Bilayered nanocrystals could bring cleaner energy

Compiled by Photonics Spectra staff

New bilayered nanocrystals made of metal-metal oxide that feature multiple catalytic sites on nanocrystal interfaces could mean big things for industrial catalysis and for clean green energy technologies such as artificial photosynthesis.

For the first time, the multiple catalytic sites created by Lawrence Berkeley National Laboratory enable multiple sequential catalytic reactions to be carried out selectively and in tandem.

While metal catalysts have been used to initiate industrial manufacturing processes that involve chemistry, in recent years – with the advent of nanosize catalysts – metal, oxide and their interfaces have surged in importance.

“High-performance metal-oxide nano-catalysts are central to the development of new-generation energy conversion and storage technologies,” said Peidong Yang, leader of the research group and a chemist who holds joint appointments with Berkeley Lab and the University of California, Berkeley.

Recent studies have found that for nanocrystals, size and shape play a large part on catalytic properties. Nanocrystal catalysts are easier to optimize for activity and selectivity than bulk-size catalysts.

The research group used an assembly technique to deposit nanocube monolayers of platinum and cerium oxide on a silica substrate. The layers were each less than 10 nm thick and stacked one on top of the other to create two distinct metal-metal oxide interfaces: platinum-silica and cerium-oxide-platinum. The two interfaces then catalyzed two separate and sequential reactions. First, the cerium oxide-platinum interface catalyzed methanol to produce carbon monoxide and hydrogen. These products then underwent ethylene hydroformylation through a reaction catalyzed by the platinum-silica interface, resulting in tandem catalysis of propanal.

“The cubic shape of the nanocrystal layers is ideal for assembling metal-metal oxide interfaces with large contact areas,” Yang said. “Integrating binary nanocrystals to form highly ordered superlattices is a new and highly effective way to form multiple interfaces with new functionalities.”

The scientists believe the tandem catalysis concept will be valuable for applications in which multiple sequential reactions are required to produce chemicals in a highly active and selective manner – for example, artificial photo-synthesis. The approach could also be relevant for photoelectrochemical reactions such as solar water splitting, but further work to explore new metal oxide or other semiconductor supports for catalyst design will have to be done, they said.

The research appeared in the April 10, 2011, issue of Nature Chemistry (doi: 10.1038/nchem.1018).