Carbon based materials have a number of properties that make them attractive as catalysts for accelerating chemical reactions. Carbons are so useful for energy storage and sensing. Carbons have been used in electrochemistry for the past decade to catalyze reactions that produce chemicals and fuel cells.
Nature Communications, Dion Vlachos of the University of Delaware and researchers at the Catalysis Center for Energy Innovation (CCEI) with collaborators at Brookhaven National Laboratory made some surprising findings as they developed techniques to better understand the role of oxygen in how catalysts work carbon based.
What found turned some of what they knew about chemistry
Not all oxygens are created equal: Despite their usefulness, carbons are not well understood. They are not even uniform. Carbon materials sometimes contain oxygen within them and this oxygen can come in many different forms such as alcohol, aldehyde, ketone or acid. An open question is what the oxygen is doing in these carbon materials.
So Vlachos and a team of researchers took carbon molecules and systematically introduced more and more oxygen, then characterized the resulting material using spectroscopic techniques to measure how much and what type of oxygen was present.
The researchers did this for a library of about 10 to 15 materials and then performed the reactions using different oxygenated carbons. This allowed them to correlate the reactivity of the carbon material with the amount and type of oxygens present using machine learning tools.
The team’s work showed a link between the amount and type of oxygen present and performance, including which oxygens are more active. Counterintuitively, the researchers also found something surprising: the far-reaching effects of aromatic rings far from the catalyst site can sometimes cause alcohol carbon groups to become more acidic than the known acidic carbon functional groups found in the small acids of organic chemistry.
At first the scientists were surprised, but then they did some calculations and confirmed that the effect was due to the oxygenated carbons on the alcohol base in the aromatic rings.
Vlachos, Unidel’s Dan Rich Chair in Energy and director of CCEI says “Carbon has aromatic rings, the greater the chance of creating a reional phenomenon where long-range effects from a long distance can have a controlling effect on the activity of the catalyst sites.”
Advanced techniques to verify the results of the mathematical modeling
This is not the case in typical catalytic chemistry, where the effect is very local. For example bond A affects bond B and that’s it. The researchers used advanced techniques to verify the results of the mathematical modeling and characterize what would happen to the oxygen in the materials under near-real-world conditions while the chemistry was taking place.
New methodology for determining what each part of the chemistry does, the research team can test different techniques for making the materials to see which approach works best. For example, are all oxygen molecules equally effective at speeding up catalytic reactions, or are some better than others? Vlachos is also curious whether the oxygen source can be used to disperse metals for reactions.
