U.S. patent application number 14/122051 was filed with the patent office on 2014-07-10 for exhaust gas oxidation catalyst.
This patent application is currently assigned to JOHNSON MATTHEY PUBLIC LIMITED COMPANY. The applicant listed for this patent is Takeshi Kadono, Satoshi Sumiya, Lifeng Wang. Invention is credited to Takeshi Kadono, Satoshi Sumiya, Lifeng Wang.
Application Number | 20140193306 14/122051 |
Document ID | / |
Family ID | 45840912 |
Filed Date | 2014-07-10 |
United States Patent
Application |
20140193306 |
Kind Code |
A1 |
Kadono; Takeshi ; et
al. |
July 10, 2014 |
EXHAUST GAS OXIDATION CATALYST
Abstract
An exhaust gas oxidation catalyst characterised as an exhaust
gas oxidation catalyst comprising a catalyst substrate, wherein a
plurality of exhaust gas channels has been formed, and a catalyst
layer formed on the surface of the exhaust gas channels in the
catalyst substrate; wherein a catalyst layer consisting of a bottom
catalyst layer, a top catalyst layer exposed within the exhaust gas
channels, and an intermediate catalyst layer located between the
bottom catalyst layer and top catalyst layer, is provided so as to
cover not less than 25% of the exhaust gas channel surface, and
wherein the bottom catalyst layer contains at least an
oxygen-occluding agent as catalyst component but does not contain a
hydrocarbon adsorbent, the intermediate catalyst layer contains at
least catalyst metal, supported on a metal oxide support, and a
hydrocarbon adsorbent as catalyst components, and the top catalyst
layer contains at least an oxygen-occluding agent and a hydrocarbon
adsorbent as catalyst components.
Inventors: |
Kadono; Takeshi; (Tochigi,
JP) ; Sumiya; Satoshi; (Tochigi, JP) ; Wang;
Lifeng; (Tochigi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kadono; Takeshi
Sumiya; Satoshi
Wang; Lifeng |
Tochigi
Tochigi
Tochigi |
|
JP
JP
JP |
|
|
Assignee: |
JOHNSON MATTHEY PUBLIC LIMITED
COMPANY
London
GB
|
Family ID: |
45840912 |
Appl. No.: |
14/122051 |
Filed: |
May 25, 2012 |
PCT Filed: |
May 25, 2012 |
PCT NO: |
PCT/GB2012/051190 |
371 Date: |
January 3, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61586447 |
Jan 13, 2012 |
|
|
|
Current U.S.
Class: |
422/168 ;
502/300; 502/304; 502/339; 502/75 |
Current CPC
Class: |
B01D 2255/908 20130101;
B01D 53/94 20130101; B01D 2255/502 20130101; B01J 23/38 20130101;
B01J 2229/42 20130101; Y02A 50/2341 20180101; B01J 35/04 20130101;
B01D 2255/407 20130101; F01N 3/2828 20130101; B01D 53/944 20130101;
B01J 23/44 20130101; B01J 37/0244 20130101; B01J 29/743 20130101;
B01J 35/0073 20130101; B01J 29/44 20130101; B01J 23/10 20130101;
B01J 2229/186 20130101; B01D 2255/912 20130101; B01D 2255/1023
20130101; B01J 37/0246 20130101; B01J 29/7415 20130101; B01J 29/67
20130101; B01J 29/80 20130101; B01D 2255/1021 20130101; Y02A 50/20
20180101; B01D 2255/9025 20130101; B01D 2255/504 20130101; B01J
29/10 20130101; F01N 2510/0684 20130101; B01D 2258/012 20130101;
F01N 2510/063 20130101 |
Class at
Publication: |
422/168 ;
502/300; 502/339; 502/75; 502/304 |
International
Class: |
B01D 53/94 20060101
B01D053/94; B01J 29/74 20060101 B01J029/74; B01J 29/80 20060101
B01J029/80 |
Foreign Application Data
Date |
Code |
Application Number |
May 25, 2011 |
JP |
2011-117314 |
Jan 25, 2012 |
GB |
1201218.3 |
Claims
1. An exhaust gas oxidation catalyst comprising a catalyst
substrate having a plurality of exhaust gas channels and a catalyst
layer formed on the surface of the exhaust gas channels in the
catalyst substrate; wherein a catalyst layer consisting of a bottom
catalyst layer, a top catalyst layer exposed in the exhaust gas
channels, and an intermediate catalyst layer located between the
bottom catalyst layer and top catalyst layer, is provided so as to
cover not less than 25% of the exhaust gas channel surface, and
wherein the bottom catalyst layer contains at least an
oxygen-occluding agent as catalyst component but does not contain a
hydrocarbon adsorbent, the intermediate catalyst layer contains at
least catalyst metal, supported on a metal oxide support, and a
hydrocarbon adsorbent as catalyst components, and the top catalyst
layer contains at least an oxygen-occluding agent and a hydrocarbon
adsorbent as catalyst components.
2. The exhaust gas oxidation catalyst according to claim 1, wherein
the intermediate catalyst layer consists of two or more layers that
have different catalyst components and/or contents.
3. The exhaust gas oxidation catalyst claim 1 wherein the top
catalyst layer further contains catalyst metal supported on a metal
oxide support.
4. The exhaust gas oxidation catalyst according to claim 3, wherein
1-10 wt % of the overall catalyst metal content is contained in the
top catalyst layer.
5. The exhaust gas oxidation catalyst according to claim 1, wherein
the catalyst metal is platinum, palladium, iridium, gold, silver or
a mixture of both platinum and palladium.
6. The exhaust gas oxidation catalyst according to claim 1, wherein
each of the intermediate catalyst layer and the top catalyst layer
contains 0.2-5.0 wt % catalyst metal relative to the combined
weight of the catalyst metal and the metal oxide.
