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Project Progress

In this reporting year, we conducted a systematic study of amorphous iron silicate smokes as catalysts for producing complex hydrocarbons in the proto-planetary disk by simultaneous Fischer-Tropsch/Haber-Bosch reactions, e.g., CO + N₂ + H₂ => complex hydrocarbons and water (Figure 1). The purpose was to measure the change in reaction rate as the silicate catalyst became coated by amorphous macromolecular carbon compounds. The first studies were conducted at 300°C where completion requires in excess of 450 hours for a single experiment. We then carried out similar experiments at 500°C and at 600°C where the time to complete a single experiment is on the order of 160 hours and 48 hours, respectively. We repeated these experimental runs ~10 – 15 times at each temperature using the same catalyst for all of the experiments at a given temperature.

SUIA intern Steve Manning (Univ. Md.) conducted the 600°C measurements of the amorphous iron silicate catalyst during summer 2007. Manning also reanalyzed the 500°C and 300°C results based on the availability of his new data in order to separate the kinetics of the coating process from the reactivity of the coated silicates. The 300°C and 500°C studies were reported at the Lunar and Planetary Science Conference (citation below). Manning plans to continue these studies in the fall, measuring the carbon and nitrogen isotopic compositions of both gas phase products as well as the organic coatings on the iron silicate grains. In addition, he will conduct a set of experiments at 600°C using an amorphous magnesium silicate smoke catalyst, as well as other materials, to measure the rate at which an amorphous carbon coating develops on them, and to compare their rates with those found for iron silicate smokes. Our hypothesis is that all of the carbonaceous coatings produced on various grain surfaces will be quite similar (if not identical) so that once these coatings form, all grain surfaces will catalyze the formation of complex hydrocarbons at roughly the same rate.
Traditional wisdom is that as grains become coated during FTT reactions in the Solar Nebula, their catalytic efficiency decreases and the FTT reactions eventually stop completely as all reactive grain sites are covered. However, our results demonstrate that the FTT catalytic efficiency of possible grain coatings is greater than that of the initial grains. This means that not only are the FTT reactions of increasing importance as the grains become coated, but that it is possible to form relatively thick layers of macromolecular carbon on many grain surfaces because the surfaces themselves are great catalysts that continue to promote the deposition of complex carbonaceous materials. Again, the old belief held that no more than a monolayer of carbon could be produced by FTT reactions since, as the reactive sites were coated, the reactions were believed to stop. The new results show that reactions could make very large quantities of organic material in the primitive solar nebula from the copious quantities of CO, N₂ and H₂ available, thus making any protostar an organic chemical factory. This greatly increases the probability that complex molecules required for the Origin of Life are available in any environment suitable for chemical evolution.

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