Abiotic Ch4 On Mars Via A Photoreductive Process, and photoreductive generation of ammonia Options

[silylene]

I thought this would be an interesting discussion subject, and appropriate for this fora given the renewed interest into possible sources of trace levels of methane (and ammonia) in the Martian atmosphere.

Part 1: Photoreductive generation of methane over metal oxide dusts
I want to repost a hypothesis which I think deserves serious consideration, and one which has not been published in the scientific literature yet. I first proposed this hypothesis on 7/19/2004 here: http://uplink.space.com/showthreaded.php?C...posts&Main=5980

Hopefully one day my job will give me the time to pursue some research in this area. Unfortunately, I don't see that happening in the next few years since I now hold a high position in research management, and am no longer a research fellow. Perhaps if someone reading this fora has the time to pursue this research direction, and they would include me as a coauthor. I would be happy to collaborate (I am a chemist, and have published papers involving photochemical mechanisms and applications.)

I first point out that the hard UV light is not filtered out of the Martian atmosphere by ozone. With this is mind, let's keep grounded by the fact that CO2 can be photoreduced to CH4 on suitable catalysts, such as metal oxides (which are common in the Martian soils). Dusts suspended inn the atmosphere and surface soils composed of metal oxides such as TiO2 and ZrO2 are examples of useful catalysts for the proposed photoreductive processes. With really DUV light (F2 laser = 157 nm), no catalysts are required.

I next note that the regions of Mars with the highest concentrations of methane in the atmosphere are the equitorial areas. If the mechanism of the formation of methane is a photoreductive process, this is exactly where you'd expect to find methane - over the surface areas with the highest leves of insolation.

I think we should pursue more research on abiotic generation of methane, specifically photoreductive processes. If we fully understand this area, we will also understand the limitations of whether abiotic methane chemistry is possible in the Martian environment.

Here are a few abstracts from the chemical literature on the photoreduction of CO2 to make methane:

vacuum-UV laser photolysis of CO2 systems. Nakashima, N.; Ojima, Y.; Kojima, M.; Izawa, Y.; Yamanaka, C.; Akano, T. Institute Laser Engineering, Osaka University, Suita, Japan. Energy Conversion and Management (1995), 36(6-9), 673-6. CODEN: ECMADL ISSN: 0196-8904. Journal written in English. CAN 123:270397 AN 1995:727451 CAPLUS

Abstract

Gaseous CO2 was photoreduced on irradn. with a vacuum-UV F2 laser (158 nm). The final products were formaldehyde, methane etc. for the case of a mixt. with hydrogen, and alc. for systems of hydrofluorocarbons.

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Photoreduction of carbon dioxide and water into formaldehyde and methanol on semiconductor materials. Aurian-Blajeni, B.; Halmann, M.; Manassen, J. Weizmann Inst. Sci., Rehovot, Israel. Solar Energy (1980), 25(2), 165-70. CODEN: SRENA4 ISSN: 0038-092X. Journal written in English. CAN 94:124490 AN 1981:124490 CAPLUS

Abstract

Heterogeneous photoassisted redn. of aq. CO2 to produce MeOH [67-56-1], HCHO [50-00-0], and CH4 [74-82-8] was achieved by using semiconductor powders with either high-pressure Hg lamps or sunlight. The reaction was carried out either as a gas-solid process, by passing CO2 and H2O vapor over illuminated semiconductor surfaces or as a liq.-solid reaction, by illuminating aq. suspensions of semiconductor powders through which CO2 was bubbled. Best results, under illumination by Hg lamps, were obtained with aq. suspensions of SrTiO3, WO3, and TiO2, resulting in absorbed energy conversion efficiencies of 6, 5.9, and 1.2%, resp.

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Reaction mechanism in the photoreduction of CO2 with CH4 over ZrO2. Kohno, Yoshiumi; Tanaka, Tsunehiro; Funabiki, Takuzo; Yoshida, Satohiro. Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Kyoto, Japan. Physical Chemistry Chemical Physics (2000), 2(22), 5302-5307. CODEN: PPCPFQ ISSN: 1463-9076. Journal written in English. CAN 134:185804 AN 2000:788525 CAPLUS

Abstract

The surface species produced during photoredn. of carbon dioxide with methane over zirconium oxide were obsd. by IR spectroscopy. One of them was a reaction intermediate and decompd. to CO at .apprx.623 K, and the other did not decompd. even at 673 K was called a carbonaceous residue. IR spectral features allowed to identify the latter as the surface acetate. Several properties of the former species were quite similar to those of the surface formate ion, which was a reaction intermediate in photoredn. of CO2 by H2 over ZrO2. The former species was assigned to the surface formate, which was also supposed to be an intermediate of photoreaction between CO2 and CH4. The existence of another carbonaceous residue different that the surface acetate was suggested. The EPR spectrum indicated the photoexcitation of adsorbed CO2 to the CO2- anion radical, and the interaction of the CO2- radical with CH4 in the dark. On the basis of these results, a possible reaction mechanism in this reaction was proposed.

