U.S. patent application number 13/665291 was filed with the patent office on 2013-03-07 for three-way catalyst having a upstream multi-layer catalyst.
This patent application is currently assigned to Umicore AG & Co. KG. The applicant listed for this patent is Ryan Andersen, Davion Clark, Raoul Klingmann, David Moser, John G. Nunan. Invention is credited to Ryan Andersen, Davion Clark, Raoul Klingmann, David Moser, John G. Nunan.
Application Number | 20130058848 13/665291 |
Document ID | / |
Family ID | 45093726 |
Filed Date | 2013-03-07 |
United States Patent
Application |
20130058848 |
Kind Code |
A1 |
Nunan; John G. ; et
al. |
March 7, 2013 |
Three-Way Catalyst Having a Upstream Multi-Layer Catalyst
Abstract
Disclosed herein is a layered, three-way conversion catalyst
having the capability of simultaneously catalyzing the oxidation of
hydrocarbons and carbon monoxide and the reduction of nitrogen
oxides being separated in a front and rear portion is disclosed.
Provided is a catalytic material of at least two front and two rear
layers in conjunction with a substrate, where each of the layers
includes a support, all layers comprise a platinum group metal
component, and the rear bottom layer is substantially free of a
ceria-containing oxygen storage component (OSC).
Inventors: |
Nunan; John G.; (Tulsa,
OK) ; Klingmann; Raoul; (Alzenau, DE) ;
Andersen; Ryan; (Owasso, OK) ; Clark; Davion;
(Macomb, MI) ; Moser; David; (Sterling Heights,
MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nunan; John G.
Klingmann; Raoul
Andersen; Ryan
Clark; Davion
Moser; David |
Tulsa
Alzenau
Owasso
Macomb
Sterling Heights |
OK
OK
MI
MI |
US
DE
US
US
US |
|
|
Assignee: |
Umicore AG & Co. KG
Hanau-Wolfgang
DE
|
Family ID: |
45093726 |
Appl. No.: |
13/665291 |
Filed: |
October 31, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12951311 |
Nov 22, 2010 |
8323599 |
|
|
13665291 |
|
|
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Current U.S.
Class: |
423/213.5 ;
422/168; 502/339 |
Current CPC
Class: |
Y02T 10/12 20130101;
B01D 53/9472 20130101; B01J 35/1019 20130101; B01J 35/0006
20130101; B01D 2255/908 20130101; B01J 35/004 20130101; B01J 35/04
20130101; B01J 23/63 20130101; B01D 53/945 20130101; B01J 37/0244
20130101; B01J 35/1014 20130101; B01D 53/9477 20130101; B01J
37/0246 20130101; B01J 23/42 20130101; B01J 23/62 20130101; B01D
2255/9022 20130101; Y02T 10/22 20130101; B01D 2255/1023 20130101;
B01D 2255/1025 20130101; B01J 21/04 20130101; B01J 23/10 20130101;
B01D 2258/014 20130101; B01J 23/464 20130101 |
Class at
Publication: |
423/213.5 ;
502/339; 422/168 |
International
Class: |
B01J 23/46 20060101
B01J023/46; B01D 53/94 20060101 B01D053/94; F01N 3/10 20060101
F01N003/10 |
Claims
1-16. (canceled)
17. A catalyst composite for the purification of exhaust gases of a
combustion engine substantially running under stoichiometric
conditions comprising in sequence and in order: a front double
layer on a substrate having a front 1.sup.st (lower) catalytic
layer and a front 2.sup.nd (upper) catalytic layer; and a rear
double layer on a substrate having a rear 1.sup.st (lower)
catalytic layer and a rear 2.sup.nd (upper) catalytic layer;
wherein the front 2.sup.nd catalytic layer and the rear 2.sup.nd
catalytic layer comprise rhodium as platinum group metal compound;
wherein the front 1.sup.st catalytic layer and the rear 1.sup.st
catalytic layer comprise palladium as platinum group metal
compound; wherein the rear 1.sup.st catalytic layer is
substantially free of an oxygen storage component (OSC); wherein
the front double layer forms a front zone and the rear double layer
forms a rear zone where the catalyst composite is a single brick
system or the front double layer is located in a front brick and
the rear double layer is located in a rear brick where the catalyst
composite is a multi-brick system; and wherein the content of
oxygen storage component (OSC) by weight of the layers are as
follows: front 1.sup.st catalytic layer--10-80% by weight of the
layer; front 2.sup.nd catalytic layer--20-80% by weight of the
layer; and rear 2.sup.nd catalytic layer--20-80% by weight of the
layer.
18. The catalyst composite according to claim 17, wherein the front
2.sup.nd catalytic layer and the rear 2.sup.nd catalytic layer
establish a continuous layer.
19. The catalyst composite according to claim 17, wherein the rear
1.sup.st catalytic layer comprises less than 1% of an oxygen
storage component (OSC) by weight of the layer.
20. The catalyst composite according to claim 17, wherein the PGM
content of the layers are as follows: front 1.sup.st catalytic
layer--0.1-12.0% by weight of the layer; rear 1.sup.st catalytic
layer--0.0106.0% by weight of the layer; front 2.sup.nd catalytic
layer--0.01-2% by weight of the layer; and rear 2.sup.nd catalytic
layer--0.01-2% by weight of the layer.
21. The catalyst composite according to claim 17, wherein the front
2.sup.nd and/or rear 2.sup.nd catalytic layer comprises
platinum.
22. The catalyst composite according to claim 21, wherein the
platinum content of the layers are as follows: front 2.sup.nd
catalytic layer--0.01-12.0% by weight of the layer; and rear
2.sup.nd catalytic layer--0.01-5.0% by weight of the layer.
23. The catalyst composite according to claim 17, further
comprising exhaust treatment materials selected from the group
consisting of hydrocarbon storage and NOx storage catalysts whereby
the HC storage and NOx storage layer are located as an undercoat WC
layer on the substrate to form the front zone or front brick and/or
the rear zone or rear brick.
24. The catalyst composite according to claim 17, further
comprising exhaust treatment materials selected from the group
consisting of hydrocarbon storage and NOx storage catalysts whereby
the HC storage and NOx storage layer are located as the top or
overcoat WC layer to form the front zone or front brick and/or the
rear zone or rear brick.
25. The catalyst composite according to claim 17, wherein the
catalyst composite is at least partially deposited on an undercoat
layer (UC) comprising material selected from the group consisting
of HC storage material or NOx storage material.
26. The catalyst composite according to claim 17, wherein the
catalyst composite comprises an inlet axial end, an outlet axial
end, wall elements having a length extending between the inlet
axial end to the outlet axial end and a plurality of axially
enclosed channels defined by the wall elements; wherein the front
1.sup.st and 2.sup.nd catalytic layers are deposited on the wall
elements adjacent the inlet axial end and having a length extending
less than the wall length of the wall elements to form the front
zone; and the rear 1.sup.st and 2.sup.nd catalytic layers are
deposited on the wall elements adjacent to the outlet axial end and
having a length extending for less than the length of the wall
elements to form the rear zone.
