A catalyst is disclosed for the combination of CO and O2 to form CO2, which includes a platinum group metal (e.g., platinum); a reducable metal oxide having multiple valence states (e.g., SnO2); and a compound which can bind water to its structure (e.g., silica gel). This catalyst is ideally suited for application to high-powered pulsed, CO2 lasers operating in a sealed or closed-cycle condition

Brown, David R.

Brown, Kenneth G.

Davis, Patricia

Miller, Irvin M.

Schryer, David R.

Upchurch, Billy T.

Vannorman, John D.

English

A catalyst for the combination of CO and O2 to form CO2 which includes a platinum group metal, e.g., platinum; a reducible metal oxide having mulitple valence states, e.g., SnO2; and a compound which can bind water to its structure, e.g., silica gel. This catalyst is ideally suited for application to high powered, pulsed, CO2 lasers operating in a sealed or closed cycle condition

Davis, Patricia P.

NASA Technical Reports Server

United States Patent [191 [ i l l  Patent Number: 4,99 1,181 
Upchurch et al. [45] Date of Patent: Feb. 5, 1991 
[54] CATALYST FOR CARBON MONOXIDE 
OXIDATION 
[75] Inventors: 
[73] Assignee: 
[21] Appl. NO.: 
[22] Filed: 
Billy T. Upchurch, Virginia Beach; 
Irvin M. Miller, Newport News; 
David R. Brown, Norfolk; Patricia P. 
Davis, Newport News; David R. 
Schryer, Hampton; Kenneth G. 
Brown, Virginia Beach; John D. Van 
Norman, Norfolk, all of Va. 
The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
443,406 
Nov. 30, 1989 
Related U.S. Application Data 
[62] 
[Sl] Int. C l . 5  ................................................ HOlS 3/22 
[52] US. Cl. ...................................... 372/59; 423/247; 
502/34; 502/324 
Division of Ser. No. 298,150, Jan. 18, 1989. 
[58] 
1561 References Cited 
Field of Search .................... 372/59; 502/34, 333, 
502/324, 328; 423/247 
U.S. PATENT DOCUMENTS 
4,524,051 6/1985 Wright et al. ....................... 502/333 
4,639,432 1/1987 Holt et al. ........................... 502/324 
4,808,394 2/1989 Kolts et al. .......................... 502/328 
4,818,745 4/1989 Kolts ................................... 502/328 
4,868,841 9/1989 Ameck et al. ........................ 372/59 
4,829,035 5/1989 Upchurch ............................. 502/34 
Primary Examiner-Lhn Scott, Jr. 
Attorney, Agent, or Firm-George F. Helfrich; Harold 
W. Adams; John R. Manning 
1571 ABSTRACT 
A catalyst for the combination of CO and 0 2  to form 
COS which includes a platinum group metal-e.g., plati- 
num; a reducible metal oxide having multiple valence 
states-e.g., SnO2; and a compound which can bind 
water to its structure-e.g., silica gel. This catalyst is 
ideally suited for application to high-powered, pulsed, 
C02 lasers operating in a sealed or closed-cycle condi- 
tion. 
7 Claims, No Drawings 
https://ntrs.nasa.gov/search.jsp?R=19910011957 2020-03-24T06:58:56+00:00Z
4,99 1,18 1 
CATALYST FOR CARBON MONOXIDE 
OXIDATION 
This is a division of application Ser. No. 07/298,150, 
filed Jan. 18, 1989. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to a catalyst for the 
combination of CO and 0 2  to form C02. It relates par- 
ticularly to a catalyst for combining CO and 0 2  to form 
C02 in a high-powered, pulsed CO2 laser. 
2. Description of the Related Art 
In many applications, it is highly desirable, even nec- 
essary, to operate a C02 laser in a sealed condition, for 
in an open system the laser requires a continuous flow of 
laser gas to remove the dissociation products,-viz., CO 
and 02-that occur in the discharge zone of the laser, in 
order to maintain a stable power output. This adds to 
the operating cost of the laser, and in airborne or space 
applications, it also adds to the weight penalty of the 
laser. In a sealed CO2 laser, a small amount of C02 gas 
is decomposed in the electrical discharge zone into 
corresponding quantities of CO and 0 2 .  As the laser 
continues to operate, the concentration of C02 de- 
creases, while the concentrations of CO and 0 2  corre- 
spondingly increase. The increasing concentration of 
0 2  reduces laser power, because 0 2  scavenges electrons 
in the electrical discharge, thereby causing arcing in the 
electric discharge and a loss of the energetic electrons 
required to boost C02 molecules to lasing energy levels. 
As a result, laser power decreases rapidly. It is known 
