Unraveling Nanoarchitectonics‐Driven Metal–Support Interactions and Size Effects Governing CO Oxidation Activity of Size‐Selected Pt Clusters on TiO ₂ and SnO ₂ Supports

Supported size‐selected clusters represent a unique class of materials offering high tunability of the chemical properties with high efficiency of material utilization. Herein, Pt n ( n = 13, 40) clusters supported on two technologically relevant supports, TiO 2 and SnO 2 , were studied for CO oxidation under atmospheric pressure conditions. The catalytic activity was found to be directly influenced by both cluster size and support material, with Pt 40 /TiO 2 showing the highest activity. In situ near‐ambient‐pressure X‐ray photoelectron spectroscopy (NAP‐XPS) revealed that, in general, a higher metallicity of the clusters promotes catalytic activity. However, the final oxidation state of Pt does not solely determine the activity, which rather evolves from a combination of factors, including strong metal–support interactions (SMSI) and size‐dependent effects. Ex situ XPS and ion scattering spectroscopy (ISS) measurements on used catalysts highlighted the role of SMSI, particularly in the case of SnO 2 , where SnO 2 overgrowth was suggested to enhance chemical stability and sintering resistance, as witnessed by stability tests conducted using NAP‐XPS. However, this overgrowth also limited access to active Pt sites, reducing CO adsorption and O 2 activation, ultimately leading to lower catalytic activity of Pt n /SnO 2 compared to TiO 2 ‐supported catalysts.