Heterogeneous catalysts underlie much of the modern chemical industry, and without such catalysts, many products that are used in daily life, from plastics to fuels, would be impossible to produce.  Most heterogeneous catalysts consist of active metal nanoparticles immobilized on an inexpensive oxide support.  Often, the oxide support is inert, and the metal nanoparticle completely controls the catalysis.  However, in certain situations, a phenomenon known as the Strong-Metal Support Interaction (SMSI) may occur, in which the oxide is chemically transformed and either partially or fully covers the active metal.  The SMSI often involves the formation of ultrathin (2-3 atomic layers thick) oxide films on the metal nanoparticles, and it can cause profound changes to the properties of the catalyst.  However, it is very challenging to control or suppress the SMSI since the chemical transformations that take place, the molecular features of the resulting ultrathin films, and the particular catalysts on which SMSI is likely to occur, are poorly understood. 

The fundamental lack of knowledge described above has motivated the present study.  To understand how, and under what circumstances, the SMSI occurs, our research team has combined molecular modeling through electronic structure calculations, ultrahigh resolution measurements of catalyst surface structures in clean environments, and practical measurements of catalytic properties under industrially-relevant conditions.  The calculations and experimental measurements have been deeply integrated to produce a detailed picture of the molecular transformations that occur when the oxide support interacts with the catalytic metal nanoparticles through the SMSI.  Three key results, as well as multiple publications in the scientific literature, have resulted from these investigations.  First, we have discovered that hydrogen, which is present in many heterogeneous catalytic reaction environments, can have a profound effect on the structure of ultrathin oxide films that are formed during the SMSI.  Second, we have developed of a simple set of physical/chemical principles that, when combined with electronic structure calculations, can estimate the particular reaction conditions (temperature, pressure) and catalyst materials that are likely to experience SMSI.  Finally, our team has found that the understanding of oxide/hydroxide structures developed during the project can be used to understand the properties of similar structures on electrocatalysts, which are central to the operation of low temperature fuel cells.  In particular, we have learned how ultrathin oxide/hydroxide films can tune the properties of the electrocatalysts, leading to more efficient fuel cell operation.

The fundamental knowledge that has emerged from this project helps to clarify longstanding questions about the nature of the SMSI.  Further, the work has facilitated the identification of conditions under which the SMSI is likely to occur, and it has identified ways in which the SMSI, and similar phenomena, may be controlled to promote more efficient heterogeneous catalysts for chemical and renewable applications. 

Last Modified: 01/21/2024
Modified by: Jeffrey Greeley