oxidation catalyst oxidizing hydrocarbons in exhaust
gas at a position at an upstream side of the NO.sub.x purification
catalyst.
7. An exhaust gas purification system as set forth in claim 6,
wherein the nanoparticles have a size of 0.2 to 100 nm.
8. An exhaust gas purification system as set forth in claim 6,
wherein the carrier particles are metal oxide particles.
9. An exhaust gas purification system as set forth in claim 6,
further provided with a hydrocarbon absorbent that absorbs
hydrocarbons in the exhaust gas at a position in the exhaust gas at
a position in the exhaust gas passage at a further upstream side
from the oxidation catalyst.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of U.S. application Ser.
No. 14/118,430 filed Nov. 18, 2013, which is a National Stage of
International Application No. PCT/JP2011/062315 filed May 24, 2011,
the contents of which are incorporated herein by reference in their
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an exhaust purification
system provided with a nitrogen oxide (below, sometimes abbreviated
as "NO.sub.X") purification catalyst, more particularly relates to
an exhaust gas purification system having an NO.sub.X purification
performance even for an exhaust gas composition including
hydrocarbons (below, sometimes abbreviated as "HC") and oxygen
(below, sometimes abbreviated as "O.sub.2").
[0004] 2. Description of the Related Art
[0005] In recent years, from the viewpoint of protection of the
global environment, exhaust gas regulations have been toughened
around the world with each passing year. As one means for dealing
with this, in internal combustion engines, exhaust gas purification
catalysts are being used. In such exhaust gas purification
catalysts, to efficiently remove HC (hydrocarbons), carbon monoxide
(CO), and NO.sub.X in the exhaust gas, as catalyst ingredients,
platinum, palladium, rhodium, and other precious metals are being
used. In motor vehicles using such purification catalysts, for
example, gasoline engine vehicles and diesel engine vehicles,
various systems are being used to improve the catalytic activity
and the fuel economy. For example, for improving fuel economy,
during steady state operation, fuel is being burned under
conditions of a lean (excess oxygen) air-fuel ratio (A/F), while to
improve the catalytic activity, fuel is being burned under
temporarily stoichiometric (stoichiometric air-fuel ratio,
A/F=14.7) to rich (excess fuel) conditions.
[0006] This is because conventionally known platinum, palladium,
rhodium, and other precious metal catalysts have low NO.sub.X
purification performances at low temperature and oxidizing
conditions. To improve the purification performance, the
purification catalyst has to be made high in temperature and HC or
CO etc. has to be added to establish a reducing atmosphere. Due to
the effects on the catalytic activity, even during steady state
operation, it is not possible to increase the air-fuel ratio (A/F).
With the above precious metal catalysts, there is therefore a limit
to the improvement of the fuel economy. In such conventionally
known precious metal catalysts, to obtain good purification
performance, energy for raising the purification catalysts to a
high temperature, fuel for temporarily making the purification
catalysts a reducing atmosphere, and reduction of the air-fuel
ratio (A/F) at the engine become necessary. To improve the fuel
economy in automobile engines and other internal combustion
engines, therefore, a new purification catalyst able to exhibit a
good NO.sub.X purification performance at a low temperature and/or
oxidizing atmosphere is being sought. On the other hand, all of the
above precious metal catalysts face the problem of resource
depletion. Catalysts using other metals to obtain purification
performances equal to or better than those of conventional precious
metal catalysts or exhaust purification catalysts able to reduce
the amounts of the precious metals used are therefore being
sought.
For this reason, various improvements are being experimented with
for purification catalysts.
[0007] For example, Japanese Patent Publication (A) No. 10-216518
describes a gold alloy catalyst comprised of gold and one or more
metals (M) selected from platinum, palladium, silver, copper, and
nickel, having a weight ratio Au/M of 1/9 to 9/1, and having an
amount of solute gold in the alloy of 20 to 80 wt %. Further, the
catalysts shown as specific examples in this publication are
catalysts carrying a gold alloy of gold and a metal of palladium or
platinum on an Al.sub.2O.sub.3 carrier. These exhibit a high
NO.sub.X purification performance in a reducing atmosphere, but
have a low NO.sub.X purification performance at a low temperature
and/or oxidizing atmosphere.
