U.S. patent application number 16/447243 was filed with the patent office on 2019-10-03 for oxidation catalyst for a diesel engine exhaust.
The applicant listed for this patent is JOHNSON MATTHEY PUBLIC LIMITED COMPANY. Invention is credited to Andrew Francis Chiffey, Oliver Cooper, Christopher Daly, Mark Feaviour, Steven Merrick, Francois Moreau, Matthew O'Brien, David Thompsett.
Application Number | 20190299159 16/447243 |
Document ID | / |
Family ID | 57680805 |
Filed Date | 2019-10-03 |
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United States Patent
Application |
20190299159 |
Kind Code |
A1 |
Chiffey; Andrew Francis ; et
al. |
October 3, 2019 |
OXIDATION CATALYST FOR A DIESEL ENGINE EXHAUST
Abstract
An oxidation catalyst is described for treating an exhaust gas
produced by a diesel engine comprising a catalytic region and a
substrate, wherein the catalytic region comprises a catalytic
material comprising: bismuth (Bi), antimony (Sb) or an oxide
thereof; a platinum group metal (PGM) selected from the group
consisting of (i) platinum (Pt), (ii) palladium (Pd) and (iii)
platinum (Pt) and palladium (Pd); and a support material, which is
a refractory oxide; wherein the platinum group metal (PGM) is
supported on the support material; and wherein the bismuth (Bi),
antimony (Sb) or an oxide thereof is supported on the support
material and/or the refractory oxide comprises the bismuth,
antimony or an oxide thereof.
Inventors: |
Chiffey; Andrew Francis;
(Royston, GB) ; Cooper; Oliver; (Royston, GB)
; Daly; Christopher; (Royston, GB) ; Feaviour;
Mark; (Reading, GB) ; Merrick; Steven;
(Reading, GB) ; Moreau; Francois; (Royston,
GB) ; O'Brien; Matthew; (Royston, GB) ;
Thompsett; David; (Royston, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
JOHNSON MATTHEY PUBLIC LIMITED COMPANY |
London |
|
GB |
|
|
Family ID: |
57680805 |
Appl. No.: |
16/447243 |
Filed: |
June 20, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15293364 |
Oct 14, 2016 |
10357743 |
|
|
16447243 |
|
|
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D 2255/50 20130101;
B01J 29/80 20130101; B01D 2255/1023 20130101; B01J 37/0205
20130101; B01J 23/6447 20130101; F01N 3/103 20130101; B01J 35/0006
20130101; F01N 2370/04 20130101; B01J 29/78 20130101; B01D 2255/902
20130101; B01J 29/7815 20130101; Y02A 50/2322 20180101; F01N
2330/60 20130101; B01D 2258/012 20130101; B01D 2255/1021 20130101;
B01J 37/0244 20130101; B01J 37/0234 20130101; B01J 2523/00
20130101; Y02T 10/24 20130101; B01D 2255/9032 20130101; B01J
37/0246 20130101; B01J 2229/186 20130101; F01N 3/0814 20130101;
B01D 2255/2096 20130101; B01J 37/10 20130101; B01J 23/6445
20130101; B01J 23/6562 20130101; B01D 2255/9022 20130101; B01D
2255/912 20130101; Y02A 50/20 20180101; B01D 2255/9025 20130101;
Y02T 10/12 20130101; B01D 2255/2092 20130101; B01J 37/0036
20130101; B01D 2255/2098 20130101; B01J 35/04 20130101; B01D
2255/30 20130101; B01D 2255/903 20130101; B01D 53/944 20130101;
B01J 37/0213 20130101; B01J 29/83 20130101; B01D 2255/91 20130101;
B01J 2523/00 20130101; B01J 2523/31 20130101; B01J 2523/41
20130101; B01J 2523/54 20130101; B01J 2523/824 20130101; B01J
2523/828 20130101; B01J 2523/00 20130101; B01J 2523/31 20130101;
B01J 2523/41 20130101; B01J 2523/53 20130101; B01J 2523/828
20130101; B01J 2523/00 20130101; B01J 2523/31 20130101; B01J
2523/54 20130101; B01J 2523/828 20130101 |
International
Class: |
B01D 53/94 20060101
B01D053/94; F01N 3/10 20060101 F01N003/10; B01J 37/00 20060101
B01J037/00; B01J 23/644 20060101 B01J023/644; B01J 37/02 20060101
B01J037/02; F01N 3/08 20060101 F01N003/08; B01J 29/78 20060101
B01J029/78; B01J 37/10 20060101 B01J037/10; B01J 35/04 20060101
B01J035/04; B01J 35/00 20060101 B01J035/00; B01J 29/80 20060101
B01J029/80; B01J 29/83 20060101 B01J029/83; B01J 23/656 20060101
B01J023/656 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 14, 2015 |
GB |
1518219.9 |
Jul 25, 2016 |
GB |
1612873.8 |
Jul 29, 2016 |
GB |
1613136.9 |
Aug 31, 2016 |
GB |
1614705.0 |
Claims
1. An oxidation catalyst for treating an exhaust gas produced by a
diesel engine comprising a catalytic region and a substrate,
wherein the catalytic region comprises a catalytic material
comprising: bismuth (Bi), antimony (Sb) or an oxide thereof; a
platinum group metal (PGM) selected from the group consisting of
(i) platinum (Pt), (ii) palladium (Pd) and (iii) platinum (Pt) and
palladium (Pd); and a support material, which is a refractory
oxide; wherein the platinum group metal (PGM) is supported on the
support material; and wherein the bismuth (Bi), antimony (Sb) or an
oxide thereof is supported on the support material.
2. An oxidation catalyst according to claim 1, wherein the
refractory oxide is a particulate refractory oxide, and the
bismuth, antimony or an oxide thereof is dispersed over a surface
of the particulate refractory oxide.
3. An oxidation catalyst according to claim 1, wherein the
catalytic material comprises bismuth (Bi) or an oxide thereof.
4. An oxidation catalyst according to claim 3, wherein the
refractory oxide is a particulate refractory oxide having a bulk
particulate structure, and the bismuth or an oxide thereof is
contained within the bulk particulate structure of the refractory
oxide.
5. An oxidation catalyst according to claim 3, wherein refractory
oxide is impregnated with bismuth or an oxide thereof.
6. An oxidation catalyst according to claim 1, wherein the
catalytic region has a total loading of bismuth or antimony of 1 to
200 g ft.sup.-3.
7. An oxidation catalyst according to claim 3, wherein the
refractory oxide further comprises tin (Sn) or an oxide
thereof.
8. An oxidation catalyst according to claim 1, wherein the
catalytic material comprises bismuth or antimony in an amount of
0.1 to 15.0% by weight.
9. An oxidation catalyst according to claim 1, wherein the
catalytic region comprises bismuth or antimony in an amount of 1.0
to 2.5% by weight.
10. An oxidation catalyst according to claim 1, wherein the
refractory oxide comprises alumina, silica or a mixed or composite
oxide of silica and alumina.
11. An oxidation catalyst according to claim 1, wherein the
refractory oxide comprises alumina doped with silica.
12. An oxidation catalyst according to claim 1, wherein the
platinum group metal (PGM) is platinum (Pt).
13. An oxidation catalyst according to claim 1, wherein the
platinum group metal (PGM) is palladium (Pd).
14. An oxidation catalyst according to claim 1, wherein the
platinum group metal (PGM) is platinum (Pt) and palladium (Pd).
15. An oxidation catalyst according to claim 1, wherein the
catalytic material comprises a ratio by weight of the platinum
group metal (PGM) to bismuth (Bi) or antimony (Sb) of 10:1 to
1:10.
16. An oxidation catalyst according to claim 1, wherein the
substrate is a flow-through monolith or a filtering monolith.
17. An exhaust system for treating an exhaust gas produced by a
diesel engine, wherein the exhaust system comprises the oxidation
catalyst of claim 1 and optionally an emissions control device.
18. A vehicle comprising a diesel engine and an exhaust system
according to claim 17.
Description
FIELD OF THE INVENTION
[0001] The invention relates to an oxidation catalyst and an
exhaust system for treating an exhaust gas produced by a diesel
engine. The invention further relates to a vehicle comprising the
oxidation catalyst or the exhaust system.
BACKGROUND TO THE INVENTION
[0002] Generally, there are four classes of pollutant that are
legislated against by inter-governmental organisations throughout
the world: carbon monoxide (CO), unburned hydrocarbons (HCs),
oxides of nitrogen (NO) and particulate matter (PM). As emissions
standards for permissible emission of pollutants in exhaust gases
from vehicular engines become progressively tightened, there is a
need to provide improved catalysts that are able to meet these
standards and which are cost-effective.
[0003] For diesel engines, an oxidation catalyst (often referred to
as a diesel oxidation catalyst (DOC)) is typically used to treat
the exhaust gas produced by such engines. Diesel oxidation
catalysts generally catalyse the oxidation of (1) carbon monoxide
(CO) to carbon dioxide (CO.sub.2), and (2) HCs to carbon dioxide
(CO.sub.2) and water (H.sub.2O). Exhaust gas temperatures for
diesel engines, particularly for light-duty diesel vehicles, are
relatively low (e.g. about 400.degree. C.) and so one challenge is
to develop durable catalyst formulations with low "light-off"
temperatures.
[0004] The activity of oxidation catalysts, such as DOCs, is often
measured in terms of its "light-off" temperature, which is the
temperature at which the catalyst starts to perform a particular
catalytic reaction or performs that reaction to a certain level.
Normally, "light-off" temperatures are given in terms of a specific
level of conversion of a reactant, such as conversion of carbon
monoxide. Thus, a T50 temperature is often quoted as a "light-off"
temperature because it represents the lowest temperature at which a
catalyst catalyses the conversion of a reactant at 50%
efficiency.
[0005] Exhaust systems for diesel engines may include several
emissions control devices. Each emissions control device has a
specialised function and is responsible for treating one or more
classes of pollutant in the exhaust gas. The performance of an
upstream emissions control device, such as an oxidation catalyst,
can affect the performance of a downstream emissions control
device. This is because the exhaust gas from the outlet of the
upstream emissions control device is passed into the inlet of the
downstream emissions control device. The interaction between each
emissions control device in the exhaust system is important to the
overall efficiency of the system.
[0006] Oxidation catalysts can also be formulated to oxidise some
of the nitric oxide (NO) that is present in the exhaust gas to
nitrogen dioxide (NO.sub.2). Even though nitrogen dioxide
(NO.sub.2) is itself a pollutant, the conversion of NO into
NO.sub.2 can be beneficial. The NO.sub.2 that is produced can be
used to regenerate particulate matter (PM) that has been trapped
by, for example, a downstream diesel particulate filter (DPF) or a
downstream catalysed soot filter (CSF). Generally, the NO.sub.2
generated by the oxidation catalyst increases the ratio of
NO.sub.2:NO in the exhaust gas from the outlet of the oxidation
catalyst compared to the exhaust gas at the inlet. This increased
ratio can be advantageous for exhaust systems comprising a
downstream selective catalytic reduction (SCR) catalyst or a
selective catalytic reduction filter (SCRF.TM.) catalyst. The ratio
of NO.sub.2:NO in the exhaust gas produced directly by a diesel
engine may be too low for optimum SCR or SCRF catalyst
performance.
SUMMARY OF THE INVENTION
[0007] The invention provides an oxidation catalyst for treating an
exhaust gas produced by a diesel engine comprising a catalytic
region and a substrate, wherein the catalytic region comprises a
catalytic material comprising: [0008] bismuth (Bi), antimony (Sb)
or an oxide thereof; [0009] a platinum group metal (PGM) selected
from the group consisting of (i) platinum (Pt), (ii) palladium (Pd)
and (iii) platinum (Pt) and palladium (Pd); and [0010] a support
material, which is a refractory oxide; wherein the platinum group
metal (PGM) is supported on the support material, and wherein the
bismuth (Bi), antimony (Sb) or an oxide thereof is supported on the
support material and/or the refractory oxide comprises the bismuth
(BD, antimony (Sb) or an oxide thereof.
[0011] The inventors have surprisingly found that:
(a) the presence of bismuth or an oxide thereof in combination with
a platinum group metal on certain support materials provides
excellent carbon monoxide (CO) oxidation activity. Advantageously,
the CO light off temperature for such oxidation catalysts is very
low; and (b) the presence of antimony or an oxide thereof in
combination with a platinum group metal on certain support
materials provides excellent carbon monoxide (CO) and hydrocarbon
(HC) oxidation activity. Advantageously, the CO and HC light off
temperatures for such oxidation catalysts are very low.
Additionally, the presence of antimony (Sb) is not detrimental to
the nitric oxide (NO) oxidation activity of the catalytic
material.
[0012] The invention also relates to an exhaust system for treating
an exhaust gas produced by a diesel engine. The exhaust system
comprises the oxidation catalyst of the invention and optionally an
emissions control device.
[0013] The invention further provides a vehicle. The vehicle
comprises a diesel engine and either an oxidation catalyst or an
exhaust system of the invention.
[0014] The invention also relates to the use of an oxidation
catalyst to treat an exhaust gas produced by a diesel engine. The
oxidation catalyst is an oxidation catalyst in accordance with the
invention.
[0015] Also provided by the invention is a method of treating an
exhaust gas produced by a diesel engine. The method comprises the
step of passing an exhaust gas produced by a diesel engine through
an exhaust system comprising the oxidation catalyst of the
invention.
[0016] In the use and method aspects of the invention, it is
preferable that the exhaust gas is produced by a diesel engine run
on fuel, preferably diesel fuel, comprising .ltoreq.50 ppm of
sulfur, more preferably .ltoreq.15 ppm of sulfur, such as
.ltoreq.10 ppm of sulfur, and even more preferably .ltoreq.5 ppm of
sulfur.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIGS. 1 to 5 are schematic representations of oxidation
catalysts of the invention. In each of the Figures, the left hand
side represents an inlet end of the substrate and the right hand
side represents an outlet end of the substrate.
[0018] FIG. 1 shows an oxidation catalyst having a first catalytic
layer (2) containing bismuth, antimony or an oxide thereof (e.g.
the refractory oxide may comprise bismuth, antimony or an oxide
thereof). The first catalytic layer (2) is disposed on a second
catalytic layer (3). The second catalytic layer (3) is disposed on
the substrate (1).
[0019] FIG. 2 shows an oxidation catalyst having a first catalytic
zone (2) containing bismuth, antimony or an oxide thereof (e.g. the
refractory oxide may comprise bismuth, antimony or an oxide
thereof). There is also a second catalytic zone (3) disposed on the
substrate (1).
[0020] FIG. 3 shows an oxidation catalyst having a first catalytic
zone (2) containing bismuth, antimony or an oxide thereof (e.g. the
refractory oxide may comprise bismuth, antimony or an oxide
thereof). The first catalytic zone (2) is disposed or supported on
a second catalytic layer (3) at or near an inlet end of the
substrate (1). The second catalytic layer (3) is disposed on the
substrate (1).
[0021] FIG. 4 shows an oxidation catalyst having a first catalytic
zone (2) containing bismuth, antimony or an oxide thereof (e.g. the
refractory oxide may comprise bismuth, antimony or an oxide
thereof). The first catalytic zone (2) is disposed on both a
substrate (1) and a second catalytic zone (3).
[0022] FIG. 5 shows an oxidation catalyst having a first catalytic
layer (2) containing bismuth, antimony or an oxide thereof (e.g.
the refractory oxide may comprise bismuth, antimony or an oxide
thereof). The first catalytic zone (2) is disposed on both a
substrate (1) and a second catalytic zone (3).
[0023] FIG. 6 shows an oxidation catalyst having a first catalytic
zone (2) containing bismuth, antimony or an oxide thereof (e.g. the
refractory oxide may comprise bismuth, antimony or an oxide
thereof), and a second catalytic zone (3). The first catalytic zone
(2) and the second catalytic zone (3) are disposed on a third
catalytic layer (4). The third catalytic layer (4) is disposed on a
substrate (1).
