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In order to investigate the microscopical aspects of the SMSI state in catalysts we performed photoemission experiments on samples consisting of submonolayer Pt deposits on a Ti(0001) surface and on a TiO2 thin film. Annealing Pt/TiO2 samples at ∼500 °C caused a change in the electronic structure of Pt atoms which was reflected in a narrowing of the Pt 4f7/2 XPS line. The width of this line became smaller than the corresponding one for a bulk Pt sample. This was interpreted as the result of an electron transfer between Pt and Ti atoms that we designed for brevity as alloying. CO adsorption on alloyed Pt–Ti exhibited in Pt/TiO2 samples an unusual C1s binding energy of 291.3 eV. The uptake of CO per Pt atom in Pt/TiO2 samples was reduced, by a factor of 2 when CO was adsorbed on surfaces previously annealed at 500 °C which is the temperature for the SMSI state in Pt/TiO2 catalysts. [ABSTRACT FROM AUTHOR]

Atomic steps at the surface of a catalyst play an important role in heterogeneous catalysis, for example as special sites with increased catalytic activity. Exposure to reactants can cause entirely new structures to form at the catalyst surface, and these may dramatically influence the reaction by ‘poisoning’ it or by acting as the catalytically active phase. For example, thin metal oxide films have been identified as highly active structures that form spontaneously on metal surfaces during the catalytic oxidation of carbon monoxide. Here, we present operando X-ray diffraction experiments on a palladium surface during this reaction. They reveal that a high density of steps strongly alters the stability of the thin, catalytically active palladium oxide film. We show that stabilization of the metal, caused by the steps and consequent destabilization of the oxide, is at the heart of the well-known reaction rate oscillations exhibited during CO oxidation at atmospheric pressure. [ABSTRACT FROM AUTHOR]