Dion Vlachos of the University of Delaware's Catalysis Center for Energy Innovation has shown that an imperfect surface may produce more effective bimetallic catalysts. Photo: Kathy F. Atkinson/University of Delaware.In the world of catalytic science and technology, the hunt is always on for catalysts that are inexpensive, highly active and environmentally friendly. Recent efforts have focused on combining two metals, often in a structure where a core of one metal is surrounded by an atom-thick layer of a second one.
The properties and performance of these so-called bimetallic core-shell catalysts can be superior to those of either of the constituent metals, but determining how to take advantage of this synergy can be challenging. Dion Vlachos, who directs the Catalysis Center for Energy Innovation at the University of Delaware, has been using various computational techniques to predict how these nanoscale materials will behave, and recently made a surprising discovery about the structure of bimetallic catalysts.
"We thought that the shell had to form a perfect concentric circle around the core," he says. "But it turns out that the apparent imperfection of a patched surface actually offers better performance and ease of synthesis." The results of this work, which Vlachos conducted with postdoctoral researcher Wei Guo, are detailed in a paper in Nature Communications.
Vlachos and Guo performed multi-scale simulations of the decomposition of ammonia (NH3) on various nickel-platinum catalysts and found that simple patches of nickel on platinum were very effective at creating and sustaining dual active sites.
"What we have is bifunctional activity, where flat nickel 'terraces' catalyze the breaking of nitrogen-hydrogen bonds, and nickel 'edges' drive the pairing of nitrogen atoms," says Vlachos, who is also professor of chemical and biomolecular engineering.
He explains that the decomposition of ammonia is often used as a representative reaction for predicting new catalytic materials and for understanding why some reactions are sensitive to a particular material's structure. In addition, the decomposition of ammonia is interesting in its own right. Not only is there a need for less-energy-intensive catalysts to break down ammonia, which is the primary chemical in most fertilizers, but ammonia could also serve as a carbon-free energy carrier for fuel cells.
Future work will investigate the feasibility of using patched surfaces to produce other bimetallic catalysts that can promote other reactions, and Vlachos is optimistic about the potential of this new approach. "What we thought of as a 'defective' catalyst was actually two to three orders of magnitude better than the so-called 'perfect catalyst'," he says. "This finding opens up broad new horizons for materials design."
"Determining that the patched structure offers dual active sites means that we can 'tune' catalysts to various chemistries and metals," he adds. "Also, with just patches of the guest metal, rather than full coverage of the core, we can use less material, which could translate into reduced cost."
This story is adapted from material from the University of Delaware, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.