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Better bimetallic catalysts for fuel and chemical industries
Nanocatalysts consisting of two metals can offer superior performance compared with those made up of only one metal, so they are widely used for industrial processes that generate fuels and chemicals from natural gas, coal or plant biomass. However, complex interactions between the two metals during catalytic reactions can lower catalytic efficiency. This study addresses this issue by directly observing the changes of platinum-cobalt nanoparticles in operating conditions. Such particles are used as catalysts to convert carbon dioxide and hydrogen into long-chain carbon fuels and are important to the operation of low-temperature fuel cells.
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The new insights on the transformations of multiple component catalysts will allow researchers to optimally design similar catalysts to improve their performance, extend their lifetime, and reduce their environmental impact. Moreover, this research could guide efforts to minimize the use of precious metal components such as platinum and therefore reduce the cost of catalysts and lead to a more economical product for consumers.
In a multi-national lab effort led by Haimei Zheng from Lawrence Berkeley National Laboratory, researchers from DOE’s Pacific Northwest National Laboratory and collaborators examined real-time changes in the atomic structure of nanoparticles consisting of platinum and cobalt during reactions with oxygen and hydrogen using environmental transmission electron microscopy (ETEM), a specialized instrument housed in the Quiet Wing at the Environmental Molecular Sciences Laboratory (EMSL), a DOE national scientific user facility. The work was supported by the Chemical Imaging Initiative at PNNL.
During oxidation in an oxygen gas environment, cobalt migrated to the nanoparticle surface, where it formed a cobalt oxide film that covered the platinum. Within ten seconds, this oxide film broke apart to form distinct islands and created voids in the interior of the particle, which can impair catalyst performance. This process was reversed during reduction in a hydrogen gas environment, which caused the cobalt oxide patches to decrease and the cobalt to migrate back to the bulk of the particle. Reduction with hydrogen also caused a layer of platinum to form on the particle surface, which is expected to improve catalyst performance.
These new insights into the atomic scale behavior of nanoparticles consisting of multiple metals in reactive environments pave the way for a deeper understanding of the properties of multi-component catalysts and will guide efforts to improve their performance. In particular, the findings can be used to design multi-component catalysts that do not form oxide islands on the nanoparticle surface, but rather retain the material with higher catalytic performance on the nanoparticle surface during catalytic reactions.
This research was supported by DOE’s Office of Science and the Office of Basic Energy Sciences’ Chemical Science Division, as well as the Chemical Imaging Initiative at PNNL through the
Laboratory Directed Research and Development Programs at PNNL and LBNL.
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