27. The catalyst composite according to claim 17, wherein the front
1.sup.st and 2.sup.nd catalytic layers are deposited on the inlet
channels of a wall flow filter to form the front zone and the rear
1.sup.st and 2.sup.nd catalytic layers are deposited on the outlet
channels of the wall flow filter to form the rear zone.
28. The catalyst composite according to claim 17, wherein the front
1.sup.st and 2.sup.nd catalytic layers are deposited on the
channels of a flow-through honeycomb substrate to form the front
zone and the rear 1.sup.st and 2.sup.nd catalytic layers are
deposited on the inlet and/or outlet channels of a wall flow filter
to form the rear zone.
29. An exhaust treatment system for the purification of exhaust
gases of a combustion engine substantially running under
stoichiometric conditions comprising the catalyst composite
according to claim 17.
30. An exhaust treatment system according to claim 29, further
comprising one or more exhaust treatment devices selected from the
group consisting of HC trap and NOx storage catalyst.
31. The method for treating the exhaust gases of a combustion
engine substantially running under stoichiometric conditions,
wherein the method comprises: contacting a gaseous stream
comprising hydrocarbons, carbon monoxide, and nitrogen oxides with
a catalyst composite of claim 17, wherein the catalyst composite is
effective to substantially simultaneously oxidize the carbon
monoxide and the hydrocarbons and reduce the nitrogen oxides.
Description
TECHNICAL FIELD
[0001] This invention pertains generally to layered catalysts used
to treat gaseous streams containing hydrocarbons, carbon monoxide,
and oxides of nitrogen. More specifically, this invention is
directed to three-way-conversion (TWC) catalysts having more than
one catalyst layer upstream and a multi-layer catalyst that is
located downstream.
BACKGROUND AND PRIOR ART
[0002] Current TWC catalysts are used for mobile emission control
from Otto engines. The technology is well developed with emission
reduction capabilities of >99% for CO, HC (hydrocarbons) and NOx
(nitrogen oxides) after heat up to operating temperatures of
greater than 250.degree. C. Typical TWC catalyst configurations
consist of single brick or multi-brick systems in the exhaust line
of the vehicle. If more than one catalyst is used, the catalysts
can be located in a single converter, butted together, or separated
by a defined space as in separate converters. A common design for
large engines is to have one converter in a hot close coupled (CC)
position (close to the manifold) with the second converter in the
cooler underbody (UB) location. Since nearly all mobile emission
control systems are passive in nature, time to heat up to the
catalyst operating temperature is critical as disclosed in
EP1900416, which is relied on and herein incorporated by reference
in its entirety.
[0003] Thus, CC catalyst designs often consist of features that
favor rapid heat up such as light, small size substrates (low
thermal inertia), high cell density (improved mass & heat
transfer) and high platinum group metal (PGM; e.g., platinum,
palladium, rhodium, rhenium, ruthenium and iridium) loading. On the
other hand the UB catalyst can be of larger volume and lower cell
density (lower pressure drop) and more often contains lower PGM
loading. For smaller vehicles that operate at high RPM only one
converter is typically used, often located in the CC position. A
disadvantage of locating catalysts close to the manifold is
increased thermal degradation, and more rapid loss of activity,
especially under high load/high speed conditions which results in
loss of support surface area or pore volume and rapid sintering of
the PGM.
[0004] Modern TWC catalysts use a variety of strategies to limit or
slow thermal degradation such as high surface area stable alumina
supports for the PGMs, the addition of promoters and stabilizers
and advanced oxygen storage components (OSCs) that both improve
performance and degrade at a slower rate (see e.g. U.S. Pat. No.
5,672,557, which is relied on and herein incorporated by reference
in its entirety).
[0005] In the art, certain design strategies have been used to
balance performance with associated costs. These strategies include
selection of PGM type and distribution, substrate volume, cell
density, WC layering, and composition of the various WC layers.
[0006] An important design feature for TWC technologies consists of
appropriate separation and configuration of both the PGM and
washcoat (WC) components either in separate WC layers and/or in
separate bricks if multi-brick systems are used. Most modern TWC
catalysts can have one to more WC layers, the most common being
2-layer systems. See e.g., EP1541220, U.S. Pat. No. 5,981,427,
WO09012348, WO08097702, WO9535152, U.S. Pat. No. 7,022,646, U.S.
Pat. No. 5,593,647, which are relied on and herein incorporated by
reference in their entirety.
[0007] For the PGMs, the most common strategy is to locate the Rh
and optionally the Pt component in the top or 2.sup.nd WC layer
with Pd preferably located in the bottom or 1.sup.st WC layer (see
e.g., U.S. Pat. No. 5,593,647). Separation of both the WC
components and PGMs can also be achieved for single bricks by
zoning whereby the front or rear zone or section of a WC layer can
consist of different support components or different PGM components
or more commonly different concentrations of a given PGM such as
Pd. One advantage for separation of the PGMs in layers or zones is
that more optimum supports and promoters for each PGM can be used
so as to maximize overall performance.
[0008] Prior to the present invention, researchers have been drawn
to certain WC composition configurations that are taught as
representing the preferred configuration for best performance.
Thus, for two-layer UB catalysts Rh is invariably located in the
top (2.sup.nd) layer with optionally Pt also present while Pd is
located in the 1.sup.st or bottom layer (see e.g., U.S. Pat. No.
5,593,647). Further, both the top (2.sup.nd) and bottom (1.sup.st)
layers ideally contain a high surface area refraction oxide support
such as a gamma or gamma/theta/delta alumina with further addition
of promoters, stabilizers and a suitable oxygen storage component
(OSC). This WC design is described in detail by Sung et al. (U.S.
Pat. No. 6,087,298) and Hu et al. (U.S. Pat. No. 6,497,851) hereby
included for reference purposes. Both Sung et al. and Hu et al.
also describe preferred WC compositions and configurations for the
CC catalysts or zones at the inlets to the exhaust gas flow. Thus,
for the inlet CC or inlet (front) zone the WC design is preferably
free of an OSC and consists of a high surface area refractory oxide
support such as a gamma or theta/delta alumina with appropriate
stabilizers and additives. On the other hand, it is preferred that
the rear catalyst, zone or UB catalyst, have an OSC present in the
bottom and top layers. These and other features are described for
example by Hu et al. and references quoted therein.
[0009] Within the TWC catalyst field new technologies and WC
configurations and systems are required to meet the ever more
stringent emission standards and the need to slow catalyst
deactivation and achieve ever increasing performance at low PGM
loadings.
SUMMARY OF THE INVENTION
[0010] This invention relates to TWC catalysts having different WC
compositions with respect to their locations relative to each other
and their use in emission control systems. Specifically, the TWC
catalysts according to the present invention comprise at least a
front (upstream) brick or zone and a rear (downstream) brick or
zone. Both the front and rear bricks or zones comprise at least two
layers; however, in the rear brick or zone, an OSC is absent in the
1.sup.st (lower) catalytic layer. In some embodiments, one or more
bricks or zones may be placed between the front and rear bricks or
zones. In some embodiments, the zones or bricks are located in a
single converter, butted together or separated by a defined space.
