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Please forgive a bumbling amateur. I have been looking up bond strengths and it seems to me that it should be possible to combine methane with carbon dioxide to make acetic acid:

$$\ce{CH4 + CO2 ->[\color{red}{?}] CH3COOH}$$

One has to break a C=O bond (745 kJ/mol) and a C–H bond (413 kJ/mol), but one gets back a C–O bond (358 kJ/mol), an O–H bond (467 kJ/mol) and a C–C bond (347 kJ/mol) so one comes out ahead. I know that bond energies vary slightly but this doesn't sound too far out of whack. Wouldn't it be rather nice if one could catalyse this reaction and soak up lots of these readily available gases? Could we induce some bacterium to do it for us?

orthocresol
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Thomas Forster
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    @ThomasForster The problem with reactions like this is that, while they might look good on paper, they are practically hard to do not least because they require complex processes (which are expensive) and large energy inputs (though biological systems can do similar things, but those are hard to scale up). – matt_black Dec 20 '18 at 12:22
  • In particular, methane is very hard to selectively activate for such reactions (burning is easy, selectively reacting it is not). – matt_black Dec 20 '18 at 12:23
  • One might as well just use methyl lithium which actually easily reacts that way. But still … problems! – Jan Dec 21 '18 at 04:06
  • Can't you activate methane to methanium in a superacid? What would methane plus CO2 do in a superacid? – Thomas Forster Dec 21 '18 at 06:34
  • Seems you still not get something. There may be a dozen of methods to make acetic acid from methane and CO2 - all of them workable, but al have nothing to do with lowering CO2 emission, rather the opposite. – Mithoron Dec 21 '18 at 18:35
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    @ThomasForster The reason things are not done on an industrial scale is usually economics. The expense of the materials, equipment and the energy inputs have to make sense given the price you can get for the products. Industry uses processes like Saabre (syngas to acetic acid) and Cativa (methanol to acetic acid) which use readily available inputs. Using carbon dioxide would require much costlier plant and a more complex process. – matt_black Dec 23 '18 at 13:30
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    @matt_black, could I encourage you to turn your comments into an answer? – orthocresol Dec 23 '18 at 14:07

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Already methanotrophic bacteria can oxidize methane to formate and the Wood-Ljungdahl pathway can take this formate and a carbon dioxide molecule and coenzyme A and produce acetyl coenzyme A so the catalysts are already there.

user5713492
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