A method for the reactivation of a tin oxide-containing catalyst of a CO.sub.2 laser is provided. First, the catalyst is pretreated by a standard procedure. When the catalyst experiences diminished activity during usage, the heated zone surrounding the catalyst is raised to a temperature which is the operating temperature of the laser and 400.degree. C. for approximately one hour. The catalyst is exposed to the same laser gas mixture during this period. The temperature of the heated zone is then lowered to the operating temperature of the CO.sub.2 laser

Brown, Kenneth G.

Hess, Robert V.

Miller, Irvin M.

Paulin, Patricia A.

Schryer, David R.

Sidney, Barry D.

Upchurch, Billy T.

Wood, George M.

NASA Technical Reports Server

United States Patent [191 
Upchurch et al. 
[54] REACI'IVATION OF A TIN 
OXIDE-CONTAINING CATALYST 
[75] Inventors: Billy T. Upchurch, Virginia Beach; 
Irvin M. Miller, Newport News; 
Kenneth G. Brown, Virginia Beach; 
Robert V. Hess, Newport News; 
David R. Scluyer, Hampton; Barry 
D. Sidney, Gloucester; George M. 
Wood, Newport News; Patricia A. 
Paulin, Hampton, all of Va. 
[73] Assignee: The United States of America as 
represented by Administrator of the 
National Aeronautics and Space 
Adminstration, Washington, D.C. 
[21] Appl. No.: 116,822 
[22] Filed: Nov. 5, 1987 
Related U.S. Application Data 
[63] Continuation-in-part of Ser. No. 874,320, Jun. 12, 1986, 
abandoned. 
[51] Int. Cl.4 .............................................. BOlJ 38/02 
[52] U.S. Cl. ........................................ 502/34; 502/56; 
502/339; 502/352; 372/59; 204A57.51 
[58] Field of Search ....................... 502/34, 42, 50, 53, 
502/56, 339, 352; 204A57.51; 372/59 
pi] Patent Number: 4,829,035 
1451 Date of Patent: May 9, 1989 
~561 References Cited 
U.S. PATENT DOCUMENTS 
2,183,301 12/1939 Bossner et al. ....................... 502/56 
2,575,258 11/1951 Corned et al. ........................ 502/50 
2,816,857 12/1957 Hemminger .......................... 502/53 
3,230,179 1/1966 Schwarzenbek ...................... 502/53 
4,077,913 3/1978 Acres et al. ......................... 502/339 
4,379,756 4/1983 Weitz et al. ........................... 502/34 
4,490,482 12/1984 Mathieu .............................. 502/339 
4,524,051 6/1985 Wright et al. ....................... 502/353 
4,547,886 10/1985 Kaminski et al. ..................... 372/59 
4,651,324 3/1987 Prein ..................................... 372/59 
4,757,512 7/1988 Macken ................................. 372/59 
FOREIGN PATENT DOCUMENTS 
2083687 3/1982 United Kingdom ................ 502/339 
Primary Examiner-Anthony McFarlane 
Attorney, Agent, or Firm-George F. Helfrich; John R. 
Manning; Charles E. B. Glenn 
A method for the reactivation of a tin oxide-containing 
catalyst of a C02 laser is provided. First, the catalyst is 
pretreated by a standard procedure. When the catalyst 
experiences diminished activity during usage, the 
heated zone surrounding the catalyst is raised to  a tem- 
perature which is the operating temperature of the laser 
and 400" C. for approximately one hour. The catalyst is 
exposed to the same laser gas mixture during this per- 
iod. The temperature of the heated zone is then lowered 
to the operating temperature of the C02 laser. 
[571 ABSTRAV 
5 Claims, No Drawings 
https://ntrs.nasa.gov/search.jsp?R=20080012346 2019-08-30T03:58:05+00:00Z
1 
4,829,035 
2 
DETAILED DESCRIPTION OF THE 
INVENTION REACTIVATION OF A TIN OXIDE-CONTAINING CATALYST 
_. 
laser discharge zone, must be recombined. A promising 
low temperature catalyst for combining CO and 0 2  is 
platinum on tin oxide (Pt/Sn02). Other comparable 
catalysts include tin oxide combined with one or more 
First, the catalyst undergoes a standard pretreatment 
process. In a particular embodiment of the present in- 
vention, a 120 mg sample of Pt/Sn02 is exposed to a 
flowing stream of reducing agent 1% CO in helium 
15 (He) for one hour while the sample is heated to a tem- 
perature of 225" C. The sample is then exposed to Dure 
10 of the noble metals such as palladium. 
In a closed-cycle, high-energy pulsed C02 laser, C02 
5 decomposition txoducts, CO and 0 7 ,  that form in the ORIGIN OF THE INVENTION 
The invention described herein was made jointly in 
the performance of work under NASA Contract Nos. 
L-79510B and L-83135B with Chemicon and NASA 
Contract NAS1-17099 with Old Dominion Research 
Foundation and employees of the United States Gov- 
ernment. In accordance with 35 USC 202, the contrac- 