7. The exhaust gas oxidation catalyst according to claim 1, wherein
the hydrocarbon adsorbent in the top catalyst layer or the
intermediate catalyst layer is a zeolite or a metallosilicate
structure wherein silicon or aluminium in a zeolite crystal lattice
is replaced with a transition metal.
8. The exhaust gas oxidation catalyst according to claim 7, wherein
the zeolite is of the BEA, FAU, MFI, FER or CHA type or a mixture
of any two or more thereof.
9. The exhaust gas oxidation catalyst according to claim 1, wherein
the oxygen-occluding agent in the top catalyst layer and the bottom
catalyst layer is cerium oxide, a complex oxide of cerium and
zirconium, or cerium oxide or a complex oxide of cerium and
zirconium to which lanthanum, praseodymium or neodymium has been
added.
10. The exhaust gas oxidation catalyst according to claim 1
comprising 10-20 g/L of oxygen occluding agent, 5-30 g/L of
hydrocarbon adsorbent and 0.1-5.0 g/L of catalyst metal.
11. The exhaust gas oxidation catalyst according to claim 1,
wherein 20-50 wt % of the overall oxygen-occluding agent content is
contained in the bottom layer.
12. The exhaust gas oxidation catalyst according to claim 1,
wherein 30-50 wt % of the overall hydrocarbon adsorbent content is
contained in the top catalyst layer.
13. The exhaust gas oxidation catalyst according to claim 1,
wherein the catalyst substrate is of honeycomb cylindrical form,
wherein the exhaust gas channels run from one face through to
another face of the cylinder; or the catalyst substrate is a porous
body in fibre form, sheet form or ceramic form.
14. The exhaust gas oxidation catalyst according to claim 1,
wherein the catalyst substrate and the bottom catalyst layer are
formed integrally as a honeycomb cylinder.
15. The exhaust gas oxidation catalyst according to claim 1,
wherein the bottom layer is formed from a slurry coating on the
catalyst substrate.
16. An exhaust system for a diesel internal combustion engine
comprising the exhaust gas oxidation catalyst according to claim
1.
17. An exhaust system according to claim 16 comprising a diesel
particulate filter.
18. The exhaust gas oxidation catalyst according to claim 1,
wherein 30-50 wt % hydrocarbon adsorbent content is contained in
the intermediate catalyst layer and 50-70 wt % of the overall
hydrocarbon adsorbent is contained in the top catalyst layer.
Description
[0001] The invention relates to an exhaust gas oxidation catalyst
for the clean-up of exhaust gas discharged from internal combustion
engines, especially diesel engines.
[0002] Exhaust gas cleaning catalysts are used to prevent pollution
by the exhaust gas discharged from internal combustion engines, and
the catalysts being developed for diesel engines include oxidation
catalysts and nitrogen oxide occlusion-reduction catalysts.
[0003] An oxidation catalyst renders the noxious substances in
exhaust gas, such as carbon monoxide (CO), unburned hydrocarbon
(HC), and soluble organic fraction (SOF), harmless by decomposition
to carbon dioxide, water, etc. U.S. Pat. No. 5,627,124 and U.S.
Pat. No. 5,491,120 disclose oxidation catalysts which use a
catalyst layer, formed in the exhaust gas channels of a substrate
of honeycomb form provided with numerous exhaust gas channels,
wherein the catalyst layer contains metal oxides such as cerium
oxide, aluminium oxide, titanium oxide, and zirconium oxide and
complexes thereof, and which further contain noble metals such as
platinum and palladium. Since an oxidation catalyst has scant
function in oxidising noxious substances such as HC if the exhaust
gas temperature is low as in low speed running, various means have
been devised to adsorb the HC at low temperature and then oxidise
the HC liberated when the exhaust gas has reached a sufficiently
high temperature; and one means proposed is to constitute the
catalyst layer so as to increase the amount of HC adsorbed (see for
example U.S. Patent publication No. 2010/0180582).
[0004] In order to increase the amount of HC occluded at low
exhaust gas temperature, the catalyst layer provided in the exhaust
gas channels in the oxidation catalyst disclosed in U.S. Patent
publication No. 2010/0180582 is constituted from three layers: a
bottom layer containing at least a molecular sieve, an intermediate
layer that contains a noble metal supported on a refractory metal
oxide but does not contain a molecular sieve, and a top layer
containing at least a molecular sieve. However, even though the
oxidation catalyst disclosed in U.S. Patent publication No.
2010/0180582 offers improved HC adsorption in low speed running,
such catalyst has been problematic in that HC adsorption efficacy
tends to deteriorate in continuous running at low temperature, as
in idling for example, and the level of CO removal is hardly
satisfactory since the recoverability of the catalyst from sulphur
poisoning due to sulphur compounds in the exhaust gas cannot be
considered adequate. The present invention was devised to solve the
problems with the exhaust gas oxidation catalysts of the aforesaid
prior art, its aim being to provide an exhaust gas catalyst whereby
the existing problems can be solved.
[0005] According to a first aspect, the invention provides an
exhaust gas oxidation catalyst characterised as comprising a
catalyst substrate, wherein a plurality of exhaust gas channels has
been formed, and a catalyst layer formed on the surface of the
exhaust gas channels in the catalyst substrate; wherein a catalyst
layer consisting of a bottom catalyst layer, a top catalyst layer
exposed in the exhaust gas channels, and an intermediate catalyst
layer located between the bottom catalyst layer and top catalyst
layer, is provided so as to cover not less than 25% of the exhaust
gas channel surface, and wherein the bottom catalyst layer contains
at least an oxygen occluding agent as catalyst component but does
not contain a hydrocarbon adsorbent, the intermediate layer
contains at least a catalyst metal, supported on a metal oxide
support, and a hydrocarbon adsorbent as catalyst components, and
the top catalyst layer contains at least an oxygen occluding agent
and hydrocarbon adsorbent as catalyst components.
[0006] In one embodiment, the intermediate catalyst layer comprises
not less than two layers with different catalyst components and/or
catalyst content.