In some embodiments, the bricks are located in separate converters.
In some embodiments, two or more separate converters are provided
and at least one converter contains a rear zone or brick with at
least two layers and the absence of OSC in the 1.sup.st catalytic
layer. In some embodiments which comprise more than one separate
converter, the furthest downstream converter contains a rear zone
or brick with at least two layers and the absence of OSC in the
1.sup.st catalytic layer.
[0011] In some embodiments, the invention is directed to a catalyst
composite for the purification of exhaust gases of a combustion
engine substantially running under stoichiometric conditions
comprising in sequence and in order: [0012] a front double layer
configuration on a substrate having a front 1.sup.st (lower)
catalytic layer and a front 2.sup.nd (upper) catalytic layer; and
[0013] a rear double layer configuration on a substrate having a
rear 1.sup.st (lower) catalytic layer and a rear 2.sup.nd (upper)
catalytic layer; [0014] wherein the front 2.sup.nd catalytic layer
and the rear 2.sup.nd catalytic layer comprise a platinum group
metal compound (PGM), such as rhodium; and [0015] wherein the front
1.sup.st catalytic layer and the rear 1.sup.st catalytic layer
comprise another platinum group metal compound (PGM), such as
palladium; and [0016] wherein the rear 1.sup.st catalytic layer is
substantially free of an oxygen storage component (OSC).
[0017] In some embodiments of the present invention, the front
2.sup.nd catalytic layer and the rear 2.sup.nd catalytic layer form
one continuous layer. In some embodiments, the continuous layer may
have a gradient from the upstream end to the downstream end. In
some embodiments, the front 2.sup.nd catalytic layer and the rear
2.sup.nd catalytic layer are made of the same materials in the same
or different concentrations.
[0018] By reference to 1.sup.st and 2.sup.nd layers, no limitation
is being placed on the location of the layer in view of the
direction of exhaust flow. Locations of the layers in view of the
exhaust flow are rather described by front (upstream) and rear
(downstream) layers. A 1.sup.st layer of the catalytic material is
deposited on a substrate or a bottom layer already deposited on a
substrate to form a lower coating. A 2.sup.nd catalytic layer is
deposited on and having physical contact with the 1.sup.st layer to
form the upper coating.
[0019] In other words, the front (upstream) zone or brick that
comes into contact with the exhaust first is closest to the engine
and can have a bottom (1.sup.st) catalytic layer and a top
(2.sup.nd) catalytic layer. The rear (downstream) zone or brick is
one that comes into contact with the exhaust after contact with a
prior zone or brick. The rear zone or brick can have a bottom
(1.sup.st) catalytic layer and a top (2.sup.nd) catalytic layer.
The front and rear zones or bricks can be in the same converter and
can be touching each other or be separated by a distance, e.g.
about an inch or so. Alternatively, the front and rear zones or
bricks can be in separate converters which may be separated by a
large distance, e.g. about 1-6 feet.
[0020] The term "substantially free of an oxygen storage component
(OSC)" refers to having a very low amount or, preferably, no OSC
in, for example, a given layer. A very low amount of OSC is
understood to mean less than or equal to about 1%, preferably about
0.5%, more preferably about 0.25%, and most preferably about 0.1%
by weight of OSC in a given layer.
[0021] In some embodiments, an exhaust treatment system comprising
the catalyst composite is provided. The exhaust treatment system
may further comprise one or more exhaust treatment devices selected
from the group consisting of gasoline particulate filter traps
(GPT), HC trap and NOx adsorber catalysts.
[0022] In some embodiments, the present invention provides methods
for treating exhaust gases which comprises contacting a gaseous
stream comprising hydrocarbons, carbon monoxide, and nitrogen
oxides with a layered catalyst composite or an exhaust treatment
system as described herein, wherein the catalytic material employed
is effective to substantially simultaneously oxidize the carbon
monoxide and the hydrocarbons and reduce the nitrogen oxides. In
some embodiments, the exhaust gas temperature at the catalyst inlet
can vary from room temperature to as high as 1100.degree. C.,
however typical catalyst operating temperatures by design fall in
the range of about 300-900.degree. C.
[0023] Both the foregoing general description and the following
detailed description are exemplary and explanatory only and are
intended to provide further explanation of the invention as
claimed. The accompanying drawings are included to provide a
further understanding of the invention and are incorporated in and
constitute part of this specification, illustrate several
embodiments of the invention, and together with the description
serve to explain the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The present invention will be further understood with
reference to the drawings wherein:
[0025] FIGS. 1a to 1e are examples of known washcoat layering and
configurations.
[0026] FIGS. 2a and 2b are examples of washcoat layering and
configurations of the present invention where the first layer of
the rear zone (FIG. 2a) or brick (FIG. 2b) does not have OSC.
[0027] FIG. 3 illustrates another embodiment of the present
invention.
[0028] FIG. 4a shows a WC configuration for a reference (prior art)
catalyst using a conventional 2-layer design which comprises
uniform Rh and Pd layers.
[0029] FIG. 4b shows a WC configuration for a catalyst according to
the present invention wherein the 1.sup.st or lower catalytic layer
of the rear brick/zone is without OSC.
[0030] FIG. 5 is a graph of the FTP evaluation of the inventive
system configuration described in FIG. 4a/b after 50 Hrs of a
thermal 4-Mode aging; Vehicle=2005 MY, BIN 5, 2.2 L/4 cylinder with
sequential fuel injection. Pd+Rh=20 g/ft.sup.3 @ 0:9:1; Average of
three FTP tests for each catalyst system comparing a reference
sample 4a and a test sample 4b for THC performance.
[0031] FIG. 6 is a graph of the FTP evaluation of the inventive
system configuration described in FIG. 4a/4b after 50 Hrs of
thermal 4-Mode aging; Vehicle=2005 MY, BIN 5, 2.2 L/4 cylinder with
sequential fuel injection. Pd+Rh=20 g/ft.sup.3 @ 0:9:1; average of
three FTP tests for each catalyst system comparing a reference
sample 4a and a test sample 4b for NOx performance.
DETAILED DESCRIPTION OF THE INVENTION
[0032] The present invention is directed to a three-way conversion
(TWC) catalyst and the compositions and locations of the catalytic
layers relative to the direction of exhaust gas flow. In
particular, the TWC catalysts according to the present invention
comprise at least a front (upstream) brick or zone and a rear
(downstream) brick or zone, wherein the rear brick or zone
comprises at least two layers, wherein an OSC is absent in the
1.sup.st (lower) catalytic layer. As disclosed herein, TWC
catalysts according to the present invention provide large
performance benefits that are unexpected based on the teachings and
best practices in the art prior to the instant invention.
[0033] The present invention relates to a layered catalyst
composite of the type generally referred to as a three-way
conversion (TWC) catalyst having the capability to simultaneously
catalyze the oxidation of hydrocarbons and carbon monoxide and the
reduction of nitrogen oxides. The catalyst composite is divided
into at least two sections either by using different zones on one
substrate or using separate bricks being located in a single
converter, butted together, or separated by a defined space as in
separate converters.
