Researchers capture images of interface-controlled bulk oxygen spillover for the first time

Recently, a research team led by Prof. ZHANG Tao, Prof. HUANG Yanqiang from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS), in collaboration with Prof. LIU Wei from DICP and Prof. WANG Yanggang from the Southern University of Science and Technology, has tracked the oxygen spillover in catalysts using environmental transmission electron microscopy and observed for the first time bulk oxygen spillover in Ru/rutile-TiO₂ catalysts. Their findings provide new approaches for using the catalyst bulk.

This study was published in Nature on April 15, 2026.

In catalytic reactions, spillover describes the migration of a species, such as hydrogen or oxygen, between an active metal and its support. Scientists have extensively investigated spillover that is confined on the catalyst surface. Yet it remains unclear whether bulk catalyst, where the entire material is the active substance, is part of these reactions through non-surface spillover.

Scientists urgently need a better understanding of the spillover process. Spillover affects interactions between different active sites. It tunes their abundance and regulates catalytic performance. Earlier studies have shown that a reducible support promotes spillover efficiency at the surface, depending on distance and velocity. However, spectroscopic methods provide little information about the microscopic spillover pathway at the single-particle level. A fuller understanding of the spillover process would allow scientists to better manipulate spillover-involving reactions.

The research team used titanium dioxide (TiO₂) in their study because its reducibility ensures its capacity to store and release oxygen. This property, along with its crystal structure diversity makes TiO₂ an ideal model and a practical support material to use for microscopic study of oxygen spillover mechanisms. The team visualized the complete oxygen spillover process directly on single ruthenium on titanium dioxide (Ru/TiO₂) particles using environmental transmission electron microscopy.

For a long time, scientists believed the spillover effect in catalytic reactions occurred on the catalyst surface. The research team, using environmental transmission electron microscopy, has for the first time observed bulk oxygen spillover in ruthenium metal on the rutile crystal form of 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. LIU Wei.

In contrast to scientists' conventional understanding of spillover proceeding primarily on the exposed surface, the team demonstrated that oxygen species are transported at the (Ru/r-TiO₂) interface from within three to five atom-layers below the r-TiO₂ surface to the metal. This process is driven by the 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. HUANG Yanqiang.

It has been nearly 50 years since scientists discovered the metal-support interaction, where metal particles are encapsulated by reducible oxide supports such as TiO₂ under strongly reductive conditions, leading to the loss of H₂ and CO adsorption capacity. Traditional metal-support interaction involves mass transport between external surfaces of metals and supporting oxides. Scientists believe that the peripheral interface between them facilitates catalytic reactions.

This research team has further extended the metal-support interaction concept by demonstratingthat unique bulk oxygen spillover enables the interior interface of a catalyst and contributes to mass transfer during catalytic reactions. This interior interface is otherwise inaccessible to reactants.

Their work underscores the critical importance of interface engineering in controlling spillover behavior and highlights the vast potential of in situ microscopic single-particle imaging in explaining the reaction pathways in catalytic conversions.

Looking ahead, the team plans to expand their work. "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. ZHANG Tao.