[0007] In a further embodiment, as well as an oxygen occluding
agent and hydrocarbon adsorbent, the top catalyst layer contains
catalyst metal supported on a metal oxide support.
[0008] In a further embodiment, the hydrocarbon adsorbent is
zeolite.
[0009] According to a second aspect, the invention provides an
exhaust system for a diesel internal combustion engine comprising
the exhaust gas oxidation catalyst according to any preceding
claim.
[0010] The inventive exhaust gas oxidation catalyst has outstanding
efficacy in removing CO and HC, is resistant to decline in HC
adsorption in low speed running, recovers rapidly from sulphur
poisoning of the catalyst, and can effectively oxidise the noxious
substances in exhaust gas, rendering them harmless.
[0011] In order that the invention may be more fully understood,
embodiments of the present invention will be described with
reference to the accompanying drawings, in which:
[0012] FIG. 1 is a view in longitudinal section showing an
embodiment of the inventive exhaust gas oxidation catalyst;
[0013] FIG. 2 is an enlarged sectional view showing the
constitution of the catalyst layer; and
[0014] FIG. 3 is an enlarged sectional view showing the
constitution of the catalyst layer in another embodiment of the
inventive exhaust gas oxidation catalyst.
[0015] FIG. 1 shows an embodiment of the inventive exhaust gas
oxidation catalyst; the exhaust gas oxidation catalyst illustrated
embodies a constitution wherein a catalyst layer 5 as shown in FIG.
2 has been provided on the walls 4 of the exhaust gas channels 2 in
a catalyst substrate 3 containing a plurality of exhaust gas
channels 2. The catalyst substrate 3 used comprises cordierite,
metal, silicon carbide, silicon nitride, aluminium nitride, or the
like. Although a catalyst substrate 3 of honeycomb cylindrical form
that has a plurality of exhaust gas channels 2 running from one
face through to the other face of the cylinder can normally be
used, the substrate can also be a porous body in fibre form, sheet
form, ceramic form, etc.
[0016] As indicated in FIG. 2, the catalyst layer 5 is constituted
from three layers: a bottom catalyst layer 6 that contains at least
an oxygen-occluding agent but does not contain a hydrocarbon
adsorbent as catalyst component, an intermediate catalyst layer 7
containing at least a catalyst metal supported on a metal oxide
support as catalyst components and a hydrocarbon adsorbent, and a
top catalyst layer 8 containing at least an oxygen-occluding agent
and hydrocarbon adsorbent as catalyst components. The bottom
catalyst layer 6 is provided so as to cover the walls 4 of the
exhaust gas channels 2, the top catalyst layer 8 is exposed within
the exhaust gas channels 2, and the intermediate catalyst layer 7
is located between the bottom catalyst layer 6 and the top catalyst
layer 8.
[0017] The respective catalyst layers can be formed by applying a
coating of a catalyst layer forming slurry wherein the catalyst
components have been dispersed in water, and then drying and
calcining. Methods of applying a coating of slurry to the catalyst
substrate 3 may be listed as including dipping the catalyst
substrate 3 in the slurry or flushing slurry into the exhaust gas
channels 2 of the catalyst substrate 3. After the slurry has been
coated on the catalyst substrate 3 and dried, it can usually be
calcined at a temperature of 700.degree. C. or less to form the
catalyst layer.
[0018] A catalyst component of oxygen-occluding agent dispersed in
water can be used as the slurry for forming the bottom catalyst
layer 6. Although any of cerium oxide, a complex oxide of cerium
and zirconium, and compounds wherein an element such as La, Pr or
Nd has been added to the said oxides, can be used as the
oxygen-occluding agent, a complex oxide of cerium and zirconium is
preferred. Since the bottom catalyst layer 6 is formed using a
slurry that does not contain hydrocarbon adsorbent or catalyst
metals, no hydrocarbon adsorbent is contained in the bottom
catalyst layer 6, but catalyst metal that has migrated from the
intermediate catalyst layer 7 formed over the bottom catalyst layer
6 may be contained therein. If catalyst metal that has migrated
from the intermediate catalyst layer 7 is contained in the bottom
catalyst layer 6, the proportion thereof is usually no more than 5
wt % of the overall catalyst metal content.
[0019] The intermediate catalyst layer 7 can be formed by coating a
slurry of catalyst metal compounds, a metal oxide support for
supporting the catalyst metal, and a hydrocarbon adsorbent,
dispersed in water, or a slurry of metal oxide support whereon
catalyst metal has been supported and a hydrocarbon adsorbent,
dispersed in water, over the bottom catalyst layer 6 on a catalyst
substrate 3 whereon a bottom catalyst layer 6 has been formed, then
drying and calcining. The catalyst metal in the intermediate
catalyst layer 7 exists as catalyst metal supported on metal oxide.
The nitrate, acetate, hydrochloride, ammine salt, etc, of a metal
such as platinum, palladium, iridium, gold or silver is used as the
catalyst metal compound in the slurry for forming the intermediate
catalyst layer 7; platinum nitrate, ammines of platinum, and
palladium nitrate are preferred. An aluminium oxide such as
.alpha.-alumina or .gamma.-alumina, zirconium oxide, silicon oxide,
titanium oxide, their mixtures and their complex oxides are used as
the metal oxide support; aluminium oxide and mixtures or complex
oxides containing aluminium oxide are preferred, and
.gamma.-alumina and mixtures or complex oxides containing
.gamma.-alumina are especially preferred. The proportion of other
metal oxides in the mixtures or complex oxides with .gamma.-alumina
preferably falls in the range 1-30 wt %. A powder of mean particle
size 1-10 .mu.m is preferably used as the metal oxide support. For
a slurry wherein catalyst metal compounds and catalyst oxide
support are dispersed, the proportion of catalyst metal compounds
to metal oxide support preferably falls in the range 0.2-5.0 wt %
of metal oxide compound with respect to the combined weight of
both. The hydrocarbon adsorbents that can be used include
mesoporous materials, or microporous materials such as zeolite or a
metallosilicate of structure wherein the silicon or aluminium in a
zeolite crystal lattice is replaced with a transition metal, though
zeolite is preferred. Zeolites of BEA, FAU, MFI, FER, CHA type,
etc, may be listed as the zeolite, one or two or more whereof can
be used together, though a zeolite with three-dimensional porosity
is preferred. A hydrocarbon adsorbent that has a trapping function
matching the hydrocarbon species contained in exhaust gas is
preferably chosen for use as the hydrocarbon adsorbent.
