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Project Progress

Reactions of CO, N₂ and H₂ on the Surfaces of Amorphous Silicates

Studies of the catalytic efficiency of amorphous iron silicate and magnesium smokes in the conversion of CO, N₂, and H₂ gas mixtures into complex hydrocarbons have finally begun to make some sense. The process is greatly complicated due to the deposition of a reactive carbonaceous coating onto the surfaces of the amorphous grains that also acts to catalyze the conversion of both CO and N₂ into complex organics. Analysis of this organic coating reveals a complex mixture of both aromatic and aliphatic hydrocarbons, similar in many respects to that found in primitive meteorites. Amorphous iron silicates easily convert CO plus H₂ gas mixtures to methane plus more complex hydrocarbons as well as N₂ plus H₂ mixtures to ammonia. Amorphous magnesium silicates convert CO plus H₂ mixtures to methane and more complex hydrocarbons less efficiently than do iron silicates and can not initially produce reduced nitrogen compounds until a significant quantity of carbonaceous contaminant has been deposited onto the grain surface. This contaminant is obviously capable of reacting with N₂, though not as efficiently as does the amorphous iron silicate.

Nuth and Johnson, together with an Astrobiology intern, have begun a systematic analysis of the changes in the rates at which CO decreases and CH₄ increases as a function of temperature and the number of experiments done on a particular batch of amorphous iron silicate grains. The initial rates are attributable to the activity of the pure silicate, while later rates are a combination of the relative areas of the carbonaceous and silicate surfaces. By refilling the system with fresh gas mixtures each time the CO is completely depleted, and waiting for the rates to approach a new, but lower, constant value, we hope to determine the relative rates of CO depletion and CH₄ generation for the carbonaceous coating, relative to those of the amorphous iron silicate (after correction for the decreased surface area of the smoke with reactive cycle). Studies of the changing surface area of the grains as a function of temperature and the number of reaction cycles will be carried out by Yuki Kimura using transmission electron microscopy ( TEM) at the University of New Mexico.