[0034] In some embodiments, the platinum group metal (PGM) loading
of the catalytic layers is about 0.001-20.0% by weight. In some
embodiments, each layer of the catalytic layers may comprise a
different composition. In some embodiments, each layer has a
loading of from about 0.2-2.8 g/in.sup.3.
[0035] In some embodiments, each layer has a PGM loading of from
about 0.01% by weight to about 20.0% by weight of the layer. In
some embodiments, each of the respective layers is deposited at a
PGM loading of about 0.02-15.0% by weight.
[0036] In some embodiments, the catalyst composite refers to a PGM
content of the layers which are as follows: [0037] front 1.sup.st
catalytic layer--0.1--about 12.0% by weight of the layer; [0038]
rear 1.sup.st catalytic layer--0.05--about 6.0% by weight of the
layer; [0039] front 2.sup.nd catalytic layer--0.01--about 12.0% by
weight of the layer; [0040] rear 2.sup.nd catalytic
layer--0.01--about 6.0% by weight of the layer.
[0041] The rear 2.sup.nd catalytic layer always comprises rhodium
as a PGM but may also comprise other PGMs as well. Rh is preferred
in the rear 2.sup.nd catalytic layer as NOx reduction based on the
2CO+2NO.fwdarw.N.sub.2+2CO.sub.2 reaction is most efficient at
intermediate temperatures in the range of 300-600.degree. C. In
some embodiments, the amount of rhodium in a layer is about
0.01-1.0% by weight, preferably 0.02-0.5%, and most preferably
0.05-0.25% by weight.
[0042] The front and rear 1.sup.st catalytic layers always comprise
palladium as a PGM but may also comprise other PGMs as well. In a
preferred embodiment, the front and rear 1.sup.st catalytic layers
only comprise palladium as a PGM. Palladium is particularly
effective for HC oxidation and is often concentrated in the front
1.sup.st catalytic layer of the front brick so as to initiate HC
light-off as soon as possible. This arises as the concentration of
HC emitted from the engine is greater in the initial stages of
vehicle operation in contrast to NOx which is emitted largely after
warm-up of the vehicle. In some embodiments, the amount of
palladium in the front and rear 1.sup.st catalytic layers is about
0.1-15.0% by weight, preferably about 0.2-10.0%, and most
preferably about 0.5-5.0% by weight.
[0043] As already indicated it may be advantageous to have Pt as a
PGM present in the layers, especially the front and rear 2.sup.nd
catalytic layers. Pt has the advantage of being particularly
effective for hard HC (saturated HCs) oxidation and may
advantageously form alloys with Rh. Under normal
stoichiometric/rich/lean exhaust gas conditions the surface of the
alloy is rich in Rh which protects this PGM from negative
interactions with the support.
[0044] In some embodiments, an amount of platinum group metal is up
to about 4% by weight of the layer. In some embodiments, the amount
of platinum in a layer is about 0.05-5% by weight, preferably about
0.1-2.0%, and most preferably about 0.3-1.0% by weight. In some
embodiments, the platinum content of the layers is as follows:
[0045] front 2.sup.nd catalytic layer--about 0.05-5.0% by weight of
the layer, preferably about 0.1-2.0%, and most preferably about
0.3-1.0%; [0046] rear 2.sup.nd catalytic layer--0.025-2.5% by
weight of the layer, preferably about 0.1-2.5%, and most preferably
about 0.3-1.0%.
[0047] Reference to OSC (oxygen storage component) refers to an
entity that has multi-valence state and can actively react with
oxidants such as oxygen or nitrogen oxides under oxidative
conditions, or reacts with reductants such as carbon monoxide (CO),
hydrocarbons (HCs) or hydrogen under reduction conditions. Suitable
oxygen storage components may include one or more oxides of one or
more rare earth or transition metals selected from the group
consisting of cerium, zirconium, terbium, iron, copper, manganese,
cobalt, praseodymium, lanthanum, yttrium, samarium, gadolinium,
dysprosium, ytterbium, niobium, neodymium, and mixtures of two or
more thereof. Examples of suitable oxygen storage components
include ceria, praseodymia, or combinations thereof.
[0048] Delivery of an OSC to the layer can be achieved by the use
of, for example, mixed oxides. For example, ceria can be delivered
by a mixed oxide of cerium and zirconium, and/or a mixed oxide of
cerium, zirconium and neodymium with optionally other rare earths
such as lanthanum or yttrium also present. For example, praseodymia
may be delivered by a mixed oxide of praseodymium and zirconium,
and/or a mixed oxide of praseodymium, cerium, lanthanum, yttrium,
zirconium, and neodymium. Suitable compositions can be found in
U.S. Pat. No. 6,387,338 and U.S. Pat. No. 6,585,944, both of which
are herein incorporated by reference in their entirety.
[0049] The OSC can be present up to about 80% by weight of the
layer, preferably about 20-70%, and most preferably about 30-60%.
The ceria or praseodymia content in the range of about 3-98%,
preferably about 10-60%, most preferably about 20-40% by weight of
OSC. Suitable oxygen storage components may include one or more
oxides of one or more rare earth or transition metals selected from
the group consisting of cerium, zirconium, terbium, iron, copper,
manganese, cobalt, praseodymium, lanthanum, yttrium, samarium,
gadolinium, dysprosium, ytterbium, niobium, neodymium, and mixtures
of two or more thereof. In some embodiments, the catalyst composite
according to the invention comprises a content of oxygen storage
component (OSC) by weight of the layer as follows: [0050] front
1.sup.st catalytic layer--about 10-80% by weight of the layer,
preferably about 20-70%, and most preferably about 30-60%; [0051]
front 2.sup.nd catalytic layer--about 10-80% by weight of the
layer, preferably about 20-70%, and most preferably about 30-60%;
[0052] rear 2.sup.nd catalytic layer--about 10-80% by weight of the
layer, preferably about 20-70%, and most preferably about
30-60%.
[0053] In some embodiments, the catalyst composite further
comprises exhaust treatment materials selected from the group
consisting of hydrocarbon storage components, NOx storage
components as the current design may have particular applicability
for exhaust treatment systems comprising HC traps and/or NOx
adsorber functionalities. Current state-of-the-art catalyzed HC
trap designs utilize an undercoat (UC--see later) consisting of HC
trapping materials inclusive of various zeolites with a TWC
overcoat (OC) of one or two layers as described in Japanese patents
JP7124468 and JP7124467 and U.S. Pat. No. 7,442,346 which are
herein incorporated by reference. Optimum performance is achieved
for designs whereby the rear 1.sup.st layer does not contain OSC
and where the rear 2.sup.nd catalytic layer does contain an OSC as
described in the current invention for optimum configuration of the
WC composition in 1.sup.st and 2.sup.nd catalytic layers of the
front and rear technology. Further, the newest design for HC trap
location is in the cooler rear or underbody (UB) location (U.S.
Pat. No. 7,442,346) as distinct from earlier strategies of placing
the HC trap in the CC position (U.S. Pat. No. 5,772,972; Silver R.
