The high molecular weight organic products of Fischer-Tropsch/Haber-Bosch syntheses on the surfaces of Fe-silicate catalysts have been studied by GCMS

Gilmour, I.

Hill, H. G. M.

Nuth, J. A.

Pearson, V.K.

Sephton, M.A

English

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Open Research OnlineThe Open University’s repository of research publicationsand other research outputsProduction of high molecular weight organiccompounds on the surfaces of amorphous iron silicatecatalysts: Implications for organic synthesis in the solarnebulaConference or Workshop ItemHow to cite:Gilmour, I.; Hill, H. G. M.; Pearson, V.K.; Sephton, M.A and Nuth, J. A. (2002). Production of high molecular weightorganic compounds on the surfaces of amorphous iron silicate catalysts: Implications for organic synthesis in the solarnebula. In: 33rd Lunar and Planetary Science Conference, 11-15 Mar 2002, Houston, Texas, USA.For guidance on citations see FAQs.c© [not recorded]Version: [not recorded]Link(s) to article on publisher’s website:http://www.lpi.usra.edu/meetings/lpsc2002/pdf/1613.pdfCopyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.ukPRODUCTION OF HIGH MOLECULAR WEIGHT ORGANIC COMPOUNDS ON THE SURFACES OFAMORPHOUS IRON SILICATE CATALYSTS: IMPLICATIONS FOR ORGANIC SYNTHESIS IN THESOLAR NEBULA  I. Gilmour1, H. G. M. Hill2, V.K. Pearson1, M.A. Sephton1 and J. A. Nuth2. 1Planetary andSpace Sciences Research Institute, The Open University, Milton Keynes MK7 6AA, U.K. 2Code 691, NASA God-dard Space Flight Center, Greenbelt MD 20771, U.S.A. (i.gilmour@open.ac.uk, hill@lepvax.gsfc.nasa.gov)Introduction:  The Fischer-Tropsch-type (FTT)and Haber-Bosch (HB) syntheses are elegant and effi-cient mechanisms for producing organic matter fromsimple precursors. The requirements are the simplecombination of CO, H2 (plus N2 for HB synthesis) anda mineral catalyst at temperatures of several hundred°C. For this reason, catalytic synthesis was widelyconsidered as the most probable means of producingorganic matter in the early Solar System [1].Previous work on the catalytic synthesis of organicmatter in the 1960’s and 1970’s [e.g., 1] employed avariety of catalytic materials including Fe-Ni meteor-ites, Fe particles or powdered carbonaceous meteor-ites. However, these materials are not appropriateanalogues for the types of catalysts that may have beenavailable in the primitive nebule [2]. Subsequent workon the relatively uncontaminated meteorites such asMurchison and isotopic studies of the proposed mete-oritic FTT products, has cast doubts over an FTT syn-thesis for meteoritic organic matter. Several key com-pounds previously attributed to this mechanism wereshown to be terrestrial contaminants [3]. Given theabundance of hydrogen and CO in the primitive solarnebula, however, it is important that the potential forthe FTT synthesis of organic matter is fully investi-gated.Silicate grain formation in O-rich circumstellar out-flows starts with SiO nucleation followed by rapidcondensation of additional refractory elements to formhighly-reduced amorphous grains [4].  Analogs ofthese "astronomical silicates" are made at GoddardSpace Flight Center.  The amorphous iron silicatesmokes are produced by the combustion of vapors (Fe-SiO-H2-O2) and the overall composition of the grainscluster around the metastable eutectics, greenalite, andiron-rich saponite dehydroxalate.The Fe silicate smokes have remarkable catalyticproperties [2, 5]. We constructed a closed gas circula-tion system whereby basic synthesis gases (CO, N2,H2) were continuously passed through ~0.5 g of Fesilicate smoke at temperatures of 200-600ºC and pres-sures close to 1 atm.  Using continuous FTIR spectros-copy, the gas was found to become increasingly en-riched with key prebiotic molecules (methane and itshomologs, water, ammonia, and CN-bonded com-pounds) via Fischer-Tropsch (FT) and Haber-Bosch(HB) syntheses.  