Smsi

Strong metal–support interaction (SMSI) is a phenomenon in heterogeneous catalysis where high-temperature reduction of metal nanoparticles supported on reducible oxide supports induces a partial covering of the metal by a thin overlayer of reduced oxide that originates from the support. This encapsulation alters the availability and electronic properties of surface metal sites, often suppressing adsorption of probe molecules such as CO while leaving the oxide support's activity for other steps intact. The concept was introduced in 1978 by Tauster and co-workers in studies of platinum on titanium dioxide.

SMSI has been observed for several metal–support pairs, particularly noble metals (Pt, Rh, Pd, Ru) on reducible oxides (TiO2, CeO2, Fe3O4, ZnO, SnO2). The effect typically requires exposure to high-temperature reduction in hydrogen or forming gas, leading to migration of reduced oxide species over the metal particles. The resulting overlayer can be partially or fully covering the metal, depending on conditions, particle size, and support composition.

Re-oxidation or high-temperature treatment can often remove the overlayer, restoring original catalytic properties.

In practice, SMSI changes adsorption properties, reaction pathways, and selectivity. It is exploited to tailor catalyst behavior, for instance by stabilizing metal particles or by modulating unintended strong adsorption. However, SMSI is not universal; it depends on specific metal–support pairs and operating conditions, and its presence can complicate catalyst design and interpretation of catalytic data. Measurement methods include CO chemisorption, TEM to visualize encapsulation, XPS, and in situ spectroscopy.