Applying Strain makes for better catalysts- New Theory
Brown University researchers have developed a new theory to explain why stretching or compressing metal catalysts can make them perform better, as published in the journal Nature Catalysis.
Catalysts are substances that speed up chemical reactions. The vast majority of industrial catalysis involves solid surfaces, often metals that catalyze reactions in liquids or gases. Researchers are also interested in using metal catalysts to convert carbon dioxide into fuels, make fertilizers from atmospheric nitrogen and drive reactions in fuel-cell cars.
It’s been shown in recent years that applying a strain to a catalyst can tune its reactivity. The theory predicts that tensile strain should in- crease reactivity, while compression should reduce it. However, Peterson and his group kept encountering systems that aren’t easily explained by the theory. That got the researchers thinking about a new way to view the problem. The new theory focuses on the mechanics of how molecules interact with a catalyst’s atomic lattice.
Peterson and his team showed that molecules bound to a catalyst’s surface will tend to either push atoms in the lattice apart or pull them closer together, depending upon the characteristics of the molecules
and the binding sites. The different forces produced by molecules have interesting implications for how external strain should affect a catalyst’s reactivity. It suggests that tension should make a catalyst more reactive to molecules that naturally want to push the lattice apart. At the same time, tension should decrease reactivity for molecules that want to pull the lattice together. Compression - squeezing the lattice has an inverse effect.
The new theory predicts a way to break traditional scaling relations between catalysts and different types of molecules.
This new theory suggests that strain can break those scaling relations by enabling a catalyst to simultaneously bind one chemical more tightly and another more loosely, depending on the chemical’s natural interaction with the catalyst’s atomic lattice and the way that the strain field is engineered on the catalyst surface.
Peterson’s team has started putting together a database of common reaction chemicals and their interactions with different catalyst surfaces. That database could serve as a guide for finding reactions that could benefit from strain and the breaking of scaling relations.