that the output of a sealed CO:! laser can be enhanced by 
the addition of a small amount of water vapor to the 
laser gas. See W.J. Witteman, “The C02 Laser”, Vol. 
53. Springer-Verlag (1987), pp. 104-108. However, this 
is a short-term effect, after which output starts to fall. 
Additionally, too much water vapor in the gas will 
decrease the laser output. See W.J. Witteman, “Increas- 
ing continuous laser-action on C02 rotational vibra- 
tional transitions through selective depopulation of the 
lower laser level by means of water vapor,” Physics 
Letters, Vol. 18, No. 2, Aug. 15, 1965; and Witteman, 
W.J., “4B4-Rate determining Drocesses for the Droduc- 
5 
10 
15 
20 
25 
30 
35 
40 
45 - .  
tion of radiation in high power molecular lasers,” IEEE 
J. of Quantum Electronics, Vol. QE-2, No. 9, September 
1966. 
A catalyst that can combine CO and 0 2  as soon as 
formed in the laser envelope would prevent the loss of 50 
laser power. T o  be effective, many catalysts must be 
heated to elevated temperatures above ambient condi- 
tions to efficiently combine the products of C02 dissoci- 
ation. This is not feasible in the laser envelope, because 
the gas in this envelope must be maintained at ambient 55 
temperature for efficient operation. This means that the 
catalyst must be located in a recirculating loop external 
to the laser; and this requires a pump, a heating system, 
and a cooling system, all of which can add to operating 
cost, as well as to weight penalty in airborne or space- 60 
borne applications. However, a catalyst effective at 
ambient operating temperatures can be installed directly 
in the laser envelope, since the laser gas, comprising 
C02, N2, and He, is under high circulation at ambient 
temperature. Many catalysts require either regeneration 65 
or replacement, because they degrade with time and 
lose their activity for combining the C02 dissociation 
products. These requirements not only add to the oper- 
L 
ating cost and weight penalty of the laser, but also ren- 
der space-borne applications unfeasible. However, if the 
ambient-temperature catalyst maintains its activity for 
long periods of time, a laser can be operated economi- 
cally in ground-based, airborne, and space-borne appli- 
cations. 
Catalyst formulations of the related prior art consist 
of (1) a dispersion of colloidal and noncolloidal particles 
of stannic oxide, either self-supporting or impregnated 
on an inert support, with a noble metal on the stannic 
oxide surface (see U.S. Pat. No. 4,524,051) and (2) parti- 
cles, granules or pellets of stannic oxide with a noble 
metal on the stannic oxide surface (see European Patent 
Application No. 83306312.6, dated Oct. 18, 1983). 
One of the primary disadvantages of the related prior 
art is that when the stannic oxide catalyst is in the form 
of particles, granules, pellets, or supports impregnated 
with colloidal particles, most of the stannic oxide is 
below the surface, is structurally bound to other stannic 
oxide molecules, and is therefore unavailable as active 
sites. Thus, there is a relatively small surface area of 
stannic oxide available as active sites for catalytic activ- 
ity. 
Another primary disadvantage of the related prior art 
is that there is no comprehension of using chemisorbed 
moisture on a Pt/SnOz catalyst surface to enhance and 
prolong its activity. 
SUMMARY O F  T H E  INVENTION 
It is accordingly the primary object of the present 
invention to provide what the prior art has been unable 
to provide, viz., a catalyst which, by composition of 
matter alone, contains chemisorbed water within and 
upon its structure, depending upon the treatment condi- 
tions to which it is exposed prior to its application, such 
bound moisture rendering the catalyst highly active and 
very long-lived, such that only a small quantity of it 
need be used internally or externally to a sealed or 
closed-cycle CO2 laser under ambient operating condi- 
tions therein for extended time periods, small concen- 
trations of laser dissociation products, viz., CO and 0 2 ,  
being combined to form CO2. 
This primary object and other objects and benefits 
are achieved by the provision of a catalyst which con- 
sists essentially of about 1 to 40 percent by weight of 
one or more platinum group metals (Pt, Pd, Rh, Ir, Ru, 
Os, platinum being preferred); about 1 to 90 percent by 
weight of one or more oxides of reducible metals having 