G., Dou D., Kirby C. W., Richmond R. P., Balland J., and Dunne S.;
SAE 972843, and references therein) again in line with the current
configuration of WC layers. For the case of NOx adsorber catalysts,
a preferred location of the adsorber is again in the cooler UB
location with an active TWC also present to both generate H.sub.2
and to complete HC/CO combustion during the rich/lean
transients.
[0054] A suitable support according to some embodiments of the
present invention is a refractory oxide support. Reference to a
"support" in a catalyst layer refers to a material onto or into
which platinum group metals, stabilizers, promoters, binders or
other additives and the like are dispersed or impregnated,
respectively. A support can be activated and/or stabilized as
desired. Examples of supports include, but are not limited to, high
surface area refractory metal oxides, composites containing oxygen
storage components, and molecular sieves as is well known in the
art. In some embodiments, the support of each layer independently
comprises a compound that is activated, stabilized, or both
selected from the group consisting of, but not limited to, alumina,
silica, silica-alumina, alumino-silicates, alumina-zirconia,
lanthana-alumina, lanthana-zirconia-alumina, baria-alumina, baria
lanthana-alumina, alumina-chromia, and alumina-ceria. The support
may comprise any suitable material, for example, a metal oxide
comprising gamma-alumina or promoter-stabilized gamma-alumina
having a specific surface area of about 50-350 m.sup.2/g,
preferably about 75-250 m.sup.2/g, and most preferably about
100-200 m.sup.2/g. In some embodiments, the alumina present in any
of the layers comprises, optionally zirconia- and
lanthana-stabilized (gamma-) alumina in a loading of about 5-90% by
weight of the layer, preferably about 20-70%, and most preferably
about 30-60%. For example, a suitable stabilized alumina may
comprise about 0.1-15% by weight of lanthana (preferably as a
stabilizer), preferably about 0.5-10%, and most preferably about
1-7%; and/or about 0.5-15%, preferably about 0.5-10%, and most
preferably about 1-7% zirconia (preferably as a stabilizer in
gamma-alumina). In some embodiments, the alumina comprises
gamma-alumina stabilized by barium oxide, neodymia, lanthana and
combinations thereof. The stabilizer loading on a suitable alumina
is about 0-4% by weight of support, preferably about 1-3%, and most
preferably about 2% barium oxide. It is noted that lanthana,
zirconia and neodymia are stabilizers and that, in some
embodiments, one or more can be at the same loading range, i.e.
lanthana, zirconia, neodymia, or a combination thereof can be
present at 0.1-15% by weight.
[0055] In some embodiments, a molecular sieve material can be
selected from the group consisting of faujasite, chabazite,
silicalite, zeolite X, zeolite Y, ultrastable zeolite Y, offretite,
Beta, ferrierite and ZSM/MFI zeolites. In particular, ion-exchanged
Beta zeolites may be used, such as Fe/Beta zeolite, or preferably,
H/Beta zeolite. The zeolites, preferably Beta zeolites may have a
silica/alumina molar ratio of from at least about 25/1 or at least
about 50/1, with useful ranges of from about 25/1 to 1000/1, 50/1
to 500/1 as well as about 25/1 to 300/1, for example.
[0056] In some embodiments, the layers provided are the 1.sup.st
front and/or 1.sup.st rear catalytic layer comprising a stabilized
alumina, such as gamma-alumina, which can be present in an amount
in the range of about 10-90% by weight of the layer, preferably
about 20-70%, and most preferably about 30-60%, substantially only
palladium, which can be present in an amount in the range of about
0.1-10.0% by weight of the layer, preferably about 0.1-5.0%, and
most preferably about 0.2-2.0%.
[0057] In some embodiments, the front and rear 2.sup.nd catalytic
layers comprise a stabilized alumina, such as gamma-alumina, which
can be present in an amount in the range of about 10-90% by weight
of the layer, preferably about 20-70%, and most preferably about
30-60%; rhodium, which can be present in an amount in the range of
about 0.01-1.0% by weight of the layer, preferably about 0.05-0.5%,
and most preferably about 0.1-0.25%.
[0058] In some embodiments, the front and rear 2.sup.nd catalytic
layers comprise a stabilized alumina, such as lanthana stabilized
gamma-alumina, which can be present in an amount in the range of
about 10-90% by weight of the layer, preferably about 20-70%, and
most preferably about 30-60%, platinum, which can be present in an
amount in the range of up to about 4.0% by weight of the layer,
preferably about 0.05-2.0%, and most preferably about 0.1-1.0%,
whereby rhodium, which can be present in an amount in the range of
about 0.01-1.0% by weight of the layer, preferably about 0.05-0.5%,
and most preferably about 0.1-0.25%.
[0059] In some embodiments, it may be desirable that a given layer
further comprises up to about 40%, preferably about 5-30%, and most
preferably about 10-20% of a stabilizer comprising one or more
non-reducible metal oxides wherein the metal is selected from the
group consisting of barium, calcium, magnesium, strontium, and
mixtures thereof. A layer may further comprise, according to one
embodiment, 0 to about 40%, preferably about 5-30%, and most
preferably about 10-30% of one or more promoters comprising one or
more rare earth or transition metals selected from the group
consisting of lanthanum, praseodymium, yttrium, zirconium,
samarium, gadolinium, dysprosium, ytterbium, niobium, neodymium,
and mixtures thereof. A layer may further comprise, according to
one embodiment, 0 to about 20%, preferably about 2-20%, and most
preferably about 5-10% of one or more binders comprising one or
more alumina boehmites, zirconia hydroxites or silica sols, and
mixtures thereof. A layer may further comprise, according to one
embodiment, 0 to about 20%, preferably about 0-12%, more preferably
about 0-6% of one or more of further additives comprising hydrogen
sulfide (H.sub.2S) control agents such as nickel, iron, zinc,
boron, manganese, strontium and mixtures thereof.
[0060] Segregated washcoats that address certain catalytic
functionalities can be used. The use of at least two layers on a
substrate can lead to more efficient use of and/or to a decrease in
overall amount of, for example, platinum group metals due to their
separation from one another.
[0061] In some embodiments, the compositions of each layer are
tailored to address a particular function of the TWC catalyst. For
example, overcoat layers that are substantially free of platinum
group metals and that comprise alumina and one or more base metal
oxides are, for example, effective to trap poisons such as sulfur,
nitrogen, magnesium, calcium, zinc and phosphorous-containing
components. Examples of base metal oxides include, but are not
limited to SrO, La.sub.20.sub.3, Nd.sub.20.sub.3, or BaO.