[0020] The top catalyst layer 8 can be formed by coating a slurry
containing an oxygen-occluding agent and hydrocarbon adsorbent over
the intermediate catalyst layer 7, drying and firing. The
oxygen-occluding agent and hydrocarbon adsorbent that can be used
are the same as for the bottom catalyst layer 6 and intermediate
catalyst layer 7.
[0021] If necessary, a binder, inorganic fibre, etc, may be
incorporated in the slurry used to form the bottom catalyst layer
6, intermediate catalyst layer 7 and top catalyst layer 8.
Aluminium oxide, which functions also as a metal oxide support, is
normally used as binder, although it is also possible to use
titanium oxide, silicon oxide, etc. Mullite fibre, titania fibre,
silica fibre, fibrous boehmite, etc, can be used as the inorganic
fibre.
[0022] The foregoing example illustrates the case where the bottom
catalyst layer 6 is formed by coating a slurry containing catalyst
metal compounds and metal oxide support (or a metal oxide support
supporting catalyst metal) on the walls 4 of the exhaust gas
channels 2 in a catalyst substrate 3, then drying and calcining,
but it is also possible to form the catalyst substrate 3 and bottom
catalyst layer 6 integrally by moulding the bottom catalyst layer
slurry into a honeycomb cylinder, for example, then drying and
calcining.
[0023] Although the foregoing example illustrates the case where
the intermediate catalyst layer 7 is constituted as a single layer,
the intermediate catalyst layer 7 can also be constituted as two
layers, a first layer 7a and second layer 7b, or a plurality of two
or more layers, as shown in FIG. 3. When the intermediate catalyst
layer 7 is constituted as a plurality of two or more layers, each
layer (the first layer 7a, second layer 7b, and so on) can be
formed from a slurry of different catalyst metal and content
thereof, different metal oxide support, etc, or from a slurry of
the same catalyst metal at a different content. Versatility in
treating exhaust gas containing noxious substances in different
proportions can be enhanced by constituting the intermediate
catalyst layer 7 as a plurality of layers whose catalyst metals,
metal oxide supports and contents thereof, etc, are different.
[0024] The inventive exhaust gas oxidation catalyst 1 may contain
catalyst metal as well as oxygen-occluding agent and hydrocarbon
adsorbent in the top catalyst layer 8. When catalyst metal is so
incorporated, it is supported on a metal oxide support.
Incorporating catalyst metal in the top catalyst layer 8 not only
improves performance in suppressing decline in HC trapping function
during low-speed running, it can also improve the fuel combustion
properties during DPF forced regeneration.
[0025] The contents of the aforesaid oxygen-occluding agent,
hydrocarbon adsorbent, and catalyst metal in the inventive exhaust
gas oxidation catalyst 1 in relation to the volume (L) of exhaust
gas oxidation catalyst 1 are preferably 10-20 g/L of
oxygen-occluding agent, 5-30 g/L of hydrocarbon adsorbent and
0.1-5.0 g/L of catalyst metal. The content of oxygen-occluding
agent is preferably constituted so that 20-50 wt % of the overall
oxygen-occluding agent content is contained in the bottom catalyst
layer 6 and 50-80 wt % of the overall oxygen-occluding agent
content is contained in the top catalyst layer 8. The content of
hydrocarbon adsorbent is preferably constituted so that 30-50 wt %
of the overall hydrocarbon adsorbent content is contained in the
intermediate catalyst layer 7 and 50-70 wt % of the overall
hydrocarbon adsorbent is contained in the top catalyst layer 8.
Where catalyst metal is additionally contained in the top catalyst
layer 8, the proportion of catalyst metal contained therein is
preferably set at 1-10 wt % of the overall catalyst metal
content.
[0026] The catalyst layer 5 comprising the bottom catalyst layer 6,
the intermediate catalyst layer 7 and the top catalyst layer 8 in
the inventive exhaust gas oxidation catalyst 1 need not be provided
over the whole of the exhaust gas channel 2 from the exhaust gas
inlet end to the exhaust gas exit end: although it may be provided
contiguously or non-contiguously as long as it is provided on not
less than 25% of the surface of the total length of the exhaust gas
channel 2, it is preferably provided on not less than 30%, more
preferably not less than 40% and in particular preferably not less
than 50% of the surface of the total length of the exhaust gas
channel 2. The catalyst layer 5 is preferably provided on not less
than 25% of the surface of the total length of the exhaust gas
channel 2 proceeding from the exhaust gas inlet end of the exhaust
gas channel 2 towards the exhaust gas exit end, and in particular
preferably provided contiguously thereon. If the catalyst layer 5
is provided on a length less than 100% of the total length of the
exhaust gas channel 2 proceeding from the exhaust gas inlet end of
the exhaust gas channel 2 towards the exhaust gas exit end, a
heretofore known catalyst layer may usually be provided on that
part of the exhaust gas channel 2 not provided with the catalyst
layer 5, in which case it is permissible for the intermediate
catalyst layer in the catalyst layer 5 to extend onto the part not
provided with the catalyst layer 5 comprising a bottom catalyst
layer 6, intermediate catalyst layer 7 and top catalyst layer
8.
[0027] By way of illustration only, the invention is described in
greater detail hereunder with working examples.
WORKING EXAMPLE 1
[0028] The following slurries for forming the respective catalyst
layers were prepared.
[0029] 1) Bottom catalyst layer: A slurry containing cerium
oxide-zirconium oxide complex as oxygen-occluding agent and
aluminium oxide (oxygen-occluding agent 63 wt %, aluminium oxide 37
wt %).
