(230e) Mechanistic Insights into CO Oxidation over Pt1/TiO2: Site-Sensitivity and Dynamic Character of Single Atoms

Atomically dispersed catalysts (ADCs) are an emerging class of heterogeneous catalysts by the virtue of their high selectivity and per-atom activity. Atomic metals bind to different sites on the surface which exhibit unique electronic and chemical properties. These sites co-exist on the surface of an ADC¹, and the single atoms adapt their local coordination based on reaction conditions.² Due to the site-distribution and dynamic nature of ADCs, their theoretical study is challenging yet essential to uncover how reactions proceed. We aim to piece together these phenomena associated with ADCs by combining density functional theory, energetic span model, and ab initio molecular dynamics. We study low-temperature CO oxidation mechanisms and kinetics over Pt₁/rutile-TiO₂ (110) catalyst. Starting with the strongest binding site on the stoichiometric surface, a rigorous analysis is done to identify preferable reaction pathways. We show that it is necessary to combine static, kinetic, and dynamic models to identify the reaction mechanisms, as the static method alone is not sufficient to assess the stability of some intermediates.Then, we expand our study to additional sites with distinct properties. We observe that the impact of binding sites on reaction kinetics is significant. The activity noticeably improves when the Pt atom is located at an anionic vacancy site. Finally, to grasp a broader view, we remove the constraint on the binding site during the reaction cycle and incorporate the dynamic behavior of the ADCs into our mechanistic studies. The Pt atom can adjust its local coordination during the reaction to ease the CO₂ desorption process, which is usually associated with the rate-limiting step.

1. Chang et al., Nano Letters 2014, 14, 134-138.

2. Tang et al., Nature Communications 2019, 10, 1-10.