Origin of Thermal and Hyperthermal CO 2 from CO Oxidation on Pt Surfaces: The Role of Post‐Transition‐State Dynamics, Active Sites, and Chemisorbed CO 2

Abstract

Abstract The post‐transition‐state dynamics in CO oxidation on Pt surfaces are investigated using DFT‐based ab initio molecular dynamics simulations. While the initial CO 2 formed on a terrace site on Pt(111) desorbs directly, it is temporarily trapped in a chemisorption well on a Pt(332) step site. These two reaction channels thus produce CO 2 with hyperthermal and thermal velocities with drastically different angular distributions, in agreement with recent experiments ( Nature , 2018 , 558 , 280–283). The chemisorbed CO 2 is formed by electron transfer from the metal to the adsorbate, resulting in a bent geometry. While chemisorbed CO 2 on Pt(111) is unstable, it is stable by 0.2 eV on a Pt(332) step site. This helps explain why newly formed CO 2 produced at step sites desorbs with far lower translational energies than those formed at terraces. This work shows that steps and other defects could be potentially important in finding optimal conditions for the chemical activation and dissociation of CO 2 .