U.S. patent application number 10/794789 was filed with the patent office on 2005-09-08 for exhaust treatment system and catalyst system.
Invention is credited to Alexander, Bobrin, Bukhtlyarov, Valerii Ivanovich, Kharas, Karl C., L'vovich, Moroz Boris, Smirnov, Mikhail Yurievich.
Application Number | 20050197244 10/794789 |
Document ID | / |
Family ID | 34750645 |
Filed Date | 2005-09-08 |
United States Patent
Application |
20050197244 |
Kind Code |
A1 |
L'vovich, Moroz Boris ; et
al. |
September 8, 2005 |
Exhaust treatment system and catalyst system
Abstract
A catalyst system comprises a gold catalyst capable of oxidizing
CO; a hydrocarbon oxidation catalyst; and a hydrocarbon adsorbing
material.
Inventors: |
L'vovich, Moroz Boris;
(Novosibirsk, RU) ; Kharas, Karl C.; (Tulsa,
OK) ; Smirnov, Mikhail Yurievich; (Novosibirsk,
RU) ; Alexander, Bobrin; (Novosibirsk, RU) ;
Bukhtlyarov, Valerii Ivanovich; (Novosibirsk, RU) |
Correspondence
Address: |
Paul L. Marshall
Delphi Technologies, Inc.
P.O. Box 5052
M/C 480-410-202
Troy
MI
48007
US
|
Family ID: |
34750645 |
Appl. No.: |
10/794789 |
Filed: |
March 5, 2004 |
Current U.S.
Class: |
502/64 ; 423/247;
502/344 |
Current CPC
Class: |
B01D 2255/912 20130101;
B01J 35/0006 20130101; B01J 29/7415 20130101; B01D 53/944 20130101;
B01J 23/40 20130101; Y02T 10/22 20130101; B01J 37/0246 20130101;
B01J 23/56 20130101; B01D 2257/702 20130101; Y02T 10/12 20130101;
B01D 2255/106 20130101; B01D 2257/502 20130101; B01D 53/945
20130101; B01J 23/52 20130101 |
Class at
Publication: |
502/064 ;
423/247; 502/344 |
International
Class: |
B01D 053/62; B01J
029/06 |
Claims
What is claimed is:
1. A catalyst system comprising: a gold catalyst capable of
oxidizing CO; a hydrocarbon oxidation catalyst; and a hydrocarbon
adsorbing material.
2. The catalyst system of claim 1, wherein the gold catalyst, the
hydrocarbon oxidation catalyst, and the hydrocarbon adsorbing
material are in a physical mixture.
3. The catalyst system of claim 1, wherein the hydrocarbon
oxidation catalyst; and the hydrocarbon adsorbing material are
disposed upstream of the gold catalyst.
4. The catalyst system of claim 1, wherein a first substrate
comprises the gold catalyst, the hydrocarbon oxidation catalyst,
and the hydrocarbon adsorbing material disposed thereon; and a
second substrate located upstream of the first substrate comprises
the hydrocarbon oxidation catalyst, and the hydrocarbon adsorbing
material disposed thereon.
5. The catalyst system of claim 1, further comprising a support
material disposed on a substrate, wherein the gold catalyst and the
hydrocarbon catalyst are disposed on the support material.
6. The catalyst system of claim 5, wherein the support material is
an alumina selected from the group consisting of the gamma alumina,
delta alumina, and theta alumina.
7. The catalyst system of claim 1, wherein the gold catalyst has a
gold particle size less than or equal to about 10 nm.
8. The catalyst system of claim 7, wherein the gold particle size
is less than or equal to about 7 nm.
9. The catalyst system of claim 8, wherein the gold particle size
is less than or equal to about 4 nm.
10. The catalyst system of claim 1, wherein the hydrocarbon
oxidation catalyst is platinum or palladium, and the adsorption
material is selected from the group consisting of beta zeolite,
ultra-stable Y zeolite and UTD-1 zeolite.
11. The catalyst system of claim 1, wherein a ratio of a gold
catalyst volume to a hydrocarbon oxidation volume is greater than
or equal to about 1:12.5.
12. The catalyst system of claim 1, wherein the gold catalyst is
capable of converting greater than or equal to 50% CO present in an
exhaust stream to CO.sub.2 at temperatures less than or equal to
about 100.degree. C. in an atmosphere comprising a hydrocarbon at a
space velocity less than or equal to 250,000 hr.sup.-1.
13. The catalyst system of claim 12, wherein the space velocity is
less than or equal to about 37,000 hr.sup.-1.
14. The catalyst system of claim 13, wherein the space velocity is
less than or equal to about 25,000 hr.sup.-1.
15. The catalyst system of claim 1, wherein the catalyst system is
used in an exhaust treatment system.
16. The catalyst system of claim 1, wherein the catalyst system is
used in air purification system for a household use.
17. A method of using a catalyst system comprising: passing an
exhaust stream over a catalyst system comprising a gold catalyst
capable of oxidizing CO, a hydrocarbon oxidation catalyst; and a
hydrocarbon adsorbing material; and oxidizing at least a portion of
CO present in the exhaust stream.
18. The method of claim 17, wherein the gold catalyst, the
hydrocarbon oxidation catalyst, and the hydrocarbon adsorbing
material are in a physical mixture.
