Hydrogen spillover is a well-established concept in heterogeneous catalysis, where hydrogen atoms migrate across solid surfaces and interfaces. However, whether a similar process could occur for metal species has long been an open question.
In a recent study published in Nature Communications, a research team led by Prof. FU Qiang from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) has demonstrated a new form of metal spillover that is mediated by water adlayers. The study reveals that metal species can spontaneously migrate across solid interfaces under mild and humid conditions.
Schematic illustration of water-adlayer-mediated metal spillover under mild conditions (Image by FAN Yamei)
The researchers found that when hydrophilic supports such as oxides, carbides, or sulfides are exposed to a humid environment, a thin layer of water forms on the surfaces. This water adlayer acts as a molecular bridge, enabling metal species—exemplified by copper—to migrate between different supports. The metal migration occurs through hydroxylated intermediates (M–OH) and proceeds spontaneously at room temperature, without requiring high-temperature activation commonly used in catalyst preparation.
The researchers further demonstrated that this spillover phenomenon is not limited to copper. Other metals, including ruthenium, cobalt, and nickel, also exhibit similar migration behavior. By tuning the surface hydrophilicity, the density of hydroxyl group, and the degree of interfacial contact, the researchers were able to control metal mobility and distribution. Catalysts synthesized through this spillover route exhibited improved low-temperature activity in reactions, including carbon monoxide oxidation, reverse water–gas shift, ammonia selective catalytic reduction, and hydrogen cyanide oxidation. These catalysts outperformed those prepared using conventional impregnation methods.
Mechanistic analysis indicated that the water adlayers and dissociated hydroxyl groups together form a hydration lubrication layer that lowers the diffusion barrier for metal atom migration. This mechanism is conceptually analogous to hydrogen spillover but represents the first direct extension of spillover to metal species. The findings highlight the active role of interfacial water in facilitating structural rearrangements in catalysts, even under ambient conditions.
"Our study extends the classical spillover concept from small molecules to metal atoms", said Prof. FU. "It also highlights how interfacial water layers and surface hydroxyls dynamically regulate catalyst structures and activities even under ambient conditions."
This work not only provides a fundamental understanding of water-mediated metal migration, but also offers a new strategy for designing dynamic catalysts operable at low temperatures, advancing the development of energy-efficient catalytic systems.