An oxidation catalyst system is formed by particles of an oxidation catalyst dispersed in a porous sol-gel binder. The oxidation catalyst system can be applied by brush or spray painting while the sol-gel binder is in its sol state

Ingram, JoAnne L.

Leighty, Bradley D.

Oglesby, Donald M.

Schryer, Jacqueline L.

Watkins, Anthony N.

NASA Technical Reports Server

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(12) United States Patent 	 (10) Patent No.:	 US 7,655,595 B2
Watkins et al.	 (45) Date of Patent:	 Feb. 2, 2010
(54) SOL-GEL BASED OXIDATION CATALYST
AND COATING SYSTEM USING SAME
(75) Inventors: Anthony N. Watkins, Hampton, VA
(US); Bradley D. Leighty, Gloucester,
VA (US); Donald M. Oglesby, Virginia
Beach, VA (US); JoAnne L. Ingram,
Manassas Park, VA (US); Jacqueline L.
Schryer, Hampton, VA (US)
(73) Assignee: United States of America as
represented by the Administrator of
the National Aeronautics and Space
Administration, Washington, DC (US)
(*) Notice: Subject to any disclaimer, the term of this
patent is extended or adjusted under 35
U.S.C. 154(b) by 435 days.
(21) Appl. No.: 11/421,924
(22) Filed:	 Jun. 2, 2006
(65)	 Prior Publication	 Data
US 2007/0281855 Al	 Dec.	 6, 2007
(51) Int. Cl.
BOIJ 23100	 (2006.01)
BOIJ 23102	 (2006.01)
BOIJ 23140	 (2006.01)
BOIJ 23142	 (2006.01)
BOIJ 23144	 (2006.01)
BOIJ 21100	 (2006.01)
BOIJ 21104	 (2006.01)
BOIJ 20100	 (2006.01)
(52) U.S. Cl . ....................... 502/326; 502/242; 502/262;
502/300; 502/304; 502/327; 502/334; 502/339;
502/349; 502/352; 502/355; 502/415; 502/439
(58) Field of Classification Search ................. 502/242,
502/262, 326, 327, 334, 355, 415, 439, 300,
502/304, 339, 349, 352
See application file for complete search history.
(56)	 References Cited
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* cited by examiner
Primary Examiner Cam N Nguyen
(74) Attorney, Agent, or Firm Helen M. Galus
(57)	 ABSTRACT
An oxidation catalyst system is formed by particles of an
oxidation catalyst dispersed in a porous sol-gel binder. The
oxidation catalyst system can be applied by brush or spray
painting while the sol-gel binder is in its sol state.
20 Claims, No Drawings
https://ntrs.nasa.gov/search.jsp?R=20100017303 2019-08-30T09:21:56+00:00Z
US 7,655,595 B2
1	 2
SOL-GEL BASED OXIDATION CATALYST	 DETAILED DESCRIPTION OF THE INVENTION
AND COATING SYSTEM USING SAME
ORIGIN OF THE INVENTION
The invention was made in part by employees of the United
States Government and may be manufactured and used by or
for the Government of the United States of America for gov-
ernmental purposes without the payment of any royalties
thereon or therefor.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to oxidation catalyst systems. More
specifically, the invention is an oxidation catalyst system that
includes a sol-gel binder that allows the system to be easily
coated onto a substrate.
2. Description of the Related Art
Oxidation involves the adding of an oxygen molecule or an
electron to an existing molecule or compound. This process
can occur naturally or can be induced. For example, a low
temperature oxidation catalyst (LTOC) is required in space-
based carbon dioxide (CO 2) lasers where carbon monoxide
(CO) produced during the lasing cycle must be converted
back to COz . Similar "CO-to-0O 2" LTOCs can be used for a
wide variety of other applications such as smoke filter masks,
three-way automotive catalyst converters, and cabin-air fil-
tration systems. Other applications of LTOCs not necessarily
related to oxidation of "CO-to-0O 2" include formaldehyde
remediation systems used in industrial smoke stacks and cata-
lytic-based sensors.
In each of these applications, preparation of the LTOC in a
usable form is problematic. Typically, the LTOC must be
applied to a substrate with the LTOC/substrate then being
heated to adhere/bond the LTOC to the substrate. The sub-
strates (e.g., silica gel in many mask and sensor applications,
honeycomb ceramic bricks for automotive catalytic converter
applications) are first coated using standard solution-based
coating techniques such as slurry casting or dip-coating.
These coating methods require excess amounts of the catalyst