19. The method of claim 17, wherein the hydrocarbon oxidation
catalyst; and the hydrocarbon adsorbing material are disposed
upstream of the gold catalyst.
20. The method of claim 17, wherein a first substrate comprises the
gold catalyst, the hydrocarbon oxidation catalyst, and the
hydrocarbon adsorbing material disposed thereon; and a second
substrate located upstream of the first substrate comprises the
hydrocarbon oxidation catalyst, and the hydrocarbon adsorbing
material disposed thereon.
21. The method of claim 17, wherein greater than or equal to 50% CO
in the exhaust stream is converted to CO.sub.2 at a space velocity
less than or equal to 250,000 hr.sup.-1 at a temperature less than
or equal to about 100.degree. C.
22. The catalyst system of claim 21, wherein the space velocity is
less than or equal to about 37,000 hr.sup.-1.
23. The catalyst system of claim 22, wherein the space velocity is
less than or equal to about 25,000 hr.sup.-1.
Description
BACKGROUND
[0001] In order to meet exhaust fluid emission standards, the
exhaust emitted from internal combustion engines is treated prior
to emission into the atmosphere. Exhaust fluids may be routed
through at least one exhaust emission treatment device disposed in
fluid communication with the exhaust outlet system of the engine,
wherein the exhaust fluids are treated by reactions with a catalyst
composition deposited on a porous support material. Examples of
exhaust emission treatment devices include catalytic converters,
catalytic absorbers, diesel particulate traps, non-thermal plasma
conversion devices, and the like. The exhaust fluid generally
contains undesirable emission components including carbon monoxide
(CO), hydrocarbons (HC), and nitrogen oxides (NO.sub.x). As a means
of simultaneously removing the objectionable CO, HC, and NO.sub.x
components, various catalyst compositions have been developed.
[0002] However, a need remains in the art for an improved catalytic
exhaust treatment device for carbon monoxide oxidation.
SUMMARY
[0003] One embodiment of a catalyst system comprises a gold
catalyst capable of oxidizing CO; a hydrocarbon oxidation catalyst;
and a hydrocarbon adsorbing material.
[0004] One embodiment of a method of using a catalyst system
comprises passing an exhaust stream over a catalyst system
comprising a gold catalyst capable of oxidizing CO, a hydrocarbon
oxidation catalyst; and a hydrocarbon adsorbing material; and
oxidizing at least a portion of CO present in the exhaust
stream.
[0005] The above-described and other features will be appreciated
and understood by those skilled in the art from the following
detailed description, drawings, and appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] Refer now to the figures, which are exemplary embodiments,
and wherein the like elements are numbered alike.
[0007] FIG. 1 is a partial cross-sectional view of an exhaust
treatment device.
[0008] FIG. 2 is a graph of performance data of a gold catalyst
tested with n-decane in the fluid stream.
[0009] FIG. 3 is a graph of performance data of a gold catalyst
after thermal aging tested with n-decane in the fluid stream.
[0010] FIG. 4 is a graph of performance data of a gold catalyst
tested without n-decane in the fluid stream.
[0011] FIG. 5 is a graph of performance data of a gold catalyst
after thermal aging tested without n-decane in the fluid
stream.
[0012] FIG. 6 is a graph of performance data of a gold catalyst
when a second catalyst comprising an oxidation component capable of
oxidizing hydrocarbons and an adsorbent component capable of
adsorbing hydrocarbons is employed upstream (upstream bed volume
300 micro-liters) of the gold catalyst (gold catalyst bed volume
700 micro-liters) and n-decane is in the fluid stream.
[0013] FIG. 7 is a graph of performance data of a gold catalyst
after thermal aging when a second catalyst comprising an oxidation
component capable of oxidizing hydrocarbons and an adsorbent
component capable of adsorbing hydrocarbons is employed upstream
(upstream bed volume 300 micro-liters) of the gold catalyst (gold
catalyst bed volume 700 micro-liters) and n-decane is in the fluid
stream.
[0014] FIG. 8 is a graph of performance data of another test of a
gold catalyst when a second catalyst comprising an oxidation
component capable of oxidizing hydrocarbons and an adsorbent
component capable of adsorbing hydrocarbons is employed upstream
(upstream bed volume 500 micro-liters) of the gold catalyst (gold
catalyst bed-volume 500 micro-liters) and n-decane is in the fluid
stream.
[0015] FIG. 9 is a graph of performance data of yet another test of
a gold catalyst after thermal aging when a second catalyst
comprising an oxidation component capable of oxidizing hydrocarbons
and an adsorbent component capable of adsorbing hydrocarbons is
employed upstream (upstream bed volume 500 micro-liters) of the
gold catalyst (gold catalyst bed volume 500 micro-liters) and
n-decane is in the fluid stream.
[0016] FIG. 10 is a graph of performance data of a gold catalyst
when a second catalyst comprising an oxidation component capable of
oxidizing hydrocarbons and an adsorbent component capable of
adsorbing hydrocarbons is in a physical mixture with gold catalyst
and n-decane is in the fluid stream.
[0017] FIG. 11 is a graph of performance data of a gold catalyst
when a second catalyst comprising an oxidation component capable of
oxidizing hydrocarbons and an adsorbent component capable of
adsorbing hydrocarbons is in a physical mixture with gold catalyst
after thermal aging and n-decane is in the fluid stream.
[0018] FIG. 12 is a graph of performance data of gold catalyst when
only a hydrocarbon adsorbent component is employed upstream of the
gold catalyst.