DETAILED DESCRIPTION OF THE INVENTION
[0024] The present invention will now be further described. The
following sections relate to different parts of the oxidation
catalyst of the invention and define each part in more detail. Each
part or aspect of the oxidation catalyst (e.g. the catalytic
region, the second catalytic region, the substrate etc.) may be
combined with any other part or aspect of the oxidation catalyst
unless clearly indicated to the contrary. In particular, any
feature indicated as being preferred or advantageous may be
combined with any other feature or features indicated as being
preferred or advantageous.
Catalytic Region (First)
[0025] The oxidation catalyst of the invention comprises a
catalytic region. In oxidation catalysts comprising two or more
catalytic regions, the catalytic region comprising bismuth,
antimony or an oxide thereof and a support material, which is a
refractory oxide (e.g. a refractory that may comprise bismuth or
antimony), is referred to herein as the "first catalytic
region".
[0026] The catalytic material may comprise, or consist essentially
of, bismuth or an oxide thereof, a platinum group metal (PGM)
selected from the group consisting of (i) platinum (Pt), (ii)
palladium (Pd) and (iii) platinum (Pt) and palladium (Pd); and a
support material, which is a refractory oxide.
[0027] Additionally or alternatively, the catalytic material may
comprise, or consist essentially of, antimony or an oxide thereof,
a platinum group metal (PGM) selected from the group consisting of
(i) platinum (Pt), (ii) palladium (Pd) and (iii) platinum (Pt) and
palladium (Pd); and a support material, which is a refractory
oxide. The platinum group metal (PGM) and the antimony (Sb) or an
oxide thereof is each supported on the support material
[0028] When the catalytic region comprises antimony or an oxide
thereof, then the antimony or an oxide thereof is preferably
supported on the support material, particularly the refractory
oxide thereof. The refractory oxide may also comprise antimony or
an oxide thereof. Small amounts of antimony may be impregnated into
the refractory oxide as part of the preparative method. It is
preferred that the bulk of the antimony is localised at the surface
of the support material.
[0029] The oxide of antimony may be diantimony tetroxide
(Sb.sub.2O.sub.4), antimony trioxide (Sb.sub.2O.sub.3), antimony
pentoxide (Sb.sub.2O.sub.5) and/or antimony hexitatridecoxide
(Sb.sub.6O.sub.13). Typically, the oxide of antimony is antimony
trioxide (Sb.sub.2O.sub.3).
[0030] The antimony or an oxide thereof is supported on the support
material. More preferably, the antimony or an oxide thereof is
disposed directly onto or is directly supported by the support
material. The antimony or an oxide thereof (e.g. particles of the
antimony or an oxide thereof) is typically supported on the support
material by being dispersed over a surface of the support material,
more preferably by being dispersed over, fixed onto a surface of
and/or impregnated onto or within the support material.
[0031] For the avoidance of doubt, when the refractory oxide
comprises antimony or an oxide thereof, the support material or the
refractory oxide thereof is not antimony or an oxide thereof (i.e.,
the support material or the refractory oxide thereof is not solely
antimony or an oxide thereof).
[0032] When the catalytic region comprises bismuth or an oxide
thereof, then the bismuth or an oxide thereof is preferably
supported on the support material, particularly the refractory
oxide thereof. More preferably, the bismuth or an oxide thereof is
disposed directly onto or is directly supported by the support
material. The bismuth or an oxide thereof (e.g. particles of the
bismuth or an oxide thereof) is typically supported on the support
material by being dispersed over a surface of the support material,
more preferably by being dispersed over, fixed onto a surface of
and/or impregnated within the support material.
[0033] The oxide of bismuth is typically bismuth (III) oxide
(Bi.sub.2O.sub.3). It is preferred that the refractory oxide
comprises an oxide of bismuth, preferably bismuth (III) oxide
(Bi.sub.2O.sub.3).
[0034] The refractory oxide may comprise bismuth or an oxide
thereof. Additionally or alternatively, bismuth or an oxide thereof
may be supported on the support material, particularly the
refractory oxide thereof.
[0035] For the avoidance of doubt, when the refractory oxide
comprises bismuth or an oxide thereof, the support material or the
refractory oxide thereof is not bismuth or an oxide thereof (i.e.
the support material or the refractory oxide thereof is not solely
bismuth or an oxide thereof).
[0036] Without being bound by theory, it is believed that the
bismuth is present in the form of an oxide, which is support on the
support material and/or in the support material. The bismuth oxide
is able to act as a promoter for CO oxidation because it has a high
oxygen ion conductivity and a high content of mobile oxide.
[0037] When the refractory oxide comprises bismuth, antimony or an
oxide thereof, then the catalytic region may comprise, or consist
essentially of, a catalytic material. The catalytic material may
comprise, or consist essentially of, a platinum group metal (PGM)
and a support material, wherein the platinum group metal (PGM) is
supported on the support material.
[0038] In general, when the refractory oxide comprise bismuth or an
oxide thereof, the refractory oxide comprises an effective amount
of bismuth or an oxide thereof to promote CO oxidation. The
effective amount may or may not be sufficient to inhibit the
oxidation of SO.sub.2 to SO.sub.3. It is, however, preferred that
the diesel engine is run on a low sulfur containing diesel fuel.
When a diesel engine is run on a low sulfur containing diesel fuel,
the effect of bismuth or an oxide thereof on the oxidation of
SO.sub.2 to SO.sub.3 is negligible.
[0039] Typically, the support material is a particulate refractory
oxide.
[0040] The bismuth or an oxide thereof is typically (i) dispersed
over a surface of the particulate refractory oxide (e.g. supported
on the refractory oxide) and/or (ii) contained within the bulk
particulate structure of the refractory oxide, such as described
below.
[0041] The antimony or an oxide thereof is typically dispersed over
a surface of the particulate refractory oxide (e.g. supported on
the refractory oxide). The antimony or an oxide thereof may also be
contained within the bulk particulate structure of the refractory
oxide.
[0042] The particulate refractory oxide may be impregnated with
bismuth, antimony or an oxide thereof. Thus, for example, particles
of a mixed or composite oxide of silica-alumina, particles of
alumina doped with silica may be impregnated with bismuth, antimony
or an oxide thereof. A particulate refractory oxide may be
impregnated with bismuth, antimony or an oxide thereof using
conventional techniques that are known in the art.
[0043] The particulate refractory oxide preferably comprises pores
(i.e. it is porous). The bismuth, antimony or oxide thereof may be
in the pores (e.g. of the particulate refractory oxide), preferably
bismuth or an oxide thereof. When the particulate refractory oxide
is impregnated with bismuth, antimony or an oxide thereof, then
bismuth, antimony or oxide thereof will be present in the pores of
the particulate refractory oxide.
[0044] Additionally or alternatively, the refractory oxide is doped
with bismuth, antimony or an oxide thereof, preferably bismuth or
an oxide thereof. It is to be understood that any reference to
"doped" in this context refers to a material where the bulk or host
lattice of the refractory oxide is substitution doped or
interstitially doped with a dopant. In some instances, small
amounts of the dopant may be present at a surface of the refractory
oxide. However, most of the dopant will generally be present in the
body of the refractory oxide.
[0045] When the refractory oxide is doped with bismuth, antimony or
an oxide thereof, it may be preferable that the refractory oxide
comprises alumina or a mixed or composite oxide of silica and
alumina.
[0046] In general, bismuth or an oxide thereof may or may not be
present (e.g. dispersed) on a surface of the particulate refractory
oxide. It is preferred that the bismuth or an oxide thereof is
present on a surface of the particulate refractory oxide.
[0047] The first catalytic region typically comprises a total
loading of bismuth of 1 to 200 g ft.sup.-3, such as 5 to 175 g
ft.sup.-3.
[0048] The first catalytic region typically comprises a total
loading of antimony of 1 to 500 g ft.sup.-3, (e.g., 1 to 200 g
ft.sup.-3), such as 5 to 175 g ft.sup.-3.
[0049] The loading refers to the amount of bismuth or antimony that
is present, whether in an elemental form or as part of a compound,
such as an oxide. It is has been found that the inclusion of large
amounts of bismuth can affect the catalytic region's oxidative
activity toward hydrocarbons.
[0050] It is preferred that the first catalytic region comprises a
total loading of bismuth or antimony of 10 to 100 g ft.sup.-3, more
preferably 25 to 75 g ft.sup.-3.
[0051] Typically, the first catalytic region, or the refractory
oxide thereof, comprises bismuth or antimony (e.g. as an element or
in the form of an oxide) in an amount of 0.1 to 15.0% by weight
(e.g. of the refractory oxide), preferably 0.5 to 10.0% by weight
(e.g. 0.75 to 5.0% by weight), more preferably 1.0 to 7.5% by
weight. These ranges refer to the amount of bismuth or antimony in
relation to the amount of the refractory oxide that is part of the
support material, whether the bismuth or antimony is (i) dispersed
over a surface of the particulate refractory oxide and/or (ii)
contained within the bulk particulate structure of the refractory
oxide (e.g. impregnated and/or in the pores) and/or (iii) as a
dopant of the refractory oxide.
[0052] The combination of bismuth or an oxide thereof with a
refractory oxide as defined below when used as a support material
for a PGM has unexpectedly been found to provide advantageous CO
oxidation activity.
[0053] The combination of antimony or an oxide thereof with a
refractory oxide as defined below when used in conjunction with a
PGM has unexpectedly been found to provide advantageous CO and HC
oxidation activity.
[0054] It is preferred that the first catalytic region comprises
bismuth or antimony in an amount of 1.0 to 2.5% by weight (e.g. of
the refractory oxide), preferably 1.25 to 2.25% by weight (e.g.
1.25. to 2.0% by weight), more preferably 1.5 to 2.0% by weight
(e.g. 1.5 to 1.75% by weight). The loading refers to the amount of
bismuth or antimony that is present, whether in an elemental form
or as part of a compound, such as an oxide. As mentioned above, the
relative proportion of bismuth or antimony to the refractory oxide
can affect the oxidative activity of the catalytic material toward
hydrocarbons.
[0055] The first catalytic region preferably comprises bismuth or
antimony in an amount of 0.25 to 1.25 mol % (e.g. relative to the
molar amount of the refractory oxide), preferably 0.50 to 1.10 mol
% (e.g. 0.50 to 1.00 mol %), more preferably 0.60 to 0.90 mol %
(e.g. 0.65 to 0.85 mol %).
[0056] Typically, the support material is a refractory oxide. The
refractory oxide preferably comprises alumina, silica or a mixed or
composite oxide of silica and alumina. It is preferred that the
refractory oxide comprises alumina. More preferably, the refractory
oxide is a mixed or composite oxide of silica-alumina.
[0057] When the refractory oxide is a mixed or composite oxide of
silica-alumina, then preferably the refractory oxide comprises 0.5
to 45% by weight of silica (i.e. 55 to 99.5% by weight of alumina),
preferably 1 to 40% by weight of silica, more preferably 1.5 to 30%
by weight of silica (e.g. 1.5 to 10% by weight of silica),
particularly 2.5 to 25% by weight of silica, more particularly 3.5
to 20% by weight of silica (e.g. 5 to 20% by weight of silica),
even more preferably 4.5 to 15% by weight of silica.
[0058] When the refractory oxide comprises, or consists essentially
of, alumina, then the alumina may optionally be doped (e.g. with a
dopant). The dopant may comprise, or consist essentially, of
silicon (Si) or an oxide thereof. Alumina doped with a dopant can
be prepared using methods known in the art or, for example, by a
method described in U.S. Pat. No. 5,045,519.
[0059] When the alumina is doped with a dopant comprising silicon
or an oxide thereof, then preferably the alumina is doped with
silica. The alumina is preferably doped with silica in a total
amount of 0.5 to 45% by weight (i.e. % by weight of the alumina),
preferably 1 to 40% by weight, more preferably 1.5 to 30% by weight
(e.g. 1.5 to 10% by weight), particularly 2.5 to 25% by weight,
more particularly 3.5 to 20% by weight (e.g. 5 to 20% by weight),
even more preferably 4.5 to 15% by weight.
[0060] The support material or the refractory oxide thereof
preferably does not comprise copper, particularly copper oxide
(CuO).
[0061] The catalytic material comprises a platinum group metal
(PGM) disposed or supported on the support material. The PGM may be
disposed directly onto or is directly supported by the support
material (e.g. there is no intervening material between the PGM and
the support material).
[0062] Typically, the PGM is dispersed on the support material
(e.g. particles of the PGM are dispersed over the surface of the
particulate refractory oxide). The PGM is preferably not in the
pores of the support material and/or the support material is not
impregnated with the PGM.
[0063] The platinum group metal (PGM) is selected from the group
consisting of (i) platinum (Pt), (ii) palladium (Pd) and (iii)
platinum (Pt) and palladium (Pd). The platinum group metal (PGM)
may be present in the catalytic material in metallic form or an
oxide thereof.
[0064] The platinum group metal (PGM) may preferably be palladium.
The catalytic material may comprise palladium as the only platinum
group metal (PGM) and/or the only noble metal. Surprisingly, it has
been found that the presence of bismuth or an oxide thereof (when
used in combination with a specific support material as defined
herein) can provide a catalytic material having excellent CO
oxidation when the catalytic material comprises palladium as the
only PGM.
[0065] The platinum group metal (PGM) may preferably be platinum.
The catalytic material may comprise platinum as the only platinum
group metal (PGM) and/or the only noble metal.
[0066] It has been found that advantageous oxidation activity
toward carbon monoxide (CO), particularly a low CO light off
temperature (T50), can be obtained when platinum is the PGM. The CO
light off temperature of a catalytic material comprising Pt as the
only PGM may be lower than some catalytic materials containing both
Pt and Pd (e.g. in a weight ratio of 2:1).
[0067] The catalytic material may comprise platinum and palladium
(i.e. the platinum group metal (PGM) is platinum and palladium).
Both the platinum and the palladium are disposed or supported on
the support material. Particles of platinum and palladium may be
dispersed over a surface of the particulate refractory oxide.
[0068] The platinum and palladium may be in the form of an alloy,
preferably a bimetallic alloy. Thus, the platinum group metal (PGM)
may therefore comprise, or consist essentially of, an alloy of
platinum and palladium.
[0069] When the catalytic material comprises platinum and
palladium, then typically the ratio by weight of platinum to
palladium is 20:1 to 1:20 (e.g. 15:1 to 1:15), preferably 10:1 to
1:10 (e.g. 7.5:1 to 1:7.5), more preferably 5:1 to 1:5 (e.g. 3:1 to
1:3). It may be preferable that the ratio by weight of platinum to
palladium is a .gtoreq.1:1, particularly >1:1.
[0070] It is particularly preferred that the ratio by weight of
platinum to palladium is 20:1 to 1:1 (e.g. 20:1 to 2:1,
particularly 20:1 to 5:1, such as 20:1 to 7:1), more preferably
17.5:1 to 2.5:1, particularly 15:1 to 5:1, and still more
preferably 12.5:1 to 7.5:1.
[0071] It has been found that CO oxidation activity, particularly a
low CO light off temperature (T50), can be obtained when the
catalytic material contains both platinum and palladium,
particularly in combination with bismuth, and the catalytic
material is relatively platinum rich. Surprisingly, the CO
oxidation activity of, for example, a catalytic material comprising
Pt and Pd in a weight ratio of 10:1 shows excellent CO oxidation
light off activity compared to a catalytic material containing Pt
only or Pt:Pd in a weight ratio of 2:1. The addition of a
relatively small amount of Pd also provides excellent hydrocarbon
(HC) and/or nitric oxide (NO) oxidation performance. Thus, the
catalytic material may have a low HC light off temperature and show
excellent NO conversion performance.
[0072] The catalytic material typically comprises a ratio by weight
of the platinum group metal (PGM) to bismuth (Bi) or antimony (Sb)
of 10:1 to 1:10 (e.g. 1:1 to 1:10), preferably 4:1 to 1:7.5 (e.g.
