The new dark gray powder is made from tiny granules of cerium oxide -- a common ingredient in ceramics -- and calcium, covered with even smaller particles of cobalt. It produces hydrogen with 90 percent efficiency at 660 degrees Fahrenheit (around 350 degrees Celsius) -- a low temperature by industrial standards.
"Whenever a process works at a lower temperature, that brings energy savings and cost savings," Ozkan said. "Also, if the catalyst is highly active and can achieve high hydrogen yields, we don't need as much of it. That will bring down the size of the reactor, and its cost".
The process starts with a liquid biofuel such as ethanol, which is heated and pumped into a reactor, where the catalyst spurs a series of chemical reactions that ultimately convert the liquid to a hydrogen-rich gas.
One of the biggest challenges the researchers faced was how to prevent "coking" -- the formation of carbon fragments on the surface of the catalyst. The combination of metals -- cerium oxide and calcium -- solved that problem, because it promoted the movement of oxygen ions inside the catalyst. When exposed to enough oxygen, the carbon, like the biofuel, is converted into a gas and gets oxidized; it becomes carbon dioxide.
At the end of the process, waste gases such as carbon monoxide, carbon dioxide and methane are removed, and the hydrogen is purified. To make the process more energy-efficient, heat exchangers capture waste heat and put that energy back into the reactor. Methane recovered in the process can be used to supply part of the energy.
Though this work was based on converting ethanol, Ozkan's team is now studying how to use the same catalyst with other liquid biofuels. Her coauthors on this presentation included Ohio State doctoral students Hua Song
|Contact: Umit Ozkan|
Ohio State University