[0008] Further, Japanese Patent Publication (A) No. 10-216519
describes a low temperature toxic gas purifying catalyst comprised
of a carrier of a metal oxide or carbonaceous material on which
ultrafine particles of at least one type of metal selected from
platinum, palladium, rhodium, ruthenium, iridium, osmium, gold,
silver, copper, magnesium, iron, and nickel is carried by using a
high temperature high pressure fluid. Further, the catalysts shown
as specific examples in this publication are purification catalysts
carrying at least one type of element of platinum, palladium,
rhodium, ruthenium, nickel, nickel, or gold. They exhibit an
NO.sub.X purification performance in a reducing atmosphere.
[0009] As related art, therefore, there are the above Japanese
Patent Publication (A) No. 10-216518 and Japanese Patent
Publication (A) No. 2001-239161.
SUMMARY OF THE INVENTION
[0010] Therefore, with exhaust gas purification systems provided
with these known NO.sub.X purification catalysts, it was difficult
to reduce the amount of precious metal used and obtain good
NO.sub.X purification performance at a low temperature and/or in an
oxidizing atmosphere. This is because the NO.sub.X reaction
activity of the NO.sub.X purification catalyst is affected by the
composition of the exhaust gas. Therefore, an object of the present
invention is to provide an exhaust gas purification system provided
with an NO.sub.X purification catalyst reducing the amount of the
precious metals used and able to give an NO.sub.X purification
performance at a low temperature and/or in an oxidizing atmosphere
and having an NO.sub.X purification performance even with an
exhaust gas composition including an HC and O.sub.2.
[0011] The present invention relates to an exhaust gas purification
system provided with an NO.sub.X purification catalyst provided in
an exhaust gas passage and comprised of carrier particles on which
nanoparticles in which gold atoms and nickel atoms are included in
close proximity are carried and an oxidation catalyst oxidizing the
HC in the exhaust gas at a position at an upstream side of the
NO.sub.X purification catalyst.
[0012] Summarizing the effects of the invention, according to the
present invention, it is possible to provide a system provided with
an NO.sub.X purification catalyst reducing the amount of use of
precious metals and able to exhibit a good NO.sub.X purification
performance at a low temperature and/or in an oxidizing atmosphere
and having an NO.sub.X purification performance even for an exhaust
gas composition including an HC and O.sub.2 together with a low
temperature and/or an oxidizing atmosphere.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] These and other objects and features of the present
invention will become clearer from the following description of the
preferred embodiments given with reference to the attached
drawings, wherein:
[0014] FIG. 1 is a graph showing a comparison of the NO
purification characteristics of NO.sub.X purification catalysts
obtained in a reference example and comparative examples;
[0015] FIG. 2 is a graph showing a comparison of the NO
purification characteristics of NO.sub.X purification catalysts
obtained in a reference invention example for exhaust gas of
various types of gas compositions;
[0016] FIG. 3 is a schematic view showing an exhaust gas
purification system of an example of the present invention;
[0017] FIG. 4 is a schematic view showing an exhaust gas
purification system of another example of the present invention;
and
[0018] FIG. 5 is a schematic view of an exhaust gas purification
system outside the scope of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] In the present invention, the exhaust gas purification
system has to be provided with an NO.sub.X purification catalyst
provided in an exhaust gas passage and comprising carrier particles
on which nanoparticles in which gold atoms and nickel atoms are
included in a state in close proximity are carried and an oxidation
catalyst oxidizing the HC in the exhaust gas at a position at an
upstream side of the NO.sub.X purification catalyst. Due to this,
it is possible to reduce the amount of use of the precious metals,
provide an NO.sub.X purification catalyst able to exhibit an
NO.sub.X purification performance at a low temperature and/or in an
oxidizing atmosphere, and obtain an NO.sub.X purification
performance even with an exhaust gas composition containing HC and
O.sub.2 such as at the time of a non-steady state operation.