multiple valence states (such as Sn, Ti, Mn, Cu, and Ce, 
with SnO2 being preferred); and about 1 to 90 percent 
by weight of a compound which can bind water to its 
structure (such as silica gel, calcium chloride, magne- 
sium sulfate, hydrated alumina, and magnesium per- 
chlorate, with silica gel being preferred). Especially 
beneficial results are obtained when platinum is present 
in the catalyst composition in an amount of about 5 to 25 
(especially 7) percent by weight, SnO2 is present in an 
amount of about 30 to 40 (especially 40) percent by 
weight, and silica gel is present in an amount of 45 to 55 
(especially 50) percent by weight. This catalyst is ide- 
ally suited for application to high-powered, pulsed, 
C02 lasers operating in a sealed or closed-cycle condi- 
tion. 
DESCRIPTION OF T H E  PREFERRED 
EMBODIMENTS 
The composition of this catalyst was suggested by 
our preliminary experiments in which we discovered 
4,991, 
3 
the need of a Pt/SnOz catalyst for bound water to en- 
hance its activity. These experimental results suggested 
that if the water were bound to the surface, this water 
would enhance and prolong catalyst activity for long 
time periods. Since the catalyst is to be exposed to a 5 
laser gas mixture, and since a CO2 laser can tolerate 
only a very small amount of moisture therein, a hygro- 
scopic support for the catalyst would provide the 
needed HzO into the gas. Of all the hygroscopic materi- 
als that would be useful as support materials, silica gel is I O  
considered to be superior because of its property to 
chemisorb water on its surface over a wide range of 
moisture content. The equilibrium weight percent of 
water chemisorbed on silica gel ranges from 0 to over 
40 percent when exposed to relative humidities of 0 to 15 
100 percent, respectively. Silica gel chemisorption char- 
acteristics result from its huge surface area, the highly 
porous nature of its particles, and its tendency toward 
hydration. The application of a very thin film of 
Pt/SnO2 on the silica gel surface preserves a large frac- 20 
tion of this area and hence, control of the moisture 
content on the catalyst surface is attained. 
The catalyst of the present invention may be pro- 
duced by first preparing a mixture of a commercially 
available, high-surface-area silica gel and an oxidizing 25 
agent. Very beneficial results have been obtained using 
nitric acid as the oxidizing agent since it leaves no resi- 
due. It is also helpful if the silica gel is first deaerated by 
boiling in water to allow the entire surface to be coated. 
A metal, such as tin, is then dissolved in the oxidizing 30 
agent/support material mixture to yield, in the case of 
tin, metastannic acid. Although tin has proven espe- 
cially beneficial for use in a closed-cycle C02 laser, in 
general any metal with multiple valence states may be 
used. The metastannic acid is adsorbed onto the high- 35 
surface-area silica gel and coats the surface thereof. 
Any excess oxidizing agent is then evaporated, and the 
resulting metastannic acid-coated silica gel is dried, 
whereby the metastannic acid becomes tin(1V) oxide 
(SnO2). 40 
The second step is accomplished by preparing an 
aqueous mixture of the tin(1V) oxide coated silica gel 
and a soluble, chloride-free salt of at least one platinum 
group metal. Extremely beneficial results have been 
obtained using chloride-free salts of platinum, palla- 45 
dium, or a combination thereof, such as tetraamine plati- 
num (11) hydroxide (Pt(NH3)4(0H)2) or tetraamine 
palladium (11) nitrate (Pd(NH3)4(N03)2). It is also bene- 
ficial if the coated silica gel is first deaerated by boiling. 
The  platinum group metal salt is adsorbed onto the high 50 
surface area and coats the surface. A chloride-free re- 
ducing agent is then added to the aqueous mixture 
whereby the p'latinum group metal is deposited onto the 
tin (IV) oxide coated silica gel. Any reducing agent 
which decomposes to volatile produces and water upon 5 5  
reaction or drying is preferred. Formic acid, hydroxy- 
lamine (NHIOH), hydrazine (N2H4). and ascorbic acid 
are particularly advantageous. After the platinum group 
metal has been deposited onto the tin (IV) oxide coated 
silica gel, the solution is evaporated to dryness, 60 
whereby the desired catalyst is obtained. 
Evaluating its performance, we found that the cata- 
