In catalytic flow-through chemical reactors being explored for space vehicle applications, the catalysts would be supported on the surfaces of wires, instead of on particles, as are typically used in traditional packed beds. The original intent of the proposal was to make it possible to build controllable, efficient catalytic hydrazine-decomposition microthrusters for small spacecraft. The basic concept of the proposal should also prove applicable to other flow-through catalytic reactors; for example, reactors that could be used in removing trace contaminants from the environment.

Catalyst-Coated Wires would be placed in tubular reactors, where they would make contact with flowing reactants. The wires could be straight or twisted, depending on the required characteristics of the flow. Other aspects of the wire and tube geometries and the nature of the catalytic coating(s) could also be chosen to suit the application.

Traditional packed catalytic beds have several disadvantageous characteristics that make control difficult and that pose obstacles to scaling down to the microthruster size range. These characteristics include high back pressures through the beds, attrition due to friability and spalling of catalyst particles, and difficulty of fabrication in small sizes. Usually, as a result, it becomes necessary to make the beds larger than desired, with the further result that propellant is wasted and thermal masses are large (and therefore response times are undesirably long).

The basic concept of the catalyzed-wire reactor allows for adaptation to numerous variations. A reactor of the proposed type could be as simple as a straight tube containing a single catalyst-coated wire suspended on the cylindrical axis. The wire and catalyst could be made of any of a variety of materials; for example, in one application, there might be a need for a tungsten wire with a washcoat (e.g., alumina) supporting a catalyst like platinum. In most cases, multiple catalyst-coated wires would likely be needed. Different wire material could be coated with different catalysts that would be optimized for different reaction temperatures. Catalyst preparation procedures (i.e., washcoat, catalyst, inclusion, etc.) would follow the protocols typically described for metal-supported catalysts. Wires could be made straight or twisted (see figure), wires could be all of the same diameter or of different diameters, and wires could be spaced apart at various distances; the foregoing choices could be made in conjunction with the choice of the shape and inside dimensions of the reactor, all in an effort to optimize the flow or to accommodate a wide range of flow variables in the reactor.

This work was done by Gerald Voecks, J. Morgan Parker, Amy Herr, and Juergen Mueller of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp  under the Materials category.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to

Technology Reporting Office
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Refer to NPO-20507, volume and number of this NASA Tech Briefs issue, and the page number.

NASA Tech Briefs Magazine

This article first appeared in the March, 2001 issue of NASA Tech Briefs Magazine.

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