[0020] Below, embodiments of the present invention will be
explained with reference to the drawings. Referring to FIG. 1, it
is shown that the NO.sub.X purification catalyst comprised of
carrier particles on which nanoparticles in which gold atoms and
nickel atoms are included in a state in close proximity are carried
according to an embodiment of present invention exhibits an NO-CO
catalytic activity in a 300 to 500.degree. C. temperature range
compared with NO.sub.X purification catalysts outside the scope of
the present invention comprised of carrier particles on which
nickel alone or gold alone is carried and has a particularly high
NO-13 CO catalytic activity at a temperature of about 425 to
500.degree. C. Further, with a simple mixture where, even when
using gold and nickel together, the gold atoms and the nickel atoms
are not included in a state of close proximity, the NO-13 CO
catalytic activity at 500.degree. C. conversely becomes lower than
a case of nickel alone.
[0021] Referring to FIG. 2, if using the NO.sub.X purification
catalyst of the present invention to treat exhaust gas of various
gas compositions, compared with the NO--CO gas composition of curve
1, in an about 425 to 500.degree. C. temperature range, with the
NO--CO--O.sub.2--C.sub.3H.sub.6 exhaust gas composition of curve 2
and the NO--CO--C.sub.3H.sub.3 exhaust gas composition curve 3, in
particular the NO--CO--O.sub.2--C.sub.3H.sub.6 exhaust gas
composition of curve 2, the NO purification rate falls. Further,
with the NO--CO--O.sub.2 exhaust gas composition of curve 4, the
NO--CO--CO.sub.2 exhaust gas composition of curve 5, and the
NO--CO--H.sub.2O exhaust gas composition of curve 6, the NO
purification rate is somewhat low, but a high NO purification rate
is still achieved. That is, from FIG. 2, it will be understood that
the NO.sub.X purification catalyst in the present invention greatly
falls in NO purification activity with exhaust gas compositions in
which the HC ingredient C.sub.3H.sub.6 is copresent with O.sub.2
but is high in NO purification activity in gas compositions not
containing C.sub.3H.sub.6.
[0022] The present invention was made based on the above discovery.
The exhaust gas purification system 1 of an embodiment of the
present invention, as shown FIG. 3, is provided with an NO.sub.X
purification catalyst 5 provided downstream of an A/F meter 4 of an
exhaust gas passage 3 from an engine 2 and comprised of carrier
particles on which nanoparticles in which gold atoms and nickel
atoms are included in a state in close proximity are carried and an
oxidation catalyst 6 oxidizing the HC in the exhaust gas at a
position at an upstream side of the NO.sub.X purification catalyst
5.
[0023] Further, the exhaust gas purification system 1 of another
embodiment of the present invention, as shown in FIG. 4, is further
provided with an NO.sub.X purification catalyst 5 provided
downstream of an A/F meter 4 of an exhaust gas passage from an
engine 2, an oxidation catalyst 6 oxidizing HC in exhaust gas at a
position at an upstream side of the NO.sub.X purification catalyst
5, and an HC adsorbent 7 adsorbing the HC in the exhaust gas at a
position at a further upstream side from the oxidation catalyst 6
of the exhaust gas passage 3. In the exhaust gas purification
system 1 which is shown in FIG. 4, the oxidation catalyst 6 and the
HC absorbent 7 can be combined into a single brick catalyst.
[0024] Further, according to the exhaust gas purification system 1
shown in an embodiment of the present invention, even if exhaust
gas exhausted from the engine is an exhaust gas composition
containing an HC such as at the time of a non-steady state
operation, the HC is removed by oxidation by the catalytic action
of the oxidation catalyst 6, so the exhaust gas composition
introduced into the NO.sub.X purification catalyst does not contain
HC and O.sub.2 together such as like with curve 4, curve 5, or
curve 6 in FIG. 2 and therefore the NO.sub.X purification catalyst
5 can have a high NO.sub.X purification performance.
