NASA Astrobiology Institute (NAI)

1. A Self-Perpetuating Catalyst for the Production of Organics in Protostellar Nebulae

   Project Investigators: Joseph Nuth

   Summary

   When hydrogen, nitrogen and CO are exposed to amorphous iron
   silicate surfaces at temperatures between 500 – 900K, a carbonaceous
   coating forms via Fischer-Tropsch type reactions. Under normal
   circumstances such a catalytic coating would impede or stop further
   reaction. However, we find that this coating is a better catalyst than
   the amorphous iron silicates that initiate these reactions. The
   formation of a self-perpetuating catalytic coating on grain surfaces
   could explain the rich deposits of macromolecular carbon found in
   primitive meteorites and would imply that protostellar nebulae should be
   rich in organic material. Many more experiments are needed to
   understand this system and its application to protostellar systems.

   Astrobiology Roadmap Objectives:

   • Objective 1.1: Models of formation and evolution of habitable planets
   • Objective 3.1: Sources of prebiotic materials and catalysts

   Project Progress

   Over the past year we have completed several studies of the generation of methane and other organics produced from a starting mixture of molecular hydrogen, nitrogen and CO in the presence of an iron silicate catalyst for various times at a temperature of 873K. Reports of these and previous studies were published in the Astrophysical Journal Letters and in the Proceedings of IAU symposium 251 “Organic Matter in Space” held in Hong Kong in February 2008. The report details the evidence that we collected over the past five years that virtually any solid surface can act to promote the reduction of CO and nitrogen in the presence of hydrogen in order to generate methane and to deposit a macro-molecular organic film onto the surface that is generally a better catalyst for this reduction than most surfaces that we have studied to date.

   Following suggestions gathered at IAU 251 we began a series of catalytic studies using graphite as our catalyst at 873K. The graphitic catalyst was first degassed under vacuum for 104 hours at 873K prior to the initiation of the first set of experiments to ensure removal of most adsorbed air. The generation of methane and macro-molecular carbon began within the first experimental run, while the CO decreased exponentially. The graphitic surface became considerably more reactive in subsequent experimental runs, as had the iron silicate catalysts that we had originally tested. The rate of methane production as a function of experimental run increased steadily through the first 6 experiments, and achieved a steady state in the seventh experimental run. We stopped these first experiments and immediately began a new set of identical measurements to confirm the behavior of this system. The result of this second set of experiments is shown in Figure 1. Figure 2 shows the experimental setup and the caption details conditions under which the experiments are carried out. More experiments to explore the temperature dependence of these reactions on graphite will be required before we submit these results for publication.

   
   

   Figure 1. Initial experimental results using graphite as a FTT catalyst show the generation of methane as a function of time and experimental run at 873K. It is obvious that the rate of methane production increases as a function of run number implying the deposition of a layer of macromolecular carbon during each experiment that increases the efficiency of the catalyst for the next run.

   
   

   Figure 2. Schematic diagram of the experimental apparatus used to carry out Fischer-Tropsch type reactions in our laboratory. The gas circulates through the test catalyst at the bottom of the heated finger of the right hand bulb, then immediately flows through an infrared cell in a FTIR Spectrometer where we obtain spectra on a regular basis to quantitatively follow the evolution of the gas-phase constituents. The gas is circulated by a bellows pump.

Publications

Nuth, J.A., Johnson, N.M. & Manning, S.  (2008).  A Self-Perpetuating Catalyst for the Production of Complex OrganicMolecules in Protostellar Nebulae.  IAU Symposium(251):403 - 408.