Carbon-based materials have many surprising properties that make them attractive as catalysts for accelerating chemical reactions. They are cheap and lightweight, and their large surface area provides a useful scaffold for anchoring catalysts, giving them a large surface area to work on to stabilize and disperse molecules. Carbons are useful for energy storage and sensing. Carbons have been used in electrochemistry for the past ten years to catalyze reactions that produce chemicals and fuel cells. However, in work recently reported in Nature Communications, Dion Vlachos of the University of Delaware and researchers at the Catalysis Center for Energy Innovation (CCEI) and collaborators at Brookhaven National Laboratory made some surprising discoveries while developing techniques to better understand the role oxygen plays in how carbon-based catalysts perform.
According to Vlachos, they discovered some of what they knew about chemistry. They are not uniform either. Carbon materials sometimes contain oxygen, and this oxygen can come in multiple forms, such as an alcohol, aldehyde, ketone, or acid. An open question is what the oxygen does in these carbon materials. So Vlachos and a group of researchers took carbon molecules and systematically introduced more and more oxygen, then used spectroscopic techniques to measure how much and what kind of oxygen the resulting material contained. The researchers did this for a library of 10 to 15 materials and then performed the reactions with different oxygen carbons. This allowed them to correlate the carbon material’s reactivity with the amount and type of oxygen present using machine learning tools.
The team’s work showed a relationship between the amount and type of oxygen present and performance, including which oxygen is more active. Conversely, the researchers also discovered something surprising: Long-range effects from aromatic rings far from a catalyst site can sometimes make the alcohol groups of the carbon more acidic than the familiar acidic carbon functional groups found in small acids in organic chemistry. At first the researchers were puzzled, but after some calculations they confirmed that this is due to carbons containing alcohol-based oxygens in aromatic rings. “Carbon has aromatic rings,” said Vlachos, the Unidel Dan Rich Chair in Energy and CCEI director. Long-range effects from afar are more likely to produce a local phenomenon that exerts a controlling influence on the activity of the catalyst sites.
This is not the case with ordinary catalysis chemistry, where the effect is very local. For example, Bond A affects Bond, and that’s it. “The whole thinking of chemistry has been turned upside down. This was not expected, he added. In terms of applications, Vlachos said, if researchers want to create a more acidic carbon catalyst, they need to use more alcohol functional groups, in which case hydroxyl.
The researchers used advanced techniques to validate the mathematical modeling results and explain what happens to oxygen in materials under real-world conditions when chemistry occurs. “The University of Delaware team achieved a remarkable achievement by using advanced tools and methods to unravel a complex catalytic system,” said Anibal Boskobonik, materials scientist at the Center for Functional Nanomaterials, a US Department of Energy (DOE) Office of Science User Facility at DOE’s Brookhaven National Laboratory.
“We are pleased to have contributed to this important achievement by performing measurements using specialized spectroscopy at the Center for Functional Nanomaterials. Using this new methodology to determine what each part of the chemistry does, the research team can test different techniques for making the materials to see which approach yields the best results. For example, are all oxygen molecules equally effective at speeding up catalytic reactions, or are some better than others? Vlachos is also curious if an oxygen source can be used to disperse metals for reactions. “Conventional methods of introducing oxygen into the reaction to form substances are destructive, so finding greener ways to do this will bring more sustainable processes closer to fruition,” Boskoboinic said. (ANI)
(This story has not been edited by DavidDiscourse staff and is automatically generated from a syndicated feed.)