[0025] According to the exhaust gas purification system 1 shown in
FIG. 4 of the embodiment of the present invention, even when the
temperature is low and the oxidation catalyst 6 is low in catalytic
activity, the HC adsorbent 7 adsorbs the HC, so until the oxidation
catalyst 6 rises in catalytic activity, the composition of the
exhaust gas introduced into the NO.sub.X purification catalyst will
be an exhaust gas composition not containing an HC and therefore
the NO.sub.X purification catalyst 5 can have a high NO.sub.X
purification performance. In this way, even when the temperature is
low, when the temperature rises due to engine operation, the HC
which had been adsorbed at the HC adsorbent 7 is oxidized by the
oxidation catalyst 6 improved in activity due to the temperature
rise, CO.sub.2 and H.sub.2O are produced and removed, the
composition of the exhaust gas introduced into the NO.sub.X
purification catalyst does not contain HC and O.sub.2 together, and
the NO.sub.X purification catalyst 5 can have a high NO.sub.X
purification performance. Note that, in the exhaust gas
purification system 1 of the present invention, the HC adsorbent is
not an essential component. For example, it is possible to find the
temperature of the oxidation catalyst by a thermocouple (not
shown), A/F meter, etc. and, when the oxidation catalyst for
oxidation of the HC is low in temperature and it is predicted that
it cannot sufficiently exhibit its oxidation performance, control
the system to the lean side so as not to discharge unburned HC from
the engine. Note that, while not illustrated in FIG. 3 and FIG. 4,
an NO.sub.X sensor can be provided downstream of the NO.sub.X
purification catalyst 5.
[0026] As opposed to this, the exhaust gas purification system 1
outside the scope of the present invention, as shown in FIG. 5, is
provided with only a purification catalyst 5 provided downstream of
the A/F meter 4 of the exhaust gas passage 3 from the engine 2.
Further, according to the exhaust gas purification system outside
the scope of the present invention shown in FIG. 5, in the case of
the NO--CO--O.sub.2--C.sub.3H.sub.6 exhaust gas composition of the
curve 2 in FIG. 2, the NO purification efficiently ends up falling
sharply. That is, according to the exhaust gas purification system
outside the scope of the present invention shown in FIG. 5, with an
exhaust gas composition including HC and O.sub.2 such as at the
time of a non-steady operation, sometimes the NO.sub.X purification
performance is low. As the reason for the low NO.sub.X purification
performance of the NO.sub.X purification catalyst with an exhaust
gas composition containing HC and O.sub.2 copresent in the
following way, the reaction of the C.sub.3H.sub.6 and O.sub.2,
production of carbonyl, and inhibition of the NO reaction ability
of the NO.sub.X purification catalyst, etc. may be considered.
[0027] The NO.sub.X purification catalyst of the present invention,
in the above way, is comprised of carrier particles on which
nanoparticles in which gold atoms and nickel atoms are included in
a state in close proximity are carried. For this reason, other
metal atoms able to alloy with the two atoms may be contained at
the parts where the two atoms are in close proximity, but inert
substances unable to alloy with the two atoms can be included only
in a range where the state in which the two atoms are in close
proximity can be secured. Therefore, the NO.sub.X purification
catalyst in the present invention can be obtained, for example, by
using nanoparticles of the material forming the carrier as the
cores and obtaining non particles in which the two metals are in
close proximity. As other metal atoms able to alloy with both atoms
of the gold atoms and nickel atoms, for example, tungsten (W),
which can improve the heat resistance of gold by alloying, may be
mentioned. Further, as the carrier particles, Al.sub.2O.sub.3,
SiO.sub.2, CeO.sub.2, CeO.sub.2--ZrO.sub.2, (hereinafter also
sometimes as abbreviated as "CZ") and other metal oxide particles
may be mentioned.
[0028] The NO.sub.X purification catalyst of the present invention
can be obtained by making the carrier carry nanoparticles in which
gold atoms and nickel atoms are included in a state of close
proximity. The nanoparticles in which gold atoms and nickel atoms
are included in a state of close proximity can be obtained by for
example reducing a mixture of gold salts and nickel salts in the
presence of a polymer protective material using a reducing agent,
for example, a polyol. The reducing reaction is preferably
performed in a solution, preferably an aqueous solution, while
under agitation. After the end of the reducing reaction, the
polymer protective material is separated and removed by any
separating means, for example, centrifugal separation, extraction,
etc., and the obtained colloid in which the gold atoms and nickel
atoms are present in a state of close proximity is uniformly mixed
with the carrier so as to make the carrier carry nanoparticles
which include gold atoms and nickel atoms in a state of close
proximity. Furthermore, exposing the carrier powder to an H.sub.2
gas reducing atmosphere is preferable. The size of the Au--Ni
particles with the gold atoms and nickel atoms contained in a state
of close proximity can be 0.2 to 100 nm or so, for example, 1 to 20
nm or so.