[0062] The catalyst composite in its zoned embodiment comprises a
substrate comprising an inlet axial end, an outlet axial end, wall
elements having a length extending between the inlet axial end to
the outlet axial end and a plurality of axially enclosed channels
defined by the wall elements; and a front part of the composite
catalyst deposited on the wall elements adjacent the inlet axial
end and having a length extending less than the wall length of the
wall elements, wherein the inlet catalyst composite comprises the
catalyst composite described above. This catalyst composite further
comprises a rear part of the catalyst composite adjacent to the
outlet axial end and having a length extending for less than the
length of the wall elements. For example, the front part of the
catalyst composite may comprise (a) a substrate; (b) a 1.sup.st
catalytic layer deposited on the substrate, the 1.sup.st catalytic
layer comprising palladium deposited on a support; (c) a 2.sup.nd
catalytic layer deposited on the 1.sup.st catalytic layer, the
2.sup.nd catalytic layer comprising rhodium deposited on a support;
and for example, the rear part of the catalyst composite may
comprise (a) a substrate; (b) a 1.sup.st catalytic layer deposited
on the substrate, the 1.sup.st catalytic layer comprising palladium
deposited on a support; (c) a 2.sup.nd catalytic layer deposited on
the 1.sup.st catalytic layer, the 2.sup.nd catalytic layer
comprising rhodium deposited on a support.
[0063] In some embodiments, the front part of the catalyst
composite overlaps the rear part of the catalyst composite. In some
embodiments, the front part of the catalyst composite comprises
between about 10-90%, more preferably about 20-60%, and most
preferably about 25-50% of the total length (e.g., 1-15 cm of total
length) of the substrate, such as a honeycomb substrate. In some
embodiments, the rear part of the catalyst composite comprises
between about 10-90%, more preferably about 40-80%, and most
preferably about 50-75% of the total length of the substrate, such
as a honeycomb substrate.
[0064] In some embodiments, one or more catalyst composites of the
invention are disposed on a substrate. The substrate may be any of
those materials typically used for preparing catalysts, and will
preferably comprise a ceramic or metal honeycomb structure. Any
suitable substrate may be employed, such as a monolithic substrate
of the type having fine, parallel gas flow passages extending there
through from an inlet or an outlet face of the substrate, such that
passages are open to fluid flow there through (referred to as
honeycomb flow through substrates). The passages, which are
essentially straight paths from their fluid inlet to their fluid
outlet, are defined by walls on which the catalytic material is
coated as a washcoat so that the gases flowing through the passages
contact the catalytic material.
[0065] The flow passages of the monolithic substrate are
thin-walled channels, which can be of any suitable cross-sectional
shape and size such as trapezoidal, rectangular, square,
sinusoidal, hexagonal, oval, circular, etc. Such structures may
contain from about 60-900 or more gas inlet openings (i.e., cells)
per square inch of cross section.
[0066] The substrate can also be a wall-flow filter substrate,
where the channels are alternately blocked, allowing a gaseous
stream entering the channels from one direction (inlet direction),
to flow through the channel walls and exit from the channels from
the other direction (outlet direction). A dual oxidation catalyst
composition can be coated on the wall-flow filter. If such a
substrate is utilized, the resulting system will be able to remove
particulate matter along with gaseous pollutants. The wall-flow
filter substrate can be made from materials commonly known in the
art, such as cordierite or silicon carbide. In some embodiments,
the catalyst composite of the present invention shows a front zone
comprising the 1.sup.st and 2.sup.nd catalytic layers deposited on
the inlet channels of a wall-flow filter, and the rear zone
comprising the 1.sup.st and 2.sup.nd catalytic layers deposited on
the outlet channels of a wall-flow filter.
[0067] In some embodiments, where the front and rear zone are
coated onto separate bricks, the front zone can be a wall-flow
filter substrate and the rear zone can be a flow-through honeycomb
substrate. In some embodiments, the front zone is a flow-through
honeycomb substrate and the rear zone is coated on a wall-flow
filter element.
[0068] The ceramic substrate may be made of any suitable refractory
material, e.g., cordierite, cordierite-alumina, silicon nitride,
zircon mullite, spodumene, alumina-silica magnesia, zircon
silicate, sillimanite, a magnesium silicate, zircon, petalite,
alumina, an aluminosilicate and the like.
[0069] The substrates useful for the catalyst composite of the
present invention may also be metallic in nature and be composed of
one or more metals or metal alloys. The metallic substrates may be
employed in various shapes such as corrugated sheet or monolithic
form. Preferred metallic supports include the heat resistant metals
and metal alloys such as titanium and stainless steel as well as
other alloys in which iron is a substantial or major component.
Such alloys may contain one or more of nickel, chromium, and/or
aluminum, and the total amount of these metals may advantageously
comprise at least about 15 wt % of the alloy, e.g., about 10-25 wt
% of chromium, about 3-8 wt % of aluminum and up to about 20 wt %
of nickel. The alloys may also contain small or trace amounts of
one or more other metals such as manganese, copper, vanadium,
titanium and the like. The surface of the metal substrates may be
oxidized at high temperatures, e.g., about 1000.degree. C. and
higher, to improve the resistance to corrosion of the alloys by
forming an oxide layer on the surfaces of the substrates. Such high
temperature-induced oxidation may enhance the adherence of the
refractory metal oxide support and catalytically promoting metal
components to the substrate. In alternative embodiments, one or
more catalyst compositions may be deposited on an open cell foam
substrate. Such substrates are well known in the art, and are
typically formed of refractory ceramic or metallic materials.
[0070] Based on the prior art, the WC composition configuration of
the present invention is not taught or recognized as having
favorable performance or other beneficial features. In fact, the
prior art specifically teaches against this configuration as
outlined in detail in the Hu et al. patent and references
therein.
Preparation:
[0071] The layered catalyst composite of the present invention may
be readily prepared by processes known in the art. See, for
example, U.S. Pat. No. 6,478,874 and EP0441173, which are herein
incorporated by reference in their entirety. A representative
process is set forth below. As used herein, the term "washcoat" has
its usual meaning in the art of a thin, adherent coating of a
catalytic or other material applied to a substrate material, such
as a honeycomb-type substrate member, which is sufficiently porous
to permit the passage there through of the gas stream being
treated.
[0072] The catalyst composite can be readily prepared in layers on
a monolithic substrate. For a first layer of a specific washcoat,
finely divided particles of a high surface area refractory metal
oxide such as gamma-alumina are slurried in an appropriate solvent,
e.g., water. The substrate may then be dipped one or more times in
such slurry or the slurry may be coated on the substrate such that
there will be deposited on the substrate the desired loading of the
metal oxide, e.g., about 0.5-2.5 g/in.sup.3. To incorporate
components such as precious metals (e.g., palladium, rhodium,
platinum, and/or combinations of the same), stabilizers, binders,
additives, and/or promoters, such components may be incorporated in
the slurry as a mixture of water soluble or water-dispersible
compounds or complexes. Thereafter the coated substrate is calcined
by heating, e.g., at about 300-800.degree. C. for about 1-3 hours.
Typically, when palladium is desired, the palladium component is
utilized in the form of a compound or complex to achieve high
dispersion of the component on the refractory metal oxide support,
e.g., activated alumina. For the purposes of the present invention,
the term "palladium component" means any compound, complex, or the
like which, upon calcination or use thereof, decomposes or
otherwise converts to a catalytically active form, usually the
metal or the metal oxide. Water-soluble compounds or
water-dispersible compounds or complexes of the metal component may
be used as long as the liquid medium used to impregnate or deposit
the metal component onto the refractory metal oxide support
particles does not adversely react with the metal or its compound
or its complex or other components which may be present in the
catalyst composite and is capable of being removed from the metal
component by volatilization or decomposition upon heating and/or
application of a vacuum. In some cases, the complete removal of the
liquid may not take place until the catalyst is placed into use and
subjected to the high temperatures encountered during operation.