[0030] 2) Intermediate catalyst layer slurry: A slurry containing
.beta.-zeolite as hydrocarbon adsorbent, platinum and palladium as
catalyst metals (added as platinum nitrate and palladium nitrate),
and aluminium oxide (hydrocarbon adsorbent 11.2 wt %, platinum 1.6
wt %, palladium 0.8 wt %, aluminium oxide 86.4 wt %).
[0031] 3) Top catalyst layer slurry: A slurry containing cerium
oxide-zirconium oxide complex as oxygen-occluding agent, platinum
as catalyst metal (added as platinum nitrate), .beta.-zeolite as
hydrocarbon adsorbent, and aluminium oxide (oxygen-occluding agent
27 wt %, .beta.-zeolite hydrocarbon adsorbent 45 wt %, platinum 0.1
wt %, aluminium oxide 27.9 wt %).
[0032] A honeycomb catalyst substrate (NGK product, 1 L) was
immersed in the bottom catalyst layer slurry, which was coated to
give a deposit when dry of 49 g/L, dried and then calcined at
500.degree. C. to form a bottom catalyst layer. The intermediate
catalyst layer slurry was then coated over the bottom catalyst
layer to give a deposit when dry of 110 g/L, dried and then
calcined at 500.degree. C. to form an intermediate catalyst layer.
The top catalyst layer slurry was then coated over the intermediate
catalyst layer to give a deposit when dry of 50 g/L, dried and then
calcined at 500.degree. C. to form a top catalyst layer, affording
an exhaust gas oxidation catalyst with a triple catalyst layer
(triple catalyst layer coverage 100% as a proportion of exhaust gas
channel surface).
WORKING EXAMPLE 2
[0033] The following slurries for forming the respective catalyst
layers were prepared.
[0034] 1) Bottom catalyst layer: A slurry containing cerium
oxide-zirconium oxide complex as oxygen-occluding agent and
aluminium oxide (oxygen-occluding agent 63 wt %, aluminium oxide 37
wt %).
[0035] 2) Intermediate catalyst layer slurry: A slurry containing
.beta.-zeolite and ZSM5 zeolite as hydrocarbon adsorbents, platinum
and palladium as catalyst metals (added as platinum nitrate and
palladium nitrate), and aluminium oxide (.beta.-zeolite 5 wt % and
ZSM5 zeolite 5 wt % as hydrocarbon adsorbents, platinum 1.1 wt %,
palladium 0.5 wt %, aluminium oxide 88.4 wt %).
[0036] 3) Top catalyst layer slurry: A slurry containing cerium
oxide-zirconium oxide complex as oxygen-occluding agent, platinum
as catalyst metal (added as platinum nitrate), .beta.-zeolite and
ZSM5 zeolite as hydrocarbon adsorbents, and aluminium oxide
(oxygen-occluding agent 27.4 wt %, .beta.-zeolite 22.5 wt % and
ZSM5 zeolite 22.5 wt % as hydrocarbon adsorbents, platinum 0.1 wt
%, aluminium oxide 27.5 wt %).
[0037] A honeycomb catalyst substrate (NGK product, 1 L) was
immersed in the bottom catalyst layer slurry, which was coated to
give a deposit when dry of 49 g/L, dried and then calcined at
500.degree. C. to form a bottom catalyst layer. The intermediate
catalyst layer slurry was then coated over the bottom catalyst
layer to give a deposit when dry of 110 g/L, dried and then
calcined at 500.degree. C. to form an intermediate catalyst layer.
The top catalyst layer slurry was then coated over the intermediate
catalyst layer to give a deposit when dry of 60 g/L, dried and then
calcined at 500.degree. C. to form a top catalyst layer, affording
an exhaust gas oxidation catalyst with a triple catalyst layer
(triple catalyst layer coverage 100% as a proportion of exhaust gas
channel surface).
WORKING EXAMPLE 3
[0038] The following slurries for forming the respective catalyst
layers were prepared.
[0039] 1) Bottom catalyst layer: A slurry containing cerium
oxide-zirconium oxide complex as oxygen-occluding agent and
aluminium oxide (oxygen-occluding agent 63 wt %, aluminium oxide 37
wt %).
[0040] 2) Intermediate catalyst layer slurry: A slurry containing
.beta.-zeolite as hydrocarbon adsorbent, platinum and palladium as
catalyst metals (added as platinum nitrate and palladium nitrate),
and aluminium oxide (.beta.-zeolite 9 wt % as hydrocarbon
adsorbent, platinum 1.1 wt %, palladium 0.5 wt %, aluminium oxide
89.4 wt %).
[0041] 3) Top catalyst layer slurry: A slurry containing cerium
oxide-zirconium oxide complex as oxygen-occluding agent, platinum
as catalyst metal (added as platinum nitrate), .beta.-zeolite as
hydrocarbon adsorbent, and aluminium oxide (oxygen-occluding agent
31 wt %, .beta.-zeolite as hydrocarbon adsorbent 36 wt %, aluminium
oxide 33 wt %).
[0042] A honeycomb catalyst substrate (NGK product, 1 L) was
immersed in the bottom catalyst layer slurry, which was coated to
give a deposit when dry of 55 g/L, dried and then calcined at
500.degree. C. to form a bottom catalyst layer. The intermediate
catalyst layer slurry was then coated over the bottom catalyst
layer to give a deposit when dry of 110 g/L, dried and then
calcined at 500.degree. C. to form an intermediate catalyst layer.
The top catalyst layer slurry was then coated over the intermediate
catalyst layer to give a deposit when dry of 60 g/L, dried and then
calcined at 500.degree. C. to form a top catalyst layer, affording
an exhaust gas oxidation catalyst with a triple catalyst layer
(triple catalyst layer coverage 100% as a proportion of exhaust gas
channel surface).