[0029] As the gold salts, aurochloric acid (HAuCl.sub.4), sodium
chloroaurate, potassium chloroaurate, gold trisodium disulfite,
potassium trisodium disulfite, etc. may be mentioned. As the nickel
salt, for example, nickel sulfate, nickel nitrate, nickel chloride,
nickel bromide, nickel acetate, nickel hydroxide, etc. may be
mentioned. As the polyols, ethylene glycol, diethylene glycol,
triethylene glycol, tetraethylene glycol, 1,2-propanediol,
dipropylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol,
2,3-butanediol, 1,5-pentanediol, polyethylene glycol, etc. may be
mentioned. To complete the reduction of the gold ions and nickel
ions by the polyol, at the final stage of reduction, for example,
boron dimethylamide, boron diethylamide, sodium borohydrate, boron
hydride, or another boron compound can be used as a reducing agent.
As the polymer protective material, poly-N-vinylpyrrolidone,
polyacrylamide, N-vinylpyrrolidone and acrylic acid copolymer,
polyvinylmethylketone, poly(4-vinylphenol), oxazoline polymer,
polyalkylene imine, and other polymers containing functional groups
may be mentioned.
[0030] The NO.sub.X purification catalyst of the present invention
preferably has nanoparticles having gold and nickel as main
ingredients in which the composition of the gold and nickel is
Au:Ni=7 to 91:93 to 9 (at %), preferably 20 to 80:80 to 20 (at %),
particularly preferably 40 to 60:60 to 40 (at %). If the
composition of gold and nickel in the solid is outside that range,
the NO.sub.X purification catalyst tends to drop in NO.sub.X
purification performance. The NO.sub.X purification catalyst of the
present invention combines gold and nickel and thereby has as a
synergistic effect a superior NO.sub.X purification performance
unable to be obtained by single ingredients and in particular has
superior catalytic activity even compared with another alloy and
rhodium or other single precious metals.
[0031] According to the NO.sub.X purification catalyst of the
present invention, the heating temperature for raising the NO.sub.X
purification activity, for example, the heating temperature by the
heater, does not have to be made a high temperature like in the
past. Even in an oxidizing atmosphere, this catalyst has an
NO.sub.X purification ability, so use of fuel for making the
atmosphere a reducing atmosphere becomes unnecessary or can be
greatly reduced. Further, according to the NO.sub.X purification
catalyst of the present invention, there is no need to lower the
air-fuel ratio (A/F) at the engine. For example, at the time of
steady state operation at a high air-fuel ratio (A/F), for example,
stoichiometric, in the case of a gasoline engine, the A/F is larger
than 14.7, for example, A/F.gtoreq.20, while in the case of a
diesel engine, A/F.gtoreq.30 is possible.
[0032] In the present invention, in the above way, it is necessary
to provide an oxidation catalyst oxidizing the HC in the exhaust
gas at a position in the exhaust gas passage at the upstream side
of the NO.sub.X purification catalyst. In the present invention, by
configuring the system in this way, even when the exhaust gas
exhausted from the engine is an exhaust gas composition including
HC at the time of a non-steady operation, the HC is removed by
oxidation by the catalytic action of the oxidation catalyst, so the
exhaust gas composition introduced into the NO.sub.X purification
catalyst does not contain HC and O.sub.2 together, so the NO.sub.X
purification catalyst can exhibit a high NO.sub.X purification
performance. The oxidation catalyst oxidizing the HC is not
particularly limited, but in general a known catalyst used as an
oxidation catalyst of HC, for example, Pd/CeO.sub.2,
Ag/Al.sub.2O.sub.3, etc. may be mentioned.
[0033] Further, in the present invention, it is also possible to
provide an HC adsorbent adsorbing the HC in the exhaust gas at a
position in the exhaust gas passage at the upstream side of the
oxidation catalyst. The HC adsorbent is not particularly limited,
but a known material generally used as an adsorbent for HC, for
example, zeolite, may be mentioned. The zeolite may also carry Cu,
Zn, Al, or another metal.
[0034] According to the exhaust gas purification system of the
present invention, the NO.sub.X purification performance can be
improved even with an exhaust gas composition including HC and
O.sub.2 such as at the time of a non-steady operation.