1:1.5 to 1:7.5), more preferably 2:1 to 1:5, particularly 1:1 to
1:4.
[0073] It is preferred that the catalytic material comprises a
ratio by weight of the platinum group metal (PGM) to bismuth (Bi)
or antimony (Sb) of 5:1 to 1:2, more preferably 4:1 to 3:5 (e.g.
5:2 to 3:5), such as 2:1 to 1:1. It has been found that the
relative proportion of PGM to bismuth can affect the oxidative
activity of the catalytic material toward hydrocarbons.
[0074] When the catalytic material comprises bismuth or an oxide
thereof, the refractory oxide may further comprise tin (Sn) or an
oxide thereof. The oxide of tin is typically tin (II) oxide (SnO)
and/or tin dioxide (SnO.sub.2). It is preferred that the refractory
oxide comprises an oxide of tin, particularly when the PGM is
platinum. When tin or an oxide thereof is included, the sintering
resistance of platinum can be improved and/or an improvement in HC
oxidation activity may be obtained.
[0075] The tin or an oxide thereof is typically contained within
the bulk particulate structure of the refractory oxide.
[0076] The particulate refractory oxide may be impregnated with tin
or an oxide thereof. Thus, for example, particles of a mixed or
composite oxide of silica-alumina, particles of alumina doped with
silica or particles alumina doped with tin or an oxide thereof may
be impregnated with both bismuth (or an oxide thereof) and tin (or
an oxide thereof). The particulate refractory oxide may be
impregnated with tin or an oxide thereof using conventional
techniques that are known in the art.
[0077] The tin or oxide thereof is preferably in the pores (e.g. of
the particulate refractory oxide). When the particulate refractory
is impregnated with tin or an oxide thereof, then tin or oxide
thereof will be present in the pores of the particulate refractory
oxide.
[0078] Typically, the refractory oxide comprises tin in an amount
of 0.1 to 10.0% by weight (e.g. of the refractory oxide),
preferably 0.5 to 7.5% by weight (e.g. 0.75 to 5.0% by weight),
more preferably 1.0 to 5.0% by weight.
[0079] The catalytic region may further comprise a hydrocarbon
adsorbent material. The hydrocarbon adsorbent material may be a
zeolite.
[0080] It is preferred that the zeolite is a medium pore zeolite
(e.g. a zeolite having a maximum ring size of ten tetrahedral
atoms) or a large pore zeolite (e.g. a zeolite having a maximum
ring size of twelve tetrahedral atoms). It may be preferable that
the zeolite is not a small pore zeolite (e.g. a zeolite having a
maximum ring size of eight tetrahedral atoms).
[0081] Examples of suitable zeolites or types of zeolite include
faujasite, clinoptilolite, mordenite, silicalite, ferrierite,
zeolite X, zeolite Y, ultrastable zeolite Y, AEI zeolite, ZSM-5
zeolite, ZSM-12 zeolite, ZSM-20 zeolite, ZSM-34 zeolite, CHA
zeolite. SSZ-3 zeolite, SAPO-5 zeolite, offretite, a beta zeolite
or a copper CHA zeolite. The zeolite is preferably ZSM-5, a beta
zeolite or a Y zeolite.
[0082] When the catalytic region comprises a hydrocarbon adsorbent,
the total amount of hydrocarbon adsorbent is 0.05 to 3.00 g
in.sup.-3, particularly 0.10 to 2.00 g in.sup.-3, more particularly
0.2 to 1.0 g in.sup.-3. For example, the total amount of
hydrocarbon adsorbent may be 0.8 to 1.75 g in.sup.-3, such as 1.0
to 1.5 g in.sup.-3.
[0083] In general, it is preferred that the oxidation catalyst of
the invention or the catalytic region or the catalytic material is
substantially free of gold. More preferably, the oxidation catalyst
of the invention or the catalytic region or the catalytic material
does not comprise gold.
[0084] Additionally or alternatively, the catalytic region or the
catalytic material is substantially free of manganese. More
preferably, the catalytic region or the catalytic material does not
comprise manganese.
[0085] In general, the catalytic region or the catalytic material
does not comprise clay, particularly bentonite.
[0086] The catalytic region is preferably substantially free of
rhodium and/or a NO.sub.x storage component comprising, or
consisting essentially of, an oxide, a carbonate or a hydroxide of
an alkali metal, an alkaline earth metal and/or a rare earth metal
(except for an oxide of cerium (i.e. from the oxygen storage
material)). More preferably, the catalytic region does not comprise
rhodium and/or a NO.sub.x storage component comprising, or
consisting essentially of, an oxide, a carbonate or a hydroxide of
an alkali metal, an alkaline earth metal and/or a rare earth
metal.
[0087] The catalytic region typically has a total loading of the
PGM of 5 to 300 g ft.sup.-3. It is preferred that the catalytic
region has a total loading of the PGM of 10 to 250 g ft.sup.-3
(e.g. 75 to 175 g ft.sup.-3), more preferably 15 to 200 g ft.sup.-3
(e.g. 50 to 150 g ft.sup.-3), still more preferably 20 to 150 g
ft.sup.-3.
[0088] Generally, the catalytic region comprises a total amount of
the support material of 0.1 to 3.0 g in.sup.-3, preferably 0.2 to
2.5 g in.sup.-3, still more preferably 0.3 to 2.0, and even more
preferably 0.5 to 1.75 g in.sup.-3.
[0089] The catalytic region may be disposed or supported on the
substrate. It is preferred that the catalytic region is directly
disposed or directly supported on the substrate (i.e. the region is
in direct contact with a surface of the substrate).
[0090] The oxidation catalyst may comprise a single catalytic
region. The catalytic region may be a catalytic layer (e.g. a
single catalytic layer).
[0091] Alternatively, the oxidation catalyst may further comprise a
second catalytic region, such as a second catalytic region
described below. The catalytic region described above (i.e. the
catalytic region comprising bismuth) is referred to below as the
first catalytic region. Thus, the oxidation catalyst comprises a
first catalytic region and a second catalytic region. For the
avoidance of doubt, the first catalytic region is different (i.e.
different composition) to the second catalytic region.
[0092] The oxidation catalyst may further comprise a third
catalytic region. When the oxidation catalyst comprises a third
catalytic region, the third catalytic region is different (i.e.
different composition) to both the first catalytic region and the
second catalytic region.
[0093] In a first arrangement, the first catalytic region is a
first catalytic layer and the second catalytic region is a second
catalytic layer. The first catalytic layer may be disposed or
supported (e.g. directly disposed or supported) on the second
catalytic layer. See, for example, FIG. 1. Alternatively, the
second catalytic layer may be disposed or supported (e.g. directly
disposed or supported) on the first catalytic layer. It is
preferred that the first catalytic layer is disposed or supported
(e.g. directly disposed or supported) on the second catalytic
layer.
[0094] When the first catalytic layer is disposed or supported
(e.g. directly disposed or supported) on the second catalytic
layer, then the second catalytic layer may be disposed or supported
(e.g. directly disposed or supported) on the substrate or on a
third catalytic region, preferably a third catalytic layer. It is
preferred that the second catalytic layer may be disposed or
supported (e.g. directly disposed or supported) on the
substrate.
[0095] When the second catalytic layer is disposed or supported
(e.g. directly disposed or supported) on the first catalytic layer,
then the first catalytic layer may be disposed or supported (e.g.
directly disposed or supported) on the substrate or on a third
catalytic region, preferably a third catalytic layer. It is
preferred that the first catalytic layer may be disposed or
supported (e.g. directly disposed or supported) on the
substrate.
[0096] The first catalytic layer typically extends for an entire
length (i.e. substantially an entire length) of the substrate,
particularly the entire length of the channels of a substrate
monolith.
[0097] The second catalytic layer typically extends for an entire
length (i.e. substantially an entire length) of the substrate,
particularly the entire length of the channels of a substrate
monolith.
[0098] In the first arrangement, when the oxidation catalyst
comprises a third catalytic layer, then the third catalytic layer
typically extends for an entire length (i.e. substantially an
entire length) of the substrate, particularly the entire length of
the channels of a substrate monolith.
[0099] In a second arrangement, the first catalytic region is a
first catalytic zone and the second catalytic region is a second
catalytic zone. The first catalytic zone may be disposed upstream
of the second catalytic zone. See, for example, FIG. 2.
Alternatively, the second catalytic zone may be disposed upstream
of the first catalytic zone. It is preferred that the first
catalytic zone is disposed upstream of the second catalytic
zone.
[0100] The first catalytic zone may adjoin the second catalytic
zone or there may be a gap (e.g. a space) between the first
catalytic zone and the second catalytic zone. Preferably, the first
catalytic zone is contact with the second catalytic zone. When the
first catalytic zone adjoins and/or is in contact with the second
catalytic zone, then the combination of the first catalytic zone
and the second catalytic zone may be disposed or supported on the
substrate as a layer (e.g. a single layer). Thus, a layer (e.g. a
single) may be formed on the substrate when the first and second
catalytic zones adjoin or are in contact with one another. Such an
arrangement may avoid problems with back pressure.
[0101] The first catalytic zone typically has a length of 10 to 90%
of the length of the substrate (e.g. 10 to 45%), preferably 15 to
75% of the length of the substrate (e.g. 15 to 40%), more
preferably 20 to 70% (e.g. 30 to 65%. such as 25 to 45%) of the
length of the substrate, still more preferably 25 to 65% (e.g. 35
to 50%).
[0102] The second catalytic zone typically has a length of 10 to
90% of the length of the substrate (e.g. 10 to 45%), preferably 15
to 75% of the length of the substrate (e.g. 15 to 40%), more
preferably 20 to 70% (e.g. 30 to 65%, such as 25 to 45%) of the
length of the substrate, still more preferably 25 to 65% (e.g. 35
to 50%).
[0103] The first catalytic zone and the second catalytic zone may
be disposed or supported (e.g. directly disposed or supported) on
the substrate. Alternatively, the first catalytic zone and the
second catalytic zone may be disposed or supported (e.g. directly
disposed or supported) on a third catalytic region, preferably a
third catalytic layer. See, for example, FIG. 6.
[0104] In the second arrangement, when the oxidation catalyst
comprises a third catalytic layer, then the third catalytic layer
typically extends for an entire length (i.e. substantially an
entire length) of the substrate, particularly the entire length of
the channels of a substrate monolith.
[0105] In a third arrangement, the first catalytic region is
disposed or supported (e.g. directly disposed or supported) on the
second catalytic region.
[0106] The second catalytic region may be disposed or supported
(e.g. directly disposed or supported) on the substrate.
Alternatively, the second catalytic region may be disposed or
supported (e.g. directly disposed or supported) on a third
catalytic region, preferably a third catalytic layer. It is
preferred that the second catalytic region is disposed or supported
(e.g. directly disposed or supported) on the substrate.
[0107] An entire length (e.g. all) of the first catalytic region
may be disposed or supported (e.g. directly disposed or supported)
on the second catalytic region. See, for example, FIG. 3.
Alternatively, a part or portion of the length of the first
catalytic region may be disposed or supported (e.g. directly
disposed or supported) on the second catalytic region. A part or
portion (e.g. the remaining part or portion) of the length of the
first catalytic region may be disposed or supported (e.g. directly
disposed or supported) on the substrate (see, for example, FIGS. 4
and 5) or a third catalytic region, preferably a third catalytic
layer.
[0108] The second catalytic region may be a second catalytic layer
and the first catalytic region may be a first catalytic zone. The
entire length of the first catalytic zone is preferably disposed or
supported on the second catalytic layer (e.g. see FIG. 3). The
second catalytic layer may be disposed or supported (e.g. directly
disposed or supported) on the substrate or a third catalytic layer.
It is preferred that the second catalytic layer is disposed or
supported (e.g. directly disposed or supported) on the
substrate.
[0109] The second catalytic layer typically extends for an entire
length (i.e. substantially an entire length) of the substrate,
particularly the entire length of the channels of a substrate
monolith.
[0110] The first catalytic zone typically has a length of 10 to 90%
of the length of the substrate (e.g. 10 to 45%), preferably 15 to
75% of the length of the substrate (e.g. 15 to 40%), more
preferably 20 to 70% (e.g. 30 to 65%, such as 25 to 45%) of the
length of the substrate, still more preferably 25 to 65% (e.g. 35
to 50%).
[0111] The first catalytic zone may be disposed at or near an inlet
end of the substrate (e.g. as shown in FIG. 3). The first catalytic
zone may be disposed at or near an outlet end of the substrate. It
is preferred that the first catalytic zone is disposed at or near
an inlet end of the substrate.
[0112] In an alternative third arrangement, the second catalytic
region is a second catalytic zone and the first catalytic region is
a first catalytic zone or a first catalytic layer. The first
catalytic zone or the first catalytic layer is disposed or
supported (e.g. directly disposed or supported) on the second
catalytic zone. See, for example, FIGS. 4 and 5.
[0113] The second catalytic zone typically has a length of 10 to
90% of the length of the substrate (e.g. 10 to 45%), preferably 15
to 75% of the length of the substrate (e.g. 15 to 40%), more
preferably 20 to 70% (e.g. 30 to 65%, such as 25 to 45%) of the
length of the substrate, still more preferably 25 to 65% (e.g. 35
to 50%).
[0114] An entire length (e.g. all) of the second catalytic zone may
be disposed or supported (e.g. directly disposed or supported) on
the substrate. Alternatively, an entire length (e.g. all) of the
second catalytic zone may be disposed or supported (e.g. directly
disposed or supported) on the third catalytic layer.
[0115] The second catalytic zone may be disposed at or near an
outlet end of the substrate (e.g. as shown in FIGS. 4 and 5). The
second catalytic zone may be disposed at or near an inlet end of
the substrate. It is preferred that the second catalytic zone is
disposed at or near an outlet end of the substrate.
[0116] In addition to being disposed or supported on the second
catalytic zone, the first catalytic zone or the first catalytic
layer may be disposed or supported (e.g. directly disposed or
supported) on the substrate or a third catalytic layer, preferably
the substrate. Thus, a part or portion of the length of the first
catalytic zone or the first catalytic layer may be disposed or
supported (e.g. directly disposed or supported) on the second
catalytic zone and a part or portion (e.g. the remaining part or
portion) of the length of the first catalytic zone or the first
catalytic layer may be disposed or supported (e.g. directly
disposed or supported) on the substrate or the third catalytic
layer, preferably the substrate.
[0117] In the alternative third arrangement, when the first
catalytic region is a first catalytic zone (e.g. as shown in FIG.
4), then the first catalytic zone typically has a length of 10 to
90% of the length of the substrate (e.g. 10 to 45%), preferably 15
to 75% of the length of the substrate (e.g. 15 to 40%), more
preferably 20 to 70% (e.g. 30 to 65%, such as 25 to 45%) of the
length of the substrate, still more preferably 25 to 65% (e.g. 35
to 50%).
[0118] The first catalytic zone may be disposed at or near an inlet
end of the substrate (e.g. as shown in FIG. 4). The first catalytic
zone may be disposed at or near an outlet end of the substrate. It
is preferred that the first catalytic zone is disposed at or near
an outlet end of the substrate.
[0119] In the alternative third arrangement, when the first
catalytic region is a first catalytic layer (e.g. as shown in FIG.
5), then the first catalytic layer typically extends for an entire
length (i.e. substantially an entire length) of the substrate,
particularly the entire length of the channels of a substrate
monolith. When the first catalytic region is a first catalytic
layer, then preferably the second catalytic zone is disposed at or
near an outlet end of the substrate.
[0120] In a fourth arrangement, the second catalytic region is
disposed or supported on the first catalytic region.
[0121] The first catalytic region may be disposed or supported
(e.g. directly disposed or supported) on the substrate.
Alternatively, the first catalytic region may be disposed or
supported (e.g. directly disposed or supported) on a third
catalytic region, preferably a third catalytic layer. It is
preferred that the first catalytic region is disposed or supported
(e.g. directly disposed or supported) on the substrate.
