Hydrogen — the lightest and most abundant element on the periodic table — is also a potential powerhouse. Today, we use pure hydrogen in a range of chemical processes, including the synthesis of ammonia for fertilizers. Some scientists believe that hydrogen could power everything from electronics to buildings to cars in a model referred to as the hydrogen economy. In order to achieve such feats, however, scientists need to produce pure hydrogen.
Chemists can obtain pure hydrogen through the water-gas shift reaction, in which carbon monoxide and water yield carbon dioxide and pure hydrogen molecules.
Four years ago, a group of Brookhaven-led researchers began to investigate a highly effective catalyst for this reaction, which combined gold and ceria. Their main objective was to understand exactly how each component of the catalyst behaved.
Beginning with this first catalyst, and gradually tweaking one variable after another, the researchers set out to find even better catalytic combinations. Using characterization techniques like photoemission, time-resolved x-ray diffraction and x-ray absorption spectroscopy at NSLS beamlines U7A, U12, X7B, and X19A, they studied details of the structural and electronic properties of the gold-ceria catalyst.
With in-situ characterization, researchers can determine two key factors: precisely when the active phase for the reaction appears on the catalyst and how it affects the reaction mechanism. These key factors allow scientists to refine the reaction, exchanging and adjusting its components.
Last year, the researchers tested a new catalyst that combines ceria in a mixed metal oxide, building upon the findings of their previous research. They found that this surface combination with a dispersion of gold, copper, or platinum nanoparticles revealed high catalytic properties.
More recently, they compared catalytic effects with a dispersion of gold, copper, and platinum nanoparticles. While platinum showed the highest catalytic activity, meaning it produced the most hydrogen for a fixed amount of ceria, copper was a close second and has the advantage of being a much less expensive metal.
Studying this next-generation catalyst could reveal more discoveries and lead to an even more potent super-catalyst.
J.B. Park, J. Graciano, J. Evans, D. Stacchiola. S.D. Senanayake, L. Barrio, P. Liu, J.F. Sanz, J. Hrbek, J.A. Rodriguez, “Gold, Copper, and Platinum Nanoparticles Dispersed on CeOx/TiO2(110) Surfaces: High Water-Gas Shift Activity and the Nature of the Mixed-Metal Oxide at the Nanometer Level,” J. Am. Chem. Soc., 132, 356 (2010).
Top: Production of hydrogen through the water-gas shift
reaction after dispersing gold (Au), copper (Cu), and platinum (Pt) on TiO2(110)
and the group’s “super-catalyst,” CeOx/TiO2(110)
Bottom: From left, Brookhaven researchers Sanjaya Senanayake, Jose A. Rodriguez, Laura Barrio, and Jonathan Hanson