DETAILED DESCRIPTION
[0019] Referring now to FIG. 1, an exemplary embodiment of an
exhaust treatment device generally designated 100 is illustrated.
The exhaust treatment device 100 may include, but is not limited
to, the following examples, catalytic converters, evaporative
emissions devices, scrubbing devices (e.g., hydrocarbon, sulfur,
and the like), particulate filters/traps, adsorbers/absorbers,
non-thermal plasma reactors, and the like, as well as combinations
comprising at least one of the foregoing devices. The exhaust
treatment device 100 comprises a substrate 12 disposed within a
retention material 14 forming a subassembly 16. A shell 18 is
disposed around the subassembly 16. An end-cone 20 comprising a
snorkel 22 having an opening 24 is in physical communication with
shell 18. Opening 24 allows exhaust fluid communication with
substrate 12. As will be discussed in much greater detail, a
catalyst may be disposed on/throughout substrate 12.
[0020] Substrate 12 may comprise any material designed for use in a
spark ignition or diesel engine environment and having the
following characteristics: (1) capable of operating at temperatures
up to about 600.degree. C., and up to about 1,000.degree. C. for
some applications, depending upon the location of a device within
the exhaust system (manifold mounted, close coupled, or underfloor)
and the type of system (e.g., gasoline or diesel); (2) capable of
withstanding exposure to hydrocarbons, nitrogen oxides, carbon
monoxide, particulate matter (e.g., soot and the like), carbon
dioxide, and/or gaseous compounds of sulfur such as SO.sub.2, COS,
and H.sub.2S; and (3) having sufficient surface area and structural
integrity to support a catalyst. Some possible materials include
cordierite, silicon carbide, metal, metal oxides (e.g., alumina,
and the like), glasses, and the like, and mixtures comprising at
least one of the foregoing materials. Some ceramic materials
include "Honey Ceram", commercially available from NGK-Locke, Inc,
Southfield, Mich., and "Celcor", commercially available from
Corning, Inc., Corning, N.Y. These materials may be in the form of
foils, perform, mat, fibrous material, monoliths (e.g., a honeycomb
structure, and the like), other porous structures (e.g., porous
glasses, sponges), foams, pellets, particles, molecular sieves, and
the like (depending upon the particular device), and combinations
comprising at least one of the foregoing materials and forms, e.g.,
metallic foils, open pore alumina sponges, and porous ultra-low
expansion glasses. Furthermore, these substrates may be coated with
oxides and/or hexaaluminates, such as stainless steel foil coated
with a hexaaluminate scale.
[0021] Although the substrate 12 may have any size or geometry, the
size and geometry are preferably chosen to optimize surface area in
the given exhaust emission control device design parameters. For
example, the substrate 12 may have a honeycomb geometry, with the
combs through-channel having any multi-sided or rounded shape, with
substantially square, triangular, pentagonal, hexagonal,
heptagonal, or octagonal or similar geometries preferred due to
ease of manufacturing and increased surface area.
[0022] Located between the substrate 12 and the shell 18 may be a
retention material 14 that insulates the shell 18 from both the
exhaust fluid temperatures and the exothermic catalytic reaction
occurring within the catalyst substrate 12. The retention material
14, which enhances the structural integrity of the substrate by
applying compressive radial forces about it, reducing its axial
movement and retaining it in place, may be concentrically disposed
around the substrate to form a retention material/substrate
subassembly 16.
[0023] The retention material 14, which may be in the form of a
mat, particulates, or the like, may be an intumescent material
(e.g., a material that comprises vermiculite component, i.e., a
component that expands upon the application of heat), a
non-intumescent material, or a combination thereof. These materials
may comprise ceramic materials (e.g., ceramic fibers) and other
materials such as organic and inorganic binders and the like, or
combinations comprising at least one of the foregoing materials.
Non-intumescent materials include materials such as those sold
under the trademarks "NEXTEL" and "INTERAM 1101HT" by the "3M"
Company, Minneapolis, Minn., or those sold under the trademark,
"FIBERFRAX" and "CC-MAX" by the Unifrax Co., Niagara Falls, N.Y.,
and the like. Intumescent materials include materials sold under
the trademark "INTERAM" by the "3M" Company, Minneapolis, Minn., as
well as those intumescents which are also sold under the
aforementioned "FIBERFRAX" trademark, as well as combinations
thereof and others.
[0024] The retention material/substrate subassembly 16 may be
concentrically disposed within a shell 18. The choice of material
for the shell 18 depends upon the type of exhaust fluid, the
maximum temperature reached by the substrate 12, the maximum
temperature of the exhaust fluid stream, and the like. Suitable
materials for the shell 18 may comprise any material that is
capable of resisting under-car salt, temperature, and corrosion.
For example, ferrous materials may be employed such as ferritic
stainless steels. Ferritic stainless steels may include stainless
steels such as, e.g., the 400--Series such as SS-409, SS-439, and
SS-441, with grade SS-409 generally preferred.
[0025] End cone 20 (or alternatively an end cone(s), end plate(s),
exhaust manifold cover(s), and the like), which may comprise
similar materials as the shell, may be disposed at one or both ends
of the shell. The end cone 20 (end plate or the like) is sealed to
the shell to prevent leakage at the interface thereof. These
components may be formed separately (e.g., molded or the like), or
may be formed integrally with the housing using a methods such as,
e.g., a spin forming, or the like.