lyst of the present invention had not only a high activ- 
ity, Le., a pumping speed of 3.2xlO-3Is-lg-~ under 
ambient temperature conditions, but also a very long 65 
lifetime, exhibiting a half life of eight months. Thus, the 
purpose of this invention, viz., to formulate a catalyst 
composition with enhanced activity and long life for 
181 
4 
sealed C02 laser applications, has been fulfilled because 
of the unique composition of this catalyst. An exem- 
plary composition consisting of 6.7% pt, 39.7% SnO2, 
and 53.6% silica gel, was tested at  30" C. for a period of 
106 days with an activity half life of eight months. The 
water content of this catalyst was determined to be 
The silica gel employed in the instant composition 
can be in the form of granules, beads, pellets or mono- 
liths. The size and shape of the particles can vary, al- 
though a uniform size and shape are desirable properties 
for good flow distribution through a bed or structure of 
these particles. The water content of the silica gel has 
varied up to 27%. 
Any other compound which can bind water to its 
structure can be substituted for silica gel in the instant 
catalyst composition. Examples of other materials in- 
clude, but are not limited to calcium chloride, magne- 
sium sulfate, hydrated alumina, and magnesium per- 
chlorate, as well as other metal oxides, hydroxides, salts 
and their hydrates. 
Witteman supra has shown that the introduction of 
water into the gas phase of a sealed C02 laser without a 
hygroscopic catalyst present can increase laser output 
by approximately 100 percent. However, this output 
decayed, whereas the hygroscopic properties of the 
catalyst of the present invention confers a long life at 
room temperature conditions: a half life of eight months 
with an initial pumping speed of 3 . 2 ~  10-31s-'g-l 
without the introduction of moisture in the gas phase. 
No other catalyst known can compare with this perfor- 
mance. Furthermore, introduction of moisture in the 
gas phase has been shown to have deleterious effects on 
the performance of some sealed CO2 lasers. 
The present invention has been described in detail 
with respect to certain preferred embodiments thereof. 
However, as is understood by those of skill in the art, 
variations and modifications in this detail can be made 
without any departure from the spirit and scope of the 
present invention as defined in the hereto-appended 
claims. 
12.5%. 
What is claimed is: 
1. A process for the combination of CO and 0 2  to 
form CO2 comprising exposing a catalyst consisting 
essentially of about 1 to 40 percent by weight of a plati- 
num group metal, about 1 to 90 percent by weight of a 
reducible metal oxide having multiple valence states 
selected from the group consisting of Sn, Mn, and Cu, 
and about 1 to 90 percent by weight of a compound 
which can bind water to its structure selected from the 
group consisting of silica gel, calcium chloride, magne- 
sium sulfate, hydrated alumina, and magnesium per- 
chlorate, to a CO and 0 2  gas mixture. 
2. A process for the combination of CO and 0 2  to 
form C 0 2  as in claim 1 wherein the CO and 0 2  gas 
mixture is contained in a sealed or closed-cycle CO2 
laser. 
3. A process for the combination of CO and 0 2  to 
form C02 as in claim 1 wherein the platinum group 
metal is platinum. 
4. A process for the combination of CO and 0 2  as in 
claim 1 wherein the platinum group metal is platinum, 
the reducible metal oxide having multiple valence states 
is SnO2, and the compound which can bind water to its 
structure is silica gel. 
5. A process for the combination of CO and 0 2  to 
form CO? as in claim 4 wherein the platinum is present 
in an amount of about 5 to 25 percent by weight, the 
4,99 1,18 1 
6 
about 40 percent by weight of SnO2, and about 50 per- 's present in an amount Of about 30 to percent cent bv weight of silica gel to a CO and O2 gas mixture. 
by weight, and the silica gel is present in an amount of 
about 45 to 55 percent by weight. 
7. A process for thecombination of CO and 0 2  to 
form C02 comprising exposing a catalyst consisting 
5 essentially of about 7 percent by weight of platinum, 
about 40 percent by weight of SnO2, and about 50 per- 6.  A process for the combination of CO and 0 2  to 
essentially of about 7 percent by weight of platinum, 
10 
15 
20 
25 
30 
35 
40 
* * * * *  
50 
55 
60 
65 


