A multi-institutional team has resolved a long-unanswered question about how two of the world’s most common substances interact. In a paper published in the journal Nature Communications, Manos Mavrikakis, the Paul A. Elfers professor of chemical and biological engineering, and his collaborators report fundamental discoveries about how water reacts with metal oxides. The paper opens doors for greater understanding and control of chemical reactions in fields ranging from catalysis to geochemistry and atmospheric chemistry.
These reactions play a huge role in the catalysis-driven creation of common chemical platforms such as methanol, produced on the order of 10 million tons per year for uses including fuel and as raw material for chemical production.
Chemists understand how water interacts with many non-oxide metals, which are very homogeneous. Metal oxides are trickier: An occasional oxygen atom is missing, causing what Mavrikakis calls “oxygen defects.” When water meets with one of those defects, it forms two adjacent hydroxyls—a stable compound comprising one oxygen atom and one hydrogen atom.
Mavrikakis, with chemical and biological engineering assistant scientist Guowen Peng and PhD student Carrie Farberow, along with researchers at Aarhus University in Denmark and Lund University in Sweden, investigated how hydroxyls affect water molecules around them, and how that differs from water molecules contacting a pristine metal oxide surface. The project yielded two dramatically different pictures of
water-metal oxide reactions. “On a smooth surface, you form amorphous networks of water molecules, whereas on a hydroxylated surface, there are much more structured, well-ordered domains of water molecules,” says Mavrikakis.
In the latter case, the researchers realized that hydroxyl behaves as a sort of anchor, setting the template for a tidy hexameric ring of water molecules attracted to the metal’s surface. “It opens the door to using hydrogen bonds to make surfaces hydrophilic, or attracted to water, and to templating these surfaces for the selective absorption of other molecules possessing fundamental similarities to water,” says Mavrikakis. “Because catalysis is at the heart of engineering chemical reactions, this is also very fundamental for atomic-scale chemical reaction engineering.”
Read more about this advance: go.wisc.edu/water-works
The importance—and impact—of a professorship
“The Paul A. Elfers professorship enables me to pursue the initial phases of high-risk, high-impact projects. After we have some encouraging preliminary results, we can write proposals to funding agencies and secure funding—but unless we can fund this preliminary research, it is really difficult to pursue these ideas. Endowed professorships can make an enormous difference in that sense. In fact, one can tell how good a certain academic department is by the number of endowed professorships it has available and the funds going with each one of them. Needless to say, endowed chairs make for a very effective tool for recruiting high caliber faculty from other institutions,” says Mavrikakis, the Paul A. Elfers professor of chemical and biological engineering.
A native of Wauwatosa, Wisconsin, Paul A. Elfers earned a bachelor’s degree in chemical engineering in 1926, and spent the majority of his career with the Fisher Governor Co. in Marshalltown, Iowa. He retired in 1962 as the company vice president of sales. In 1988, Elfers’ generous gift created the Paul A. Elfers Chair in Chemical Engineering at UW-Madison.