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Project Progress

Probing the Structure and Nitrogen Reduction Activity of Iron-Sulfur Minerals

(Schoonen, Strongin, & Parise)

While metals, alloys, and metal sulfides have been invoked as possible reactants or catalysts in prebiotic synthesis reactions, there is very limited experimental work to support this notion. Using nitrogen fixation as a central reaction, a subgroup within our center is embarking on a comprehensive study how metals, alloys, and metal sulfides may promote this process. Metals and alloys are relevant in meteorites as well as komatiites, while metal sulfides—particularly iron sulfides—are central to the theories championed by Wächtershauser. We are integrating in situ vibrational spectroscopy observations over a wide temperature and pressure regime with hydrothermal batch experiments. X-ray amorphous materials can be characterized using synchrotron-based Pair Distribution Function (PDF) analysis. The first year’s activity focused on defining suitable model systems and developing experimental protocols.

A study of dinitrogen reduction driven by the conversion of pyrrothite to pyrite (FeS + H₂S → FeS₂ + 2H⁺ + 2e^-) is spearheaded by the Strongin group. This study makes use of a diamond Attenuated Total Reflection FTIR cell that can be heated to 300°C and withstand a pressure of 400 bar. This affords for the first time an in situ study of this system. Experiments conducted at 120°C show the formation of a nitrogen-containing species. More experiments are underway to resolve the nature of this species, which is most likely bound to the mineral surface.

The work on FeS/FeS2 is complemented by hydrothermal studies using chromium-bearing mineral phases that are common in meteorites or ultramafic rocks. Some of the phases used in these studies need to be synthesized. The characterization of these synthesized materials is conducted under the direction of Parise, while the hydrothermal experiments are conducted in the Schoonen lab. Several hydrothermal experiments with Cr metal, NiCrFe and Ni-doped chromite have been completed and all show reactivity toward N².