[0026] In an alternative method, for example, the shell may
comprise two half shell components, also known as clamshells. The
two half shell components are compressed together about the
retention material/substrate subassembly, such that an annular gap
preferably forms between the substrate and the interior surface of
each half shell as the retention material becomes compressed about
the substrate.
[0027] The exhaust emission treatment device 100 may be
manufactured by one or more techniques, and, likewise, the
retention material/substrate subassembly 16 may be disposed within
the shell 18 using one or more methods. For example, the retention
material/substrate subassembly 16 may be inserted into a variety of
shells 18 using a stuffing cone. The stuffing cone is a device that
compresses the retention material 14 concentrically about the
substrate 12. The stuffing cone then stuffs the compressed
retention material/substrate subassembly 16 into the shell, such
that an annular gap preferably forms between the substrate 12 and
the interior surface of the shell 18 as the retention material 14
becomes compressed about the substrate 12. Alternatively, if the
retention material 14 is in the form of particles (e.g., pellets,
spheres, irregular objects, or the like) the substrate 12 may be
stuffed into the shell 18 and the retention material may be
disposed in the shell 18 between the substrate 12 and the shell
18.
[0028] As briefly mentioned above, a catalyst may be disposed on
and/or throughout (hereinafter "on") substrate 12. The catalyst may
comprise any material capable of carbon monoxide oxidation. For
example, the catalyst preferably comprises gold. The gold catalyst
may be supported on a support material. Additionally, the gold
catalyst is sufficiently dispersed throughout the support material
and has a particle size (taken along the major diameter (i.e., the
longest diameter)) sufficient to be active for carbon monoxide
oxidation at temperatures as low as -70.degree. C. For example, the
gold catalyst may have a particle size of less than or equal to
about 10 nanometers (nm). With in this range, a particle size of
less than or equal to about 7 nm is preferred, with a particle size
of less than or equal to about 4 nm more preferred. Preferably,
greater than or equal to about 80% of the number of particles have
a particle size less than or equal to 10 nm, with greater than or
equal to about 90% more preferred. With regard to the dispersion of
the gold, the gold catalyst is preferably "highly dispersed", i.e.,
the gold particles are substantially evenly distributed throughout
the metal oxide (i.e., the concentration gradient of gold particles
varies less than or equal to about 7 wt % throughout the substrate,
based on a total weight of the gold particles disposed on the
substrate).
[0029] The gold catalyst may be prepared by any number of methods,
e.g., impregnation of a support material with a salt of gold
catalyst, followed by drying and reduction, and exchange of protons
or other cations associated with the support material for cations
of the gold catalyst, followed by washing, drying and
reduction.
[0030] However, the gold catalyst is preferably prepared by 1)
coprecipitation of hydroxides or similar precursors to both support
material and metal, followed by drying, calcination, and reduction;
or 2) precipitation-deposition of gold onto a support material by
initial neutralization of chloroauric acid with base, with
concurrent partial or total substitution of hydroxide for chloride
within the gold coordination sphere, followed by adsorption of the
hydroxogold or chlorohydroxogold complexes onto the support
material, followed by an effective sequence of washing and
calcination steps to yield the catalyst.
[0031] One method of making a gold catalyst may comprise mixing a
support material (e.g., metal oxide) with an acidified solution
comprising a gold compound to form a metal oxide/gold complex;
contacting the metal oxide/gold complex with a base to form a metal
oxide/gold hydroxide complex; washing the metal oxide/gold
hydroxide complex with water; and transforming the metal oxide/gold
hydroxide complex to the gold catalyst. The metal oxide/gold
hydroxide complex is then treated, e.g., with heat, to transform
the metal oxide/gold hydroxide complex to the gold catalyst.
[0032] Without being bound by theory, it is believed that washing
the metal oxide/gold complex with a strong base results in
replacement of some or all of the negatively charged ligand(s) with
hydroxide ions with the resultant formation of a metal oxide/gold
hydroxide complex. The term "ligand" as used herein includes
functionalities such as counterion that are bound primarily through
ionic interactions and functionalities whose bonds to gold are more
covalent in character. The negatively charged ligand(s), if
present, would contribute to the growth of gold particle size when
the catalyst is exposed to elevated temperatures whereas the
hydroxide ions do not. It is further believed that some or all of
the hydroxide ions are removed through calcination.
[0033] Useful gold compounds comprise gold in the +3 oxidation and
one or more negatively charged ligands. Examples of useful gold
compounds include HAuCl.sub.4, NaAuCl.sub.4, (AuBr.sub.3).sub.2,
AuF.sub.3, and combinations comprising at least one of the
foregoing compounds. Preferably, the gold compound is
HAuCl.sub.4.
[0034] Useful support metal oxides include, but are not limited to,
alumina, zirconia, titania, ceria, tin oxide, iron oxide
(Fe.sub.2O.sub.3), lead oxide, and combinations comprising at least
one of the foregoing oxides. It is envisioned that silica and
aluminosilicates may also be used. Preferably, the aluminosilicates
are derivatized with reagents such as
N,N,N-trimethyl-3-(trimethoxysilyl)-1-p- ropanaminium chloride.