EXAMPLES
[0035] Below, examples of the present invention will be shown. In
the following examples, the obtained catalysts were evaluated by
the methods of measurement shown below.
1. Measurement of Alloy Composition of Catalyst
[0036] Measurement method: Measurement of composition of bulk as a
whole by XRD (X-ray diffraction)
[0037] Measurement apparatus: RIGAKU RINT-2000
2. Measurement of Particle Shape and Particle Size
[0038] Distribution of Alloy Nanoparticles
[0039] Measurement method 1: Measurement by TEM (transmission
electron microscope)
[0040] TEM measurement apparatus: HITACHI HD-2000
[0041] Measurement method 2: Measurement by HRTEM (high resolution
transmission electron microscope)
[0042] HRTEM Measurement apparatus: HITACHI HD2000
3. Measurement of Elemental Analysis of Alloy Nanoparticles
[0043] Measurement method: Measurement of ratio of composition by
TEM-EDS (EDS: energy dispersive X-ray spectroscopy)
[0044] TEM-EDS measurement apparatus: HITACHI HD2000
4. Measurement of Catalytic Activity
[0045] Catalyst pellets were packed in a glass reaction tube and
anchored by glass wool. A gas mixed in advance was run through the
glass reaction tube. The gas temperature was raised by a
temperature elevation rate of 20.degree. C./min from 100.degree. C.
to 500.degree. C. The NO concentration was measured by an exhaust
gas analyzer (HORIBA MEXA7100H) or MS (mass spectrometry). Note
that, when running a gas not including H.sub.2, the measurement was
conducted at 500.degree. C. after hydrogen reduction.
Reference Example 1
1) Synthesis of AuNi Nanoparticles
[0046] In a two-necked flask, 1.1 g of poly-n-vinylpyrrolidone
(PVP) was added to 120 ml of anhydrous ethylene glycol. Into this
mixture, 0.1404 g of nickel sulfate was added. The mixture was
agitated at 80.degree. C. for 3 hours to obtain a solution
(solution 1). Separately, in a two-necked flask, 0.1809 g of
NaAuCl.sub.4 was added to 50 ml of distilled water. The mixture was
strongly agitated for 2 hours or more to cause dissolution and
obtain a bright red colored solution (solution 2). The solution 1
was cooled by a cooling bath down to 0.degree. C., then the
solution 2 was poured into the solution 1 in the flask and the two
were uniformly agitated. The mixed solution was adjusted by a 1M
NaOH solution (about 5 ml) to give a pH of 9 to 10. The mixed
solution was heated by an oil bath to 100.degree. C. and was held
for 2 hours while being agitated. After this, the flask was lifted
up from the oil bath and allowed to stand until the colloidal
suspension was cooled to room temperature. To completely reduce all
of the ions in the flask, sodium borohydrate 0.038 g was added,
then the suspension was allowed to stand for a while. The produced
nanoparticles were refined by treating a certain fraction including
a predetermined amount of nanoparticles by a large amount of
acetone. Due to this, the PVP polymer protective material was
extracted in the acetone phase, and the metal nanoparticles
coagulated. The supernatant was transferred (decanted) or
centrifuged to obtain the colloid. The acetone phase was removed,
then the refined colloid was gently stirred to disperse in pure
ethanol.
2. Carrying of AuNi Nanoparticles on Carrier
[0047] In a 100 ml Schlenk flask, 1 g of the carrier
(Al.sub.2O.sub.3) was inserted. The inside of the Schlenk flask was
evacuated, then N.sub.2 was run into it to clean the piping and
completely remove the air. The concentration of the suspension of
the colloid previously synthesized (both the refined colloid and
remaining solution) was determined in advance, and a refined
colloidal suspension containing Rh0.5 wt % molar equivalents of
amounts of gold and nickel metal was poured through a rubber septum
into the Schlenk flask. The mixture was agitated at room
temperature for 3 hours, then the solvent was removed by vacuum.
After this, the remaining polymer protective material of the
colloidal precipitate was removed and the result dried at 200 to
600.degree. C. by vacuum heating. The obtained catalyst powder was
pressed to obtain pellets of approximately 2 mm size.