Here we report the results of an ex-periment designed to identify and quantify chemicalspecies produced and remaining on the surface of thesmokes used for an extended series of FT/HB synthe-ses. We compare these species with the organic matterfound in carbonaceous meteorites.Organic Analysis of Smokes:  The organic matterassociated with two smoke samples and one blanksample were analyzed using pyrolysis-gas chromatog-raphy mass spectrometry. The samples (ca. 20 mg ofpowdered catalyst) were flash pyrolysed at 610°C fol-lowed by analysis on an Agilent Technologies 5973GCMS [6].Figure 1. Total ion current chromatogram of pyrolysatereleased from the surface of an Fe-silicate catalyst used for 9consecutive FTT and HB-type runs in the temperature range200-600°C.Results: Two smoke samples were examined inthis study. The first (FESIL91500) was processed inthe presence of CO (150 Torr) and hydrogren (~650Torr), the second (FESIL102700) was processed in thesame manner but half the CO in the original mixturewas replaced with nitrogen. Smoke FESIL91500 gave mean abundances of 7.9wt% C and <0.02 wt% N. FESIL102700 gave meanabundances of 11.6 wt% C and 0.16 wt% N.The total ion current chromatogram for sampleFESIL102700 is shown in Fig. 1. The amount andcomplexity of organic matter released on pyrolysis wasgreater for sample FESIL102700 which is dominated5 10 15 20 25 30C N(C N)2CN  Retention time (mins)Lunar and Planetary Science XXXIII (2002) 1613.pdfCATALYTIC SYNTHESIS OF ORGANICS:  I. Gilmour et al.by a strong peak with a retention time of around 8.24mins. and identified as benzonitrile from its massspectrum. Other aromatic compounds are also presentand abundant including benzene, toluene, naphthalene,methyl- and cyano-substituted benzenes and biphenyl.In general aromatic and substituted aromatic speciespredominate over aliphatic species. . FESIL91500 alsoyielded aromatic species including benzene and tolu-ene, however, yields were low and only trace quanti-ties of compounds such as benzonitrile and naphthale-nes could be detected. A more detailed examination ofthe products released from the catalyst surfaces bypyrolysis can be undertaken by examining ions char-acteristic of species of interest and producing recon-structed ion chromatograms (RIC) that shows the dis-tribution of these species. RICs for aromatic and ali-phatic series of compounds are shown in Fig. 2.Aliphatic Hydrocarbons: Figures 2a and 2b arem/z 57 RICs that selectively display the distribution ofaliphatic hydrocarbons. An homologous series of n-alkanes was observed ranging from n-C10 to n-C19,with a maximum at n-C14. However, aromatics pre-dominate over this molecular weight range.Nitriles and Naphthalenes: Figures 2c and 2d areRICs (m/z 128, 142, 156) that selectively displays thedistrubtion of  C0-C2 alkyl substituted naphthalenesand di-cyano benzenes. In addition to the significantamount of benzonitrile observed in the TIC (Fig. 1) forthe catalyst exposed to N2, it is apparent that signifi-cant quantities of nitrogen-containing aromatics aresynthesized.Discussion: The results obtained in these experi-ments show both similarities and some marked differ-ences to the results of previous FTT synthesis experi-ments. In their original studies, Anders and his col-leagues [1] used the apparent isomeric selectivity ofFTT, in particular a strong predominance of n-alkanes,to argue that such compounds in meteorites wereformed by a catalytic synthesis in the early solar neb-ula. It is now commonly believed that the majority ofstraight chain hydrocarbons in meteorites representterrestrial contaminants [3], however, there is clearisotopic evidence that aromatic species are indigenousto carbonaceous chondrites [6]. The data reported here,indicate that aromatic and N-containing aromatic spe-cies can be readily formed by FTT/HB syntheses onFe-silicate smokes raising the possibility of a nebularorigin for at least some of the compounds in meteor-ites. References:  [1] Studier M.H., Hayatsu R. and AndersE. (1968) Geochim. Cosmochim. Acta, 32, 151-173.[2] Nuth J.A., III and Hill, H.G.M. (2001) LPSC, 32,2061. [3] Sephton M.A., Pillinger C.T. and Gilmour I.(2001) Precamb. Res., 106, 47. [4] Donn, B. and Nuth,J.A. (1985) Ap. J., 1, 288, 187-190. [5] Hill, H.G.M.and Nuth, J.A., III (2000) Meteoritics & PlanetaryScience, 35, A73. [6] Gilmour I., Pearson V.K. andSephton M.A. (2001) LPSC, 32, 1993.10 15 20 25 305 10 15 20 25 30(a)C2C1C1  (b)  (d)Branched alkanes Branched alkanes  (c)n-C14n-C14(C N)2  Relative IntensityRetention time (mins)Lunar and Planetary Science XXXIII (2002) 1613.pdf

Production of high molecular weight organic compounds on the surfaces of amorphous iron silicate catalysts: Implications for organic synthesis in the solar nebula

http://oro.open.ac.uk/8166/1/Production_of_High_Molecular_Weight_Organic_Compounds_on_the_Surfaces_of_Amorphous_Iron_Silicate_Catalysts_-_Implications_for_Organic_Synthesis_in_the_Solar_Nebula.pdf

Production of high molecular weight organic compounds on the surfaces of amorphous iron silicate catalysts: Implications for organic synthesis in the solar nebula

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