This reagent will derivatize the surface with a
N,N,N-trimethyl-3-silylpropylammonium cation, rendering the surface
positively charged and susceptible to adsorbing anionic gold
complexes. Preferably, the metal oxide is alumina, e.g., alpha
(.alpha.) alumina, delta (.delta.) alumina, gamma (.gamma.) alumina
and/or theta (.theta.) alumina. Useful bases are those capable of
replacing the negatively charged ligand(s) with hydroxide ions.
Exemplary strong bases include ammonium hydroxide,
tetralkylammonium hydroxide, ammonium carbonate, tetraalkylammonium
carbonate, sodium hydroxide, potassium hydroxide, cesium hydroxide,
rubidium hydroxide, and combinations comprising at least one of the
foregoing compounds.
[0035] One method of making a gold catalyst comprises preparing a
slurry of the metal oxide and adding an acidified solution of the
gold compound to the slurry, preferably in a drop wise manner. The
acidified solution of the gold compound comprises a gold compound
or mixture of gold compounds and a solvent. The solvent may be
water or an organic solvent capable of dissolving the gold
compound. The concentration of gold in the solution affects the
amount of gold adsorbed. Generally, increasing the concentration of
gold in the solution results in increased gold adsorption. In an
exemplary embodiment, the pH of the acidified solution of gold is
less than or equal to about 4.5. In another exemplary embodiment,
the pH of the acidified solution of gold is chosen such that the pH
of the metal oxide slurry, after addition of the acidified gold
solution, is less than or equal to the pH at zero charge of the
metal oxide. Preferably, the pH of the metal oxide slurry after
addition of the acidified gold solution is about 1 to about 2 pH
units less than the pH at zero charge of the metal oxide.
[0036] The gold containing slurry is allowed to stir for a time
sufficient to permit adsorption of the gold compound onto the metal
oxide. The amount of time spent stirring is dependent upon, for
example, the identity of the gold compound as well as the identity
of the metal oxide. When the gold compound is HAuCl.sub.4 and the
metal oxide is alumina, for example, the amount of stir time may be
about 1 hour and the alumina is observed to develop a yellowish
color.
[0037] After adsorption, the metal oxide/gold complex is separated
from a majority of the slurry liquid by a solid/liquid separation
technique such as filtration, centrifugation, or simple
decantation. The metal oxide/gold complex may then be washed with
water, preferably deionized water. The metal oxide/gold complex is
then contacted with a base to from a metal oxide/gold hydroxide
complex and the pH of the resulting solution is monitored. Base is
added until the solution pH reaches a constant level. The metal
oxide/gold hydroxide complex is then separated from the solution
and preferably washed with water. Preferably, the water is
deionized. The metal oxide/gold hydroxide complex may then be dried
in an oven or exposed to the ambient atmosphere to dry. Drying may
be performed in addition to the calcining described below or drying
and calcinations may be performed together.
[0038] The metal oxide/gold hydroxide complex is calcined at a
sufficient temperature and sufficient time to fix the gold onto the
support material such that the gold does not leach into wash water
intended to remove chloride ion, and to partially reduce gold into
a mixed valent state, including elemental gold and oxidized gold.
Suitable calcination temperatures are less than or equal to about
600.degree. C., preferably less than or equal to about 400.degree.
C. Additionally, calcination temperatures are greater than or equal
to about 50.degree. C., preferably greater than or equal to about
100.degree. C., and more preferably greater than or equal to about
200.degree. C. The calcination may be conducted for about 0.5 hours
to about 6 hours, preferably about 1 hour to about 5 hours, and
more preferably about 2 hours to about 4 hours. Calcination results
in the formation of a gold catalyst. However, calcination may not
be necessary when the metal oxide/gold hydroxide complex is located
in reaction environments having temperatures greater than or equal
to about 50.degree. C. In these environments, the gold catalyst may
be formed from the metal oxide/adsorbed gold complex in situ.
[0039] Preferably, in yet another method of making a gold catalyst,
the method comprises preparing a gold solution by reacting a
chloroauric acid (e.g., HAuCl.sub.4) slowly with a solution of a
strong base (e.g., sodium hydroxide) resulting in an intermediate
gold complex (or mixture of complexes) that is then precipitated or
deposited onto a support material (e.g., alumina), which may be
either in the form of an aqueous or non-aqueous slurry or granules
mixed with a solvent, followed by washing, calcination and,
optionally, washing again. Preferably, the solvent is water.
Preferably, the gold-alumina mixture is washed once after
precipitation/deposition, then calcined at a temperature of about
100.degree. C. to about 600.degree. C., with a temperature of about
350.degree. C. to about 450.degree. C. preferred, and then washed
again repeatedly to remove chloride from the catalyst. Optionally,
the catalyst may be calcined again after essentially all of the
chloride is washed away. Preferably, the calcination are performed
under humid conditions in an oxidizing atmosphere.
[0040] For example, the gold solution may be obtained by reacting
HAuCl.sub.4, having a pH less than or equal to about 2, slowly with
sodium hydroxide until the pH of the solution has a pH of about 6
to about 8, with a neutral pH of 7 preferred. A support material,
e.g., alumina, may be added to the solution and heated at a
temperature sufficient and for a sufficient duration for the gold
to adsorb onto the support material, e.g., at a temperature of
about 75.degree. C. to 125.degree. C. for about 1 hr. After
adsorption, the metal oxide/gold precipitate may be separated from
a majority of the solution liquid by a solid/liquid separation
technique such as filtration, centrifugation, or simple
decantation. The metal oxide/gold complex may then be washed with
water, preferably deionized water to remove Cl.sup.- and Na.sup.+
ions. Optionally, acetone may than be used to wash the precipitate.