tors have elected not to retain title. 
This application is a continuation-in-part of co-pend- 
ing application, Ser. No. 874,320, filed June 12, 1986, 
abandoned. 
BACKGROUND OF THE INVENTION He flow for one hour at the Hame temperiture, in order 
to prevent any CO from being trapped in the lattice 
structure of the sample while the sample is exposed to 
a catalyst and in Particular to the reactivation of a tin 20 the higher temperature. Finally, the sample is cooled to 
oxide-containing catalyst. loo" C. in a pure He flow for about one hour. The 
New approaches for extending the life of lasers used steady-state activity of the catalyst after this pretreat- 
in a wide variety of applications are under investigation. ment was double the activity of the catalyst without any 
One aspect of the rapid progress in this area is that new pretreatment or with a pretreatment for the same length 
techniques for long lifetime space applications of high 25 of time in pure He as opposed to 1% CO in He. Thus, 
pulse energy, common and rare isotope, closed-cycle pretreatment with the reducing agent CO significantly 
C02 lasers are being studied. The high-energy, pulsed increased the activity of the Pt/SnO2 catalyst. Note that 
CO2 lasers must be operated closed-cycle to conserve the size of the sample is arbitrary. The process will 
gas, especially if rare-isotope gases are used. Rare- work effectively on a tin oxide-containing catalyst of 
isotope gases, such as c1802 are used for improved 30 any size provided that an adequate volume of CO is 
transmission of the laser beam in the atmosphere. used. 
The electrons in electric-disharge co2 lasers cause co is used because of its ability to be chemisorbed by 
dissociation of Some co2 into o2 and co and attach the Surface Of the Pt/SnOz Catalyst. The percentage Of 
themselves to electronegative molecules such as 0 2 ,  co in He is arbitrary* One percent was chosen for 
forming negative 02- ions, as well as larger negative 35 safety reasons. In addition, the He serves as an inert 
ion clusters by collisions with co Or mo~ecu~es. carrier for the CO and therefore could be suitably re- 
For closed-cycle, sealed C02 laser operation, the con- placed by any Other Of the Group gases. Note that 
agent and the catalyst. ciently high to form discharge instabilities which may 
ultimately disrupt the CO2 laser operation. The de- 
crease in C02 concentration due to dissociation into CO 
continuous wave laser power, even if no disruptive 
negative ion instabilities occur. 
to extend the lifetime of a catalyst used to combine the 
CO and 0 2  products formed in a laser discharge. 
It is a further object of this invention to accomplish 
the primary object simply and inexpensively. 
specification which follows. 
This invention relates generally to the reactivation Of 
centration of negative ions/clusters may become suffi- the carrier must be inert with respect to the reducing 
40 The 1 hour pretreatment time described above is 
A enhancement in activity could 
after a shorter or longer pretreatment time de- 
the carrier gas, the gas flow rate, the heating tempera- 
45 ture of the catalyst and the sue of the catalyst sample. 
surable quantity of co2 is given off by the catalyst. 
The pretreatment temperature of the catalyst will be 
effective in the range of 1 o o " e  C. H ~ ~ ~ ~ ~ ~ ,  2250 C. 
50 was chosen as an optimum for achieving a pretreatment 
of the surface area of the catalyst, since higher tempera- 
SUMMARY OF THE INVENTION tures may damage the integrity of the surface. 
After this standard pretreatment, the catalyst is ready 
According to the Present invention, the foregoing 55 for its low temperature use in the sealed, high-energy, 
and additional objects are obtained by a reactivation of pulsed co2 laser. However, after about 3000 minutes of 
the tin oxide-containing catalyst of a C02 laser. First, operation, the activity of the catalyst begins to slowly 
the catalyst is Pretreated by a standard Procedure. diminish. Thus, a method is required to reactivate the 
When the catalyst experiences diminished activity dur- catalyst 
ing exPosure to the circulating gas stream inside O r  60 The present invention provides such a method. First, 
external to the laser, the heated Zone mrounding the the heated zone surrounding the catalyst is heated be- 
catalyst is raised to a temperature between loo" C. and tween loo" C. and 400" C. by an external heating 
400" C. for approximately one hour. During this period, source. A lower limit of loo" C. was chosen because this 
