# How can carbon dioxide be converted into carbon and oxygen?

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

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

Alternatively:

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

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.

• 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 process. Using $\ce{KNO3}$ Aug 25 '12 at 6:22

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.
• Aren't they using something like this in the International Space Station to provide astronauts with fresh oxygen? May 10 '14 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. May 21 '14 at 16:09

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 :

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

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

• How can we start burning magnesium in CO2? Jul 6 '14 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.

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

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

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.

• Link only answers are discouraged, could you give an explanation of the method listed there (a summary is OK if it's too long) 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. Mar 8 '14 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.

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.

• $\ce{CO2}$ 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 $1072\ kJ/mol$. May 9 '14 at 11:27
• 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. Jun 25 '15 at 17:50
• 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? Aug 14 '18 at 23:51
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.