[0122] An entire length (e.g. all) of the second catalytic region
may be disposed or supported (e.g. directly disposed or supported)
on the first catalytic region. Alternatively, a part or portion of
the length of the second catalytic region may be disposed or
supported (e.g. directly disposed or supported) on the first
catalytic region. A part or portion (e.g. the remaining part or
portion) of the length of the second catalytic region may be
disposed or supported (e.g. directly disposed or supported) on the
substrate or a third catalytic region, preferably a third catalytic
layer.
[0123] The first catalytic region may be a first catalytic layer
and the second catalytic region may be a second catalytic zone. The
entire length of the second catalytic zone is preferably disposed
or supported on the first catalytic layer. The first catalytic
layer may be disposed or supported (e.g. directly disposed or
supported) on the substrate or a third catalytic layer. It is
preferred that the first catalytic layer is disposed or supported
(e.g. directly disposed or supported) on the substrate.
[0124] The first catalytic layer typically extends for an entire
length (i.e. substantially an entire length) of the substrate,
particularly the entire length of the channels of a substrate
monolith.
[0125] The second catalytic zone typically has a length of 10 to
90% of the length of the substrate (e.g. 10 to 45%), preferably 15
to 75% of the length of the substrate (e.g. 15 to 40%), more
preferably 20 to 70% (e.g. 30 to 65%, such as 25 to 45%) of the
length of the substrate, still more preferably 25 to 65% (e.g. 35
to 50%).
[0126] The second catalytic zone may be disposed at or near an
inlet end of the substrate (e.g. as shown in FIG. 3). The second
catalytic zone may be disposed at or near an outlet end of the
substrate. It is preferred that the second catalytic zone is
disposed at or near an outlet end of the substrate.
[0127] In an alternative fourth arrangement, the first catalytic
region is a first catalytic zone and the second catalytic region is
a second catalytic zone or a second catalytic layer. The second
catalytic zone or the second catalytic layer is disposed or
supported (e.g. directly disposed or supported) on the first
catalytic zone.
[0128] The first catalytic zone typically has a length of 10 to 90%
of the length of the substrate (e.g. 10 to 45%), preferably 15 to
75% of the length of the substrate (e.g. 15 to 40%), more
preferably 20 to 70% (e.g. 30 to 65%, such as 25 to 45%) of the
length of the substrate, still more preferably 25 to 65% (e.g. 35
to 50%).
[0129] An entire length (e.g. all) of the first catalytic zone may
be disposed or supported (e.g. directly disposed or supported) on
the substrate. Alternatively, an entire length (e.g. all) of the
first catalytic zone may be disposed or supported (e.g. directly
disposed or supported) on the third catalytic layer.
[0130] The first catalytic zone may be disposed at or near an
outlet end of the substrate. The first catalytic zone may be
disposed at or near an inlet end of the substrate. It is preferred
that the first catalytic zone is disposed at or near an inlet end
of the substrate.
[0131] In addition to being disposed or supported on the first
catalytic zone, the second catalytic zone or the second catalytic
layer may be disposed or supported (e.g. directly disposed or
supported) on the substrate or a third catalytic layer, preferably
the substrate. Thus, a part or portion of the length of the second
catalytic zone or the second catalytic layer may be disposed or
supported (e.g. directly disposed or supported) on the first
catalytic zone and a part or portion (e.g. the remaining part or
portion) of the length of the second catalytic zone or the second
catalytic layer may be disposed or supported (e.g. directly
disposed or supported) on the substrate or the third catalytic
layer, preferably the substrate.
[0132] In the alternative fourth arrangement, when the second
catalytic region is a second catalytic zone, then the second
catalytic zone typically has a length of 10 to 90% of the length of
the substrate (e.g. 10 to 45%), preferably 15 to 75% of the length
of the substrate (e.g. 15 to 40%), more preferably 20 to 70% (e.g.
30 to 65%, such as 25 to 45%) of the length of the substrate, still
more preferably 25 to 65% (e.g. 35 to 50%).
[0133] The second catalytic zone may be disposed at or near an
inlet end of the substrate. The second catalytic zone may be
disposed at or near an outlet end of the substrate. It is preferred
that the second catalytic zone is disposed at or near an outlet end
of the substrate.
[0134] In the alternative fourth arrangement, when the second
catalytic region is a second catalytic layer, then the second
catalytic layer typically extends for an entire length (i.e.
substantially an entire length) of the substrate, particularly the
entire length of the channels of a substrate monolith. When the
second catalytic region is a second catalytic layer, then
preferably the first catalytic zone is disposed at or near an inlet
end of the substrate.
[0135] As a general feature of the third arrangement or the fourth
arrangement, when the oxidation catalyst comprises a third
catalytic layer, the third catalytic layer typically extends for an
entire length (i.e. substantially an entire length) of the
substrate, particularly the entire length of the channels of a
substrate monolith.
[0136] In the first to fourth arrangements above, the second
catalytic region, layer or zone may have DOC activity, PNA activity
or LNT activity, as described below. When the oxidation catalyst
comprises a third catalytic region layer or zone, it is preferred
that (i) the second catalytic region, layer or zone has DOC
activity and the third catalytic region, layer or zone has either
PNA activity or LNT activity or (ii) the second catalytic region,
layer or zone has either PNA activity or LNT activity and the third
catalytic region, layer or zone has DOC activity. More preferably,
the second catalytic region, layer or zone has DOC activity and the
third catalytic region, layer or zone has either PNA activity or
LNT activity. Even more preferably, the second catalytic region,
layer or zone has DOC activity and the third catalytic region,
layer or zone has PNA activity.
[0137] The regions, zones and layers described hereinabove may be
prepared using conventional methods for making and applying
washcoats onto a substrate are also known in the art (see, for
example, our WO 99/47260, WO 2007/077462 and WO 2011/080525).
Second Catalytic Region and/or Third Catalytic Region
[0138] The second catalytic region may be formulated to provide the
oxidation catalyst with additional functionality. The presence of
the first catalytic region in combination with the second catalytic
region may enhance the activity of the oxidation catalyst as whole
or the activity of the second catalytic region. This enhancement in
activity may result from a synergistic interaction between the
first catalytic region and the second catalytic region. The low CO
light off temperature of the first catalytic region may generate an
exotherm that is able to rapidly bring the second catalytic region
up to its light off temperature.
[0139] The second catalytic region may have NO.sub.x storage
activity, such as lean NO.sub.x trap (LNT) activity or passive
NO.sub.x absorber (PNA) activity. Additionally or alternatively,
the second catalytic region may be for oxidising hydrocarbons (HCs)
and/or nitric oxide (NO) in the exhaust gas produced by the diesel
engine (e.g. the second catalytic region is a diesel oxidation
catalytic region).
Catalytic Region Having PNA Activity
[0140] The second or third catalytic region may have PNA activity.
A passive NO.sub.x absorber (PNA) is able to store or absorb
NO.sub.x at relatively low exhaust gas temperatures (e.g. less than
200.degree. C.), usually by adsorption, and release NO.sub.x at
higher temperatures. The NO.sub.x storage and release mechanism of
PNAs is thermally controlled, unlike that of LNTs which require a
rich purge to release stored NO.sub.x.
[0141] When the second or third catalytic region has NO.sub.x
storage activity (e.g. PNA activity), then the second or third
catalytic region comprises, or consists essentially of, a molecular
sieve catalyst comprising a noble metal and a molecular sieve,
wherein the molecular sieve contains the noble metal.
[0142] The noble metal is typically selected from the group
consisting of palladium (Pd), platinum (Pt) and rhodium (Rh). More
preferably, the noble metal is selected from palladium (Pd),
platinum (Pt) and a mixture thereof.
[0143] Generally, it is preferred that the noble metal comprises,
or consists of, palladium (Pd) and optionally a second metal
selected from the group consisting of platinum (Pt), rhodium (Rh),
gold (Au), silver (Ag), iridium (Ir) and ruthenium (Ru).
Preferably, the noble metal comprises, or consists of, palladium
(Pd) and optionally a second metal selected from the group
consisting of platinum (Pt) and rhodium (Rh). Even more preferably,
the noble metal comprises, or consists of, palladium (Pd) and
optionally platinum (Pt). More preferably, the molecular sieve
catalyst comprises palladium as the only noble metal.
[0144] When the noble metal comprises, or consists of, palladium
(Pd) and a second metal, then the ratio by mass of palladium (Pd)
to the second metal is >1:1. More preferably, the ratio by mass
of palladium (Pd) to the second metal is >1:1 and the molar
ratio of palladium (Pd) to the second metal is >1:1.
[0145] The molecular sieve catalyst may further comprise a base
metal. Thus, the molecular sieve catalyst may comprise, or consist
essentially of, a noble metal, a molecular sieve and optionally a
base metal. The molecular sieve contains the noble metal and
optionally the base metal.
[0146] The base metal may be selected from the group consisting of
iron (Fe), copper (Cu), manganese (Mn), chromium (Cr), cobalt (Co),
nickel (Ni), zinc (Zn) and tin (Sn), as well as mixtures of two or
more thereof. It is preferred that the base metal is selected from
the group consisting of iron, copper and cobalt, more preferably
iron and copper. Even more preferably, the base metal is iron.
[0147] Alternatively, the molecular sieve catalyst may be
substantially free of a base metal, such as a base metal selected
from the group consisting of iron (Fe), copper (Cu), manganese
(Mn), chromium (Cr), cobalt (Co), nickel (Ni), zinc (Zn) and tin
(Sn), as well as mixtures of two or more thereof. Thus, the
molecular sieve catalyst may not comprise a base metal.
[0148] In general, it is preferred that the molecular sieve
catalyst does not comprise a base metal.
[0149] It may be preferable that the molecular sieve catalyst is
substantially free of barium (Ba), more preferably the molecular
sieve catalyst is substantially free of an alkaline earth metal.
Thus, the molecular sieve catalyst may not comprise barium,
preferably the molecular sieve catalyst does not comprise an
alkaline earth metal.
[0150] The molecular sieve is typically composed of aluminium,
silicon, and/or phosphorus. The molecular sieve generally has a
three-dimensional arrangement (e.g. framework) of SiO.sub.4,
AlO.sub.4, and/or PO.sub.4 that are joined by the sharing of oxygen
atoms. The molecular sieve may have an anionic framework. The
charge of the anionic framework may be counterbalanced by cations,
such as by cations of alkali and/or alkaline earth elements (e.g.,
Na, K, Mg, Ca, Sr, and Ba), ammonium cations and/or protons.
[0151] Typically, the molecular sieve has an aluminosilicate
framework, an aluminophosphate framework or a
silico-aluminophosphate framework. The molecular sieve may have an
aluminosilicate framework or an aluminophosphate framework. It is
preferred that the molecular sieve has an aluminosilicate framework
or a silico-aluminophosphate framework. More preferably, the
molecular sieve has an aluminosilicate framework.
[0152] When the molecular sieve has an aluminosilicate framework,
then the molecular sieve is preferably a zeolite.
[0153] The molecular sieve contains the noble metal. The noble
metal is typically supported on the molecular sieve. For example,
the noble metal may be loaded onto and supported on the molecular
sieve, such as by ion-exchange. Thus, the molecular sieve catalyst
may comprise, or consist essentially of, a noble metal and a
molecular sieve, wherein the molecular sieve contains the noble
metal and wherein the noble metal is loaded onto and/or supported
on the molecular sieve by ion exchange.
[0154] In general, the molecular sieve may be a metal-substituted
molecular sieve (e.g. metal-substituted molecular sieve having an
aluminosilicate or an aluminophosphate framework). The metal of the
metal-substituted molecular sieve may be the noble metal (e.g. the
molecular sieve is a noble metal substituted molecular sieve).
Thus, the molecular sieve containing the noble metal may be a noble
metal substituted molecular sieve. When the molecular sieve
catalyst comprises a base metal, then the molecular sieve may be a
noble and base metal-substituted molecular sieve. For the avoidance
of doubt, the term "metal-substituted" embraces the term
"ion-exchanged".
[0155] The molecular sieve catalyst generally has at least 1% by
weight (i.e. of the amount of noble metal of the molecular sieve
catalyst) of the noble metal located inside pores of the molecular
sieve, preferably at least 5% by weight, more preferably at least
10% by weight, such as at least 25% by weight, even more preferably
at least 50% by weight.
[0156] The molecular sieve may be selected from a small pore
molecular sieve (i.e. a molecular sieve having a maximum ring size
of eight tetrahedral atoms), a medium pore molecular sieve (i.e. a
molecular sieve having a maximum ring size of ten tetrahedral
atoms) and a large pore molecular sieve (i.e. a molecular sieve
having a maximum ring size of twelve tetrahedral atoms). More
preferably, the molecular sieve is selected from a small pore
molecular sieve and a medium pore molecular sieve.
[0157] In a first molecular sieve catalyst embodiment, the
molecular sieve is a small pore molecular sieve. The small pore
molecular sieve preferably has a Framework Type selected from the
group consisting of ACO, AEI, AEN, AFN, AFT, AFX, ANA, APC, APD,
ATT, CDO, CHA, DDR, DFT, EAB, EDI, EPI, ERI, GIS, GOO, IHW, ITE,
ITW, LEV, KFI, MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV,
SIV, THO, TSC, UEI, UFI, VNI, YUG and ZON, as well as a mixture or
intergrowth of any two or more thereof. The intergrowth is
preferably selected from KFI-SIV, ITE-RTH, AEW-UEI, AEI-CHA, and
AEI-SAV. More preferably, the small pore molecular sieve has a
Framework Type that is AEI, CHA or an AEI-CHA intergrowth. Even
more preferably, the small pore molecular sieve has a Framework
Type that is AEI or CHA, particularly AEI.
[0158] Preferably, the small pore molecular sieve has an
aluminosilicate framework or a silico-aluminophosphate framework.
More preferably, the small pore molecular sieve has an
aluminosilicate framework (i.e. the molecular sieve is a zeolite),
especially when the small pore molecular sieve has a Framework Type
that is AEI, CHA or an AEI-CHA intergrowth, particularly AEI or
CHA.
[0159] In a second molecular sieve catalyst embodiment, the
molecular sieve has a Framework Type selected from the group
consisting of AEI, MFI, EMT, ERI, MOR, FER, BEA, FAU, CHA, LEV,
MWW, CON and EUO, as well as mixtures of any two or more
thereof.
[0160] In a third molecular sieve catalyst embodiment, the
molecular sieve is a medium pore molecular sieve. The medium pore
molecular sieve preferably has a Framework Type selected from the
group consisting of MFI, FER, MWW and EUO, more preferably MFI.
[0161] In a fourth molecular sieve catalyst embodiment, the
molecular sieve is a large pore molecular sieve. The large pore
molecular sieve preferably has a Framework Type selected from the
group consisting of CON, BEA, FAU, MOR and EMT, more preferably
BEA.
[0162] In each of the first to fourth molecular sieve catalyst
embodiments, the molecular sieve preferably has an aluminosilicate
framework (e.g. the molecular sieve is a zeolite). Each of the
aforementioned three-letter codes represents a framework type in
accordance with the "IUPAC Commission on Zeolite Nomenclature"
and/or the "Structure Commission of the International Zeolite
Association".
[0163] The molecular sieve typically has a silica to alumina molar
ratio (SAR) of 10 to 200 (e.g. 10 to 40), such as 10 to 100, more
preferably 15 to 80 (e.g. 15 to 30). The SAR generally relates to a
molecular having an aluminosilicate framework (e.g. a zeolite) or a
silico-aluminophosphate framework, preferably an aluminosilicate
framework (e.g. a zeolite).
