Photochemically Induced Formation of Mars-Relevant Oxygenates and Methane from Carbon Dioxide and Water"

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1 Photochemically Induced Formation of Mars-Relevant Oxygenates and Methane from Carbon Dioxide and Water" M. Wecks, M. Bartoszek, G. Jakobs, and D. Möhlmann ESA / ESRIN, Frascati,

2 (Photo)Chemistry a Source for Methane? by reduction of oxygenates (CO 2, HCHO, and other) Reduction (non-radical) + H 2 + H 2 + H 2 + H 2 CO 2 HCOOH HCHO CH 3 OH - H 2 O - H 2 O CH 4 A probably way is a reaction via radicals formed by UV-radiation or photocatalysis. CO 2 HCOOH HCHO CH 3 OH CH 4 C 2 and C 3 molecules (recombination of radicals)

3 Reaction Conditions and Equipment Reaction cell with quartz window, volume: 53 ml UV-radiation: Radiation time: HBO 100 (mercury short arc light source, 100 watt) up to 5 hours Temperature: room temperature (25 C) or 70 C Solid / Catalyst: hematite, synthetic Fe 2 O 3 as nanomaterial, TiO 2 Atmosphere: Pressure: Water: CO 2 ; 2% CO 2 in He 1013 mbar 0 70 µl per cell volume (as moistened hematite) ~3 µl results in a saturated atmosphere at room temperature

Measurement Set-up (1) Mercury short arc lamp 2 3 4 (2) Helium-inlet for flushing or 1 5 injection (3) Septa for injection (4) Cell outlet (to analyzing

4 Measurement Set-up (1) Mercury short arc lamp (2) Helium-inlet for flushing or 1 5 injection (3) Septa for injection (4) Cell outlet (to analyzing system) 7 6 (5) Valves for injection to analytic system Photo of measurement set-up including analytic system (6) Reaction cell with Hematite sample (7) Quartz window

5 Equipment Spectral irradiance of a mercury short arc lamp Quartz shell with hematite

6 Analysis Gas chromatography with mass spectroscopy Simultaneous qualitative determination of all components Quantitative determination of methanol, formaldehyde, carbon dioxide and further oxygenates (C 2 and C 3 components) Quantitative determination of methane by modification of analytical system Analysis of gas phase: at reaction temperature (on-line), gas phase after thermal desorption at 70 C ( adsorbed molecules at surface of solids)

7 Influence of Radiation Time Reaction conditions: CO 2 atmosphere, Hematite with 70 µl H 2 O 500 Concentration / nmol l Acetone Methanol Formaldehyde Methyl formate Ethanol Acetaldehyde Radiation time / min Same products with similar distribution

8 Influence of Reaction Temperature Reaction conditions: CO 2 atmosphere, Hematite, 2 h radiation time Concentration [nmol/l] Acetone Formaldehyde Ethanol Methanol Methyl formate Acetaldehyde without H 2 O T = 25 C 70 µl H 2 O T = 25 C 70 µl H 2 O T = 70 C Same products with similar distribution

9 Influence of Solid / Catalyst Reaction conditions: CO 2 atmosphere, 70 µl water, 2 h radiation time 800 Acetone Concentration / nmol l Methanol Formaldehyde Methyl formate Ethanol Acetaldehyde Formation of products by gas phase reaction No influence of inner surfaces 100 Solid as a possible 0 without solid Hematite Fe 2 O 3 - nano sized TiO 2 catalyst surface area (BET) 2 m 2 /g 49 m 2 /g 307 m 2 /g

10 Influence of CO 2 Concentration Reaction conditions: Hematite with 70 µl H 2 O, 2 h radiation time Pure CO 2 -atmosphere 2 % CO 2 in He Acetone; 13,37 Acetone; 8,58 Acetaldehyde; 23,58 Methanol; 62,87 Acetaldehyde; 37,27 Methanol; 50,08 Ethanol; 0,01 Methyl formate; 0,16 Formaldehyde; 0,01 Ethanol; 0,01 Methyl formate; 0,17 Formaldehyde; 3,89 Same products with similar concentrations

11 Influence of Water Content Reaction conditions: 2 % CO 2 in helium, Hematite, 2 h radiation time 700 Concentration / nmol l Acetone Formaldehyde Ethanol Methanol Methyl formate Acetaldehyde Volume H 2 O / µl Without water no reaction, with 1 µl water favored formation of acetaldehyde, with 3 70 µl water formation of same products with similar distribution

12 Quantitative Determination of Methane Reaction conditions: 2 % CO 2 in helium, 70 µl water, 2 h radiation time Concentration / nmol l Acetone Methanol Formaldehyde Methyl formate Ethanol Acetaldehyde Methane Formation of 260 nmol/l methane, conversion of CO 2 : 0.16 %

13 Isotope Investigations Reaction conditions: 2 % CO 2 in helium, H 2 18 O water, 2 h radiation time 1 µl H 2 18 O 3 µl H 2 18 O Peak area Peak area Methanol Acetaldehyde Acetone Methanol Acetaldehyde Acetone No water saturated atmosphere molecules are formed with oxygen ( 16 O) from CO 2 Water saturated atmosphere molecules are formed also with oxygen ( 18 O) from water Indication of different reaction pathways and mechanisms

14 Results

15 Results - 2 CO 2 + water + UV-radiation are necessary requirement for chemical reactions Formation of organic molecules including methane and further C 2 and C 3 components Gas phase reactions and also reactions at surfaces Influence of water content on concentration of reaction products indication of different reaction pathways and mechanisms Experiments in lab with high UV density high proportion of gas phase reaction low selectivity In lab experiments conversion of 0.16 % CO 2 Formation of methane under Martian conditions should be possible by (photo)chemistry.

16 Next Steps Long-time experiments (starting from CO 2 or CH 4 and mixtures of them) Kinetic studies (determination of reaction rates) Investigation of further solids / minerals (as catalysts) Reaction under Martian conditions (low pressure, lower temperature) Xenon light source for a continuous UV spectrum (imitation of sun light) Further experiments with gases with a special stable isotope ratio for determination of reaction channels

17 Acknowledgement Dr. Michael Bartoszek and Gunnar Jakobs (Leibniz Institute for Catalysis) Prof. Dietrich Möhlmann (German Aerospace Center) Further information and contact: Dr. Mike Wecks Institut für Nichtklassische Chemie e.v. Permoserstr. 15 D Leipzig web: phone: ++49 / 341/

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