Catalyst for carbon monoxide oxidation

United States Patent E191 [i i]  Patent Number: 4,912,082 
Upchurch et al. [451 Date of Patent: Mar. 27, 1990 
CATALYST FOR CARBON MONOXIDE 
OXIDATION 
Inventors: Billy T. Upchurch, Virginia Beach; 
Irvin M. Miller, Newport News; 
David R. Brown, Norfolk; Patricia P. 
Davis, Newport News; David R. 
Schryer, Hampton; Kenneth G. 
Brown, Virginia Beach; John D. Van 
N o m ,  Norfolk, all of Va. 
Assignee: The United States of America as 
represeted by the Administrator of the 
National Aeronautics and Space 
Administration, Washington, D.C. 
Appl. No.: 298,150 
Filed: Jan. 18, 1989 
Int. Cl.4 ......................... BOlJ 21/00; BOlJ 23/56 
U.S. Cl. .................................... 502/218; 502/217; 
502/226; 502/239; 502/241; 502/245; 502/324; 
502/327; 502/346 
Field of Search ............... 502/239, 242, 262, 241, 
502/245,218,223,226,324, 327, 346; 423/437 
1561 References Cited 
U.S. PATENT DOCUMENTS 
2,049,608 SA936 Forrester ............................. 502/226 
3,632,525 1/1972 Rausch ................................ 502/223 
4,117,082 9/1978 Matsuyarna ......................... 502/242 
4,240,933 12/1980 Copelin ............................... 502/242 
4,514,515 4/1985 Travers et al. ...................... 502/242 
4,521,531 6/1985 Coates ................................. 502/242 
4,524,051 6/1985 Wright et al. ....................... 423/247 
4,642,374 2/1987 Lucy et al. .......................... 502/223 
4,830,844 5/1989 Kolts ................................... 423/437 
FOREIGN PATENT DOCUMENTS 
36417 3/1980 Japan ................................... 502/218 
Primary Examiner-Carl F. Dees 
Attorney, Agent, or Firm-George F. Helfrich; John R. 
Manning; Charles E. B. Glenn 
E571 ABSTRACT 
A catalyst for the combination of CO and 0 2  to form 
C02 which includes a platinum group metal-e.g., plati- 
num; a reducible metal oxide having multiple valence 
states-e.g., SnOz; and a compound which can bind 
water to its structure-e.g., silica gel. This catalyst is 
ideally suited for application ,to high-powered, pulsed, 
C02 lasers operating in a sealed or closed-cycle condi- 
tion. 
5 Claims, No Drawings 
https://ntrs.nasa.gov/search.jsp?R=19900014201 2020-03-24T03:04:38+00:00Z
4,912,082 
1 2 
cost, as well as to weight penalty in airborne or space- 
CATALYST FOR CARBON MONOXIDE borne applications. However, a catalyst effective at 
OXIDATION ambient operating temperatures can be installed directly 
in the laser envelope, since the laser gas, comprising 
ORIGIN OF THE INVENTION 5 COz, Nz, and He, is under high circulation at ambient 
ne invention described herein was made jointly in temperature. Many catalysts require either regeneration 
the performance of work under a NASA contract and or replacement, because they degrade with time and 
employees ofthe U.S. Government. In accordance with lose their activity for combining the coz dissociation 
35 USC 202, the contractors elected not to retain title. products. These requirements not only add to the OPer- 
10 ating cost and weight penalty of the laser, but also ren- 
CROSS REFERENCE TO RELATED der space-borne applications unfeasible. However, if the 
APPLICATION ambient-temperature catalyst maintains its activity for 
This application is related to co-pending application long periods of time, a laser can be operated economi- 
Ser. No. 07/090,874, filed Aug. 31, 1987 now U.S. Pat. cally in ground-based, airborne, and space-borne appli- 
No. 4,855,274. 15 cations. 
Catalyst formulations of the related prior art consist 
of (1) a dispersion of colloidal and noncolloidal particles BACKGROUND OF THE INVENTION . 
1. Field of the Invention of stannic oxide, either self-supporting or impregnated 
This invention relates generally to a catalyst for the on an inert support, with a noble metal on the stannic 
combination of co and 0 2  to form COZ. It relates Par- 2o oxide surface (see U.S. Pat. No. 4,524,051) and (2) parti- 
ticularlY to a catalyst for Combining co and 0 2  to form cles, granules or pellets of stannic oxide with a noble 
C02 in a high-powered, pulsed C02 laser. metal on the stannic oxide surface (see European Patent 
