Analysis of Preferred Mechanisms of CO Oxidation with Atomically Dispersed Pt1/TiO2 Using the Energetic Span Model

Abstract

This work examines mechanisms of low-temperature CO oxidation over a single binding site of atomically dispersed Pt on rutile TiO2 (110) using density functional theory and the energetic span model (ESM). Of the 12 distinct pathways spanning Eley- Rideal (ER), termolecular ER (TER), Langmuir-Hinshelwood (LH), Mars-Van Krevelen (MvK) mechanisms as well as their combinations, TER with CO-assisted CO2 desorption yields the highest turnover frequency (TOF). However, this pathway is ruled out because Pt is dynamically unstable in an intermediate state in the TER cycle, determined in a prior ab initio molecular dynamics study by our group. We instead find, depending on reaction conditions, that either H1 is rendered inactive upon CO adsorption or the ER mechanism is preferred if O2 dissociatively adsorbs. ER exhibits the second highest TOF and the TOF-determining state is in qualitative agreement with experiment. TOFs for all MvK pathways are several orders of magnitude lower than ER and LH. By comparing TOFs for Pt1/TiO2 with prior mechanistic studies of various oxide-supported atomically dispersed catalysts in the literature, we identify the most active metal and support materials for low-temperature CO oxidation.