Claims
- 1. A process for the combination of CO and O.sub.2 to form CO.sub.2 comprising exposing a catalyst consisting essentially of about 1 to 40 percent by weight of a platinum 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, magnesium sulfate, hydrated alumina, and magnesium perchlorate, to a CO and O.sub.2 gas mixture.
- 2. A process for the combination of CO and O.sub.2 to form CO.sub.2 as in claim 1 wherein the CO and O.sub.2 gas mixture is contained in a sealed or closed-cycle CO.sub.2 laser.
- 3. A process for the combination of CO and O.sub.2 to form CO.sub.2 as in claim 1 wherein the platinum group metal is platinum.
- 4. A process for the combination of CO and O.sub.2 as in claim 1 wherein the platinum group metal is platinum, the reducible metal oxide having multiple valence states is SnO.sub.2, and the compound which can bind water to its structure is silica gel.
- 5. A process for the combination of CO and O.sub.2 to form CO.sub.2 as in claim 4 wherein the platinum is present in an amount of about 5 to 25 percent by weight, the SnO.sub.2 is present in an amount of about 30 to 40 percent by weight, and the silica gel is present in an amount of about 45 to 55 percent by weight.
- 6. A process for the combination of CO and O.sub.2 to form CO.sub.2 comprising exposing a catalyst consisting essentially of about 7 percent by weight of platinum, about 40 percent by weight of SnO.sub.2, and about 50 percent by weight of silica gel to a CO and O.sub.2 gas mixture.
- 7. A process for the combination of CO and O.sub.2 to form CO.sub.2 comprising exposing a catalyst consisting essentially of about 7 percent by weight of platinum, about 40 percent by weight of SnO.sub.2, and about 50 percent by weight of silica gel to a CO and O.sub.2 gas mixture contained in a sealed or closed-cycle CO.sub.2 laser.
BACKGROUND OF THE INVENTION
This is a division of application Ser. No. 07/298,150, filed Jan. 18, 1989.
1. Field of the Invention
This invention relates generally to a catalyst for the combination of CO and O.sub.2 to form CO.sub.2. It relates particularly to a catalyst for combining CO and O.sub.2 to form CO.sub.2 in a high-powered, pulsed CO.sub.2 laser.
2. Description of the Related Art
In many applications, it is highly desirable, even necessary, to operate a CO.sub.2 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 O.sub.2 --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 CO.sub.2 laser, a small amount of CO.sub.2 gas is decomposed in the electrical discharge zone into corresponding quantities of CO and O.sub.2. As the laser continues to operate, the concentration of CO.sub.2 decreases, while the concentrations of CO and O.sub.2 correspondingly increase. The increasing concentration of O.sub.2 reduces laser power, because O.sub.2 scavenges electrons in the electrical discharge, thereby causing arcing in the electric discharge and a loss of the energetic electrons required to boost CO.sub.2 molecules to lasing energy levels. As a result, laser power decreases rapidly. It is known that the output of a sealed CO.sub.2 laser can be enhanced by the addition of a small amount of water vapor to the laser gas. See W.J. Witteman, "The CO.sub.2 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, "Increasing continuous laser-action on CO.sub.2 rotational vibrational 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 processes for the production 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 O.sub.2 as soon as formed in the laser envelope would prevent the loss of laser power. To be effective, many catalysts must be heated to elevated temperatures above ambient conditions to efficiently combine the products of CO.sub.2 dissociation. 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 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-borne applications. However, a catalyst effective at ambient operating temperatures can be installed directly in the laser envelope, since the laser gas, comprising CO.sub.2, N.sub.2, and He, is under high circulation at ambient temperature. Many catalysts require either regeneration or replacement, because they degrade with time and lose their activity for combining the CO.sub.2 dissociation products. These requirements not only add to the operating cost and weight penalty of the laser, but also render space-borne applications unfeasible. However, if the ambient-temperature catalyst maintains its activity for long periods of time, a laser can be operated economically in ground-based, airborne, and space-borne applications.
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) particles, 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 activity.
Another primary disadvantage of the related prior art is that there is no comprehension of using chemisorbed moisture on a Pt/SnO.sub.2 catalyst surface to enhance and prolong its activity.
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 conditions 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 CO.sub.2 laser under ambient operating conditions therein for extended time periods, small concentrations of laser dissociation products, viz., CO and O.sub.2, being combined to form CO.sub.2.
This primary object and other objects and benefits are achieved by the provision of a catalyst which consists 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 SnO.sub.2 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, magnesium sulfate, hydrated alumina, and magnesium perchlorate, 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, SnO.sub.2 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 ideally suited for application to high-powered, pulsed, CO.sub.2 lasers operating in a sealed or closed-cycle condition.
US Referenced Citations (6)
Divisions (1)
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Number |
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298150 |
Jan 1989 |
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Patent Grant
4991181