2. Description of the Related Art Application No. 83306312.6, dated Oct. 18, 1983). 
In many applications, it is highly desirable, even nec- One of the primary disadvantages of the related prior e s s q ,  to operate a coz laser in a sealed condition, for 25 art is that when the stannic oxide catalyst is in the form 
in an Open system the laser requires a continuous flow Of of particles, granules, pellets, or supports impregnated 
laser gas to remove the dissociation products,-viz., CO with colloidal particles, of the stannic oxide is 
and 02-that occur in the discharge ‘One Of the laser, in below the surface, is structurally bound to other stannic 
Order to maintain a power Output* This adds to oxide molecules, and is therefore unavailable as active 
- 
the Operating Of the laser, and in 
Or ‘pace 30 sites. Thus, there is a relatively small surface area of 
stannic oxide available as active sites for catalytic activ- it adds to the weight penalty Of the laser. In a sealed COz laser, a small amount of COz gas 
is decomposed in the electrical discharge zone into 
corresponding quantities of co and oz. As the laser 
creases, the concentrations of co and o2 corre- 
spondingly increase. The increasing concentration of 
0 2  reduces laser power, because 02 scavenges electrons 
in the electrical discharge, thereby causing arcing in the 
electric discharge and a loss of the energetic electrons 40 
ity. 
Another primary disadvantage of the related prior art 
to operate, the concentration of coz de- 35 is that there is no comprehension of using chemisorbed 
moisture on a Pt/SnOz catalyst surface to enhance and 
prolong its activity* 
SUMMARY OF THE INVENTION 
It is accordingly the primary object of the present 
required to boo; COz molecules to lasingenergy levels. 
As a result, laser power decreases rapidly. It is known 
that the output of a sealed COz laser can be enhanced by 
the addition of a small amount of water vapor to the 
laser gas. See W. J Witteman, “The CO2 Laser”, Vol. 45 
53, Springer-Verlag (1987), pp. 104-108. However, this 
is a short-term effect, after which output starts to fall. 
Additionally, too much water vapor in the gas will 
decrease the laser output. See W. J. Witteman, “In- 
creasing continuous laser-action on C02 rotational vi- 50 
brational transitions through selective depopulation of 
the lower laser level by means of water vapor,” Physics 
Letters, Vol. 18, No. 2, Aug. 15, 1965; and Witteman, W. 
J., “4B4Rate determining processes for the production 
of radiation in high power mqlecular lasers,” IEEE J.  of .55 
Quantum Electronics, Vol. QE-2, No. 9, September 
1966. 
A catalyst that can combine CO and 0 2  as soon as 
formed in the laser envelope would prevent the loss of 
laser power. To be effective, many catalysts must be 60 
heated to elevated temperatures above ambient condi- 
tions to efficiently combine the products of C0.r dissoci- 
ation. This is not feasible in the laser envelope, because 
the gas in this envelope must be maintained at ambient 
temperature for efficient operation. This means that the 65 
catalyst must be located in a recirculating loop external 
to the laser; and this requires a pump, a heating system, 
and a cooling system, all of which can add to operating 
invention to provide what the prior art has been unable 
to provide, viz., a catalyst which, by composition of 
matter alone, contains chemisorbed water within and 
upon its structure, depending upon the treatment condi- 
tions to which it is exposed prior to its application, such 
bound moisture rendering the catalyst highly active and 
very long-lived, such that only a small quantity of it 
need to be used internally or externally to a sealed or 
closed-cycle COz laser under ambient operating condi- 
tions therein for extended (time periods, small concen- 
trations of laser dissociation products, viz., CO and 02, 
being combined to form COS. 
This primary object and other objects and benefits 
are achieved by the provision of a catalyst which con- 
sists essentially of about 1 to 40 percent by weight of 
one or more platinum group metals (Pt, Pd, Rh, Ir, Ru, 
Os, platinum being preferred); about 1 to 90 percent by 
