Thermal Chemistry of Carbon Dioxide Reduction: An Obscure Point. [View All]

Self cleaning ovens are coated with ceric oxide, and one factor in the way they work is that they are Boudouard catalysts, a Boudouard catalyst, being a catalyst that causes the following reaction to take place: C + CO₂ <-> 2 CO. The bidirectional arrow (which properly should be used for all chemical reactions) refers to the fact that the reaction can go in either direction, and the direction it chooses to go is a function of concentration and temperature.

If the carbon monoxide formed reacts with oxygen on the surface, it will oxidize to form carbon dioxide, the famous dangerous fossil fuel waste that is continuously being dumped into the atmosphere, and for which there is no permanent repository.

This reaction is 2CO + O₂ <-> 2CO₂.

The net reaction is of course, just combustion. C + O₂ <-> CO₂.

As a catalyst, the ceric oxide is not consumed in this reaction although it is involved in reaction intermediates. Cerium, unlike other lanthanides has two oxidation states that are commonly stable in air, +3 and +4, and the catalytic reaction almost certainly involves the reduction of the +4 oxide by carbon to the +3 oxide, and reoxidation by air, giving the original oxide.

Recently in this space, I wrote about the carbon dioxide radical anion, which is involved in schemes to electrolytically reduce carbon dioxide to the monoxide, the monoxide being useful for chemical synthesis that might replace oil. I also noted that this anion can be formed radiolytically, by the interaction of high energy radiation, gamma, x-rays, and short wavelength UV.

http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=228x56433">An Interesting Chemical Radical Species: The Carbon Dioxide Anion.

One possible fate of this ion is to produce oxalate, which may be thought of a kind of dimer of CO₂.

Many years back, nuclear chemists studied the decomposition (thermal) of cerium (and other lanthanide) oxalates to give CO gas and carbon dioxide gas. This type of reaction is known as a disproportionation reaction ^-O₂CCO₂^- <-> CO + CO₂. A disproportionation reaction is one in which a substance, usually an element but sometimes an organic compound, oxidizes itself and reduces itself at the same time.

The reference for a discussion of these reactions, which also take place with neodymium, samarium and praesodymium, but not europium, is discussed in J. Inorg. Nucl. Chem., 1961, Vol. 22, pp. 39 to 48.

The reactions were conducted under vacuum, but what they suggest is that lower oxidation states may exist for neodymium and praesodymium. (A lower oxidation state of samarium is well known.)

I have no idea whether anyone has exhaustively studied that point.

It's esoteric, but cool, since any mechanism for the reduction of carbon dioxide to its monoxide is of interest.

I like to advocate for the importance to humanity of nuclear chemistry and chemistry in general, vastly under appreciated (by the public) sciences that are critical to the future of humanity.