Generally, both from the point of view of economics and
environmental aspects, aqueous solutions of soluble compounds or
complexes of the precious metals are utilized. For example,
suitable compounds are palladium nitrate or rhodium nitrate. During
the calcination step, or at least during the initial phase of use
of the composite, such compounds are converted into a catalytically
active form of the metal or a compound thereof.
[0073] In some embodiments, the slurry is thereafter milled to
result in substantially all of the solids having particle sizes of
less than about 20 microns, i.e., between about 0.1-15 microns, in
an average diameter. The combination may be accomplished in a ball
mill or other similar equipment, and the solids content of the
slurry may be, e.g., about 15-60 wt %, more particularly about
25-40 wt %.
[0074] Additional layers may be prepared and deposited upon the
first (1.sup.st) catalytic layer in the same manner as described
above for deposition of the first (1.sup.st) catalytic layer upon
the substrate.
[0075] Before describing several exemplary embodiments of the
invention, it is to be understood that the invention is not limited
to the details of construction or process steps set forth in the
following description. The invention is capable of other
embodiments and of being practiced in various ways.
Front 1.sup.st Catalytic Layer Embodiments
[0076] According to some embodiments, the first layer which is
deposited upon, i.e., coated upon and adhered to, the substrate
comprises palladium deposited on a support. A suitable support is a
high surface area refractory metal oxide. In a specific embodiment,
the loading of the first layer upon the substrate is between about
0.2-2.8 g/in.sup.3. Examples of high surface area refractory metal
oxides include, but are not limited to, alumina, silica, titania
and zirconia and mixtures thereof. The refractory metal oxide may
consist of or contain a mixed oxide such as silica-alumina,
alumino-silicates which may be amorphous or crystalline,
alumina-zirconia, alumina-lanthana,
alumina-baria-lanthana-neodymia, alumina-chromia, alumina-baria,
alumina-ceria, and the like. An exemplary refractory metal oxide
comprises gamma-alumina having a specific surface area of about
50-350 m.sup.2/g and which is present in a loading of about 10-90%
by weight of the washcoat. The first layer typically will have
oxygen storage components in the range of about 10-90% by weight
with ceria content ranging form about 3-98% by weight of the layer
material.
[0077] Examples of palladium loading in the first layer include up
to about 15% by weight, alternatively, between about 0.05 and about
10% by weight, of palladium. This layer may also contain up to
about 40% of stabilizers/promoters/binders/additives. Suitable
stabilizers include one or more non-reducible metal oxides wherein
the metal is selected from the group consisting of barium, calcium,
magnesium, strontium, and mixtures thereof. In some embodiments,
the stabilizer comprises one or more oxides of barium and/or
strontium. Suitable promoters include one or more non-reducible
oxides, or rare earth and transition metals selected from the group
consisting of lanthanum, neodymium, praseodymium, yttrium,
zirconium, samarium, gadolinium, dysprosium, ytterbium, niobium,
and mixtures thereof.
Front and Rear 2.sup.nd Catalytic Layer Embodiments
[0078] A 2.sup.nd catalytic layer, which is deposited upon, i.e.,
coated upon and adhered to, the front 1.sup.st catalytic layer,
comprises rhodium or rhodium and platinum deposited on a high
surface area refractory metal oxide and/or oxygen storage component
which may be any of those mentioned above with respect to the
1.sup.st catalytic layer. The 2.sup.nd catalytic layer will be
present in a loading of about 0.2-2.8 g/in.sup.3, alternatively,
between about 1-1.6 g/in.sup.3 and will have substantially an
amount of oxygen storage component at a loading of about 10-90% by
weight. Oxygen storage components can be ceria containing
ceria/zirconia composite with ceria in the range of from about 3-90
as weight percent. Preferably, about 5-55% of ceria by weight is in
the composite. The 2.sup.nd catalytic layer also can comprise
gamma-alumina or stabilized gamma-alumina having a specific surface
area of about 50-350 m.sup.2/g and which is present in a loading of
about 10-90% by weight.
[0079] In some embodiments, rhodium will be present in the 2.sup.nd
catalytic layer in a loading of about 0.01-1.0% by weight,
alternatively about 0.05-0.5% by weight of rhodium, preferably
about 0.1-0.25% by weight of rhodium. In some embodiments,
palladium will be present in the 2.sup.nd catalytic layer in a
loading of about 0.1-10% by weight, alternatively about 0.1-5.0% by
weight of palladium, preferably about 0.2-2.0% by weight of
palladium. In some embodiments, platinum will be present in the
2.sup.nd catalytic layer in a loading of about 0.01-2.0% by weight,
alternatively about 0.05-1.0% by weight of platinum, preferably
about 0.1-0.5% by weight of platinum. The 2.sup.nd catalytic layer
may also contain about 0-40% by weight of a promoter(s). Suitable
promoters include one or more base metal oxides wherein the metal
is selected from the group consisting of barium, calcium,
magnesium, strontium, one or more rare earth and transition metals
selected from the group consisting of zirconium, lanthanum,
praseodymium, yttrium, samarium, gadolinium, dysprosium, ytterbium,
niobium, neodynium, and mixtures thereof.
Rear 1.sup.st Catalytic Layer Embodiments
[0080] According to some embodiments, the rear 1.sup.st catalytic
layer which is deposited upon, i.e., coated upon and adhered to,
the substrate comprises palladium deposited on a support. A
suitable support may be a high surface area refractory metal oxide.
In a specific embodiment, the loading of the first layer upon the
substrate is between about 0.2-2.8 g/in.sup.3. Examples of high
surface refractory metal oxides include, but are not limited to, a
high surface area refractory metal oxide such as alumina, silica,
titania and zirconia and mixtures thereof. The refractory metal
oxide may consist of or comprise a mixed oxide such as
silica-alumina, alumo-silicates which may be amorphous or
crystalline, alumina-zirconia, alumina-lanthana,
alumina-baria-lanthana-neodymia, alumina-chromia, alumina-baria,
and the like. An exemplary refractory metal oxide comprises
gamma-alumina having a specific surface area of about 50-350
m.sup.2/g and which is present in a loading of about 0.5-2.8
g/in.sup.3. The first layer which is applied in the rear zone is
free of ceria-comprising oxygen storage materials.
[0081] Examples of palladium loading in the first layer include up
to about 15% by weight, alternatively, between about 0.05-10% by
weight of palladium, This layer may also contain up to about 40% by
weight of stabilizers/promoters/binders/additives. Suitable
stabilizers include one or more non-reducible metal oxides wherein
the metal is selected from the group consisting of barium, calcium,
magnesium, strontium, and mixtures thereof. In some embodiments,
the stabilizer comprises one or more oxides of barium and/or
strontium. Suitable promoters include one or more non-reducible
oxides, or rare earth and transition metals selected from the group
consisting of lanthanum, neodymium, praseodymium, yttrium,
zirconium, samarium, gadolinium, dysprosium, ytterbium, niobium,
and mixtures thereof.
