How can $\ce{CO2}$ be converted into carbon and oxygen?

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


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

I'm aware that plants are capable of transforming $\ce{CO2 + H2O}$ to glucose and oxygen via photosynthesis, but I'm interested in chemical or physical means rather than biological.

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    $\begingroup$ 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. $\endgroup$
    – Laar
    Commented Aug 7, 2012 at 21:19
  • $\begingroup$ You can use scrubbing process. Using $\ce{KNO3}$ $\endgroup$
    – BigSack
    Commented Aug 25, 2012 at 6:22

7 Answers 7


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,[1] they heated magnetite ($\ce{Fe3O4}$) at 290 °C for 4 hours 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.

  1. Tamaura, Y.; Tahata, M. Complete reduction of carbon dioxide to carbon using cation-excess magnetite. Nature 1990, 346 (6281), 255–256. DOI: 10.1038/346255a0.
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    $\begingroup$ Aren't they using something like this in the International Space Station to provide astronauts with fresh oxygen? $\endgroup$ Commented May 10, 2014 at 0:19
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    $\begingroup$ @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. $\endgroup$
    – Greg E.
    Commented May 21, 2014 at 16:09
  • $\begingroup$ @GregE. generating oxygen is a separate concern from CO2 removal (i.e. wouter dorgelo's 'providing astronauts with fresh oxygen' ... stated in the context of CO2 conversion to C and O2). Yes, you can generate O2 via electrolysis, but it is the concentration of CO2 and its build-up that creates a hazard for humans. The EPA lays out concentration levels and their effects on humans. Problems start at 1000 ppm (mental fog) and progress from there. I believe Wouter's intended question was "isn't this how the CO2 scrubbers in the ISS work?" $\endgroup$
    – eAndy
    Commented Jul 5, 2023 at 18:21

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

Reference: L. Massot, P. Chamelot, F. Bouyer, P. Taxil; Electrodeposition of carbon films from molten alkaline fluoride media. Electrochimica Acta, 2002, 47 (12), 1949-1957. https://doi.org/10.1016/S0013-4686(02)00047-6


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 :

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

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

  • $\begingroup$ How can we start burning magnesium in CO2? $\endgroup$
    – Kartik
    Commented Jul 6, 2014 at 17:09

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 kcal of energy is required per mol of $\ce{CO2}$ (about 44 g). 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:

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

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 1500 °C using a solar concentrator. Iron oxide acts as an extractor of oxygen from $\ce{CO2}$ forming $\ce{CO}$. But, the main aim of this method is to produce fuel and not carbon. But it’ll take at least 15–20 years to come into usage because, only the prototype of this machine has been invented and tested.

  1. React carbon-dioxide with hydrogen in the Sabatier process to get methane. 400 °C, high pressure and Nickel catalyst needed. The process is slighly exothermic so it can keep going on its own:

    $$\ce{CO2} + \ce{4H2} \rightarrow \ce{CH4} + 2\ce{H2O}$$

    This process have been proposed to generate fuel on Mars, and used on the ISS to process exhaled carbon-dioxide.

  2. Split the resulting water (use electrolysis or some other thermochemical cycle) take the oxygen, bring the hydrogen back to Step 1:

    $$2\ce{H2O} \rightarrow 2\ce{H2} + \ce{O2}$$

    Electricity for this may come off solar panels.

  3. Methane decomposes at high temperatures. The process goes to completion around 1200°C. Collect the condensed carbon, bring the hydrogen back to step 1.

    $$\ce{CH4} \rightarrow \ce{C} + 2\ce{H2}$$

    This process is proposed as an emissions free alternative to produce hydrogen from natural gas. Heat may come from concentrated solar light.


$\ce{CO2}$ into $\ce{CO + O2}$ is easier but you need a catalyst and about 1500C


In short:
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.

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    $\begingroup$ Link only answers are discouraged, could you give an explanation of the method listed there (a summary is OK if it's too long) $\endgroup$ Commented Aug 8, 2012 at 6:20
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    $\begingroup$ 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. $\endgroup$ Commented Mar 8, 2014 at 18:46

The electronic configuration of carbon is $\ce{1s^2 2s^2 2p^2}$. So a carbon atom requires 4 electrons to complete its outermost orbital. The electronic configuration of oxygen is $\ce{1s^2 2s^2 2p^4}$ 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 $\pu{298 K}$ so carbon becomes gaseous and oxygen becomes part of air.

Edit from another deleted answer:

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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    $\begingroup$ $\ce{CO2}$ 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 $1072\ kJ/mol$. $\endgroup$ Commented May 9, 2014 at 11:27
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    $\begingroup$ I would bet that diatomic oxygen dissociates at much lower temperatures than CO, in which case it will be impossible to use thermal methods to get C + O2. $\endgroup$
    – Curt F.
    Commented Jun 25, 2015 at 17:50
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    $\begingroup$ CO2 should be heated at room temperature so carbon becomes gaseous and oxygen becomes part of air. What the hell are you talking about? That is obvious nonsense and clearly doesn't happen. Wha the hell did you mean? $\endgroup$
    – matt_black
    Commented Aug 14, 2018 at 23:51
  • $\begingroup$ 298K is room temperature, in case anyone didn't spot that. $\endgroup$
    – amh15
    Commented Jul 3, 2023 at 16:50

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