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A carbon dioxide reduction system is being developed for long-duration manned space missions. The system incorporates a Sabatier methanation reactor, utilizing previously developed catalyst materials, and a hollow fiber membrane unit to separate the products of reaction. Heat produced by the exothermic Sabatier reaction is absorbed by an air stream, which also regulates the reactor temperature to maximize yield. This absorbed heat can be utilized elsewhere in the carbon dioxide management system to reduce power requirements. The Sabatier process combines carbon dioxide and hydrogen to form methane and water. In a manned space environnent, the water is then either electrolyzed to form oxygen for breathing and hydrogen to drive the reaction, or recycled to the potable water system. A computer-based performance model using finite elements has been developed to evaluate reactor design and catalyst performance.

A model for conversion from partially poisoned monoliths has been developed. The model includes a variation of washcoat thickness in the corners. Calculations predict that the use of fillets to obtain more uniform washcoats is advantageous for fresh catalyst activity at high catalytic rate constants. Conventional non-uniform washcoat distributions show improved durability, especially for lower rate constants.

In order to meet the emission standards of 1980 and 1981, catalysts which can simultaneously reduce hydrocarbon, carbon monoxide and nitric oxide emissions will come into wide usage. Just as important will be fuel management systems that maintain tight control of the air/fuel ratio. Since the 1981 standards will be quite stringent, the effects of poisons such as lead, phosphorus and sulfur on the catalyst will be very important. A study was conducted to determine the effects of different amounts of sulfur dioxide on the activity of a Pt, a Rh catalyst and a fully formulated three component control catalyst. These catalysts were tested in the laboratory employing a synthetic exhaust, that which simulates real automotive exhaust. The catalysts were tested under various conditions that would be encountered during normal closed-loop operation. SO2 affects the catalysts differently under each of the above conditions.

The selectivities of iridium (Ir), platinum (Pt) and rhodium (Rh) catalysts for reducing NO in the presence of excess O2 in two synthetic fuel-lean exhaust gases have been determined, before and after a severe heat treatment. When tested at 500°C, the order of selectivity was Ir>>Rh>Pt for fresh catalysts, and Pt>Rh for treated catalysts. When tested at 400°C, the treated Pt and Rh catalysts were identical in selectivity to the fresh Ir catalyst. A catalyst called Leanox* was developed which showed higher NO selectivity than the fresh Ir catalyst. The advantages of incorporating this catalyst upstream of a conventional three-component-control catalyst to improve NO conversion on the fuel-lean side of stoichiometry were demonstrated in laboratory tests.