The precipitate is then dried and calcined at a sufficient
temperature and sufficient time to fix the gold onto the support
material. Suitable calcination temperatures are less than or equal
to about 600.degree. C., preferably less than or equal to about
400.degree. C. Additionally, calcination temperatures are greater
than or equal to about 50.degree. C., preferably greater than or
equal to 100.degree. C., and more preferably greater than or equal
to about 200.degree. C. The calcination may be conducted for about
0.5 hours to about 6 hours, preferably about 1 hour to about 5
hours, and more preferably about 2 hours to about 4 hours.
[0041] The gold catalyst may be prepared by any of the above
methods to obtain a gold catalyst capable of being active for
carbon monoxide oxidation at temperatures less than or equal to
about 100.degree. C. Preferably, the gold catalyst has a metal
loading (e.g., gold loading) of greater than or equal to about 0.1
weight percent (wt %), preferably greater than or equal to about
0.5 wt %, and more preferably greater than or equal to about 0.75
wt %, based on the total weight of the catalyst and support
material. The gold catalyst may have a metal loading of less than
or equal to about 7 wt %, preferably less than or equal to about 5
wt %, and more preferably less than or equal to about 2.5 wt %,
based on the total weight of the catalyst and support material.
[0042] The gold catalyst is active for carbon monoxide oxidation.
However, gold catalysts may be very readily deactivated, i.e.,
poisoned, by hydrocarbons, e.g., n-decane. Since exposing the gold
catalyst to hydrocarbons may deactivate it, the gold catalyst is
preferably protected from hydrocarbons. As will be discussed in
much greater detail, the gold catalyst may be protected by a second
catalyst disposed in a physical mixture with the gold catalyst, a
second catalyst disposed upstream of the gold catalyst in an
exhaust system, or a second catalyst disposed both in physical
mixture with the gold catalyst and disposed upstream of the gold
catalyst in an exhaust system.
[0043] The second catalyst comprises an adsorbent material (e.g.,
.beta.-zeolite), a support material, (e.g., theta alumina
(.theta.-Al.sub.2O.sub.3)), and an oxidation catalyst (e.g.,
platinum),wherein the adsorbent material is capable of adsorbing
hydrocarbons and the oxidation catalyst is active for the oxidation
of hydrocarbons. However, it is noted that employing only an
adsorbent material, e.g., .beta.-zeolite, may not protect the gold
catalyst.
[0044] The adsorbent material comprises a material capable of
adsorbing or trapping hydrocarbons. For example, the adsorbent
material may include, but is not limited to, zeolites that are
capable of trapping hydrocarbons at low temperatures (i.e., less
than or equal to about 250.degree. C., with less than or equal to
about 150.degree. C. more preferred) and releasing those
hydrocarbons at higher temperatures where they may oxidize more
readily. In particular, the zeolite may be characterized in that it
maintains crystalline structure over extended operation at
temperatures in the range of 750.degree. C. to about 850.degree. C.
in air, has an average pore size (taken along the major diameter
(i.e., the longest diameter)) of greater than or equal to about 0.6
nanometers (nm), and a has a Si/Al ratio of preferably about 30 to
about 100. Examples of suitable zeolites are beta zeolite,
ultra-stable Y zeolite, and UTD-1 zeolite, with beta and Y being
preferred. In an exemplary embodiment, more than one type of
zeolite may be used. For example, a blend of beta and Y zeolites
may be used, or two or more zeolites each having a different range
of pore sizes may be used.
[0045] Additionally, the support material may comprise an inorganic
oxide, which may improve adhesion of the zeolite to a carrier
substrate in, for example, a washcoat process or act as a binder
for catalysts formed without a carrier substrate. In addition, the
inorganic oxide, (e.g., alumina and titania), may aid in the
oxidation of carbon monoxide. Moreover, both alumina and titania
may tend to also promote the oxidation of hydrocarbons. The alumina
may be in the gamma, delta, or theta forms. The titania is
preferably in the anatase phase.
[0046] The oxidation catalyst of the second catalyst is active for
the oxidation of hydrocarbons. Preferably, oxidation catalyst of
the second catalyst contains palladium or platinum. Additionally,
it is noted that suitable oxidation catalyst precursor compounds
include, but is not limited to, tetraamine platinum hydroxide,
platinum nitrate, platinum sulfite, platinum dicarbonyl dichloride,
dinitrodiamino platinum, palladium nitrate, diamminepalladium
hydroxide, tetraamminepalladium chloride, palladium citrate,
rhodium trichloride, hexaamminerhodium chloride, rhodium
carbonylchloride, rhodium trichloride hydrate, rhodium nitrate,
hexachloroiridate (IV) acid, hexachloroiridate (III) acid,
dichlorodhydroiridate (III) acid, ammonium hexachloroiridate (III)
acid, ammonium aquohexachloroiridate (IV),
tetraammine-dichloroiridate (III) chloride, and
tetraamminedichloroiridate (III) chloride.