[0164] The molecular sieve catalyst of the first, third and fourth
molecular sieve catalyst embodiments (and also for some of the
Framework Types of the second molecular sieve catalyst embodiment),
particularly when the molecular sieve is a zeolite, may have an
infrared spectrum having a characteristic absorption peak in a
range of from 750 cm.sup.-1 to 1050 cm.sup.-1 (in addition to the
absorption peaks for the molecular sieve itself). Preferably, the
characteristic absorption peak is in the range of from 800
cm.sup.-1 to 1000 cm.sup.-1, more preferably in the range of from
850 cm.sup.-1 to 975 cm.sup.-1.
[0165] The molecular sieve catalyst of the first molecular sieve
catalyst embodiment has been found to have advantageous passive
NO.sub.x adsorber (PNA) activity. The molecular sieve catalyst can
be used to store NO.sub.x when exhaust gas temperatures are
relatively cool, such as shortly after start-up of a lean burn
engine. NO.sub.x storage by the molecular sieve catalyst occurs at
low temperatures (e.g. less than 200.degree. C.). As the lean burn
engine warms up, the exhaust gas temperature increases and the
temperature of the molecular sieve catalyst will also increase. The
molecular sieve catalyst will release adsorbed NO.sub.x at these
higher temperatures (e.g. 200.degree. C. or above).
[0166] The second molecular sieve catalyst embodiment has cold
start catalyst activity. Such activity can reduce emissions during
the cold start period by adsorbing NO.sub.x and hydrocarbons (HCs)
at relatively low exhaust gas temperatures (e.g. less than
200.degree. C.). Adsorbed NO.sub.x and/or HCs can be released when
the temperature of the molecular sieve catalyst is close to or
above the effective temperature of the other catalyst components or
emissions control devices for oxidising NO and/or HCs.
[0167] When the second or third catalytic region has PNA activity,
then typically the second or third catalytic region comprises a
total loading of noble metal of 1 to 250 g ft.sup.-3, preferably 5
to 150 g ft.sup.-3, more preferably 10 to 100 g ft.sup.-3.
Catalytic Region Having LNT Activity
[0168] The second or third catalytic region may have LNT activity.
During normal operation, a diesel engine produces an exhaust gas
having a "lean" composition. An LNT comprises a NO.sub.x storage
component that is able to store or trap nitrogen oxides (NO.sub.x)
from the exhaust gas by forming an inorganic nitrate. To release
the NO.sub.x from the NO.sub.x storage component, such as when the
NO.sub.x storage component is about to reach its storage capacity,
the diesel engine may be run under rich conditions to produce an
exhaust gas having a "rich" composition. Under these conditions,
the inorganic nitrates of the NO.sub.x storage component decompose
and form mainly nitrogen dioxide (NO.sub.2) and some nitric oxide
(NO). The LNT may contain a platinum group metal component that is
able to catalytically reduce the released NO.sub.x to N.sub.2 or
NH.sub.3 with hydrocarbons (HCs), carbon monoxide (CO) or hydrogen
(H.sub.2) present in the exhaust gas.
[0169] When the second or third catalytic region has NO.sub.x
storage activity (e.g. LNT activity), then the second or third
catalytic region comprises, or consists essentially of, a nitrogen
oxides (NO.sub.x) storage material. The nitrogen oxides (NO.sub.x)
storage material comprises, or consists essentially of, a nitrogen
oxides (NO.sub.x) storage component on a support material. It is
preferred that the second catalytic region further comprises at
least one platinum group metal (PGM). The at least one platinum
group metal (PGM) may be provided by the NO.sub.x treatment
material described herein below.
[0170] The NO.sub.x storage material comprises, or may consist
essentially of, a NO.sub.x storage component on a support
material.
[0171] The NO.sub.x storage component typically comprises an alkali
metal, an alkaline earth metal and/or a rare earth metal. The
NO.sub.x storage component generally comprises, or consists
essentially of, (i) an oxide, a carbonate or a hydroxide of an
alkali metal; (ii) an oxide, a carbonate or a hydroxide of an
alkaline earth metal; and/or (iii) an oxide, a carbonate or a
hydroxide of a rare earth metal.
[0172] When the NO.sub.x storage component comprises an alkali
metal (or an oxide, a carbonate or a hydroxide thereof), then
preferably the alkali metal is selected from the group consisting
of potassium (K), sodium (Na), lithium (Li), caesium (Cs) and a
combination of two or more thereof. It is preferred that the alkali
metal is potassium (K), sodium (Na) or lithium (Li), more
preferably the alkali metal is potassium (K) or sodium (Na), and
most preferably the alkali metal is potassium (K).
[0173] When the NO.sub.x storage component comprises an alkaline
earth metal (or an oxide, a carbonate or a hydroxide thereof), then
preferably the alkaline earth metal is selected from the group
consisting of magnesium (Mg), calcium (Ca), strontium (Sr), barium
(Ba) and a combination of two or more thereof. It is preferred that
the alkaline earth metal is calcium (Ca), strontium (Sr), or barium
(Ba), more preferably strontium (Sr) or barium (Ba), and most
preferably the alkaline earth metal is barium (Ba).
[0174] When the NO.sub.x storage component comprises a rare earth
metal (or an oxide, a carbonate or a hydroxide thereof), then
preferably the rare earth metal is selected from the group
consisting of cerium (Ce), lanthanum (La), yttrium (Y) and a
combination thereof. More preferably, the rare earth metal is
cerium (Ce).
[0175] Typically, the NO.sub.x storage component comprises, or
consists essentially of, (i) an oxide, a carbonate or a hydroxide
of a rare earth metal and/or (ii) an oxide, a carbonate or a
hydroxide of an alkaline earth metal. It is preferred that the
NO.sub.x storage component comprises, or consists essentially of,
an oxide, a carbonate or a hydroxide of an alkaline earth
metal.
[0176] It is preferred that the NO.sub.x storage component
comprises barium (Ba) (e.g. an oxide, a carbonate or a hydroxide of
barium (Ba)). More preferably, the NO.sub.x storage component
comprises barium (e.g. an oxide, a carbonate or a hydroxide of
barium (Ba)) and cerium (e.g. an oxide, a carbonate or a hydroxide
of cerium (Ce), preferably ceria).
[0177] Typically, the NO.sub.x storage component is disposed or
supported on the support material. The NO.sub.x storage component
may be disposed directly onto or is directly supported by the
support material (e.g. there is no intervening support material
between the NO.sub.x storage component and the support
material).
[0178] The support material generally comprises an oxide of
aluminium. Typically, the support material comprises alumina. The
alumina may or may not be doped with a dopant.
[0179] The alumina may be doped with a dopant selected from the
group consisting of silicon (Si), magnesium (Mg), barium (Ba),
lanthanum (La), cerium (Ce), titanium (Ti), zirconium (Zr) and a
combination of two or more thereof. It is preferred that the dopant
is selected from the group consisting of silicon (Si), magnesium
(Mg), barium (Ba) and cerium (Ce). More preferably, the dopant is
selected from the group consisting of silicon (Si), magnesium (Mg)
and barium (Ba). Even more preferably, the dopant is magnesium
(Mg).
[0180] When the alumina is doped, the total amount of dopant is
0.25 to 5% by weight, preferably 0.5 to 3% by weight (e.g. about 1%
by weight) of the alumina.
[0181] In general, it is preferred that the support material
comprises, or consists essentially of, an oxide of magnesium and
aluminium. The oxide of magnesium and aluminium may comprise, or
consist essentially of, magnesium aluminate (MgAl.sub.2O.sub.4
[e.g. spinel]) and/or a mixed oxide of magnesium oxide (MgO) and
aluminium oxide (Al.sub.2O.sub.3). A mixed oxide of magnesium oxide
and aluminium oxide can be prepared using methods known in the art,
such as by using the processes described in U.S. Pat. No. 6,217,837
or DE 19503522 A1.
[0182] The mixed oxide of magnesium oxide (MgO) and aluminium oxide
(Al.sub.2O.sub.3) typically comprises, or consists essentially of,
1.0 to 40.0% by weight of magnesium oxide (based on the total
weight of the mixed oxide), such as 1.0 to 30.0% by weight,
preferably 5.0 to 28.0% by weight (e.g. 5.0 to 25.0% by weight),
more preferably 10.0 to 25.0% by weight of magnesium oxide.
[0183] The mixed oxide of magnesium oxide (MgO) and aluminium oxide
(Al.sub.2O.sub.3) is typically a homogeneous mixed oxide of
magnesium oxide (MgO) and aluminium oxide (Al.sub.2O.sub.3). In a
homogeneous mixed oxide, magnesium ions occupy the positions within
the lattice of aluminium ions.
[0184] Generally, a support material comprising, or consisting
essentially of, a mixed oxide of magnesium oxide (MgO) and
aluminium oxide (Al.sub.2O.sub.3) is preferred.
[0185] The NO.sub.x storage material may further comprise a
platinum group metal (PGM). The PGM may be selected from the group
consisting of platinum, palladium, rhodium and a combination of any
two or more thereof. Preferably, the PGM is selected from platinum,
palladium and a combination of platinum and palladium.
[0186] When the NO.sub.x storage material comprises a PGM, then
generally the PGM is disposed or supported on the support material.
The PGM is preferably disposed directly onto or is directly
supported by the support material (e.g. there is no intervening
support material between the PGM and the support material).
[0187] Typically, the second or third catalytic region further
comprises a NO.sub.x treatment material. For the avoidance of
doubt, the NO.sub.x treatment material is different (e.g. different
composition) to the NO.sub.x storage material. The NO.sub.x
treatment material may have (a) NO.sub.x storage activity and/or NO
oxidative activity [e.g. under lean conditions]; and/or (b)
NO.sub.x reductive activity [e.g. under rich conditions].
[0188] The NO.sub.x treatment material comprises, or consists
essentially of, a NO.sub.x treatment component.
[0189] Typically, the NO.sub.x treatment component (NTC) comprises
a support material. The support material of the NO.sub.x treatment
component (NTC) is referred to herein as the NTC support
material.
[0190] The NTC support material comprises, or consists essentially
of, ceria, or a mixed or composite oxide of ceria, such as a
ceria-zirconia.
[0191] When the NTC support material comprises, or consists
essentially of, a ceria-zirconia, then the ceria-zirconia may
consist essentially of 20 to 95% by weight of ceria and 5 to 80% by
weight of zirconia (e.g. 50 to 95% by weight ceria and 5 to 50% by
weight zirconia), preferably 35 to 80% by weight of ceria and 20 to
65% by weight zirconia (e.g. 55 to 80% by weight ceria and 20 to
45% by weight zirconia), even more preferably 45 to 75% by weight
of ceria and 25 to 55% by weight zirconia.
[0192] In general, the NO.sub.x treatment component may comprise a
platinum group metal (PGM) and/or a NO.sub.x storage component.
[0193] The NO.sub.x treatment component may comprise, or consist
essentially of, a platinum group metal (PGM) disposed or supported
(e.g. directly disposed or supported) on the first support
material. The PGM may be selected from the group consisting of
platinum, palladium, rhodium, a combination of platinum and
palladium, a combination of platinum and rhodium, a combination of
palladium and rhodium, and a combination of platinum, palladium and
rhodium. It is preferred that the PGM is selected from the group
consisting of palladium, rhodium and a combination of palladium and
rhodium.
[0194] The PGM (i.e. of the NO.sub.x treatment component) may be
rhodium. The PGM may be palladium. Preferably, the PGM is
palladium.
[0195] Additionally or alternatively, the NO.sub.x treatment
component may comprise, or consist essentially of, a NO.sub.x
storage component disposed or supported (e.g. directly disposed or
supported) on the NTC support material. The NO.sub.x storage
component generally comprises, or consists essentially of, (i) an
oxide, a carbonate or a hydroxide of an alkali metal; (ii) an
oxide, a carbonate or a hydroxide of an alkaline earth metal;
and/or (iii) an oxide, a carbonate or a hydroxide of a rare earth
metal, preferably a rare earth metal other than cerium (Ce). It is
preferred that the NO.sub.x storage component comprises, or
consists essentially of, an oxide, a carbonate or a hydroxide of an
alkaline earth metal. The alkaline earth metal is preferably barium
(Ba).
Catalytic Region Having DOC Activity
[0196] The second or third catalytic region may be for oxidising
hydrocarbons (HCs) and/or nitric oxide (NO) in the exhaust gas
produced by the diesel engine (e.g. the second or third catalytic
region is a diesel oxidation catalytic region or has diesel
oxidation catalyst (DOC) activity).
[0197] When the second or third catalytic region is for oxidising
hydrocarbons (HCs) and/or nitric oxide (NO) in the exhaust gas
produced by the diesel engine, the second or third catalytic region
comprises platinum (Pt) and a support material. It is particularly
preferred that the second or third catalytic region comprises, or
consists essentially of, platinum (Pt), manganese (Mn) and a
support material. The second or third catalytic region is for
oxidising hydrocarbons (HCs) and/or nitric oxide (NO) in the
exhaust gas produced by the diesel engine
[0198] The platinum (Pt) is typically disposed or supported on the
support material. The platinum may be disposed directly onto or is
directly supported by the support material (e.g. there is no
intervening support material between the platinum and the support
material). For example, platinum can be dispersed on the support
material.
[0199] The second or third catalytic region may further comprise
palladium, such as palladium disposed or supported on the support
material. When the second or third catalytic region comprises
palladium, then the ratio of platinum to palladium by total weight
is generally .gtoreq.2:1 (e.g. Pt:Pd 1:0 to 2:1), more preferably
.gtoreq.4:1 (e.g. Pt:Pd 1:0 to 4:1).
[0200] It is generally preferred that the second or third catalytic
region is substantially free of palladium, particularly
substantially free of palladium (Pd) disposed or supported on the
support material. More preferably, the second or third catalytic
region does not comprise palladium, particularly palladium disposed
or supported on the support material. The presence of palladium,
particularly in a large amount, in the second catalytic region can
be detrimental to NO oxidation activity. The NO oxidising activity
of palladium is generally poor under the typical usage conditions
for a diesel oxidation catalyst. Also, any palladium that is
present may react with some of the platinum that is present to form
an alloy. This can also be detrimental to the NO oxidation activity
of the second catalytic region because platinum-palladium alloys
are not as active toward NO oxidation as platinum is by itself.
[0201] Generally, the second or third catalytic region comprises
platinum (Pt) as the only platinum group metal. The second or third
catalytic region preferably does not comprise one or more other
platinum group metals, such as ruthenium (Ru), rhodium (Rh),
palladium (Pd), osmium (Os) and/or iridium (Ir).
[0202] The second or third catalytic region typically has a total
loading of platinum of 5 to 300 g ft.sup.-3. It is preferred that
the second or third catalytic region has a total loading of
platinum of 10 to 250 g ft.sup.-3 (e.g. 75 to 175 g ft.sup.-3),
more preferably 15 to 200 g ft.sup.-3 (e.g. 50 to 150 g ft.sup.-3),
still more preferably 20 to 150 g ft.sup.-3.
[0203] It is preferable that a primary function of the second or
third catalytic region is oxidising nitric oxide (NO) to nitrogen
dioxide (NO.sub.2). However, it is appreciated that in some
embodiments of the oxidation catalyst, the second or third
catalytic region will also oxidise some hydrocarbons (HCs) during
use.
[0204] The second or third catalytic region may also comprise
manganese (Mn). The manganese may be present in an elemental form
or as an oxide. The second or third catalytic region typically
comprises manganese or an oxide thereof.
[0205] The manganese (Mn) is typically disposed or supported on the
support material. The manganese (Mn) may be disposed directly onto
or is directly supported by the support material (e.g. there is no
intervening support material between the Mn and the support
material).
[0206] The second or third catalytic region typically has a total
loading of manganese (Mn) of 5 to 500 g ft.sup.-3. It is preferred
that the second or third catalytic region has a total loading of
manganese (Mn) of 10 to 250 g ft.sup.-3 (e.g. 75 to 175 g
ft.sup.-3), more preferably 15 to 200 g ft.sup.-3 (e.g. 50 to 150 g
ft.sup.-3), still more preferably 20 to 150 g ft.sup.-3.