Comparative Example 1
[0043] An exhaust gas oxidation catalyst was produced without
forming a bottom catalyst layer containing oxygen-occluding agent,
using the following slurries for forming a catalyst metal layer and
a top catalyst layer,.
[0044] 1) Slurry for forming a layer containing catalyst metal: A
slurry containing platinum and palladium as catalyst metals (added
as platinum nitrate and palladium nitrate) and aluminium oxide
(platinum 1.0 wt %, palladium 0.5 wt %, inorganic support 98.5 wt
%).
[0045] 2) Top catalyst layer slurry: A slurry containing
.beta.-zeolite as hydrocarbon adsorbent, platinum as catalyst metal
(added as platinum nitrate), and aluminium oxide (.beta.-zeolite as
hydrocarbon adsorbent 63.9 wt %, platinum 0.1 wt %, aluminium oxide
36 wt %).
[0046] A honeycomb catalyst substrate (NGK product, 1 L) was
immersed in the slurry for forming a layer containing catalyst
metal, which was coated to give a deposit when dry of 178 g/L,
dried and then calcined at 500.degree. C. to form a catalyst
metal-containing layer. The top catalyst layer slurry was then
coated over the catalyst metal-containing layer to give a deposit
when dry of 60 g/L, dried and then calcined at 500.degree. C. to
form a top catalyst layer, affording an exhaust gas oxidation
catalyst with a dual catalyst layer (dual catalyst layer coverage
100% as a proportion of exhaust gas channel surface).
Comparative Example 2
[0047] A slurry containing .beta.-zeolite as hydrocarbon adsorbent,
platinum and palladium as catalyst metals (added as platinum
nitrate and palladium nitrate), and aluminium oxide (.beta.-zeolite
as hydrocarbon adsorbent 47.72 wt %, platinum 1.44 wt % and
palladium 0.72 wt % as catalyst metals, aluminium oxide 50.12 wt %)
was coated on a honeycomb catalyst substrate (NGK product, 1 L) to
give a deposit when dry of 180 g/L, dried and then calcined at
500.degree. C. to form a catalyst layer; an exhaust gas oxidation
catalyst with a single catalyst layer containing catalyst metals
was thereby obtained (single catalyst layer coverage 100% as a
proportion of exhaust gas channel surface).
Comparative Example 3
[0048] The following slurries were prepared to form the respective
catalyst layers.
[0049] 1) Bottom catalyst layer slurry: A slurry containing
aluminium oxide 100 wt % (containing no oxygen-occluding
agent).
[0050] 2) Intermediate catalyst layer slurry: A slurry containing
.beta.-zeolite as hydrocarbon adsorbent, platinum and palladium as
catalyst metals (added as platinum nitrate and palladium nitrate),
and aluminium oxide (.beta.-zeolite 11.2 wt % as hydrocarbon
adsorbent, platinum 1.6 wt %, palladium 0.8 wt %, aluminium oxide
86.4 wt %).
[0051] 3) Top catalyst layer slurry: A slurry containing
.beta.-zeolite as hydrocarbon adsorbent, platinum as catalyst metal
(added as platinum nitrate), and aluminium oxide (contains no
oxygen-occluding agent; .beta.-zeolite as hydrocarbon adsorbent
63.9 wt %, platinum 0.1 wt %, aluminium oxide 36 wt %).
[0052] A honeycomb catalyst substrate (NGK product, 1 L) was
immersed in the bottom catalyst layer slurry, which was coated to
give a deposit when dry of 49 g/L, dried and then calcined at
500.degree. C. to form a bottom catalyst layer. The intermediate
catalyst layer slurry was then coated over the bottom catalyst
layer to give a deposit when dry of 110 g/L, dried and then
calcined at 500.degree. C. to form an intermediate catalyst layer.
The top catalyst layer slurry was then coated over the intermediate
catalyst layer to give a deposit when dry of 50 g/L, dried and then
calcined at 500.degree. C. to form a top catalyst layer, affording
an exhaust gas oxidation catalyst with a triple catalyst layer
(triple catalyst layer coverage 100% as a proportion of exhaust gas
channel surface).
Comparative Example 4
[0053] The following slurries were prepared to form the respective
catalyst layers.
[0054] 1) Bottom catalyst layer slurry: A slurry containing cerium
oxide-zirconium oxide complex oxide as oxygen-occluding agent, and
aluminium oxide (oxygen-occluding agent 63 wt %, aluminium oxide 37
wt %).
[0055] 2) Intermediate catalyst layer slurry: A slurry containing
.beta.-zeolite as hydrocarbon adsorbent, platinum and palladium as
catalyst metals (added as platinum nitrate and palladium nitrate),
and aluminium oxide (.beta.-zeolite 11.2 wt % as hydrocarbon
adsorbent, platinum 1.6 wt %, palladium 0.8 wt %, aluminium oxide
86.4 wt %).
[0056] 3) Top catalyst layer slurry: A slurry containing
.beta.-zeolite as hydrocarbon adsorbent, platinum as catalyst metal
(added as platinum nitrate), and aluminium oxide (contains no
oxygen-occluding agent; .beta.-zeolite as hydrocarbon adsorbent
63.9 wt %, platinum 0.1 wt %, aluminium oxide 36 wt %).
[0057] A honeycomb catalyst substrate (NGK product, 1 L) was
immersed in the bottom catalyst layer slurry, which was coated to
give a deposit when dry of 49 g/L, dried and then calcined at
500.degree. C. to form a bottom catalyst layer. The intermediate
catalyst layer slurry was then coated over the bottom catalyst
layer to give a deposit when dry of 110 g/L, dried and then
calcined at 500.degree. C. to form an intermediate catalyst layer.
The top catalyst layer slurry was then coated over the intermediate
catalyst layer to give a deposit when dry of 50 g/L, dried and then
calcined at 500.degree. C. to form a top catalyst layer, affording
an exhaust gas oxidation catalyst with a triple catalyst layer
(triple catalyst layer coverage 100% as a proportion of exhaust gas
channel surface).