precursors to ensure adequate substrate coverage. This leads
to an increase in material cost as well as causing waste han-
dling concerns as the excess materials must be properly
stored/disposed. Further, these substrate/LTOC "systems"
generally require high temperature heating (i.e., up to 550'C.
for many systems) to complete the LTOC-to-substrate adher-
ing/bonding process.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to
provide an oxidation catalyst system.
Another object of the present invention is to provide an
oxidation catalyst system that can be easily applied to a sub-
strate or surface.
Still another object of the present invention is to provide an
oxidation catalyst system adapted for one-step application to
a substrate or surface.
Other objects and advantages of the present invention will
become more obvious hereinafter in the specification.
In accordance with the present invention, an oxidation
catalyst system is formed by particles of an oxidation catalyst
dispersed in a porous sol-gel binder. The oxidation catalyst
system can then be applied in a one-step application process
such as brush or spray painting while the sol-gel binder is in
its solution (or "sol") state. If necessary, a thinning solution
can be combined with the porous sol-gel binder in its sol state
with the oxidation catalyst particles already dispersed
therein.
The present invention is an oxidation catalyst system that
lends itself to one-step application to a substrate or surface,
5 the choice of which is not a limitation of the present invention.
By way of illustrative example, the system described herein
can be used in the oxidation of CO back to COz . However, it
will be readily understood by one of ordinary skill in the art
that the novel aspects of the present invention can be extended
10 to a wide variety of oxidation (and oxidation/reduction) pro-
cesses.
In accordance with the present invention, an oxidation
catalyst system is created when particles of an oxidation
catalyst are dispersed in a sol-gel binder. In the illustrative
example, the oxidation catalyst is platinum-coated tin oxide.
15 More specifically, particles of platinum-coated tin oxide are
fabricated in a size range that is comparable to the size of
pigments used in conventional paint products that can be
brushed or sprayed onto a substrate or surface. Accordingly,
in this example, the particles of platinum-coated tin oxide (or
20 other suitable catalyst material) have diameters on the order
of approximately 10 microns or less.
As would be understood in the art of such particle fabrica-
tion, a tin oxide dust is first made by mixing tin metal and
nitric acid. One method for coating the tin oxide with plati-
25 num is described in U.S. Pat. No. 4,912,082, the contents of
which are hereby incorporated by reference. Briefly, the tin
oxide dust is mixed with a solution containing a platinum
precursor, such as tetraamine platinum (II) hydroxide [Pt
(NH3)4(OH)2] dissolved in water, which coats the tin oxide
30 particles. The platinum-coated tin oxide is then heated/sin-
tered, resulting in a conversion of the platinum precursor on
the tin oxide to platinum metal. As would be understood in the
art of such catalyst formulation, other established methods
could also be used. If agglomeration of the platinum-coated
35 tin oxide particles occurs duringthis heating step, the material
is simply re-ground to create small particles suitable for dis-
persion. Depending on the particular oxidation application,
the weight percent of platinum in the platinum-coated tin
oxide is typically in the range of 3-20% platinum.
The sol-gel binder in which the oxidation catalyst particles
40 are mixed can be made from any of a variety of precursors
that, when processed, form a porous sol-gel network. For
example, suitable sol-gel precursors include silica, alumina,
zirconia, ceria, vanadia, metal oxides, and mixtures of these
precursors. In the illustrative example, an alumina sol-gel
45 binder was prepared for use with the platinum-coated tin
oxide oxidation catalyst particles. A detailed description of
sol-gel preparation is provided by X. J. Wang et al. in "Phase
