Solar Furnace Test Utilizing Cerium (IV) Oxide

Earlier this morning, I was able to participate in a test reaction in solar furnace CR5.  The test utilized a heliostat controlled remotely through large shutters.  The heliostat mirrors directed sunlight onto a focusing dish which was projected onto the reaction vessel.  The reaction vessel contained four discs containing fingers of cerium (IV) oxide, which are rotated in opposing directions throughout the course of the reaction.

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As the sunlight was slowly ramped up, the temperature inside the reaction vessel climbed, ultimately reaching a temperature in excess of 1400 C.  Once the vessel reached 1200 C, a flow of carbon dioxide was initiated.  Ideally, the expected result would be the reduction of cerium (IV) to cerium (II) to form cerium (II) oxide as shown below:

Reduction of cerium

This initial process occurs around 1400 C.  After the cerium has been reduced, it is subjected to a flow of carbon dioxide gas which causes the cerium to be oxidized to a +4 state.

Oxidation of cerium using carbon dioxide

This reaction is key to the formation of a useable fuel precursor (CO gas).  The reaction kinetics require a high temperature above 900 C for this process to occur.

Once the vessel had ramped up to temperature and gases began to flow, we began to notice erratic disc behavior.  What at first was minor rapidly evolved into a complete disc failure.  As soon as the discs ceased rotating, the experiment was shutdown and the furnace shuttered until the vessel could be torn apart for failure analysis.  It was interesting to note that while the experiment was ongoing, little CO was being measured, but upon cessation of the flow of gases a measurable amount of CO was detectable.  If this process can be optimized, it seems completely plausible that concentrated solar sources can be used to revert carbon dioxide into usable fuel precursors which can then be processed into traditional liquid fuels.

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