CO chemisorption on monodispersed platinum clusters on SiO₂: Detection of CO chemisorption on single platinum atoms

Monodispersed Pt₁, Pt₂, and Pt₃ clusters have been deposited on an atomically clean SiO₂ film in ultrahigh vacuum to surface coverages of about 0.01 monolayer. CO chemisorption/desorption experiments at 300 K exhibit a distinct 340 K CO desorption state with an activation energy of ∼16 kcal/mol. Comparisons with CO desorption from Pt(111), Pt(112), and bulk Pt films on SiO₂ are made, showing that the 340 K CO desorption process is a unique feature of highly dispersed Pt atoms on SiO₂. CO desorption from other Pt sites is also detected exhibiting higher desorption activation energies, but the nature of these sites cannot be ascertained in these experiments with certainty.