[0207] Typically, the second or third catalytic region comprises a
ratio of Mn:Pt by weight of .ltoreq.5:1, more preferably
<5:1.
[0208] In general, the second or third catalytic region comprises a
ratio of Mn:Pt by weight of .gtoreq.0.2:1 (e.g. .gtoreq.0.5:1),
more preferably >0.2:1 (e.g. >0.5:1).
[0209] The second or third catalytic region may comprise a ratio by
total weight of manganese (Mn) to platinum of 5:1 to 0.2:1, such as
5:1 to 0.5:1 (e.g. 5:1 to 2:3 or 5:1 to 1:2), preferably 4.5:1 to
1:1 (e.g. 4:1 to 1.1:1), more preferably 4:1 to 1.5:1. The ratio of
Mn:Pt by weight can be important in obtaining advantageous NO
oxidation activity.
[0210] Typically, the support material comprises, or consists
essentially of, a refractory oxide.
[0211] The refractory oxide is typically selected from the group
consisting of alumina, silica, titania, zirconia, ceria and a mixed
or composite oxide thereof, such as a mixed or composite oxide of
two or more thereof. For example, the refractory oxide may be
selected from the group consisting of alumina, silica, titania,
zirconia, ceria, silica-alumina, titania-alumina, zirconia-alumina,
ceria-alumina, titania-silica. zirconia-silica, zirconia-titania,
ceria-zirconia and alumina-magnesium oxide.
[0212] The support material, or the refractory oxide thereof, may
optionally be doped (e.g. with a dopant). The dopant may be
selected from the group consisting of zirconium (Zr), titanium
(Ti), silicon (Si), yttrium (Y), lanthanum (La), praseodymium (Pr),
samarium (Sm), neodymium (Nd) and an oxide thereof.
[0213] When the support material, or the refractory oxide thereof,
is doped, the total amount of dopant is 0.25 to 5% by weight,
preferably 0.5 to 3% by weight (e.g. about 1% by weight).
[0214] The support material, or the refractory oxide thereof, may
comprise, or consist essentially of, alumina doped with a dopant.
It is particularly preferred that the support material, or the
refractory oxide thereof, comprises, or consists essentially of,
alumina doped with a dopant. It has been found that the combination
of manganese (Mn), platinum (Pt) and a doped alumina support
material, particularly an alumina support material doped with
silica, provides excellent NO oxidation activity and can stabilise
NO oxidation activity of the oxidation catalyst over its
lifetime.
[0215] The alumina may be doped with a dopant comprising silicon
(Si), magnesium (Mg), barium (Ba), lanthanum (La), cerium (Ce),
titanium (Ti), or zirconium (Zr) or a combination of two or more
thereof. The dopant may comprise, or consist essentially of, an
oxide of silicon, an oxide of magnesium, an oxide of barium, an
oxide of lanthanum, an oxide of cerium, an oxide of titanium or an
oxide of zirconium. Preferably, the dopant comprises, or consists
essentially of, silicon, magnesium, barium, cerium, or an oxide
thereof; particularly silicon, cerium, or an oxide thereof. More
preferably, the dopant comprises, or consists essentially of,
silicon, magnesium, barium, or an oxide thereof; particularly
silicon, magnesium, or an oxide thereof; especially silicon or an
oxide thereof.
[0216] Examples of alumina doped with a dopant include alumina
doped with silica, alumina doped with magnesium oxide, alumina
doped with barium or barium oxide, alumina doped with lanthanum
oxide, or alumina doped with ceria, particularly alumina doped with
silica, alumina doped with lanthanum oxide, or alumina doped with
ceria. It is preferred that the alumina doped with a dopant is
alumina doped with silica, alumina doped with barium or barium
oxide, or alumina doped with magnesium oxide. More preferably, the
alumina doped with a dopant is alumina doped with silica or alumina
doped with magnesium oxide. Even more preferably, the alumina doped
with a dopant is alumina doped with silica.
[0217] When the alumina is alumina doped with silica, then the
alumina is doped with silica in a total amount of 0.5 to 45% by
weight (i.e. % by weight of the alumina), preferably 1 to 40% by
weight, more preferably 1.5 to 30% by weight (e.g. 1.5 to 10% by
weight), particularly 2.5 to 25% by weight, more particularly 3.5
to 20% by weight (e.g. 5 to 20% by weight), even more preferably
4.5 to 15% by weight.
[0218] When the alumina is alumina doped with magnesium oxide, then
the alumina is doped with magnesium in an amount as defined above
or an amount of 1 to 30% by weight (i.e. % by weight of the
alumina), preferably 5 to 25% by weight.
[0219] It is preferred that the support material, or the refractory
oxide thereof, is not doped with a dopant comprising, or consisting
essentially of, manganese. Thus, the support material, or the
refractory oxide thereof, is not promoted with a promoter, such as
a promoter selected from the group consisting of tin, manganese,
indium, group VIII metal (e.g. Fe. Co, Ni, Ru, Rh, Pd, Os, Ir and
Pt, particularly Ir) and combinations thereof.
[0220] In general, when the support material, or the refractory
oxide thereof, comprises or consists essentially of a mixed or
composite oxide of alumina (e.g. silica-alumina, alumina-magnesium
oxide or a mixture of alumina and ceria), then preferably the mixed
or composite oxide of alumina comprises at least 50 to 99% by
weight of alumina, more preferably 70 to 95% by weight of alumina,
even more preferably 75 to 90% by weight of alumina.
[0221] When the support material, or refractory oxide thereof,
comprises or consists essentially of ceria-zirconia, then the
ceria-zirconia may consist essentially of 20 to 95% by weight of
ceria and 5 to 80% by weight of zirconia (e.g. 50 to 95% by weight
ceria and 5 to 50% by weight zirconia), preferably 35 to 80% by
weight of ceria and 20 to 65% by weight zirconia (e.g. 55 to 80% by
weight ceria and 20 to 45% by weight zirconia), even more
preferably 45 to 75% by weight of ceria and 25 to 55% by weight
zirconia. Typically, the second or third catalytic region comprises
an amount of the support material of 0.1 to 4.5 g in.sup.-3 (e.g.
0.25 to 4.0 g in.sup.-3), preferably 0.5 to 3.0 g in.sup.-3, more
preferably 0.6 to 2.5 g in.sup.-3 (e.g. 0.75 to 1.5 g
in.sup.-3).
[0222] In some applications, it may generally be preferable that
the second or third catalytic region is substantially free of a
hydrocarbon adsorbent material, particularly a zeolite. Thus, the
second or third catalytic region may not comprise a hydrocarbon
adsorbent material.
[0223] The second or third catalytic region typically does not
comprise indium and/or iridium. More preferably, the second or
third catalytic region does not comprise indium, iridium and/or
magnesium.
[0224] It may be preferable that the second or third catalytic
region does not comprise cerium oxide or a mixed or composite oxide
thereof, such as (i) a mixed or composite oxide of cerium oxide and
alumina and/or (ii) a mixed or composite oxide of cerium oxide and
zirconia.
[0225] Additionally or alternatively, the second or third catalytic
region may be substantially free of rhodium, an alkali metal and/or
an alkaline earth metal, particularly an alkali metal and/or an
alkaline earth metal disposed or supported on the support material.
Thus, the second or third catalytic region may not comprise
rhodium, an alkali metal and/or an alkaline earth metal,
particularly an alkali metal and/or an alkaline earth metal
disposed or supported on the support material.
Substrate
[0226] The oxidation catalyst of the invention comprises a
substrate. The substrate typically has an inlet end and an outlet
end.
[0227] In general, the substrate has a plurality of channels (e.g.
for the exhaust gas to flow through). Generally, the substrate is a
ceramic material or a metallic material.
[0228] It is preferred that the substrate is made or composed of
cordierite (SiO.sub.2--Al.sub.2O.sub.3--MgO), silicon carbide
(SiC), Fe--Cr--Al alloy, Ni--Cr--Al alloy, or a stainless steel
alloy.
[0229] Typically, the substrate is a monolith (also referred to
herein as a substrate monolith). Such monoliths are well-known in
the art.
[0230] The substrate monolith may be a flow-through monolith.
Alternatively, the substrate may be a filtering monolith.
[0231] A flow-through monolith typically comprises a honeycomb
monolith (e.g. a metal or ceramic honeycomb monolith) having a
plurality of channels extending therethrough, which each channel is
open at the inlet end and the outlet end.
[0232] A filtering monolith generally comprises a plurality of
inlet channels and a plurality of outlet channels, wherein the
inlet channels are open at an upstream end (i.e. exhaust gas inlet
side) and are plugged or sealed at a downstream end (i.e. exhaust
gas outlet side), the outlet channels are plugged or sealed at an
upstream end and are open at a downstream end, and wherein each
inlet channel is separated from an outlet channel by a porous
structure.
[0233] When the monolith is a filtering monolith, it is preferred
that the filtering monolith is a wall-flow filter. In a wall-flow
filter, each inlet channel is alternately separated from an outlet
channel by a wall of the porous structure and vice versa. It is
preferred that the inlet channels and the outlet channels are
arranged in a honeycomb arrangement. When there is a honeycomb
arrangement, it is preferred that the channels vertically and
laterally adjacent to an inlet channel are plugged at an upstream
end and vice versa (i.e. the channels vertically and laterally
adjacent to an outlet channel are plugged at a downstream end).
When viewed from either end, the alternately plugged and open ends
of the channels take on the appearance of a chessboard.
[0234] In principle, the substrate may be of any shape or size.
However, the shape and size of the substrate is usually selected to
optimise exposure of the catalytically active materials in the
catalyst to the exhaust gas. The substrate may, for example, have a
tubular, fibrous or particulate form. Examples of suitable
supporting substrates include a substrate of the monolithic
honeycomb cordierite type, a substrate of the monolithic honeycomb
SiC type, a substrate of the layered fibre or knitted fabric type,
a substrate of the foam type, a substrate of the crossflow type, a
substrate of the metal wire mesh type, a substrate of the metal
porous body type and a substrate of the ceramic particle type.
Exhaust System
[0235] The invention also provides an exhaust system comprising the
oxidation catalyst and an emissions control device. Examples of an
emissions control device include a diesel particulate filter (DPF),
a lean NO.sub.x trap (LNT), a lean NO.sub.x catalyst (LNC), a
selective catalytic reduction (SCR) catalyst, a diesel oxidation
catalyst (DOC), a catalysed soot filter (CSF), a selective
catalytic reduction filter (SCRF.TM.) catalyst, an ammonia slip
catalyst (ASC) and combinations of two or more thereof. Such
emissions control devices are all well known in the art.
[0236] Some of the aforementioned emissions control devices have
filtering substrates. An emissions control device having a
filtering substrate may be selected from the group consisting of a
diesel particulate filter (DPF), a catalysed soot filter (CSF), and
a selective catalytic reduction filter (SCRF.TM.) catalyst.
[0237] It is preferred that the exhaust system comprises an
emissions control device selected from the group consisting of a
lean NO.sub.x trap (LNT), an ammonia slip catalyst (ASC), diesel
particulate filter (DPF), a selective catalytic reduction (SCR)
catalyst, a catalysed soot filter (CSF), a selective catalytic
reduction filter (SCRF.TM.) catalyst, and combinations of two or
more thereof. More preferably, the emissions control device is
selected from the group consisting of a diesel particulate filter
(DPF), a selective catalytic reduction (SCR) catalyst, a catalysed
soot filter (CSF), a selective catalytic reduction filter
(SCRF.TM.) catalyst, and combinations of two or more thereof. Even
more preferably, the emissions control device is a selective
catalytic reduction (SCR) catalyst or a selective catalytic
reduction filter (SCRF.TM.) catalyst.
[0238] When the exhaust system of the invention comprises an SCR
catalyst or an SCRF.TM. catalyst, then the exhaust system may
further comprise an injector for injecting a nitrogenous reductant,
such as ammonia, or an ammonia precursor, such as urea or ammonium
formate, preferably urea, into exhaust gas downstream of the
oxidation catalyst and upstream of the SCR catalyst or the SCRF.TM.
catalyst. Such an injector may be fluidly linked to a source (e.g.
a tank) of a nitrogenous reductant precursor. Valve-controlled
dosing of the precursor into the exhaust gas may be regulated by
suitably programmed engine management means and closed loop or open
loop feedback provided by sensors monitoring the composition of the
exhaust gas. Ammonia can also be generated by heating ammonium
carbamate (a solid) and the ammonia generated can be injected into
the exhaust gas.
[0239] Alternatively or in addition to the injector, ammonia can be
generated in situ (e.g. during rich regeneration of a LNT disposed
upstream of the SCR catalyst or the SCRF.TM. catalyst). Thus, the
exhaust system may further comprise an engine management means for
enriching the exhaust gas with hydrocarbons.
[0240] The SCR catalyst or the SCRF.TM. catalyst may comprise a
metal selected from the group consisting of at least one of Cu, Hf,
La, Au, In, V, lanthanides and Group VIII transition metals (e.g.
Fe), wherein the metal is supported on a refractory oxide or
molecular sieve. The metal is preferably selected from Ce, Fe, Cu
and combinations of any two or more thereof, more preferably the
metal is Fe or Cu.
[0241] The refractory oxide for the SCR catalyst or the SCRF.TM.
catalyst may be selected from the group consisting of
Al.sub.2O.sub.3, TiO.sub.2, CeO.sub.2, SiO.sub.2, ZrO.sub.2 and
mixed oxides containing two or more thereof. The non-zeolite
catalyst can also include tungsten oxide (e.g.
V.sub.2O.sub.5/WO.sub.3/TiO.sub.2, WO.sub.x/CeZrO.sub.2,
WO.sub.x/ZrO.sub.2 or Fe/WO.sub.x/ZrO.sub.2).
[0242] It is particularly preferred when an SCR catalyst, an
SCRF.TM. catalyst or a washcoat thereof comprises at least one
molecular sieve, such as an aluminosilicate zeolite or a SAPO. The
at least one molecular sieve can be a small, a medium or a large
pore molecular sieve. By "small pore molecular sieve" herein we
mean molecular sieves containing a maximum ring size of 8, such as
CHA; by "medium pore molecular sieve" herein we mean a molecular
sieve containing a maximum ring size of 10, such as ZSM-5; and by
"large pore molecular sieve" herein we mean a molecular sieve
having a maximum ring size of 12, such as beta. Small pore
molecular sieves are potentially advantageous for use in SCR
catalysts.
[0243] In the exhaust system of the invention, preferred molecular
sieves for an SCR catalyst or an SCRF.TM. catalyst are synthetic
aluminosilicate zeolite molecular sieves selected from the group
consisting of AEI, ZSM-5, ZSM-20, ERI including ZSM-34, mordenite,
ferrierite, BEA including Beta, Y, CHA, LEV including Nu-3, MCM-22
and EU-1, preferably AEI or CHA, and having a silica-to-alumina
ratio of about 10 to about 50, such as about 15 to about 40.
[0244] In a first exhaust system embodiment, the exhaust system
comprises the oxidation catalyst of the invention and a catalysed
soot filter (CSF). The oxidation catalyst may comprise a second
catalytic region having PNA. LNT and/or DOC activity. The oxidation
catalyst is typically followed by (e.g. is upstream of) the
catalysed soot filter (CSF). Thus, for example, an outlet of the
oxidation catalyst is connected to an inlet of the catalysed soot
filter.
[0245] A second exhaust system embodiment relates to an exhaust
system comprising the oxidation catalyst of the invention, a
catalysed soot filter (CSF) and a selective catalytic reduction
(SCR) catalyst. The oxidation catalyst may comprise a second
catalytic region having PNA, LNT and/or DOC activity. Such an
arrangement is a preferred exhaust system for a light-duty diesel
vehicle.