Comparative Example 5
[0058] The following slurries for forming the respective catalyst
layers were prepared.
[0059] 1) Bottom catalyst layer: A slurry containing cerium
oxide-zirconium oxide complex oxide as oxygen-occluding agent,
aluminium oxide, platinum as catalyst metal (added as platinum
nitrate) and .beta.-zeolite as hydrocarbon adsorbent
(.beta.-zeolite as hydrocarbon adsorbent 47 wt %, oxygen-occluding
agent 29 wt %, aluminium oxide 23.9 wt %, platinum 0.1 wt %).
[0060] 2) Intermediate catalyst layer slurry: A slurry containing
platinum and palladium as catalyst metals (added as platinum
nitrate and palladium nitrate), and aluminium oxide (platinum 2.4
wt %, palladium 1.2 wt %, aluminium oxide 96.4 wt %).
[0061] 3) Top catalyst layer slurry: A slurry containing
.beta.-zeolite as hydrocarbon adsorbent, cerium oxide-zirconium
oxide complex oxide as oxygen-occluding agent, platinum as catalyst
metal (added as platinum nitrate), and aluminium oxide
(oxygen-occluding agent 37.5 wt %, .beta.-zeolite as hydrocarbon
adsorbent 37.5 wt %, platinum 0.1 wt %, aluminium oxide 24.9 wt
%).
[0062] A honeycomb catalyst substrate (NGK product, 1 L) was
immersed in the bottom catalyst layer slurry, which was coated to
give a deposit when dry of 52 g/L, dried and then calcined at
500.degree. C. to form a bottom catalyst layer. The intermediate
catalyst layer slurry was then coated over the bottom catalyst
layer to give a deposit when dry of 72 g/L, dried and then calcined
at 500.degree. C. to form an intermediate catalyst layer. The top
catalyst layer slurry was then coated over the intermediate
catalyst layer to give a deposit when dry of 81 g/L, dried and then
calcined at 500.degree. C. to form a top catalyst layer, affording
an exhaust gas oxidation catalyst with a triple catalyst layer
(triple catalyst layer coverage 100% as a proportion of exhaust gas
channel surface).
Comparative Example 6
[0063] The following slurries were prepared to form the respective
catalyst layers.
[0064] 1) Bottom catalyst layer slurry: A slurry containing cerium
oxide-zirconium oxide complex oxide as oxygen-occluding agent, and
aluminium oxide (oxygen-occluding agent 63 wt %, aluminium oxide 37
wt %).
[0065] 2) Intermediate catalyst layer slurry: A slurry containing
platinum and palladium as catalyst metals (added as platinum
nitrate and palladium nitrate), and aluminium oxide (platinum 1.1
wt %, palladium 0.5 wt %, aluminium oxide 98.4 wt %).
[0066] 3) Top catalyst layer slurry: A slurry containing
.beta.-zeolite and ZSM-5 as hydrocarbon adsorbent, cerium
oxide-zirconium oxide complex oxide as oxygen-occluding agent,
platinum as catalyst metal (added as platinum nitrate), and
aluminium oxide (oxygen-occluding agent 27.4 wt %; .beta.-zeolite
25 wt % and ZSM5 zeolite 20 wt % as hydrocarbon adsorbents,
platinum 0.1 wt %, aluminium oxide 27.5 wt %).
[0067] A honeycomb catalyst substrate (NGK product, 1 L) was
immersed in the bottom catalyst layer slurry, which was coated to
give a deposit when dry of 49 g/L, dried and then calcined at
500.degree. C. to form a bottom catalyst layer. The intermediate
catalyst layer slurry was then coated over the bottom catalyst
layer to give a deposit when dry of 110 g/L, dried and then
calcined at 500.degree. C. to form an intermediate catalyst layer.
The top catalyst layer slurry was then coated over the intermediate
catalyst layer to give a deposit when dry of 67 g/L, dried and then
calcined at 500.degree. C. to form a top catalyst layer, affording
an exhaust gas oxidation catalyst with a triple catalyst layer
(triple catalyst layer coverage 100% as a proportion of exhaust gas
channel surface).
Comparative Example 7
[0068] The following slurries were prepared to form the respective
catalyst layers.
[0069] 1) Bottom catalyst layer slurry: A slurry containing alumina
100 wt % as binder (contains no oxygen-occluding agent).
[0070] 2) Intermediate catalyst layer slurry: A slurry containing
platinum as catalyst metal (added as platinum nitrate), and
aluminium oxide (contains no hydrocarbon adsorbent; platinum 3.3 wt
%, aluminium oxide 97.9 wt %).
[0071] 3) Top catalyst layer slurry: A slurry containing 100 wt %
aluminium oxide (contains no oxygen-occluding agent and no
hydrocarbon adsorbent).
[0072] A honeycomb catalyst substrate (NGK product, 1 L) was
immersed in the bottom catalyst layer slurry, which was coated to
give a deposit when dry of 73 g/L, dried and then calcined at
500.degree. C. to form a bottom catalyst layer. The intermediate
catalyst layer slurry was then coated over the bottom catalyst
layer to give a deposit when dry of 55 g/L, dried and then calcined
at 500.degree. C. to form an intermediate catalyst layer. Th top
catalyst layer slurry was then coated over the intermediate
catalyst layer to giv a deposit when dry of 47 g/L, dried and then
calcined at 500.degree. C. to form a top catalyst layer, affording
an exhaust gas oxidation catalyst with a triple catalyst layer
(triple catalyst layer coverage 100% as a proportion of exhaust gas
channel surface).
[0073] The exhaust gas oxidation catalysts of Working Examples 1-2
and Comparative Examples 1-6 were heat-treated for 50 hours in an
oven at 700.degree. C. and then mounted in the exhaust pipe of an
in-line 4-cylinder diesel engine. A sulphur poisoning test was
conducted at 300.degree. C. using light fuel oil with an addition
of 500 ppm of organosulphur compound. The throughput of sulphur was
set at 4.6 g/L. The catalyst was then restored by forced
regeneration for 15 min at 600.degree. C. using commercial light
oil (JIS2).