Examples
[0082] This invention will be illustrated by the following examples
and descriptions. The following examples are intended to illustrate
but not to limit the invention.
[0083] The WC composition configurations for a conventional
reference catalyst (FIG. 4a) and a catalyst according to the
present invention (FIG. 4b) were manufactured and compared as
follows.
Manufacture of the 1.sup.st Catalytic Layer of the Conventional
Reference Catalyst (4a):
[0084] Preparation of the washcoats and coating has previously been
described in U.S. Pat. No. 7,041,622, Column 9, Lines 20-40; Column
10, lines 1-15, which is herein incorporated by reference in its
entirety. Alumina stabilized with 4% by weight of lanthanum oxide,
barium sulfate and a mixed oxide oxygen storage material with a
composition of 42% ZrO.sub.2+HfO.sub.2, 43% CeO.sub.2, 5%
Pr.sub.6O.sub.11 and 10% La.sub.2O.sub.3 by weight were used in the
preparation of the slurry. In making the layered catalysts, a
slurry was prepared by first adding nitric acid to water at 1 wt %
based on the total solids in the slurry. BaSO.sub.4 was then added
with stirring followed by the OSC. The slurry was stirred for 15
minutes and then the alumina was added slowly and stirred for 30
minutes. The slurry was then milled (using a Sweco type mill) such
that the d.sub.50 was 4.5-5.5 microns; the d.sub.90 was 17-21
microns, and 100% pass was less than 65 microns (i.e., 100% of the
particles had a size less than 65 micrometers). The slurry was then
weighed and the LOT (loss on ignition) was measured at 540.degree.
C. to determine the total calcined solids content. Based on this
value the weight of Pd solution need was calculated. Pd nitrate
solution was then added to the slurry dropwise while stirring.
After the Pd addition the slurry specific gravity was in the range
of 1.49 to 1.52, parts were coated by dipping one end of a
honeycomb ceramic monolith into the washcoat slurry, followed by
drawing the slurry up into the channels using a vacuum. The part
was then removed from the slurry and the channels cleared by
applying a vacuum to the other end of the part. Washcoat loading
was controlled by varying specific gravity, and other coating
parameters such as vacuum time and the amount of slurry drawn into
the honeycomb channels. After applying the washcoat, the parts were
calcined at 540.degree. C. for 2 hours. After calcination the
composition of the 1.sup.st catalytic layer was as follows: [0085]
56.5 g/l Lanthanum-stabilized alumina; [0086] 36.5 g/l oxygen
storage material; [0087] 16.5 g/l Barium sulfate; and [0088] 0.635
g/l palladium.
Manufacture of the 2.sup.nd Catalytic Layer of the Conventional
Reference Catalyst:
[0089] The 2.sup.nd catalytic layer of the conventional reference
catalyst consisted of alumina stabilized with 4% by weight of
lanthanum oxide, barium sulfate and a mixed oxide oxygen storage
material with a composition of 58% ZrO.sub.2+HfO.sub.2, 32%
CeO.sub.2, 8% Y.sub.2O.sub.3 and 2% La.sub.2O.sub.3. The slurry was
prepared as described above for the front 1.sup.st catalytic layer.
Rh was added drop-wise to the slurry over a period of 30 minutes
while stirring. After coating and calcination at 540.degree. C. for
2 hours the composition of the front 2.sup.nd catalytic layer of
the catalyst was as follows: [0090] 61 g/l Lanthanum-stabilized
alumina; [0091] 61.5 g/l oxygen storage material; [0092] 1.65 g/l
Barium sulfate; and [0093] 0.071 g/l Rhodium.
Manufacture of the Rear 2.sup.nd Catalytic Layer of the Catalyst
According to the Invention:
[0094] The composition and manufacture of the rear 2.sup.nd
catalytic layer was identical with the conventional reference
catalyst.
Manufacture of the Rear 1.sup.st Catalytic Layer of the Catalyst
According to the Invention:
[0095] The rear 1.sup.st catalytic layer consisted of alumina
stabilized with 4% by weight of lanthanum oxide and barium sulfate.
The slurry was prepared as described above for the front 1.sup.st
catalytic layer. After calcination at 540.degree. C. for 2 hours
the composition of the rear 1.sup.st catalytic layer was as
follows: [0096] 73.0 g/l Lanthanum-stabilized alumina; [0097] 21.0
g/l Barium sulfate; and [0098] 0.635 g/l Palladium.
[0099] As noted above the same oxygen storage material was used in
the Rh layer of both the reference conventional uniform design and
the zoned design according to the invention where the rear 1.sup.st
catalytic layer of the rear zone or brick does not contain an
oxygen storage material. The reference catalyst in the current case
consisted of a 6'' long monolith while the test system consisted of
a 3'' front brick of identical WC design and composition. The 3''
rear brick was identical to the front catalyst except the OSC was
removed from the rear 1.sup.st catalytic layer and some extra
alumina/promoter was added in its place to give a total WC load for
the 1.sup.st layer of 1.8 g/in.sup.3.
[0100] Both front and rear 3'' bricks were butted together in the
converter to represent a zoned configuration.
[0101] Aging consisted of 50 or 100 hours of a 4-mode thermal aging
protocol. The cycle consisted of four modes within a period of 60
seconds. The first mode consisted of a stoichiometric cruise,
followed by a rich condition, a rich condition with secondary air
injection and finally a stoichiometric condition with secondary air
injection. Mode 1 lasted for 40 seconds with a catalyst inlet bed T
(thermocouple placed 1'' from the catalyst inlet face) of
904.+-.2.degree. C. Mode 2 lasted for 6 seconds with a catalyst
inlet CO concentration at 4.0.+-.0.1%. Mode 3 lasted for 10 seconds
with a catalyst inlet bed T of 980.degree. C..+-.2.degree. C.; the
engine out CO concentration was 4.0.+-.0.1 vol % and a secondary
air injection at the catalyst inlet was used to give an O.sub.2
concentration of 2.5.+-.0.1 vol %. Mode 4 lasted for 4 seconds with
an engine out stoichiometric exhaust gas composition and secondary
air injection to give an O.sub.2 concentration of 4.5.+-.0.1 vol %
at the catalyst inlet. The engine used for the aging was a 7.4 L
V-8 equipped with sequential multi-port fuel injection.
[0102] The performance results are summarized in FIGS. 5 and 6
where it is seen that the catalyst design of the current invention
shows clear advantages for THC and NOx in Phases 2 and 3 of the FTP
test.
[0103] To the extent necessary to understand or complete the
disclosure of the present invention, all publications, and patent
applications mentioned herein are expressly incorporated by
reference therein to the same extent as though each were
individually so incorporated.
[0104] Having thus described exemplary embodiments of the present
invention, it should be noted by those skilled in the art that the
within disclosures are exemplary only and that various other
alternatives, adaptations, and modifications may be made within the
scope of the present invention. Accordingly, the present invention
is not limited to the specific embodiments as illustrated herein,
but is only limited by the following claims.
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