[0246] The oxidation catalyst is typically followed by (e.g. is
upstream of) the catalysed soot filter (CSF). The catalysed soot
filter is typically followed by (e.g. is upstream of) the selective
catalytic reduction (SCR) catalyst. A nitrogenous reductant
injector may be arranged between the catalysed soot filter (CSF)
and the selective catalytic reduction (SCR) catalyst. Thus, the
catalysed soot filter (CSF) may be followed by (e.g. is upstream
of) a nitrogenous reductant injector, and the nitrogenous reductant
injector may be followed by (e.g. is upstream of) the selective
catalytic reduction (SCR) catalyst.
[0247] In a third exhaust system embodiment, the exhaust system
comprises the oxidation catalyst of the invention, a selective
catalytic reduction (SCR) catalyst and either a catalysed soot
filter (CSF) or a diesel particulate filter (DPF). The oxidation
catalyst may comprise a second catalytic region having PNA, LNT
and/or DOC activity.
[0248] In the third exhaust system embodiment, the oxidation
catalyst of the invention is typically followed by (e.g. is
upstream of) the selective catalytic reduction (SCR) catalyst. A
nitrogenous reductant injector may be arranged between the
oxidation catalyst and the selective catalytic reduction (SCR)
catalyst. Thus, the oxidation catalyst may be followed by (e.g. is
upstream of) a nitrogenous reductant injector, and the nitrogenous
reductant injector may be followed by (e.g. is upstream of) the
selective catalytic reduction (SCR) catalyst. The selective
catalytic reduction (SCR) catalyst are followed by (e.g. are
upstream of) the catalysed soot filter (CSF) or the diesel
particulate filter (DPF).
[0249] A fourth exhaust system embodiment comprises the oxidation
catalyst of the invention and a selective catalytic reduction
filter (SCRF.TM.) catalyst. The oxidation catalyst of the invention
is typically followed by (e.g. is upstream of) the selective
catalytic reduction filter (SCRF.TM.) catalyst. The oxidation
catalyst may comprise a second catalytic region having PNA, LNT
and/or DOC activity.
[0250] A nitrogenous reductant injector may be arranged between the
oxidation catalyst and the selective catalytic reduction filter
(SCRF.TM.) catalyst. Thus, the oxidation catalyst may be followed
by (e.g. is upstream of) a nitrogenous reductant injector, and the
nitrogenous reductant injector may be followed by (e.g. is upstream
of) the selective catalytic reduction filter (SCRF.TM.)
catalyst.
[0251] When the exhaust system comprises a selective catalytic
reduction (SCR) catalyst or a selective catalytic reduction filter
(SCRF.TM.) catalyst, such as in the second to fourth exhaust system
embodiments described hereinabove, an ASC can be disposed
downstream from the SCR catalyst or the SCRF.TM. catalyst (i.e. as
a separate substrate monolith), or more preferably a zone on a
downstream or trailing end of the substrate monolith comprising the
SCR catalyst can be used as a support for the ASC.
[0252] In general, the exhaust system of the invention may comprise
a hydrocarbon supply apparatus (e.g. for generating a rich exhaust
gas), particularly when the second catalytic region of the
oxidation catalyst has LNT activity. The hydrocarbon supply
apparatus may be disposed upstream of the catalyst of the
invention. The hydrocarbon supply apparatus is typically disposed
downstream of the exhaust outlet of the diesel engine.
[0253] The hydrocarbon supply apparatus may be electronically
coupled to an engine management system, which is configured to
inject hydrocarbon into the exhaust gas for releasing NO.sub.x
(e.g. stored NO.sub.x) from the catalyst.
[0254] The hydrocarbon supply apparatus may be an injector. The
hydrocarbon supply apparatus or injector is suitable for injecting
fuel into the exhaust gas.
[0255] Alternatively or in addition to the hydrocarbon supply
apparatus, the diesel engine may comprise an engine management
system (e.g. an engine control unit [ECU]). The engine management
system is configured for in-cylinder injection of the hydrocarbon
(e.g. fuel) for releasing NO.sub.x (e.g. stored NO.sub.x) from the
catalyst.
[0256] Generally, the engine management system is coupled to a
sensor in the exhaust system, which monitors the status of the
catalyst. Such a sensor may be disposed downstream of the catalyst.
The sensor may monitor the NO.sub.x composition of the exhaust gas
at the outlet of the catalyst.
[0257] In general, the hydrocarbon is fuel, preferably diesel
fuel.
Vehicle
[0258] Another aspect of the invention relates to a vehicle. The
vehicle comprises a diesel engine. The diesel engine is coupled to
an exhaust system of the invention.
[0259] It is preferred that the diesel engine is configured or
adapted to run on fuel, preferably diesel fuel, comprises
.ltoreq.50 ppm of sulfur, more preferably .ltoreq.15 ppm of sulfur,
such as .ltoreq.10 ppm of sulfur, and even more preferably
.ltoreq.5 ppm of sulfur.
[0260] The vehicle may be a light-duty diesel vehicle (LDV), such
as defined in US or European legislation. A light-duty diesel
vehicle typically has a weight of <2840 kg, more preferably a
weight of <2610 kg.
[0261] In the US, a light-duty diesel vehicle (LDV) refers to a
diesel vehicle having a gross weight of s 8,500 pounds (US lbs). In
Europe, the term light-duty diesel vehicle (LDV) refers to (i)
passenger vehicles comprising no more than eight seats in addition
to the driver's seat and having a maximum mass not exceeding 5
tonnes, and (ii) vehicles for the carriage of goods having a
maximum mass not exceeding 12 tonnes.
[0262] Alternatively, the vehicle may be a heavy-duty diesel
vehicle (HDV), such as a diesel vehicle having a gross weight of
>8,500 pounds (US lbs), as defined in US legislation.
Definitions
[0263] The expression "bismuth (Bi), antimony (Sb) or an oxide
thereof" includes "bismuth (Bi), or an oxide thereof or antimony
(Sb) or an oxide thereof".
[0264] The term "region" as used herein refers to an area on a
substrate, typically obtained by drying and/or calcining a
washcoat. A "region" can, for example, be disposed or supported on
a substrate as a "layer" or a "zone". The area or arrangement on a
substrate is generally controlled during the process of applying
the washcoat to the substrate. The "region" typically has distinct
boundaries or edges (i.e. it is possible to distinguish one region
from another region using conventional analytical techniques).
[0265] Typically, the "region" has a substantially uniform length.
The reference to a "substantially uniform length" in this context
refers to a length that does not deviate (e.g. the difference
between the maximum and minimum length) by more than 10%,
preferably does not deviate by more than 5%, more preferably does
not deviate by more than 1%, from its mean value.
[0266] It is preferable that each "region" has a substantially
uniform composition (i.e. there is no substantial difference in the
composition of the washcoat when comparing one part of the region
with another part of that region). Substantially uniform
composition in this context refers to a material (e.g. region)
where the difference in composition when comparing one part of the
region with another part of the region is 5% or less, usually 2.5%
or less, and most commonly 1% or less.
[0267] The term "zone" as used herein refers to a region having a
length that is less than the total length of the substrate, such as
.ltoreq.75% of the total length of the substrate. A "zone"
typically has a length (i.e. a substantially uniform length) of at
least 5% (e.g. .gtoreq.5%) of the total length of the
substrate.
[0268] The total length of a substrate is the distance between its
inlet end and its outlet end (e.g. the opposing ends of the
substrate).
[0269] Any reference to a "zone disposed at an inlet end of the
substrate" used herein refers to a zone disposed or supported on a
substrate where the zone is nearer to an inlet end of the substrate
than the zone is to an outlet end of the substrate. Thus, the
midpoint of the zone (i.e. at half its length) is nearer to the
inlet end of the substrate than the midpoint is to the outlet end
of the substrate. Similarly, any reference to a "zone disposed at
an outlet end of the substrate" used herein refers to a zone
disposed or supported on a substrate where the zone is nearer to an
outlet end of the substrate than the zone is to an inlet end of the
substrate. Thus, the midpoint of the zone (i.e. at half its length)
is nearer to the outlet end of the substrate than the midpoint is
to the inlet end of the substrate.
[0270] When the substrate is a wall-flow filter, then generally any
reference to a "zone disposed at an inlet end of the substrate"
refers to a zone disposed or supported on the substrate that is:
[0271] (a) nearer to an inlet end (e.g. open end) of an inlet
channel of the substrate than the zone is to a closed end (e.g.
blocked or plugged end) of the inlet channel, and/or [0272] (b)
nearer to a closed end (e.g. blocked or plugged end) of an outlet
channel of the substrate than the zone is to an outlet end (e.g.
open end) of the outlet channel.
[0273] Thus, the midpoint of the zone (i.e. at half its length) is
(a) nearer to an inlet end of an inlet channel of the substrate
than the midpoint is to the closed end of the inlet channel, and/or
(b) nearer to a closed end of an outlet channel of the substrate
than the midpoint is to an outlet end of the outlet channel.
[0274] Similarly, any reference to a "zone disposed at an outlet
end of the substrate" when the substrate is a wall-flow filter
refers to a zone disposed or supported on the substrate that is:
[0275] (a) nearer to an outlet end (e.g. an open end) of an outlet
channel of the substrate than the zone is to a closed end (e.g.
blocked or plugged) of the outlet channel, and/or [0276] (b) nearer
to a closed end (e.g. blocked or plugged end) of an inlet channel
of the substrate than it is to an inlet end (e.g. an open end) of
the inlet channel.
[0277] Thus, the midpoint of the zone (i.e. at half its length) is
(a) nearer to an outlet end of an outlet channel of the substrate
than the midpoint is to the closed end of the outlet channel,
and/or (b) nearer to a closed end of an inlet channel of the
substrate than the midpoint is to an inlet end of the inlet
channel.
[0278] A zone may satisfy both (a) and (b) when the washcoat is
present in the wall of the wall-flow filter (i.e. the zone is
in-wall).
[0279] The term "adsorber" as used herein, particularly in the
context of a NO.sub.x adsorber, should not be construed as being
limited to the storage or trapping of a chemical entity (e.g.
NO.sub.x) only by means of adsorption. The term "adsorber" used
herein is synonymous with "absorber".
[0280] The term "mixed oxide" as used herein generally refers to a
mixture of oxides in a single phase, as is conventionally known in
the art. The term "composite oxide" as used herein generally refers
to a composition of oxides having more than one phase, as is
conventionally known in the art.
[0281] The acronym "PGM" as used herein refers to "platinum group
metal". The term "platinum group metal" generally refers to a metal
selected from the group consisting of Ru, Rh, Pd, Os, Ir and Pt,
preferably a metal selected from the group consisting of Ru, Rh,
Pd, Ir and Pt. In general, the term "PGM" preferably refers to a
metal selected from the group consisting of Rh, Pt and Pd.
[0282] The expression "consist essentially" as used herein limits
the scope of a feature to include the specified materials, and any
other materials or steps that do not materially affect the basic
characteristics of that feature, such as for example minor
impurities. The expression "consist essentially of" embraces the
expression "consisting of".
[0283] The expression "substantially free of" as used herein with
reference to a material, typically in the context of the content of
a washcoat region, a washcoat layer or a washcoat zone, means that
the material in a minor amount, such as .ltoreq.5% by weight,
preferably .ltoreq.2% by weight, more preferably .ltoreq.1% by
weight. The expression "substantially free of" embraces the
expression "does not comprise".
[0284] The expression "about" as used herein with reference to an
end point of a numerical range includes the exact end point of the
specified numerical range. Thus, for example, an expression
defining a parameter as being up to "about 0.2" includes the
parameter being up to and including 0.2.
[0285] Any reference to an amount of dopant, particularly a total
amount, expressed as a % by weight as used herein refers to the
weight of the support material or the refractory oxide thereof.
[0286] The term "selective catalytic reduction filter catalyst" as
used herein includes a selective catalytic reduction formulation
that has been coated onto a diesel particulate filter (SCR-DPF),
which is known in the art.
EXAMPLES
[0287] The invention will now be illustrated by the following
non-limiting examples.
Example 1
[0288] Pd nitrate was added to slurry of small pore zeolite with
the AEI structure and was stirred. Alumina binder was added then
the slurry was applied to a cordierite flow through monolith having
400 cells per square inch structure using established coating
techniques. The coating was dried and calcined at 500.degree. C. A
coating containing a Pd-exchanged zeolite was obtained. The Pd
loading of this coating was 80 g ft.sup.-3.
[0289] A second slurry was prepared by milling silica-alumina to a
d90<20 micron and adding a solution of bismuth nitrate. An
appropriate amount of soluble Pt salt was added followed by beta
zeolite such that the slurry comprised 23% zeolite and 77% alumina.
The slurry was stirred to homogenise then applied to the inlet
channels of the cordierite flow through monolith. The coating was
dried at 100.degree. C.
[0290] A third slurry was prepared by milling manganese
oxide-alumina to a d90<20 micron. An appropriate amount of
soluble Pt salt was added and the mixture stirred to homogenise.
The slurry was applied to the outlet channels of the cordierite
flow through monolith. The coating was dried at 100.degree. C. and
the catalyst calcined at 500.degree. C. The Pt loading of the
finished catalyst was 67 g ft.sup.-3
Example 2 (Reference)
[0291] Pd nitrate was added to slurry of small pore zeolite with
the AEI structure and was stirred. Alumina binder was added then
the slurry was applied to a cordierite flow through monolith having
400 cells per square inch structure using established coating
techniques. The coating was dried and calcined at 500.degree. C. A
coating containing a Pd-exchanged zeolite was obtained. The Pd
loading of this coating was 80 g ft.sup.-3.
[0292] A second slurry was prepared by milling silica-alumina to a
d90<20 micron. An appropriate amount of soluble Pt salt was
added followed by beta zeolite such that the slurry comprised 23%
zeolite and 77% alumina. The slurry was stirred to homogenise then
applied to the inlet channels of the cordierite flow through
monolith. The coating was dried at 100.degree. C.
[0293] A third slurry was prepared by milling manganese
oxide-alumina to a d90<20 micron. An appropriate amount of
soluble Pt salt was added and the mixture stirred to homogenise.
The slurry was applied to the outlet channels of the cordierite
flow through monolith. The coating was dried at 100.degree. C. and
the catalyst calcined at 500.degree. C. The Pt loading of the
finished catalyst was 67 g ft.sup.-3
Experimental Results
[0294] The catalysts of examples 1 and 2 were hydrothermally aged
(with water) at 750.degree. C. for 15 hours. The aged catalysts
were testing by fitting to a 2.0 litre bench mounted diesel engine.
The engine ran simulated MVEG-B cycles with exhaust gas emissions
measured at both pre- and post-catalyst positions. The CO and HC
oxidation performance and NO.sub.x storage properties over the
MVEG-B cycle were evaluated. The results are shown in Table 1.
TABLE-US-00001 TABLE 1 Example Total CO Total HC conversion
Cumulative NO.sub.x No. conversion (%) (%) storage at 850 s (g) 1
64 75 0.85 2 52 70 0.7
[0295] The catalyst of example 1 shows higher CO and HC conversion
efficiency over the MVEG-B cycle than the catalyst of example 2.
Example 1 comprises bismuth at the inlet end of the catalyst.
Example 1 also shows higher NO.sub.x storage capacity at 850
seconds into the MVEG-B cycle than example 2.
[0296] Example 1 (according to the invention) shows improved CO and
HC oxidation performance and improved NO.sub.x storage properties
than example 2.
Example 3
[0297] Silica-alumina powder was slurried in water and milled to a
d.sub.90 <20 micron. A solution of bismuth nitrate was added
followed by an appropriate amount of soluble Pt salt. The slurry
was stirred to homogenise. The resulting washcoat was applied to a
cordierite flow through monolith having 400 cells per square inch
structure using established coating techniques. The coating was
dried at 100.degree. C., and calcined at 500.degree. C. The
finished catalyst has a Pt loading of 60 g ft.sup.-3 and a Bi
loading of 50 g ft.sup.-3, and a washcoat loading of 1.7 g
in.sup.-3.
