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How can $\small\cf{CO2}$ be converted into Carbon and Oxygen?

$\cf{CO2 -> C + O2}$

Alternatively:

$\cf{CO2 + ? -> C + O2}$

I know that plants are able to do this. But I'm wondering if it can be done without using plants?

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Plants do not exaclty do this, they do $2n CO_2 + 2n H_2O + photons \rightarrow 2(CH_2O)_n + 2n O_2$ according to en.wikipedia.org/wiki/Photosynthesis In quite a complicated reaction schema. –  Laar Aug 7 '12 at 21:19
    
You can use scrubbing proccess. Using KN0\subscript=3 –  BigSack Aug 25 '12 at 6:22
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I believe you would save a lot of head ache if you just used a plant. –  user1697 May 25 '13 at 21:32
    
...without using plants We can't use plants for doing so because of the same reason pointed out by @Laar –  Awal Garg May 24 at 9:59

6 Answers 6

up vote 14 down vote accepted

In my opinion, the catalytic, solar-driven conversion of carbon dioxide to methanol, formic acid, etc. is much more interesting and promising, but since Enrico asked for the conversion of carbon dioxide to carbon itself:

The group around Yutaka Tamaura was/is active in this field. In one of their earlier publications:

Yutaka Tamaura and Masahiro Tahata, Complete reduction of carbon dioxide to carbon using cation-excess magnetite, Nature, 1990, 346, 255-256, [DOI]

they heated magnetite ($\ce{Fe3O4}$) at 290 °C for 4 hrs in a stream of hydrogen to yield a material which turned out to be stable at room temperature under nitrogen. This material, $\ce{Fe_{3+\delta}O4} (\delta=0.127)$, i.e. the metastable cation-excess magnetite is able to incorporate oxygen in the form of $\ce{O^2-}$.

Under a $\ce{CO2}$ atmosphere, the oxygen-deficient material converted to "ordinary" $\ce{Fe3O4}$ with carbon deposited on the surface.

This remarkable reaction however is not catalytic, but a short recherche showed that the authors have published a tad more in this field. Maybe somebody else finds a a report on a catalytic conversion among their publications.

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Aren't they using something like this in the International Space Station to provide astronauts with fresh oxygen? –  Enrico Pallazzo May 10 at 0:19
    
@EnricoPallazzo, evidently, the ISS life support systems produce oxygen primarily by electrolysis of water. It can also be chemically generated by the actions of strong oxidizers (chlorates, perchlorates, peroxides, superoxides, etc.), though whether those technologies are used in the ISS, I don't know. –  Greg E. May 21 at 16:09

Since the carbon atom is linked to two oxygen atoms via double bonds, usually more amount of energy must be supplied in order to separate it. About 94 k-cal of energy is required per mol of $\cf{CO2}$ (about 44g). This energy input could come from any source, but the major source of conversion is through photosynthesis using solar energy which is very well known by the famous equation:

$\cf{6CO2 + 6H2O -> C6H12O6 + 6O2}$

But in fact, there is a machine built by Sandia researchers known as Counter-Rotating-Ring Receiver Reactor Recuperator (CR5), which uses solar power to convert carbon dioxide and water to carbon monoxide, water, hydrogen and oxygen at a temperature of about 1500⁰C using a solar concentrator. Iron Oxide acts as an extractor of oxygen from $\cf{CO2}$ forming $\cf{CO}$. But, the main aim of this method is to produce fuel and not carbon. But it'll take atleast 15-20 years to come into usage because, only the prototype of this machine has been invented and tested.

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Electrolysis of carbonates in anhydrous environment can produce either $CO + O_2$ or $C + O_2$, [1] depending on conditions. A base, remaining in electrolyzed liquid then can capture carbon dioxide from other sources and be recirculated.

[1] http://dx.doi.org/10.1016/S0013-4686(02)00047-6

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Use Exploit the fact that burning magnesium continues to burn in atmosphere of carbon dioxide. $${\ce{Mg}}+\color{\red}{\ce{CO2}}\to \ce{MgO}+\color{\red}{\ce{C}} $$

Now you can electrolyse your mixture :

$$\ce{MgO}+\ce{H2O}\to \ce{Mg(OH)2} $$

$$\ce{4OH-}\to\color{\red}{\ce{ O2}}+\ce{2H2O}+\ce{4e-}$$

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How can we start burning magnesium in CO2? –  Kartik Jul 6 at 17:09

CO2 into CO + O2 is easier but you need a catalyst and about 1500deg C

http://www.rsc.org/chemistryworld/news/2008/january/03010801.asp

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Link only answers are discouraged, could you give an explanation of the method listed there (a summary is OK if it's too long) –  ManishEarth Aug 8 '12 at 6:20
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Fe3O2 is heated to 1500C driving off oxygen. The resulting FeO is moved to CO2 chamber where it absorbs oxygen from the CO2. Result is CO and cooled Fe3O2. Cycle repeats. –  Jesse Chisholm Mar 8 at 18:46

The electronic configuration of carbon is $1s^2 2s^2 p^2$. So a carbon atom requires 4 electrons to complete its outermost orbital. The electronic configuration of oxygen is $1s^2 2s^2 p^4$ so an oxygen atom requires 2 electrons to complete its octet configuration.

Thus two oxygen atoms and 1 carbon atom form a double bond between them so more energy is required to break this bond. In this way $\ce{CO2}$ is formed.

For converting $\ce{CO2}$ back into carbon and oxygen atoms, $\ce{CO2}$ should be heated at almost 298K so C becomes gaseous and oxygen becomes part of air.


[from another deleted answer -ed.]

If $\ce{CO2}$ can be produced by combining $\ce{C}$ and $\ce{O2}$ under the presence of air; then oppositely $\ce{CO2}$ can be separated to $\ce{C}$ and $\ce{O2}$ by heating $\ce{CO2}$ at almost that temperature which is impossible for $\ce{CO2}$ to absorb heat.

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$\ce{CO2}$ probably doesn't thermally dissociate into $\ce{C + O2}$ until the temperature is at least several thousand kelvin. It takes around 1000 K to perform $\ce{CO2 -> CO + 1/2 O2}$, and removal of the last oxygen atom from $\ce{CO}$ is an extremely difficult process, as carbon monoxide contains the strongest covalent bond known with a bond energy of $1072\ kJ/mol$. –  Nicolau Saker Neto May 9 at 11:27

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