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I think we should pursue more research on abiotic generation of methane, specifically photoreductive processes. If we fully understand this area, we will also understand the limitations of whether abiotic methane chemistry is possible in the Martian environment.

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Part 2: Generation of trace NH3 in the Martian atmosphere via photoreduction from N2

Finally I wish to also point out that there photoreductive processes to produce NH3 from N2. I first posted this hypothesis on 7/15/2004: http://uplink.space.com/showthreaded.php?C...posts&Main=3562

Photoreduction of nitrogen and water on montmorillonite clays loaded with hydrous ferric oxide.
O.A Ileperuma, W.C.B Kiridena and W.D.D.P Dissanayake. J. Photochem. And Photobiol. A: Chem., Vol.59, 1991, 191.

Endoh, E., Bard, AJ. "HETEROGENEOUS PHOTOREDUCTION OF NITROGEN TO AMMONIA ON CATALYST-LOADED
TIO2 POWDERS." New Journal of Chemistry 11 217 - 219, 1987

E. Endoh, JK Leland, AJ Bard, "Heterogeneous Photoreduction of Nitrogen
to Ammonia on Tungsten Oxide," J. Phys. Chem., 90, 6223 (1986).

[Guest_Myran_*]

deglr6328 said: Nice. Occam strikes again.

Yes I did tell Occam to sharpen the knife the other day, didnt I?

Serious now, yes I have to say that you seem to be onto something here silylene.
Im not a scientist in any which way, but im fully aware of the H2O + CO2 catalyst/cracking => CH4 from the suggestion of a means for providing fuel for a sample return or even a human mission.

In Part 2: You make a reference to "Photoreduction of nitrogen and water on montmorillonite clays"
To my knowledge no clays have been found on Mars as of yet.

But the rest might very well be valid, and no hot subsurface lava needed for the very small levels of methane and possibly for ammonia.

[Guest_RGClark_*]

Serious now, yes I have to say that you seem to be onto something here silylene.
Im not a scientist in any which way, but im fully aware of the H2O + CO2 catalyst/cracking => CH4 from the suggestion of a means for providing fuel for a sample return or even a human mission.
In Part 2: You make a reference to "Photoreduction of nitrogen and water on montmorillonite clays"
To my knowledge no clays have been found on Mars as of yet.
...

Actually clays have been detected by Mars Express:

Where there's clay, there's water
Mars Express instrument discovers evidence of past water on Red Planet.
Bruce Moomaw
December 14, 2005
http://www.astronomy.com/asy/default.aspx?c=a&id=3782

(Nice article Bruce!)

Old rocks the key to life on Mars
By Jonathan Amos
BBC News science reporter, San Francisco
Tuesday, 6 December 2005, 07:02 GMT
"Jean-Pierre Bibring says the instruments on ExoMars should be equipped to look for large carbon molecules in amongst the clays of Marwth Vallis as a possible signature of past life."
http://news.bbc.co.uk/2/hi/science/nature/4502018.stm


And clay has found been in a rock by Spirit in Gusev:

Evidence of Phyllosilicate in Wooly Patch - an Altered Rock
Encountered on the Spirit Rover Traverse [#2327].
Wang A. Haskin L. A. Korotev R. L. Jolliff B. L. de Souza P. A. Jr.
Kusack A. G. Athena Team.
"Rock Wooly Patch on West Spur has several specific physical and
chemical features. Based on our analyses, phyllosilicates of kaolinite,
serpentine, and chlorite types, plus some feldspar and pyroxene are
prime candidates to constitute this rock."
http://www.lpi.usra.edu/meetings/lpsc2005/pdf/2327.pdf

Kaolinite is a type of clay.


- Bob Clark

[Guest_paulanderson_*]

Actually clays have been detected by Mars Express:

And also this new one (apparent montmorillonite clays on Husband Hill):

http://www.agu.org/cgi-bin/SFgate/SFgate?&...&=%22P12A-04%22

I had previously linked to reports of the clays being found as well.

This is why the Mars Express findings, combined with Spirit's also in particular now, are so important. I'm glad you are reporting on the phyllosilicates / clays, Bruce, because it still seems a lot of the other science media have left this out of their reports (but hyping the highly acidic sulphates in Meridiani results)...?? It's a shame too that Astronomy magazine cut out so much of your report. Interested in the new MARSIS update you have, also, look forward to it!