Trans Formation of Er 3 '-doped Al203 Powders Prepared by
the Sol-Gel Method," J. Mater. Res., Vol. 18, No. 10, 2003, pp.
50 2401-2405, the contents of which are hereby incorporated by
reference. Briefly, an aqueous solution of aluminum isopro-
poxide was refluxed at 90° C. under vigorous stirring for two
hours. After heating, a small amount of nitric acid was added
to catalyze the hydrolysis of the alumina and refluxed for an
55 
additional 16 hours resulting in the formation of a clear sol.
The above-described platinum-coated tin oxide particles
were then mixed with the above-described clear sol. The
sizing of the particles as described above provided for their
dispersion in the sol-gel binder. In testing various examples of
this exemplary formulation, it was found that effective "CO-
60 to-0O2" oxidation resulted when there was approximately
10-20% by weight of the platinum-coated tin oxide particles
in the sol-gel mixture. When this mixture turns to a gel, an
embodiment of the present invention's oxidation catalyst sys-
tem is formed.
65 Prior to gel formation, the mixture of the oxidation catalyst
particles in the porous sol-gel binder can be applied in one
step by brushing or spraying. If the mixture is too viscous for
US 7,655,595 B2
3
conventional paint applications or if the mixture gels too
quickly, the mixture may need to be "thinned". That is, the
particle-binder mixture (while the binder is in its sol state) can
be thinned as necessary for ease of application and/or to retard
the "sol-to-gel" conversion of the sol-gel binder. Such thin-
ning is a process well-known in the paint formulation art with
the thinner being selected to prevent unwanted reactions with
the sol-gel binder and the oxidation catalyst particles. For the
illustrated example of alumina sol-gel and platinum-coated
tin oxide particles, a suitable thinner is 2-butanone or methyl
ethyl ketone (MEK) as it is also known.
Once the above-described oxidation catalyst system in its
sol state is coated (e.g., sprayed, brushed, etc.) on a substrate
or surface, some drying time is required to allow any excess
water to be removed. The coating can also be exposed to low
temperature heat (e.g., on the order of 100-110° C. for the
illustrated example) to speed up the drying process.
The advantages of the present invention are numerous. The
oxidation catalyst system described herein can be applied in
one step while the system's binder is in its sol state. Such
application involves conventional painting techniques. The
system is therefore readily applied to cloth-based filters, flex-
ible substrates, thin screens, etc., using just the amount of
material needed to coat the substrate. The sol-gel binder pro-
vides for (i) mechanical stabilization of the oxidation catalyst
particles within the porous structure of the sol-gel binder, (ii)
adhesion of the "system" to a substrate, and (iii) catalytic
conversion of CO to CO z and water owing to the porous
nature of the sol-gel binder. Tests of the present invention
yielded effective catalytic reactions.
Although the invention has been described relative to a
specific embodiment thereof, there are numerous variations
and modifications that will be readily apparent to those
skilled in the art in light of the above teachings. It is therefore
to be understood that, within the scope of the appended
claims, the invention may be practiced other than as specifi-
cally described.
What is claimed as new and desired to be secured by
Letters Patent of the United States is:
1. An oxidation catalyst system, comprising:
a porous sol-gel binder; and
particles of an oxidation catalyst dispersed in said porous
sol-gel binder;
wherein said particles comprise approximately 10-20% by
weight of said catalyst system.
2. An oxidation catalyst system as claimed in claim 1
wherein said porous sol-gel binder is based on at least one
sol-gel precursor selected from the group consisting of silica,
alumina, zirconia, ceria, vanadia, metal oxides, and mixtures
thereof.
3. An oxidation catalyst system as claimed in claim 1
wherein said porous sol-gel binder in its sol state with said
particles dispersed therein forms a mixture adapted for one-
