Sep 20, 2013
Islands in the sea configuration exposes platinum nanoparticles
A sinter-resistant, tri-phasic catalyst made of platinum (Pt), titanium dioxide (TiO2), and silica (SiO2) has been developed by researchers at Georgia Institute of Technology in the US. The catalyst has the much sought after "islands in the sea" configuration, in which the Pt nanoparticles are fully exposed, making them completely accessible to the reagents in a catalytic reaction. The system, which works efficiently at temperatures of up to 700 °C, might be ideal for use in the three-way catalytic converter.
The researchers, led by Younan Xia, made their catalyst in three steps: the first involved synthesising Pt nanoparticles coated with a small amount of the plastic, poly(vinyl pyrrolidone) (PVP). The researchers then loaded the Pt nanoparticles onto a fibrous structure of TiO2 and finally coated the Pt/TiO2 with SiO2. The Pt nanoparticles were not covered by the SiO2 thanks to the very little PVP employed in the first step, explained Xia, "and the result is a new Pt-based catalytic system where the Pt nanoparticles are fully exposed rather than being covered by the SiO2 coating," he told nanotechweb.org.
The TiO2 fibrous structure acts as a strongly interacting oxide support, the Pt nanoparticles as the active catalyst and the SiO2 layer between the Pt nanoparticles as a weakly interacting oxide. The SiO2 layer isolates the Pt nanoparticles from each other, something that, importantly, prevents them from sintering during heating. Sintering is bad for catalysts since it deactivates them.
High catalytic activity
"The uncovered catalyst can be readily accessed by the reactants in a catalytic reaction and thus its activity remains high," says Xia. "If the SiO2 layer covers the particles, on the other hand, it blocks the active sites on the Pt nanoparticles, which is a major deterrent to practical use of these catalysts."
According to the Georgia Tech team, the catalyst might be ideal in the three-way catalytic converter for emissions control in cars. This device converts the three main pollutants in vehicle exhausts (carbon monoxide, unburned hydrocarbons and nitrogen oxides) into less harmful carbon dioxide, water and nitrogen.
The researchers say that now they plan to make sinter-resistant catalysts from nanocrystals whose size, shape and compositions can be controlled, for use in specific applications – like carbon monoxide oxidation, for example.
The present research is detailed in Nano Lett. DOI: 10.1021/nl4029973.
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About the author
Belle Dumé is contributing editor at nanotechweb.org.