[0047] The second catalyst comprising may be in a physical mixture
with the gold catalyst. In other words, the second catalyst may be
added to the slurry used in making the gold catalyst. In an
exemplary embodiment, a ratio of the volume of catalyst metal used
for the second catalyst, e.g., platinum, to the volume of gold
catalyst used in the first catalyst is less than or equal to about
2, with a ratio of less than or equal to about 1 more preferred. In
another exemplary embodiment, the ratio of the second metal
catalyst volume to first metal catalyst volume is greater than or
equal to about 1:12.5.
[0048] In other embodiments, the second catalyst may, additionally
or alternatively, be disposed upstream of the gold catalyst. The
term upstream as used herein has its ordinary meaning, and is used
herein to generally denote the position of a component relative to
the other component in a system, for example, an exhaust system. By
having the second catalyst disposed upstream of the gold catalyst,
hydrocarbons in the exhaust system may be trapped and oxidized,
thereby substantially reducing/eliminating hydrocarbons in the
exhaust stream. The gold catalyst may be used in the reduction of
carbon monoxide that may be present in the exhaust fluid. Since the
hydrocarbons are substantially reduced/eliminated, the gold
catalyst may be protected from being deactivated. As such, the gold
catalyst having a second catalyst disposed upstream, or disposed in
a physical mixture therewith, or a combination comprising at least
one of the foregoing, may have an extended life, i.e., a greater
activity for a longer period of time, compared to a gold catalyst
that is not protected from hydrocarbons.
[0049] Additionally, controlling the space velocity of exhaust
fluid through the exhaust treatment device comprising the gold
catalyst may further protect the gold catalyst. For example, at
temperatures lower than about 100.degree. C., the space velocity
may be less than or equal to about 250,000 hr.sup.-1, with a space
velocity of less than or equal to about 37,000 hr.sup.-1 preferred,
and a space velocity of less than or equal to about 25,000
hr.sup.-1 more preferred.
EXAMPLES
[0050] A precipitation/deposition approach was used to make the
gold catalyst used herein. An exemplary procedure for making the
gold catalyst is as follows:
[0051] To 22 ml of aqueous solution of HAuCl.sub.4 containing 4.39
mg Au/ml (pH is 1.8), 2 milliliters (ml) of 0.95 Molar (M) NaOH
solution was added at 23.degree. C. by portions of 50 micro-liters
(.mu.l) to 200 (.mu.l) until a pH value of 6.75 (a [OH]:[Au] molar
ratio is 3.9)
[0052] The obtained solution was heated with 5 g of
.gamma.-Al.sub.2O.sub.3 (pre-calcined in a dry air flow at
750.degree. C. for 4 hr; S.sub.BET is 200 m.sup.2/g, pore volume is
1.15 ml/g, particle size 0.25 millimeters (mm) to 0.5 mm in a
sealed, shaken, temperature controlled reactor at 70.degree. C. for
2 hr. The solution was decanted and a precipitate was washed by
vigorous agitation with some portions of distilled water (0.8
liter, 14 times) at 35.degree. C. to remove chlorine ions
(Cl.sup.-) and sodium ions (Na.sup.+) and then filtered using a
Buchner funnel, washed with a small volume of acetone (5 ml to 10
ml) and dried at room temperature and 0.02 Torr for 12 hours. A
dried sample was heated in air to 400.degree. C. during 2 hours and
then calcined at this temperature for another 4 hours. The content
of gold in the sample prepared was 1.2% by weight, as measured by
ICP.
[0053] The catalytic activity in CO oxidation was tested at space
velocity SV=18,300 h.sup.-1, which corresponds to the contact time
.tau.=0.2 seconds (s). The linear velocity of gas flow was about
0.06 meters per second (m/s). Initially, the gold catalyst diluted
with quartz particles of about 1 millimeter (mm) to about 2 mm in
size was loaded into the reactor. A second catalyst (as described
above, and in, for example, U.S. Pat. No. 6,127,300 to Kharas et
al. and U.S. Pat. No. 5,897,846 to Kharas et al., which are herein
incorporated in their entirety.) granular bed was situated upstream
of the gold catalyst bed. The gold and the second catalyst beds
were divided by means of a pure quartz bed.
[0054] The initial reaction mixture for testing had the following
composition: 0.1% carbon monoxide (CO), 10% water (H.sub.2O), 14%
oxygen (O.sub.2), 0.075% n-decane (n-C.sub.10H.sub.22), and
nitrogen as a balance gas. Temperature was linearly varied from
30.degree. C. to 300.degree. C. with the heating rate of 10.degree.
C./min controlled by a personal computer. Three sequential
heating--cooling cycles (runs) were carried out during a single
testing procedure.
[0055] The thermal aging procedure was performed at 700.degree. C.
for 4 hours; the flowing gas mixture (a feeding blend) had the
following composition: 10% water vapor, air as a balance gas. After
the thermal aging procedure, three subsequent cycles of the
catalytic activity measurements were repeated.
[0056] The gold catalyst was tested fresh, three times, using the
above described synthetic gas mixture, which includes n-decane. As
is shown in FIG. 2, performance is substantially poorer in the
second temperature rise and even slightly worse in the third
temperature rise. In other words, the percent conversion of carbon
monoxide was lower at the second temperature rise and the third
temperature rise compared to the first temperature rise.
[0057] After thermal aging, the catalyst sample initially tested in
the presence of n-decane was essentially inactive, as shown in FIG.
3.