the catalyst is still exposed to the circulating gas inside temperature is usually the maximum operating tempera- 
or external to the laser. The heated zone is then lowered 65 ture of a C02 laser and the heated zone must be raised 
to the nominal operating temperature of the catalyst. above this temperature. An upper limit of 400" C. was 
Accordingly, the activity of the catalyst for the C02 chosen because temperature in excess of this limit may 
laser is reactivated. result in damage to the surface integrity of the catalyst. 
and O2 reduce the average pulsed Or pending on the percentage of the CO reducing agent in 
Accordingly, it is the primary Object Of this invention The pretreatment is considered complete when no mea- 
Other objects and advantages will be apparent in the time of about one hour while maintaining the integrity 
4,829,035 
3 4 
A temperature of 225" C.  was experimentally found to steady state, but resulted in a 10% improvement over 
provide an adequate temperature for reactivation. the initial steady state value. 
The catalyst is exposed to the same circulating stream Accordingly, the present invention allows for a resto- 
of gas that was continually drawn from and returned to ration to the initial steady state activity Of the catalyst Of 
the laser envelope. This laser gas mixture may contain a 5 a C02 laser. In addition, the present invention exceeds 
rare oxygen isotope in the co2 molecule. ne oxide this steady state value, thus resulting in improved com- 
bination activity. The present invention accomplishes containing catalyst may contain the same rare oxygen these desirable results simply and inexpensively. isotope so that contained in the C02 molecule. 
laser gas mixture is maintained for an hour. However, tin and a noble metal, wherein said catalyst is used 
neither the time of heating and exposing nor the amount to combine a laser gas of co and o2 to form 
of heating is specific. Rather, they are functions of the co2 for use in a co2 laser having an operating tempera- 
integrity of the surface of the catalyst and the desired ture between about 230 c. and 110" c., said method 
reactivation time, respectively. Note, however, that 15 comprising: 
while the reactivation time may be decreased by in- exposing the catalyst to a stream of the laser gas 
creasing the temperature, this also increases the risk of mixture which is drawn from and returned to the 
damaging the integrity of the surface of the catalyst. laser; 
Thus, the temperature and heating time will vary with increasing the ambient temperature surrounding the 
the catalyst material. catalyst between a temperature above the operat- 
After heating and exposing for an appropriate ing temperature of the laser and 400" C.  for a time 
amount of time, the heated zone around the catalyst is sufficient to reactivate the catalyst; 
temperature of the laser; of the C02 laser. This temperature normally resides in 
improved. the range of 23" C.  to loo" C.  . 
We claim: This constant heating and exposing the to the 10 1. A method for reactivating a catalyst comprised of 
20 
allowed to return to the nominal operating temperature reducing said ambient temperature to the operating 
25 whereby the combination activity of the catalyst is 
Catalyst activity can be as the percentage 
conversion Of co to 'O2' In the specific embodiment 2. The method of claim 1 wherein the ambient tern- perature surrounding the catalyst is increased to 225" C.  
described above, the initial steady state conversion per- 3. The method of claim wherein said temperature of 
centage was 70%. After four days this conversion per- 30 2250 C.  is maintained for one hour prior to reduction to 
centage decreased to 67%. NO decrease in activity is the operating temperature of the laser. 
acceptable because the Catalyst must maintain its aCtiV- 4. The method of claim 1 wherein the laser gas mix- 
ity for 1% periods of time. However, after being sub- ture contains a rare oxygen isotope in the C02 molecule. 
jected to the reactivation process of the present inven- 5. The method of claim 4 wherein the oxide of the 
tion, the conversion percentage rose to 77%. Such a 35 catalyst contains the same rare oxygen isotope. 
reactivation not only returned the catalyst to its initial * * * * *  
40 
45 
50 
55 
60 
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Reactivation of a tin oxide-containing catalyst

Reactivation of a tin oxide-containing catalyst

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