(638f) An Analysis of Preferred Mechanisms of CO Oxidation in TiO2-Supported Atomically Dispersed Catalysts Using the Energetic Span Model

Atomically dispersed catalysts (ADCs) are novel class of catalysts that have individual atoms anchored to support surfaces. ADCs have been receiving attention due to their ability to tune the activity and selectivity of reactions by controlling the active sites. Therefore, understanding the nature of active site and reaction mechanism are crucial in designing high performance catalysts. The atoms at different positions on the support have distinct electronic and chemical properties, making their study non-trivial. Reactions on these distinct binding sites might proceed via different mechanisms which might explain the discrepancies in the literature regarding the activities of ADCs. The aim of this study is to compare various reaction mechanisms of low-temperature CO oxidation to detect the most preferred route on Pt₁/rutile-TiO₂ (110) surface by using quantitative methods and gain insights about the states that limit the rate at atomic level. We use density functional theory to explore the reaction at room temperature via Eley-Rideal (ER), Tri-molecular Eley-Rideal (TER), Langmuir-Hinshelwood (LH), and Mars-van Krevelen (MvK) mechanisms. We look at the mechanisms with respect to single CO since our dynamics studies indicate that Pt is highly mobile when two CO molecules are simultaneously adsorbed and comes out of the surface at around 500 K. By constructing the free energy profiles of these paths (see Figure 1), we determine the rate limiting states and calculate the turnover frequencies (TOFs) utilizing the energetic span model (see Table 1). We identify the most favorable mechanism for CO oxidation on H1 site as ER. The differences between TOF determining intermediates and transition states cause significant differences in the TOF values, emphasizing the importance of rigorous analysis of TOFs in addition to potential/free energy curves for identifying the preferred mechanisms and rate limiting states.