[0058] When the same catalyst is tested fresh without n-decane,
performance improved with testing time. As shown in FIG. 4, the
first temperature rise is the worst, and the subsequent two
temperature rises show light-off temperatures well below room
temperature.
[0059] When the gold catalyst, initially tested in the absence of
n-decane, was then subjected to thermal aging and tested again, it
was even more active compared to a sample that had not been
subjected to thermal aging. As shown in FIG. 5, conversion was
always 100%, and apparently light off temperature had moved to
temperatures even further below room temperature.
[0060] FIG. 6 shows the results of a 300 micro-liter second
catalyst granular bed of a second catalyst (Pt-zeolite-alumina
diesel oxidation catalyst) was situated upstream of a 700
micro-liter bed of the gold catalyst. This dual bed system was then
tested with the fully formulated model gas blend, including
n-decane. As is illustrated in FIG. 6, low-temperature CO oxidation
activity was observed, i.e., CO oxidation activity was observed at
temperatures below 100.degree. C. Additionally, the first
temperature rise had the worst, not the best, performance. The CO
oxidation activity shown in FIG. 6 is a little worse than that of
FIG. 4, but much better than FIG. 2. The slightly inferior low
temperature CO oxidation results of FIG. 5, compared to FIG. 3, may
be attributed to the fact that the gold bed is small than in FIG.
4. The total bed volume was held constant, as such the gold bed was
30% smaller in FIG. 6 than in FIG. 4.
[0061] FIG. 7 shows the results, after thermal aging, of a test 300
micro-liter second catalyst granular bed of a second catalyst
(Pt-zeolite-alumina diesel oxidation catalyst) was situated
upstream of a 700 micro-liter bed of the gold catalyst. In
comparing FIG. 7 to FIG. 3, it appears that the use of the second
catalyst protects the low-temperature CO oxidation function of the
gold catalyst from hydrocarbon-associated deactivation, because
under similar conditions the gold alone was essentially deactivated
as illustrated in FIG. 3.
[0062] In another experiment, 500 micro-liter of the second
catalyst guard bed was employed upstream of 500 micro-liter of the
gold catalyst. As was the case in the first experiment, the first
rise of the fresh composite catalyst was the worst. As shown in
FIG. 8, this mixed catalyst is also active near at low
temperatures, i.e. temperatures below 100.degree.0 C.
[0063] After thermal aging, this catalyst began to show signs of
decane-induced deactivation, as shown in FIG. 9. Specifically,
after thermal aging, Rise-1 shows the highest conversions.
Conversion levels drop for Rise-2 and drop a little more for
Rise-3. The space velocity through the gold bed was about 37000
hr.sup.-1 in this particular experiment.
[0064] Additional experiments were conducted to determine if the
benefits of protecting the gold catalyst against
hydrocarbon-induced deactivation might be obtained when physical
mixtures of the second catalyst and the gold catalyst are employed.
The conclusion was that the benefits were obtained by having the
second catalyst in a physical mixture with the gold catalyst. These
results are illustrated in FIGS. 10-11.
[0065] When the second catalyst contained only calcined beta
zeolite, rather than containing
Pt/(.theta.-Al.sub.2O.sub.3+.beta.-zeolite), as a guard bed, the
results obtain were even worse than in the absence of the guard
bed. Compare FIG. 12 to FIG. 2. Without being bound by theory, this
observation may be attributed to the fact that the zeolite may have
cracked decane to unsaturated species that very effectively
poisoned the gold catalyst.
[0066] In various embodiments, an exhaust treatment system
comprising a gold catalyst and a second catalyst in a physical
mixture with the gold catalyst or located upstream of the gold
catalyst has a carbon monoxide conversion greater than or equal to
about 45% at temperatures of about 25.degree. C. to about
100.degree. C. after thermal aging (i.e., the gold catalyst and the
second catalyst are exposed to temperatures of up to about
800.degree. C. for a period of time up to about 4 hours). More
particularly, at temperatures of about 50.degree. C. to about
75.degree. C., a CO conversion is greater than or equal to 50%,
with greater than or equal to 70% preferred. Additionally, at
temperatures greater than about or equal to about 125.degree. C.,
the exhaust treatment system has a carbon monoxide conversion
system greater than or equal to about 90% conversion, with 100%
conversion preferred.
[0067] Advantageously, embodiments disclosed herein allow for
carbon monoxide oxidation at temperatures below 100.degree. C. by
employing a second catalyst to protect the gold catalyst from
hydrocarbon deactivation. As such, a reduction in carbon monoxide
emissions may be realized, since greater than 50% of the allowed
carbon monoxide emissions may occur during start-up conditions,
i.e., temperatures below 100.degree. C. For example, greater than
or equal to 50% CO may be converter to CO.sub.2 at temperatures
less than or equal to about 100.degree. C. in an atmosphere
comprising a hydrocarbon at a space velocity less than or equal to
50,000 hr.sup.-1.
[0068] Additionally, it is noted that the disclosed gold catalyst
with second protection catalyst may be used in any application
where carbon monoxide oxidation at temperatures less than or equal
to about 100.degree. C. is desirable. For example, the catalyst
system comprising the gold catalyst and second protection cold
catalyst may be used in the automotive industry for exhaust gas
treatment; and in home use, such as in a purification system for
treatment of household air, which may be incorporated as part of a
home heating system.
[0069] While the invention has been described with reference to an
exemplary embodiment, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended
claims.
* * * * *