Published on July 17th, 2013 | by James Ayre5
Ethanol Steam Reforming For Fuel Cells — Major Obstacle Overcome
Ethanol steam reforming is a process whereby hydrogen gas can be generated directly within fuel cell systems by decomposing bioethanol — all that’s necessary are catalysts. The main appeal of the approach is that it would allow the continued use of our current gasoline delivery infrastructures, no need for new infrastructure. There are still some issues with the approach, though — primarily, the reality that its “multiple reaction pathways” can lead to the creation of toxic carbon monoxide byproducts which then damage the fuel cell membranes.
But, now, researchers at the A*STAR Institute of Chemical and Engineering Sciences in Singapore may have finally found a solution to that problem — a novel metal catalyst that can eradicate CO emissions from ethanol-derived H2 at temperatures 50 °C lower than previous catalysts.
The press release from A*STAR gets into the details:
Low-temperature ethanol steam reforming boosts the safety and efficiency of fuel processing onboard vehicles, but requires a careful choice of catalysts. Rhodium (Rh), a relatively scarce transition metal, has gained attention among chemists because it targets ethanol’s carbon-carbon bond — the most difficult part of the alcohol to decompose. However, Rh catalysts tend to generate CO and methane byproducts when steam reforming conditions fall below 350 °C.
Lin Huang, Jianyi Lin and co-workers from the A*STAR Institute of Chemical and Engineering Sciences in Singapore investigated whether they could resolve Rh’s shortcomings with cobalt (Co), a less expensive transition metal that has high selectivity toward H2 production at low temperatures. They explored whether Co could be combined with Rh on a nanostructured oxide surface to produce a dual-component catalyst. While making a mixed catalyst is relatively straightforward, finding one that maximizes the benefits of both metals for efficient steam reforming is not as easy. Therefore, the team investigated how different metallic precursors could achieve an ideal interaction between Rh and Co atoms on the supporting surface.
Their experiments revealed that catalysts consisting of Rh and Co, prepared from metal carbonyl precursors, gave high yields of extraordinarily clean H2 with no CO emissions at temperatures as low as 300 °C. According to Huang, these findings indicate that atomic interactions between the metals favor a particular pathway, known as the water-gas shift, which converts CO and water into H2 and carbon dioxide. However, mixed catalysts made from metal nitrate precursors failed to yield CO-free H2, presumably because of poor atomic interactions.
The researchers are now planning to continue the research by attempting to determine the mechanistic reasons behind the great effectiveness of the Rh-Co dual-component catalysts; and will also be working to develop a means of “reducing the build-up of carbonaceous coke deposits that adversely affect catalytic activity and stability during ethanol steam reforming.”
In related news, the US Army recently announced that they have begun working on a new “green” fuel cell — one designed specifically to run on corn ethanol. The project is courtesy of the US Army’s “Center of Lethality,” aka the Armament Research, Development and Engineering Center headquartered at Picatinny Arsenal in New Jersey.