Example 4
[0298] Silica-alumina powder was slurried in water and milled to a
d.sub.90 <20 micron. A solution of bismuth nitrate was added
followed by appropriate amounts of soluble Pt and Pd salts. The
slurry was stirred to homogenise. The resulting washcoat was
applied to a cordierite flow through monolith having 400 cells per
square inch structure using established coating techniques. The
coating was dried at 100.degree. C. and calcined at 500.degree. C.
The finished catalyst has a total PGM loading of 60 g ft.sup.-3
with a Pt:Pd weight ratio of 20:1, and a Bi loading of 50 g
ft.sup.-3, and a washcoat loading of 1.7 g in.sup.-3.
Example 5
[0299] Silica-alumina powder was slurried in water and milled to a
d.sub.90 <20 micron. A solution of bismuth nitrate was added
followed by appropriate amounts of soluble Pt and Pd salts. The
slurry was stirred to homogenise. The resulting washcoat was
applied to a cordierite flow through monolith having 400 cells per
square inch structure using established coating techniques. The
coating was dried at 100.degree. C., and calcined at 500.degree. C.
The finished catalyst has a total PGM loading of 60 g ft.sup.-3
with a Pt:Pd weight ratio of 7:1, and a Bi loading of 50 g
ft.sup.-3, and a washcoat loading of 1.7 g in.sup.-3.
Example 6
[0300] Silica-alumina powder was slurried in water and milled to a
d.sub.90 <20 micron. A solution of bismuth nitrate was added
followed by appropriate amounts of soluble Pt and Pd salts. The
slurry was stirred to homogenise. The resulting washcoat was
applied to a cordierite flow through monolith having 400 cells per
square inch structure using established coating techniques. The
coating was dried at 100.degree. C., and calcined at 500.degree. C.
The finished catalyst has a total PGM loading of 60 g ft.sup.-3
with a Pt:Pd weight ratio of 5:1, and a Bi loading of 50 g
ft.sup.-3, and a washcoat loading of 1.7 g in.sup.-3.
Example 7 (Reference)
[0301] Silica-alumina powder was slurried in water and milled to a
d.sub.90 <20 micron. An appropriate amount of soluble Pt salt
was added and the slurry was stirred to homogenise. The resulting
washcoat was applied to a cordierite flow through monolith having
400 cells per square inch structure using established coating
techniques. The coating was dried at 100.degree. C., and calcined
at 500.degree. C. The finished catalyst has a Pt loading of 60 g
ft.sup.-3 and does not comprise Bi.
Example 8
[0302] Silica-alumina powder was slurried in water and milled to a
d.sub.90 <20 micron. A solution of bismuth nitrate was added
followed by an appropriate amount of soluble Pt salt. The slurry
was stirred to homogenise. The resulting washcoat was applied to a
cordierite flow through monolith having 400 cells per square inch
structure using established coating techniques. The coating was
dried at 100.degree. C., and calcined at 500.degree. C. The
finished catalyst has a Pt loading of 60 g ft.sup.-3 and a Bi
loading of 50 g ft.sup.-3.
Example 9
[0303] Silica-alumina powder was slurried in water and milled to a
d.sub.90 <20 micron. A solution of bismuth nitrate was added
followed by an appropriate amount of soluble Pt salt. The slurry
was stirred to homogenise. The resulting washcoat was applied to a
cordierite flow through monolith having 400 cells per square inch
structure using established coating techniques. The coating was
dried at 100.degree. C., and calcined at 500.degree. C. The
finished catalyst has a Pt loading of 60 g ft.sup.-3 and a Bi
loading of 100 g ft.sup.-3.
Example 10
[0304] Silica-alumina powder was slurried in water and milled to a
d.sub.90 <20 micron. A solution of bismuth nitrate was added
followed by an appropriate amount of soluble Pt salt. The slurry
was stirred to homogenise. The resulting washcoat was applied to a
cordierite flow through monolith having 400 cells per square inch
structure using established coating techniques. The coating was
dried at 100.degree. C., and calcined at 500.degree. C. The
finished catalyst has a Pt loading of 60 g ft.sup.-3 and a Bi
loading of 150 g ft.sup.-3.
Example 11 (Reference)
[0305] Silica-alumina powder was slurried in water and milled to a
d.sub.90 <20 micron. An appropriate amount of soluble Pt salt
was added. The slurry was stirred to homogenise. The resulting
washcoat was applied to a cordierite flow through monolith having
400 cells per square inch structure using established coating
techniques. The coating was dried at 100.degree. C., and calcined
at 500.degree. C. The finished catalyst has a Pt loading of 60 g
ft.sup.-3 and a washcoat loading of 1.0 g in.sup.-3.
Example 12 (Reference)
[0306] Silica-alumina powder was slurried in water and milled to a
d.sub.90 <20 micron. An appropriate amount of soluble Pt salt
was added. The slurry was stirred to homogenise. The resulting
washcoat was applied to a cordierite flow through monolith having
400 cells per square inch structure using established coating
techniques. The coating was dried at 100.degree. C., and calcined
at 500.degree. C. The finished catalyst has a Pt loading of 60 g
ft.sup.-3 and a washcoat loading of 1.5 g in.sup.-3.
Example 13
[0307] Silica-alumina powder was slurried in water and milled to a
d.sub.90 <20 micron. A solution of bismuth nitrate was added
followed by an appropriate amount of soluble Pt salt. The slurry
was stirred to homogenise. The resulting washcoat was applied to a
cordierite flow through monolith having 400 cells per square inch
structure using established coating techniques. The coating was
dried at 100.degree. C., and calcined at 500.degree. C. The
finished catalyst has a Pt loading of 60 g ft.sup.-3, a Bi loading
of 50 g ft.sup.-3 and a washcoat loading of 1.0 g in.sup.-3. The
weight ratio of washcoat:Bi was approximately 35:1.
Example 14
[0308] Silica-alumina powder was slurried in water and milled to a
d.sub.90 <20 micron. A solution of bismuth nitrate was added
followed by an appropriate amount of soluble Pt salt. The slurry
was stirred to homogenise. The resulting washcoat was applied to a
cordierite flow through monolith having 400 cells per square inch
structure using established coating techniques. The coating was
dried at 100.degree. C., and calcined at 500.degree. C. The
finished catalyst has a Pt loading of 60 g ft.sup.-3, a Bi loading
of 50 g ft.sup.-3 and a washcoat loading of 1.5 g in.sup.-3. The
weight ratio of washcoat:Bi weight was approximately 52:1.
Experimental Results
[0309] Core samples were taken from the catalysts of Examples 3 to
14. The cores were hydrothermally aged at 800.degree. C. for 16
hours using 10% water.
[0310] The catalytic activity for all cores was determined using a
synthetic gas bench catalytic activity test (SCAT). The aged cores
were tested in a simulated exhaust gas mixture shown in Table 2. In
each case the balance is nitrogen.
TABLE-US-00002 TABLE 2 CO 1500 ppm HC (as C.sub.1) 430 ppm NO 100
ppm CO.sub.2 4% H.sub.2O 4% O.sub.2 14% Space velocity
55000/hour
[0311] The oxidation activity for CO and HC is determined by the
light off temperature whereby 50% conversion is achieved (T50).
SCAT results are shown in Tables 3 to 5.
TABLE-US-00003 TABLE 3 Example No. T50 CO (.degree. C.) T50 HC
(.degree. C.) 3 137 176 4 141 177 5 164 191 6 168 190
[0312] The results shown in Table 3 show the CO and HC light off
temperatures for the catalysts of Examples 3 to 6.
[0313] Examples 3 and 4 show a low light off temperature for both
CO and HC. Examples 3 and 4 have Pt:Pd weight ratios of 1:0 and
20:1 respectively.
[0314] Examples 5 and 6 have higher light off temperatures for CO
and HC. Examples 5 and 6 have Pt:Pd weight ratios of 7:1 and 5:1
respectively.
TABLE-US-00004 TABLE 4 Example No. T50 CO (.degree. C.) T50 HC
(.degree. C.) 7 (Reference) 187 192 8 147 196 9 143 222 10 194
369
[0315] The results shown in Table 4 show the CO and HC light off
temperatures for the catalysts of Examples 7 to 10.
[0316] Example 8 has a low light off temperature for both CO and
HC. Example 8 comprises Bi at 50 g ft.sup.-3 loading.
[0317] Example 9 has a low light off temperature for CO, but a
relatively high light off temperature for HC. Example 9 comprises a
Bi loading of 100 g ft.sup.-3.
[0318] Example 10 comprises Bi at the highest loading of 150 g
ft.sup.-3 and has the highest light off temperatures for CO and
HC.
TABLE-US-00005 TABLE 5 Example No. T50 CO (.degree. C.) T50 HC
(.degree. C.) 11 (Reference) 182 188 12 (Reference) 176 183 13 145
214 14 145 190
[0319] The results shown in Table 5 show the CO and HC light off
temperatures for the catalysts of Examples 11 to 14. All catalysts
have the same Pt loading and same Bi loading where applicable.
[0320] Examples 13 and 14 have a low light off temperature for CO
compared with Examples 11 and 12. Examples 13 and 14 comprise Bi.
Example 14 also has a low light off temperature for HC. Example 14
has a washcoat:Bi weight ratio of 52:1. Example 13 which has a
higher light off temperature for HC has a washcoat:Bi weight ratio
of 35:1.
[0321] The results for Examples 3 to 6 show that the inclusion of
Bi with a higher weight ratio of Pt:Pd provides a lower CO and HC
light off temperature. Examples 8 and 9 show that lower loadings of
Bi are preferred to maintain both good CO and good HC oxidation
activity. Examples 11 to 14 show that a high weight ratio of
washcoat:Bi provides both good CO and good HC oxidation
activity.
Example 15
[0322] Bismuth nitrate was dissolved in 2M nitric acid and
impregnated onto a silica-alumina powder (5% silica by mass) using
an incipient wetness method. The material was dried at 105.degree.
C. then calcined at 500.degree. C. The calcined powder was
impregnated with a platinum nitrate solution by an incipient
wetness method. The material was dried at 105.degree. C. then
calcined at 500.degree. C. The final catalyst powder had a Pt
loading of 1.7 wt % and a Bi loading of 4 wt %.
Example 16
[0323] Bismuth nitrate was dissolved in 2M nitric acid and
impregnated onto an alumina powder using an incipient wetness
method. The material was dried at 105.degree. C. then calcined at
500.degree. C. The calcined powder was impregnated with platinum
nitrate solution by an incipient wetness method. The material was
dried at 105.degree. C. then calcined at 500.degree. C. The final
catalyst powder had a Pt loading of 1.7 wt % and a Bi loading of 4
wt %.
Experimental Results
[0324] The catalysts of Examples 15 and 16 were hydrothermally aged
in an oven at 750.degree. C. for 15 hours using 10% water. The
catalytic activity was determined using a synthetic gas bench
catalytic activity test (SCAT). 0.4 g of aged catalyst powder in
the size fraction of 255 to 350 microns was tested in a simulated
exhaust gas mixture shown in Table 6. In each case the balance is
nitrogen. The oxidation activities for CO and HC are determined by
the light off temperature whereby 50% conversion is achieved (T50).
SCAT results are shown in Table 7.
TABLE-US-00006 TABLE 6 CO 1500 ppm HC (as C.sub.1) 480 ppm NO 150
ppm CO.sub.2 5% H.sub.2O 5% O.sub.2 14% Gas hourly space velocity
28000 ml/hr/ml
TABLE-US-00007 TABLE 7 Example No. T50 CO aged condition (.degree.
C.) T50 HC aged condition (.degree. C.) 1 121 163 2 138 186
[0325] Table 7 shows the CO and HC T50 light off temperatures for
Examples 15 and 16. Example 15 has a lower light off temperature
than Example 16. Example 15 comprises Pt/Bi and a silica-alumina
refractory oxide support material. Example 16 comprises Pt/Bi and
an alumina refractory oxide support material.
Example 17
[0326] Antimony was impregnated onto a silica-alumina powder (5%
silica by mass) using a soluble antimony salt (an antimony tartrate
solution) via an incipient wetness method. The antimony tartrate
solution was prepared by refluxing antimony oxide in an excess of
tartaric acid.
[0327] The Sb-impregnated silica-alumina material was dried at
105.degree. C. then calcined at 500.degree. C. The calcined powder
was then impregnated with platinum nitrate solution by an incipient
wetness method. The material was dried at 105.degree. C. then
calcined at 500.degree. C. The final catalyst powder had a Pt
loading of 1.7 wt % and a Sb loading of 4 wt %.
Example 18
[0328] Antimony was impregnated onto a silica-alumina powder (5%
silica by mass) using an antimony tartrate solution via an
incipient wetness method. The material was dried at 105.degree. C.
then calcined at 500.degree. C. The calcined powder was impregnated
with platinum nitrate solution by an incipient wetness method. The
material was dried at 105.degree. C. then calcined at 500.degree.
C. The final catalyst powder had a Pt loading of 1.7 wt % and a Sb
loading of 2 wt %.
Example 19
[0329] Bismuth nitrate was dissolved in 2M nitric acid and
impregnated onto an alumina powder using an incipient wetness
method. The material was dried at 105.degree. C. then calcined at
500.degree. C. The calcined powder was impregnated with platinum
nitrate solution by an incipient wetness method. The material was
dried at 105.degree. C. then calcined at 500.degree. C. The final
catalyst powder had a Pt loading of 1.7 wt % and a Bi loading of 4
wt %.
Example 20
[0330] Platinum was impregnated onto a silica-alumina powder (5%
silica by mass) using a platinum nitrate solution via an incipient
wetness method. The material was dried at 105.degree. C. then
calcined at 500.degree. C. The final powder had a Pt loading of 1.7
wt %.
Experimental Results
[0331] The catalytic activity of the catalysts of Examples 17, 19
and 20 in a fresh (i.e. unaged) state was determined using a
synthetic gas bench catalytic activity test (SCAT). 0.4 g of
catalyst powder in the size fraction of 255 to 350 microns was
tested in a simulated exhaust gas mixture having a composition as
shown in Table 6. In each case the balance is nitrogen. The
oxidation activities for CO and HC are determined by the light off
temperature whereby 50% conversion is achieved (T50). The SCAT
results are shown in Table 8.
TABLE-US-00008 TABLE 8 NO Oxidation T50 CO fresh T50 HC at
250.degree. C. (%) Example No. condition (.degree. C.) fresh
condition (.degree. C.) fresh condition 17 115 147 75 19 113 167 26
20 138 153 84
[0332] Table 8 shows the CO and HC T50 light off temperatures as
well as NO oxidation at 250.degree. C. for Examples 17, 19 and 20
in the fresh condition. Example 17 has a lower light off
temperature than Example 20. Example 17 comprises Pt/Sb and a
silica-alumina refractory oxide support material. Example 20
comprises Pt and a silica-alumina refractory oxide support
material. Example 17 has a lower HC light off than Example 19 and
better NO oxidation activity. Example 19 comprises Pt/Bi and a
silica-alumina refractory oxide support material.
[0333] The catalysts of Examples 17 to 20 were hydrothermally aged
in an oven at 750.degree. C. for 15 hours using 10% water. Their
catalytic activity was determined using a SCAT as described above
using 0.4 g of aged catalyst powder in the size fraction of 255 to
350 microns and the simulated exhaust gas mixture shown in Table 6
(the balance is nitrogen). The SCAT results are shown in Table
9.
TABLE-US-00009 TABLE 9 NO Oxidation T50 CO aged T50 HC at
250.degree. C. (%) Example No. condition (.degree. C.) aged
condition (.degree. C.) aged condition 17 162 179 82 18 167 178 82
19 130 162 73 20 184 187 84
[0334] Table 9 shows the CO and HC T50 light off temperatures as
well as NO oxidation at 250.degree. C. for Examples 17 to 20 in the
aged condition. Example 17 has a lower light off temperature than
Example 20.
[0335] For the avoidance of any doubt, the entire content of any
and all documents cited herein is incorporated by reference into
the present application.
* * * * *