Ru-Pt nanoparticles clean up hydrogen
Catalysis
April 22, 2008
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| Transmission electron microscopy images of the catalytic Ru-Pt core-shell nanoparticles. (Courtesy of Bryan Eichhorn.) |
Commercially produced H2 typically contains a significant amount of CO. This CO must be removed if the H2 is to be used in fuel cell devices because it poisons the expensive Pt catalyst.
Chemists from the University of Maryland and the University of Wisconsin-Madison have now synthesized nanoparticles that could cleanse these H2 streams by promoting selective CO oxidation [Alayoglu et al., Nat. Mater. (2008) 7, 333].
Researchers used a sequential polyol process to create Ru nanoparticles surrounded by one or two monolayers of Pt atoms. “The key step is to deposit the Pt shell on the Ru core below the self-nucleation temperature of Pt. In this way, we avoid forming monometallic Pt particles,” says lead author Bryan Eichhorn of the University of Maryland.
The core-shell nanoparticles were deployed in H2 streams containing 0.1–0.2% CO by volume, and 0.5% oxygen. They proved to be far better at promoting the preferential oxidation of CO than either a conventional PtRu nanoalloy, or pure Pt or Ru nanoparticles. CO was also converted to CO2 at much lower temperatures when using the Ru-Pt core-shell nanoparticles.
The team suggests two reasons for the nanoparticles’ higher catalytic efficiency. Fewer sites on the core-shell structure are available to bind with CO, leaving empty sites for O2 to come in and react. They have also identified a completely new reaction mechanism favoring selective CO oxidation.
“To capitalize on any large-scale or commercial applications, we are developing synthesis methods that employ standard, off-the-shelf reagents and protocols that can be scaled up,” Eichhorn says.
The study’s results may provide important information for the design of catalysts, as well as furthering understanding about CO oxidation process in H2, says Atsushi Fukuoka of Hokkaido University, Japan. “One of the most challenging tasks is still the complete oxidation of CO over wide reaction temperatures. For practical purposes, the catalysts still need further improvement,” he notes.
Paula Gould