weight of one or more oxides of reducible metals having 
multiple valence states (such as Sn, Ti, Mn, Cu, and Ce, 
with SnOZ being preferred); and about 1 to 90 percent 
by weight of a compound which can bind water to its 
structure (such as silica gel, calcium chloride, magne- 
sium sulfate, hydrated alumina, and magnesium per- 
chlorate, with silica gel being preferred). Especially 
beneficial results are obtained when platinum is present 
in the catalyst composition in an amount of about 5 to 25 
(especially 7) percent by weight, SnO2 is present in an 
amount of about 30 to 40 (especially 40) percent by 
4,9 12,082 
3 4 
weight, and silica gel is present in an amount of 45 to 55 metal has been deposited onto the tin(Iv) oxide coated 
(especially 50) percent by weight. This catalyst is ide- silica gel, the solution is evaporated to dryness, 
ally suited for application to high-powered, pulsed, whereby the desired catalyst is obtained. 
C02 lasers operating in a sealed or closed-cycle condi- Evaluating its performance, we found that the cata- 
tion. 5 lyst of the present invention has not only a high activity, 
ire., a pumping speed of 3.2X lO-3/s-~g-1under ambi- 
ent temperature conditions, but also a very long life- 
time. exhibiting: a half life of eieht months. Thus, the 
DESCRIPTION OF THE PREFERRED 
EMBODIMENTS 
Y I 
The composition of this catalyst was suggested by purpose of this invention, viz., to formulate a catalyst 
our preliminary experiments in which we discovered 10 composition with enhanced activity and long life for 
the need of a Pt/SnOz catalyst for bound water to en- sealed C02 laser applications, has been fulfilled because 
hance its activity. These experimental results suggested of the unique composition of this catalyst. An exem- 
that if the water were bound to the surface, this water plary composition consisting of 6.7% Pt, 39.7% SnO2, 
would enhance and prolong catalyst activity for long and 53.6% silica gel, was tested at 30" C. for a period of 
time periods. Since the catalyst is to be exposed to a 15 106 days with an activity half life of eight months. The 
laser gas mixture, and since a C02 laser can tolerate water content of this catalyst was determined to be 
only a very small amount of moisture therein, a hygro- 12.5%. 
scopic support for the catalyst would provide the The silica gel employed in the instant composition 
needed H20 into the gas. Of all the hygroscopic materi- can be in the form of granules, beads, pellets or mono- 
als that would be useful as support materials, silica gel is 20 liths. The size and shape of the particles can vary, al- 
considered to be superior because of its property to though a uniform size and shape are desirable properties 
chemisorb water on its surface over a wide range of for good flow distribution through a bed or structure of 
moisture content. The equilibrium weight percent of these particles. The water content of the silica gel has 
water chemisorbed on silica gel ranges from 0 to over varied up to 27%. 
40 percent when exposed to relative humidities of 0 to 25 Any other compound which can bind water to its 
100 percent, respectively. Silica gel chemisorption char- structure can be substituted for silica gel in the instant 
acteristics result from its huge surface area, the highly catalyst composition. Examples of other materials in- 
porous nature of its particles, and its tendency toward clude, but are not limited to calcium chloride, magne- 
hydration. The application of a very thin film of sium sulfate, hydrated alumina, and magnesium per- 
Pt/SnO;! on the silica gel surface preserves a large frac- 30 chlorate, as well as other metal oxides, hydroxides, salts 
tion of this area and hence, control of the moisture and their hydrates. 
content on the catalyst surface is attained. Witteman supra has shown that the introduction of 
The catalyst of the present invention may be pro- water into the gas phase of a sealed C02 laser without a 
duced by fust preparing a mixture of a commercially hygroscopic catalyst present can increase laser output 
available, high-surface-area silica gel and an oxidizing 35 by approximately 100 percent. However, this output 
