Iron electrocatalysis breaks down polystyrene and delivers green hydrogen
Plastics are inescapable in our daily lives. The vast
amounts of plastic garbage heaped in landfills and in the environment,
however, are as problematic as the plastics are useful. In the journal Angewandte
Chemie, a German research team has now introduced a new method for
recycling polystyrene waste. Their efficient electrochemical process
uses an inexpensive iron catalyst, produces hydrogen as a byproduct, and
can be powered by solar panels.
© Wiley-VCH, re-use with credit to 'Angewandte Chemie' and a link to the original article.
Less than 10% of the plastic produced in the world is
recycled. Plastic waste is accumulating in landfills and waterways,
threatening wildlife and the environment. By 2025, this pile of plastic
is predicted to reach 40 billion tons. Globally, about 33 % of the
material deposited in landfills consists of polystyrene (PS), which is
widely used in packaging and construction. Only about 1 % of polystyrene
is recycled. Worldwide production capacity of polystyrene reached 15.4
million tons in 2022 and continues to increase. Recycling of plastics,
particularly polystyrene, is one of the biggest societal challenges of
our time. Efficient, cost-effective recycling methods that convert
plastic waste to valuable small molecules that can be used in chemical
syntheses would be a step toward a sustainable circular carbon economy.
A team led by Lutz Ackermann at the Friedrich Wöhler
Research Institute for Sustainable Chemistry in Göttingen (Germany) has
now developed an electrocatalytic method for the efficient degradation
of polystyrenes. The degradation produces a relatively high fraction of
monomeric benzoyl products that can be used as starting materials for
chemical processes, as well as some short polymer chains.
The key to this success is a powerful iron-based catalyst,
an iron porphyrin complex that resembles hemoglobin. Its advantage over
many other catalytically active metals is that iron is nontoxic,
inexpensive, and easy to obtain. During the electrocatalytic reaction,
the iron compound cycles between different oxidation steps (IV, III, and
II). A series of reaction steps and intermediate products eventually
result in splitting of the carbon-carbon bonds in the polymer backbone.
The main products are benzoic acid and benzaldehyde. Benzoic acid is a
starting material for a variety of chemical syntheses in the production
of scents and preservatives, for example. The robustness of this novel
electrocatalysis was demonstrated by the efficient degradation of
real-life plastic waste on the gram scale.
This polystyrene degradation process could be fully powered
with electricity from commercially available solar panels. In addition,
a useful side reaction occurs during the degradation process: production
of hydrogen. In this way, the new electrocatalytic process, which can
easily be scaled to an industrial level, combines efficient plastic
recycling with decentralized, green hydrogen production.
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About the Author
Dr. Lutz Ackermann is a Full Professor at the Georg August
University in Göttingen. His research is concentrated on the development
and study of new concepts for sustainable catalysis, with a current
focus on electrocatalysis. He is also the founder and director of the
Wöhler Research Institute for Sustainable Chemistry.
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