Adsorbate-Induced Structural Changes in 1–3\nnm Platinum Nanoparticles

Abstract

We investigated changes in the Pt–Pt\nbond distance, particle\nsize, crystallinity, and coordination of Pt nanoparticles as a function\nof particle size (1–3 nm) and adsorbate (H₂, CO)\nusing synchrotron radiation pair distribution function (PDF) and X-ray\nabsorption spectroscopy (XAS) measurements. The ∼1 nm Pt nanoparticles\nshowed a Pt–Pt bond distance contraction of ∼1.4%. The\nadsorption of H₂ and CO at room temperature relaxed the\nPt–Pt bond distance contraction to a value close to that of\nbulk fcc Pt. The adsorption of H₂ improved the crystallinity\nof the small Pt nanoparticles. However, CO adsorption generated a\nmore disordered fcc structure for the 1–3 nm Pt nanoparticles\ncompared to the H₂ adsorption Pt nanoparticles. <i>In situ</i> XANES measurements revealed that this disorder results\nfrom the electron back-donation of the Pt nanoparticles to CO, leading\nto a higher degree of rehybridization of the metal orbitals in the\nPt-adsorbate system.