Compiled by Photonics Spectra staff
BERKELEY, Calif. – 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