C1 to C2:
Connecting carbons by reductive deoxygenation and coupling of CO
Credit: Kyle Horak
and Joshua Buss/Caltech
(December 23, 2015) In
the quest for sustainable alternative energy and fuel sources, one viable
solution may be the conversion of the greenhouse gas carbon dioxide (CO2) into
liquid fuels.
Through photosynthesis, plants convert sunlight, water, and
CO2 into sugars, multicarbon molecules that fuel cellular processes. CO2 is
thus both the precursor to the fossil fuels that are central to modern life as
well as the by-product of burning those fuels. The ability to generate
synthetic liquid fuels from stable, oxygenated carbon precursors such as CO2
and carbon monoxide (CO) is reminiscent of photosynthesis in nature and is a
transformation that is desirable in artificial systems. For about a century, a
chemical method known as the Fischer-Tropsch process has been utilized to
convert hydrogen gas (H2) and CO to liquid fuels. However, its mechanism is not
well understood and, in contrast to photosynthesis, the process requires high
pressures (from 1 to 100 times atmospheric pressure) and temperatures (100–300
degrees Celsius).
More recently, alternative conversion chemistries for the
generation of liquid fuels from oxygenated carbon precursors have been
reported. Using copper electrocatalysts, CO and CO2 can be converted to
multicarbon products. The process proceeds under mild conditions, but how it
takes place remains a mystery.
Now, Caltech chemistry professor Theo Agapie and his
graduate student Joshua Buss have developed a model system to demonstrate what
the initial steps of a process for the conversion of CO to hydrocarbons might
look like.
The findings, published as an advanced online publication
for the journal Nature on December 21, 2015 (and appearing in print on January
7, 2016), provide a foundation for the development of technologies that may one
day help neutralize the negative effects of atmospheric accumulation of the
greenhouse gas CO2 by converting it back into fuel. Although methods exist to
transform CO2 into CO, a crucial next step, the deoxygenation of CO molecules
and their coupling to form C–C bonds, is more difficult.