step application as a surface coating.
4. An oxidation catalyst system as claimed in claim 1
further comprising a solvent thinning solution, wherein said
porous sol-gel binder with said particles dispersed therein is
combined with said thinning solution to form a mixture
adapted for one-step application as a surface coating.
5.An oxidation catalyst as claimed in claim 1 wherein said
particles have diameters that do not exceed approximately 10
microns.
6. An oxidation catalyst system comprising:
a porous sol-gel binder; and
particles of an oxidation catalyst dispersed in said porous
sol-gel binder;
wherein said oxidation catalyst is platinum-coated tin
oxide.
4
7.An oxidation catalyst system as claim in claim 6 wherein
said platinum-coated tin oxide comprises a weight percent of
platinum in the range of about 3-20%.
8. An oxidation catalyst system, comprising:
5 a sol-gel binder based on at least one sol-gel precursor
selected from the group consisting of silica, alumina,
zirconia, ceria, vanadia, metal oxides, and mixtures
thereof; and
particles of platinum-coated tin oxide dispersed in said
10	 porous sol-gel binder.9. An oxidation catalyst system as claimed in claim 8
wherein said particles of platinum-coated tin oxide comprise
a weight percent of platinum in the range of about 3-20%.
10. An oxidation catalyst system as claimed in claim 8
wherein said sol-gel binder in its sol state with said particles
15 dispersed therein forms a mixture adapted for one-step appli-
cation as a surface coating.
11. An oxidation catalyst system as claimed in claim 8
further comprising a thinning solution, wherein said sol-gel
binder with said particles dispersed therein is combined with
20 said thinning solution to form a mixture adapted for one-step
application as a surface coating.
12. An oxidation catalyst as claimed in claim 8 wherein
said particles have diameters that do not exceed approxi-
mately 10 microns.
25	 13. An oxidation catalyst coating system, comprising:
a porous sol-gel binder;
particles of an oxidation catalyst having diameters that do
not exceed approximately 10 microns dispersed in said
porous sol-gel binder; and
30	 said particles comprising platinum-coated tin oxide.14. An oxidation catalyst coating system as claimed in
claim 13 wherein said porous sol-gel binder is based on at
least one sol-gel precursor selected from the group consisting
of silica, alumina, zirconia, ceria, vanadia, metal oxides, and
mixtures thereof.
35 15. An oxidation catalyst coating system as claimed in
claim 13 further comprising a solvent thinning solution,
wherein said porous sol-gel binder with said particles dis-
persed therein is combined with said thinning solution to
form a mixture adapted for one-step application as a surface
40 coating.
16. An oxidation catalyst coating system as claimed in
claim 13 wherein said platinum-coated tin oxide comprises a
weight percent of platinum in the range of about 3-20%.
17. An oxidation catalyst coating system as claimed in
45 claim 13 wherein said particles comprise approximately
10-20% by weight of said catalyst coating system.
18. An oxidation catalyst coating system, comprising:
a porous sol-gel binder in its sol state, said porous sol-gel
binder being based on at least one sol-gel precursor
selected from the group consisting of silica, alumina,
So	
zirconia, ceria, vanadia, metal oxides, and mixtures
thereof,
particles of platinum-coated tin oxide having diameters
that do not exceed approximately 10 microns dispersed
in said porous sol-gel binder in said sol state to thereby
55	 form a first mixture; and
a solvent thinning solution combined with said first mix-
ture to form a second mixture adapted for one-step appli-
cation as a surface coating.
19. An oxidation catalyst coating system as claimed in
60 claim 18 wherein said particles of platinum-coated tin oxide
comprise a weight percent of platinum in the range of about
3-20%.
20. An oxidation catalyst coating system as claimed in
claim 18 wherein said particles comprise approximately
65 10-20% by weight of said first mixture.


Sol-gel based oxidation catalyst and coating system using same

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