Single-site catalysts create more hydrogen at lower cost
A new class of catalysts created at the US Department of Energy's Argonne National Lab in Illinois may help overcome some of the hurdles that have inhibited hydrogen production for use in fuel cells. Argonne chemist Michael Krumpelt and his colleagues in the Chemical Engineering Division are using 'single-site' catalysts based on ceria or lanthanum chromite, doped with either platinum or ruthenium, to boost hydrogen production at lower temperatures during reforming.
Most hydrogen produced industrially is created through steam reforming. In this process a nickel-based catalyst is used to react natural gas with steam to produce pure hydrogen and CO 2 . These nickel catalysts typically consist of metal grains tens of thousands of atoms in diameter that speckle the surface of metal oxide substrates.
Conversely, the catalysts being developed by Krumpelt's team consist of single atomic sites embedded in an oxide matrix. Because some reforming processes tend to clog much of the larger catalysts with carbon or sulfur by-products, smaller catalysts process the fuel much more efficiently, and can produce more hydrogen at lower temperatures.
Krumpelt's initial experiments with single-site catalysts used platinum in gadolinium-doped ceria. Although it started to reform hydrocarbons at 450°C, it became unstable at higher temperatures. Searching for more robust materials that would support the oxidation-reduction reaction cycle at the heart of hydrocarbon reforming, Krumpelt found that if he used ruthenium -which costs only 1% as much as platinum -in a perovskite matrix, then he could initiate reforming at 450°C and still have good thermal stability.
The use of the LaCrRuO 3 perovskite offers an additional advantage over traditional catalysts. While sulfur species in the fuel degrade the traditional nickel, and to a lesser extent even the single-site platinum catalysts, the crystalline structure of the perovskite lattice acts as a 'stable shell' that protects the ruthenium catalyst from deactivation by sulfur.