A team led by Prof. Tao Zhang and Prof. Yanqiang Huang at the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS), working with Prof. Wei Liu of DICP and Prof. Yanggang Wang of the Southern University of Science and Technology, has directly tracked oxygen movement in catalysts. Using environmental transmission electron microscopy, they observed bulk oxygen spillover in Ru/rutile-TiO2 catalysts for the first time. The discovery points to new ways of using the interior of catalysts, which has often been overlooked.
The findings were published in Nature on April 15, 2026.
What Is Oxygen Spillover in Catalysis
In catalytic reactions, spillover refers to the movement of atoms or molecules such as hydrogen or oxygen between a metal and the material that supports it. Most past research has focused on spillover occurring along the surface of catalysts. It has remained uncertain whether the interior, or bulk, of a catalyst also plays a role in these processes through non-surface pathways.
Understanding spillover is important because it influences how different active sites interact. It can change how many of these sites are available and affect how well a catalyst performs. Previous work has shown that materials capable of being reduced can improve spillover on surfaces, depending on how far and how fast atoms move. However, traditional spectroscopic techniques have struggled to reveal the exact pathways involved at the level of individual particles. Gaining a clearer picture could help scientists better control reactions that depend on spillover.
Why Titanium Dioxide Was Chosen
The researchers selected titanium dioxide (TiO2) because it can store and release oxygen efficiently. Its ability to change oxidation states, along with its variety of crystal structures, makes it a useful model for studying oxygen behavior. Using environmental transmission electron microscopy, the team was able to directly observe oxygen movement on individual ruthenium on titanium dioxide (Ru/TiO2) particles.
First Direct Evidence of Bulk Oxygen Spillover
For decades, scientists believed that spillover mainly took place on catalyst surfaces. In this study, the team provided the first direct observation of oxygen moving within the bulk of a catalyst in ruthenium supported on rutile titanium dioxide (Ru/r-TiO2).
“A channel has been disclosed in TiO2 support to facilitate oxygen spillover, meanwhile the metal-support interface acts like an atomic scale guard, controlling whether oxygen spillover can pass through. This finding inspires a new strategy for utilizing catalyst bulk that is conventionally believed useless in catalysis,” said Prof. Wei Liu.
Oxygen Movement Beneath the Surface
The researchers showed that oxygen atoms travel through the (Ru/r-TiO2) interface from layers located three to five atoms below the surface of r-TiO2 to the metal. This movement is driven by differences in oxygen chemical potential.
“This unique oxygen spillover in our work enables the bulk of a catalyst, which is otherwise inaccessible to reactants, to contribute to mass transfer during catalytic reactions, underscoring the critical importance of interface engineering in controlling spillover behavior,” said Prof. Yanqiang Huang.
Expanding the Concept of Metal-Support Interaction
Nearly 50 years ago, scientists identified metal-support interactions, where metal particles become surrounded by oxide materials such as TiO2 under strongly reducing conditions. This process can reduce the ability of the metal to adsorb molecules like H2 and CO. Traditionally, these interactions were thought to involve material exchange only at the outer surfaces of metals and their supports, with the boundary between them playing a key role in reactions.
This new work expands that concept by showing that bulk oxygen spillover allows the inner regions of a catalyst to take part in mass transfer during reactions. These internal interfaces were previously considered inaccessible.
Toward More Efficient Catalyst Design
The findings highlight how important interface engineering is for controlling spillover behavior. They also demonstrate the power of in situ microscopic imaging at the single-particle level for uncovering reaction pathways in catalytic systems.
Looking ahead, the researchers aim to build on this discovery. “Taking this excellent opportunity, we can improve architecture of catalysis from two-dimensional surface reactions to the three dimensional ‘surface-interface-bulk’ synergy. It provides fresh insights into interfacial atomic engineering in heterogeneous catalysis and the dynamic catalytic behavior of supported metal catalyst. The next goal is to develop practical catalysts that utilize the bulk to directly contribute to chemical reactions,” said Prof. Tao Zhang.