[0074] A simulated EC mode test was then conducted and the catalyst
performance was evaluated. The results are shown in Table 1.
TABLE-US-00001 TABLE 1 Catalyst Catalyst layers metal Catalyst
layers containing CO THC content Catalyst containing hydro-
oxygen-occluding conversion conversion (g/L) layering carbon
adsorbent agent (%) (%) Working Example 1 2.7 Triple layer Top
layer Top layer 62.7 82.1 Intermediate layer Bottom layer
Comparative 2.7 Double Catalyst metal- None 54.3 79.8 Example 1
layer containing layer Comparative 3.9 Single layer Single layer
None 54.1 85.2 Example 2 containing catalyst metal Comparative 2.7
Triple layer Top layer None 55.0 80.1 Example 3 Comparative 2.7
Triple layer Top layer Top layer 58.8 80.3 Example 4 Intermediate
layer Bottom layer Comparative 2.7 Triple layer Top layer Top layer
44.4 80.1 Example 5 Bottom layer Bottom layer Working Example 2 1.8
Triple layer Top layer Top layer 55.6 80.5 Intermediate layer
Bottom layer Comparative 1.8 Triple layer Top layer Top layer 51.1
80.5 Example 6 Bottom layer
[0075] From the results in Table 1, Working Example 1 has a higher
CO conversion than Comparative Examples 1-5 and Working Example 2
has a higher CO conversion than Comparative Example 5, confirming
that the exhaust gas oxidation catalyst of the invention has a
better exhaust gas cleaning efficacy than the prior art.
[0076] The exhaust gas oxidation catalysts of Working Example 3 and
Comparative Example 7 were heat-treated for 50 hours in an oven at
700.degree. C. and then mounted in the exhaust gas pipe of an
in-line 4-cylinder diesel engine. Using commercial light oil (JIS
2), simulated mode tests were run in the actual exhaust gas, and
the temperature (COT50) at which the CO conversion reached 50% was
recorded. The results are given in Table 2.
TABLE-US-00002 TABLE 2 COT50 Working Example 3 203 Comparative
Example 7 212
[0077] From the results in Table 2, the exhaust gas oxidation
catalyst of Working Example 3 has a lower COT50 than the exhaust
gas oxidation catalyst of Comparative Example 6, confirming that
the invention has superior exhaust gas cleaning efficacy.
WORKING EXAMPLE 4
[0078] An exhaust gas oxidation catalyst with a triple catalyst
layer (triple catalyst layer coverage 80% as a proportion of
exhaust gas channel surface) was obtained using the same bottom
catalyst layer slurry, intermediate catalyst layer slurry and top
catalyst layer slurry as in Working Example 1: firstly a honeycomb
catalyst substrate (NGK product, 1 L) was immersed in the bottom
catalyst layer slurry, which was coated to a bottom catalyst layer
slurry coverage of 80% of exhaust gas channel length in the
catalyst substrate, dried (deposit when dry 49 g/L) and then
calcined at 500.degree. C. to form a bottom catalyst layer. The
intermediate catalyst layer slurry was then coated over this to a
coverage of 100% of exhaust gas channel length, dried (deposit when
dry 110 g/L) and then calcined at 500.degree. C. to form an
intermediate catalyst layer. The top catalyst layer slurry was then
coated over this for a length equal to 80% of exhaust gas channel
length at a position overlapping the position of the bottom
catalyst layer slurry coating, dried (deposit when dry 50 g/L), and
then calcined at 500.degree. C. to form a top catalyst layer.
WORKING EXAMPLE 5
[0079] An exhaust gas oxidation catalyst with a triple catalyst
layer (triple catalyst layer coverage 50% as a proportion of
exhaust gas channel surface) was obtained using the same bottom
catalyst layer slurry, intermediate catalyst layer slurry and top
catalyst layer slurry as used in Working Example 1: firstly a
honeycomb catalyst substrate (NGK product, 1 L) was immersed in the
bottom catalyst layer slurry, which was coated to a coverage by
bottom catalyst layer slurry equal to 50% of exhaust gas channel
length in the catalyst substrate, dried (deposit when dry 49 g/L)
and then calcined at 500.degree. C. to form a bottom catalyst
layer. The intermediate catalyst layer slurry was then coated over
this to a coverage of 100% of exhaust gas channel length, dried
(deposit when dry 110 g/L) and then calcined at 500.degree. C. to
form an intermediate catalyst layer. The top catalyst layer slurry
was then coated over this for a length equal to 50% of exhaust gas
channel length at a position overlapping the position of the bottom
catalyst layer slurry coating, dried (deposit when dry 50 g/L), and
then calcined at 500.degree. C. to form a top catalyst layer.
[0080] The exhaust gas oxidation catalysts of Working Examples 4
and 5 were tested under the same conditions as in Working Example
1. The results are shown in Table 3.
TABLE-US-00003 TABLE 3 CO conversion THC conversion (%) (%) Working
Example 4 59.7 79.2 Working Example 5 56.2 75.6 Comparative Example
1 54.3 79.8
[0081] From the results in Table 3, the exhaust gas oxidation
catalysts of Working Examples 4 and 5 have a higher CO conversion
than the exhaust gas oxidation catalyst of Comparative Example 1,
confirming that they have superior exhaust gas cleaning
efficacy.
[0082] For the avoidance of doubt any and all patent or other
publications referred to herein are incorporated herein by
reference in their entirety.
Key to Drawings
[0083] 1 Exhaust gas oxidation catalyst [0084] 2 Exhaust gas
channel [0085] 3 Catalyst substrate [0086] 4 Exhaust gas channel
surface [0087] 5 Catalyst layer [0088] 6 Bottom catalyst layer
[0089] 7 Intermediate catalyst layer [0090] 8 Top catalyst
layer
* * * * *