3. Evaluation of Catalyst
[0048] The obtained AuNi (50:50)/Al.sub.2O.sub.3 catalyst was
measured for shape, particle size distribution, and elemental
analysis of the alloy particles by TEM and TEM-EDS. The size of the
nanoparticles was 3.75 nm.+-.0.70 nm. Further, from the TEM-EDS
spectrum measured for an AuNi (50:50) colloid on a copper coated
grid, it is shown that all individual particles include gold and
nickel. Furthermore, the obtained AuNi (50:50)/Al.sub.2O.sub.3
catalyst was measured for NO purification characteristics under the
following gas flow conditions.
Gas Flow Conditions
[0049] Gas composition: NO 1000 ppm, CO 1000 ppm, N.sub.2 bal/10
liter
[0050] Flow rate: 500 ml/min, pellets: 150 mg,
[0051] Space velocity: 3.3 liters/ming
[0052] Ni, base metal concentrations: each 0.0486 mmol/g-cat
[0053] The results are shown together with other results in FIG.
1.
Comparative Example 1
[0054] Except for not using the solution 1, the same procedure was
followed as in Reference Example 1 to obtain an Au/Al.sub.2O.sub.3
catalyst. The obtained Au/Al.sub.2O.sub.3 catalyst was measured for
NO purification characteristics in the same way as in Reference
Example 1. The results are shown together with other results in
FIG. 1.
Comparative Example 2
Synthesis of Nickel Nanoparticles
[0055] In a two-necked flask, 1.1 g of poly-n-vinylpyrrolidone
(PVP) was added to 120 ml of anhydrous ethylene glycol. Into this
mixture, 0.1404 g of nickel sulfate was added. The mixture was
agitated at 80.degree. C. for 3 hours. The obtained solution was
cooled to 0.degree. C. and the pH was adjusted to 9 to 10. Next,
the mixed solution was heated by an oil bath to 180.degree. C. and
was held for 2 hours while being agitated. After this, the flask
was lifted up from the oil bath and allowed to stand until the
colloidal suspension was cooled to room temperature. The produced
nanoparticles were refined by treating a certain fraction including
a predetermined amount of nanoparticles by a large amount of
acetone. Due to this, the protective PVP was extracted in the
acetone phase, and the metal nanoparticles coagulated. The
supernatant was decanted or centrifuged to obtain the colloid. The
acetone phase was removed, then the refined colloid was gently
stirred to disperse in pure ethanol.
Carrying of Nickel Nanoparticles
[0056] In a 100 ml Schlenk flask, 1 g of the carrier
(Al.sub.2O.sub.3) was inserted. The inside of the Schlenk flask was
evacuated, then N.sub.2 was used to purge the piping. The
concentration of the suspension of the colloid previously
synthesized (both the refined colloid and remaining solution) was
determined in advance, and a refined colloidal suspension
containing Rh0.5 wt % molar equivalents of amounts of nickel metal
was poured into the Schlenk flask. The mixture was agitated at room
temperature for 3 hours, then the solvent was removed by vacuum.
After this, the remaining protective material of the colloidal
precipitate was removed and the result dried at 200 to 600.degree.
C. by firing in a vacuum or in the air. The obtained catalyst
powder was pressed to obtain Ni/Al.sub.2O.sub.3 catalyst pellets of
approximately 2 mm size. The obtained Ni/Al.sub.2O.sub.3 catalyst
was measured in the same way as in Reference Example 1 for NO
purification characteristics. The results are shown together with
other results in FIG. 1.
Comparative Example 3
[0057] Except for separately using, as two types of metal salts,
nickel sulfate and NaAuCl.sub.4, the same procedure was followed as
in Comparative Example 2 to cause metal to precipitate by
evaporation of a gold and nickel mixed metal ion solution and
thereby obtain (Au+Ni)mixture/Al.sub.2O.sub.3 catalyst pellets in
which gold and nickel are not present in a state of close
proximity. The obtained catalyst was measured in the same way as in
Reference Example 1 for NO purification characteristics. The
results are shown together with other results in FIG. 1.
