"We set out to develop an effective catalyst that can convert large
amounts of the greenhouse gases carbon dioxide and methane without
failure," said Cafer T. Yavuz, paper author and associate professor of
chemical and biomolecular engineering and of chemistry at KAIST.
The catalyst, made from inexpensive and abundant nickel, magnesium,
and molybdenum, initiates and speeds up the rate of reaction that
converts carbon dioxide and methane into hydrogen gas. It can work
efficiently for more than a month.
This conversion is called 'dry reforming', where harmful gases, such
as carbon dioxide, are processed to produce more useful chemicals that
could be refined for use in fuel, plastics, or even pharmaceuticals. It
is an effective process, but it previously required rare and expensive
metals such as platinum and rhodium to induce a brief and inefficient
chemical reaction.
Other researchers had previously proposed nickel as a more economical
solution, but carbon byproducts would build up and the surface
nanoparticles would bind together on the cheaper metal, fundamentally
changing the composition and geometry of the catalyst and rendering it
useless.
"The difficulty arises from the lack of control on scores of active
sites over the bulky catalysts surfaces because any refinement
procedures attempted also change the nature of the catalyst itself,"
Yavuz said.
The researchers produced nickel-molybdenum nanoparticles under a
reductive environment in the presence of a single crystalline magnesium
oxide. As the ingredients were heated under reactive gas, the
nanoparticles moved on the pristine crystal surface seeking anchoring
points. The resulting activated catalyst sealed its own high-energy
active sites and permanently fixed the location of the nanoparticles --
meaning that the nickel-based catalyst will not have a carbon build up,
nor will the surface particles bind to one another.
"It took us almost a year to understand the underlying mechanism,"
said first author Youngdong Song, a graduate student in the Department
of Chemical and Biomolecular Engineering at KAIST. "Once we studied all
the chemical events in detail, we were shocked."
The researchers dubbed the catalyst Nanocatalysts on Single Crystal
Edges (NOSCE). The magnesium-oxide nanopowder comes from a finely
structured form of magnesium oxide, where the molecules bind
continuously to the edge. There are no breaks or defects in the surface,
allowing for uniform and predictable reactions.
"Our study solves a number of challenges the catalyst community
faces," Yavuz said. "We believe the NOSCE mechanism will improve other
inefficient catalytic reactions and provide even further savings of
greenhouse gas emissions."
This work was supported, in part, by the Saudi-Aramco-KAIST CO2 Management Center and the National Research Foundation of Korea.
Other contributors include Ercan Ozdemir, Sreerangappa Ramesh, Aldiar
Adishev, and Saravanan Subramanian, all of whom are affiliated with the
Graduate School of Energy, Environment, Water and Sustainability at
KAIST; Aadesh Harale, Mohammed Albuali, Bandar Abdullah Fadhel, and Aqil
Jamal, all of whom are with the Research and Development Center in
Saudi Arabia; and Dohyun Moon and Sun Hee Choi, both of whom are with
the Pohang Accelerator Laboratory in Korea. Ozdemir is also affiliated
with the Institute of Nanotechnology at the Gebze Technical University
in Turkey; Fadhel and Jamal are also affiliated with the
Saudi-Armco-KAIST CO2 Management Center in Korea.
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