Chemical Bonds Affected by Atoms Several Nanometers Away... New Principle for Catalyst Design Discovered [Reading Science]

Joint IBS-Max Planck research team in Germany precisely measures molecular bond strength on platinum surfaces
Finds differences of up to 0.2 electron volts and proposes a new model to explain long-range electronic interactions

It has been found that the strength of a bond between a molecule attached to a metal surface and the metal varies depending on the atomic structure several nanometers (nm, one-billionth of a meter) away. Chemical bonds have generally been explained by interactions with nearby atoms that directly contact the molecule, but the findings show that electronic properties across a much wider area can also have an effect. The discovery is expected to offer new clues for understanding how metal catalysts work and predicting their performance.

The Ministry of Science and ICT announced on October 30 that a joint research team from the Center for Quantum Nanoscience at the Institute for Basic Science (IBS) and Germany's Max Planck Institute for Multidisciplinary Sciences had established that atomic structures far from a metal catalyst's surface affect the strength of the bond between a molecule and the metal. The findings were published that day in the international journal Science.

A schematic illustrating how the electronic response spreads across the surface beyond the binding site when a molecule bonds to a metal surface. It shows how the metal's electron sea responds to the molecule, allowing the effects of the bond to extend across a wide area. Provided by the researchers.

Metal catalysts help speed up chemical reactions and are used in various industries, including the production of ammonia, a raw material for fertilizer. Catalytic reactions begin when molecules attach to a metal surface, and the strength of the bond determines how readily subsequent chemical reactions proceed.

Until now, bonds between molecules and metals have generally been explained by interactions with atoms in direct contact. Although the effects of more distant atomic structures were known, they were thought to be insufficient to alter the strength of an actual chemical bond.

Changing the Distance Between Atomic Steps Alters Bond Strength

The research team tested this conventional understanding using platinum surfaces with atoms arranged in a staircase pattern. After preparing platinum surfaces with different distances between their atomic steps, the team compared the strength of bonds formed between the metal and molecules of ammonia (NH3), carbon monoxide (CO), and nitric oxide (NO).

The results showed that even when the atomic structure at the point where a molecule attaches was similar, bond strength varied depending on the distance to neighboring steps. The difference in bond energy reached about 0.2 electron volts (eV), while the characteristic distance over which long-range effects appeared was about 4-7 nm, depending on the type of molecule. This is roughly the distance occupied by several dozen atoms lined up side by side.

The research team explained that this phenomenon results from interactions among electrons that are widely distributed within the metal. When a molecule attaches to a metal surface, its electrons interact with electrons inside the metal, making the molecule susceptible to the effects of distant atomic structures as well.

To explain why long-range effects vary from one molecule to another, the research team also proposed the "Frontier Orbital-Band Model." The model combines the chemical concept of "molecular orbitals," which describes the electronic states of molecules, with the physics concept of "electronic bands," which describes the energy states of electrons inside metals.

Dmitry Borodin, group leader at the IBS Center for Quantum Nanoscience. Provided by the Ministry of Science and ICT.

Florian Nitz, a researcher at the Max Planck Institute for Multidisciplinary Sciences, said, "To properly understand surface chemistry, we need to integrate chemistry's molecule-centered perspective with physics' approach to the electronic properties of metals. This achievement was made possible by combining the Max Planck researchers' precision measurement techniques for metal surfaces with the IBS researchers' solid-state physics analysis."

The significance of this research lies not in directly improving catalyst performance, but in establishing fundamental principles that can more accurately explain chemical bonding on catalyst surfaces. The findings may be used to develop computational models that take into account both the atomic structures and electronic properties of catalysts.

Dmitry Borodin, group leader at the IBS Center for Quantum Nanoscience, said, "Catalyst development has long relied on extensive experimentation and trial and error, but the field is now moving toward predicting and designing desired properties based on the principles of chemical reactions. We expect this research to broaden our understanding of chemical bonds and contribute to more precise calculations and more efficient catalyst design."

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