Reference Example 2
[0058] Except for changing the carrier particles from
Al.sub.2O.sub.3 to CeO.sub.2--ZrO.sub.2(CZ), the same procedure was
followed as in Reference Example 1 to obtain an AuNi(50:50)/CZ
catalyst. The obtained AuNi(50:50)/CZ catalyst was measured for
shape and particle size distribution of the alloy particles and
analyzed by elementary analysis by TEM and TEM-EDS. The
nanoparticles had a size of 3.61 nm.+-.0.9 nm. Further, from the
TEM-EDS spectrum measured for the AuNi(50:50) colloid on the Cu
covered grid, all of the individual particles contained Au and Ni.
Further, the obtained AuNi(50:50)/CZ catalyst was measured for
catalytic activity under the following conditions and various gas
flow conditions.
[0059] Space Velocity (SV): 100000 (0.6 g, 1 L/min)
[0060] All conditions are stoichiometry, N.sub.2 balance
[0061] The O.sub.2, H.sub.2 treatment is performed under
500.degree. C. before the catalytic activity test
Gas Flow Conditions
[0062] (1) NO: 3000 ppm, CO: 3000 ppm
[0063] (2) NO: 1500 ppm, CO: 6500 ppm, O.sub.2: 7000 ppm,
C.sub.3H.sub.6: 1000 ppm
[0064] (3) NO: 3000 ppm, CO: 1500 ppm, C.sub.3H.sub.6: 167 ppm
[0065] (4) NO: 1500 ppm, CO: 1.55%, O.sub.2: 7000 ppm,
[0066] (5) NO: 3000 ppm, CO: 3000 ppm, CO.sub.2: 10%
[0067] (6) NO: 3000 ppm, CO: 3000 ppm, H.sub.2O: 3%
[0068] The obtained results are shown together with other results
in FIG. 2.
Examples 1 to 2
[0069] In the apparatus used for measurement of the catalytic
activity described above, as the HC oxidation catalyst,
Pd/CeO.sub.2 prepared by an ordinary method (Example 1) or
Ag/Al.sub.2O.sub.3 prepared by an ordinary method (Example 2) was
placed upstream of the NO.sub.X purification catalyst. As the
NO.sub.X purification catalyst, the AuNi(50:50)/CZ catalyst
obtained in Reference Example 2 was used to prepare the exhaust gas
purification system. This exhaust gas purification system was fed
with gas of the gas composition (2) to purify the exhaust gas and
obtain NO purification characteristics the same as the curve shown
by the curve 5 of FIG. 2. The above results show that according to
the exhaust gas purification system of the present invention, the
NO purification characteristics are greatly improved from the curve
2 to the curve 5 of FIG. 2.
[0070] According to the exhaust purification system of the present
invention, from the viewpoint of resource depletion, by using an
NO.sub.X purification catalyst using gold and nickel present in
about the same extent as copper, the heating temperature for
raising the NO.sub.X purification activity does not have to be made
a high temperature like in the past, and there is an NO.sub.X
purification activity even in an oxidizing atmosphere, so use of
fuel for making the atmosphere a reducing state becomes unnecessary
or at least can be greatly reduced, and a high NO.sub.X
purification performance can be obtained over a broad range of
exhaust gas compositions.
EXPLANATION OF REFERENCES
[0071] Curve 1. Relationship of temperature and NO purification
rate in NO--CO gas composition
[0072] Curve 2. Relationship of temperature and NO purification
rate in NO--CO--O.sub.2--C.sub.3H.sub.6 exhaust gas composition
Curve 3. Relationship of temperature and NO purification rate in
NO--CO--C.sub.3H.sub.6 exhaust gas composition Curve 4.
Relationship of temperature and NO purification rate in
NO--CO--O.sub.2 exhaust gas composition Curve 5. Relationship of
temperature and NO purification rate in NO--CO--CO.sub.2 exhaust
gas composition Curve 6. Relationship of temperature and NO
purification rate in NO--CO-H.sub.2O exhaust gas composition [0073]
1. exhaust gas purification system [0074] 2. engine [0075] 3.
exhaust gas passage [0076] 4. A/F meter [0077] 5. NO.sub.X
purification catalyst [0078] 6. oxidation catalyst oxidizing HC
[0079] 7. HC adsorbent
[0080] While the invention has been described with reference to
specific embodiments chosen for purpose of illustration, it should
be apparent that numerous modifications could be made thereto by
those skilled in the art without departing from the basic concept
and scope of the invention.
* * * * *