Physically confined spaces can make for more efficient chemical reactions, according to recent studies led by scientists from the U.S. Department of Energy's (DOE) Brookhaven National Laboratory. They found that partially covering metal surfaces acting as catalysts, or materials that speed up reactions, with thin films of silica can impact the energies and rates of these reactions. The thin silica forms a two-dimensional (2-D) array of hexagonal-prism-shaped "cages" containing silicon and oxygen atoms.Get more news about Oxide Deoxidizing Catalyst,you can vist our website!
"These porous silica frameworks are the thickness of only three atoms," explained Samuel Tenney, a chemist in the Interface Science and Catalysis Group of Brookhaven Lab's Center for Functional Nanomaterials (CFN). "If the pores were too tall, certain branches of molecules wouldn't be able to reach the interface. There's a particular geometry in which molecules can come in and bind, sort of like the way an enzyme and a substrate lock together. Molecules with the appropriate size can slip through the pores and interact with the catalytically active metal surface."
"The bilayer silica is not actually anchored to the metal surface," added Calley Eads, a research associate in the same group. "There are weak forces in between. This weak interaction allows molecules not only to penetrate the pores but also to explore the catalytic surface and find the most reactive sites and optimized reaction geometry by moving horizontally in the confined space in between the bilayer and metal. If it was anchored, the bilayer would only have one pore site for each molecule to interact with the metal."
The scientists are discovering that the confined spaces modify different types of reactions, and they are working to understand why.
Tenney and Eads are co-corresponding authors on recently published research in Angewandte Chemie, demonstrating this confinement effect for an industrially important reaction: carbon monoxide oxidation. Carbon monoxide is a toxic component of engine exhaust from vehicles and thus must be removed. With the help of an appropriate precious metal catalyst such as palladium, platinum, or rhodium, catalytic converters in vehicles combine carbon monoxide with oxygen to form carbon dioxide.
Tenney, Eads, and colleagues at the CFN and Brookhaven's National Synchrotron Light Source II (NSLS-II) showed that covering palladium with silica boosts the amount of carbon dioxide produced by 20 percent, as compared to the reaction on bare palladium.
To achieve this performance enhancement, the scientists first had to get a full bilayer structure across the palladium surface. To do so, they heated a calibrated amount of silicon to sublimation temperatures in a high-pressure oxygen environment. In sublimation, a solid directly transforms into a gas. As the thin film of silica was being created, they probed its structure with low-energy electron diffraction. In this technique, electrons striking a material diffract in a pattern characteristic of the material's crystalline structure.
