# How to convert Carbon dioxide into Carbon and Oxygen?

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
I believe you would save a lot of head ache if you just used a plant. –  user1697 May 25 '13 at 21:32

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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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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.

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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
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
I'm not quite sure that this answers the question. The question is how to break down $\ce{CO2}$ into $\ce{C}$ and $\ce{O2}$. You seem to answer the question where to get the energy to do that and just refer to the reaction as 'breaking the CO2 down into C and O'. Could you extent your answer, including HOW you would go about breaking down the CO2?! –  Michiel Apr 13 at 8:01