Nanostructured Catalyst Produces Hydrogen from Ammonia
28 March 2005
Researchers at Rutgers are exploring the use of an iridium-based nanostructured catalyst to extract hydrogen from ammonia for use in a fuel cell.
The research team found that iridium heated to temperatures above 300 ºC (approx. 600 ºF) in the presence of oxygen morphs into uniform arrays of nanosized pyramids. The shape change is caused by the atomic forces from the adjacent oxygen atoms pulling the iridium atoms into a more tightly ordered crystalline state.
This pyramidal surface allows the ammonia molecules, themselves tetrahedral in shape, to nestle in nicely “like matching puzzle pieces.” This sets up the molecules to undergo complete and efficient decomposition.
Different annealing temperatures create different-sized facets on the pyramids, which affect how well the iridium catalyzes ammonia decomposition. The researchers are performing additional studies to characterize the process more completely.
Ammonia (NH3) is mostly manufactured through a catalytic industrial process using natural gas and air. The natural gas is reformed to create hydrogen gas, which is then processed to create the ammonia. The Rutgers process, in essence, undoes the initial manufacturing process.
Liquid ammonia could—in theory—be handled much like today’s gasoline and diesel fuel. Conceptually, a vehicle with a catalyst such as the one at Rutgers could produce hydrogen on-board for use in a fuel cell.
However, there are probably some practical barriers in the way. Ammonia is a hazardous substance that can cause bodily damage. Broad-based refueling might offer some challenges.
Second, although it is one of the most widely produced chemicals worldwide (140 million tonnes per year), 80% of that goes into the production of fertilizer. Any substantive use in transportation would require a major increase in chemical manufacturing capabilities.
All that aside, this work illustrates the potential in tailoring nanostructured metal surfaces on supported industrial catalysts to make new forms of catalysts that are more robust and selective.
A paper describing the research is to be published April 20 in the Journal of the American Chemical Society.
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