Chemistry - How can carbon dioxide be converted into carbon and oxygen?
Solution 1:
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.
- 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.
Solution 2:
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
Solution 3:
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.
Solution 4:
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 :
$$\ce{MgO}+\ce{H2O}\to \ce{Mg(OH)2} $$
$$\ce{4OH-}\to\color{\red}{\ce{ O2}}+\ce{2H2O}+\ce{4e-}$$
Solution 5:
$\ce{CO2}$ 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.