agent. Very beneficial results have been obtained using decayed, whereas the hygroscopic properties of the 
nitric acid as the oxidizing agent since it leaves no resi- catalyst of the present invention confers a long life at 
due. It is also helpful if the silica gel is first deaerated by room temperature conditions: a half life of eight months 
boiling in water to allow the entire surface to be coated. with an initial pumping speed of 3.2X lO-3/s-lg-1 
A metal, such as tin, is then dissolved in the oxidizing 40 without the introduction of moisture in the gas phase. 
agent/support material mixturc to yield, in the case of No other catalyst known can compare with this perfor-. 
tin, metastannic acid. Although tin has proven espe- mance. Furthermore, introduction of moisture in the 
cially beneficial for use in a closed-cycle CO2 laser, in gas phase has been shown to have deleterious effects on 
general any metal with multiple valence states may be the performance of some sealed C02 lasers. 
used. The metastannic acid is adsorbed onto the high- 45 The present invention has been described in detail 
surface-area silica gel and coats the surface thereof. with respect to certain preferred embodiments thereof. 
Any excess oxidizing agent is then evaporated, and the However, as is understood by those of skill in the art, 
resulting metastannic acid-coated silica gel is dried, variations and modifications in this detail can be made 
whereby the metastannic acid becomes tin(1V) oxide without any departure from the spirit and scope of the 
(Sn02). 50 present invention as defined in the hereto-appended 
The second step is accomplished by preparing an claims. 
aqueous mixture of the tin(Iv) oxide coated silica gel What is claimed is: 
and a soluble, chloride-free salt of at least one platinum 1. A catalyst for the combination of CO and 0 2  to 
group metal. Extremely beneficial results have been form C02, the catalyst consisting essentially of about 1 
obtained using chloride-free salts of platinum, palla- 55 to 40 percent by weight of a platinum group metal, 
dium, or a combination thereof, such as tetraamine plati- about 1 to 90 percent by weight of a reducible metal 
num(I1) hydroxide (Pt(NH3)4(0H)z) or tetraamine pal- oxide, such metal having multiple valence states se- 
ladium(1I) nitrate (Pd(NH3)@03)2). It is also benefi- lected from the group consisting of Sn, Mn, and Cu, and 
cial if the coated silica gel is fust deaerated by boiling. about 1 to 90 percent by weight of a compound which 
The platinum group metal salt is adsorbed onto the high 60 can bind water to its structure selected from the group 
surface area and coats the surface. A chloride-free re- consisting of silica gel, calcium chloride, magnesium 
ducing agent is then added to the aqueous mixture sulfate, hydrated alumina, and magnesium perchlorate. 
whereby the platinum group metal is deposited onto the 2. The catalyst of claim 1, wherein the platinum 
tin(1V) oxide coated silica gel. Any reducing agent group metal is platinum. 
which decomposes to volatile products and water upon 65 3. The catalyst of claim 1, wherein the platinum 
reaction or drying is preferred. Formic acid, hydroxy- group metal is platinum, the reducible metal oxide hav- 
lamine (NHzOH), hydrazine (NZH~), and ascorbic acid ing multiple valence states is SnO2, and the compound 
are particularly advantageous. After the platinum group which can bind water to its structure is silica gel. 
4,912,082 
5 6 
4. The catalyst of Claim 3, wherein the Plathum is 
present in an Of about to 25 percent by weight* 
the SnO2 is present in an amount of about 30 to 40 per- 
of about 45 to 55 percent by weight. 
form COz in a sealed CO2 laser, the catalyst consisting 
essentially of about 7 percent by .weight of platinum, 
5 cent by weight of silica gel. 
cent by weight, and the silica gel is present k an amount about 40 percent by weight Of Sno2, and about 50 per- 
* * * * *  5. A catalyst for the combination of CO and 0 2  to 
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Catalyst for carbon monoxide oxidation

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