CO Oxidation with Atomically Dispersed Catalysts: Insights from the Energetic Span Model

Using density functional theory and
the energetic span model (ESM),
this work examines the activity of a single hollow site (H1) of atomically
dispersed Pt on rutile TiO2 (110) toward low-temperature
CO oxidation by enumerating all possible pathways and calculating
the turnover frequencies (TOFs). Of the 12 distinct pathways spanning
the Eley–Rideal (ER) mechanism, termolecular ER (TER) mechanism,
Langmuir–Hinshelwood (LH) mechanism, Mars–van Krevelen
(MvK) mechanism, and their combinations, the TER mechanism with CO-assisted
CO2 desorption yields the highest TOF. However, this pathway
is ruled out because Pt is unstable under the reaction conditions
in an intermediate state when bound to two CO molecules, determined
in a prior ab initio molecular dynamics study by our group. Combined
with the fact that other pathways initiated with CO adsorption (including
the MvK mechanism) exhibit negligibly low TOFs, we conclude that H1
exhibits little activity toward CO oxidation. By employing the ESM
to calculate the TOFs for pathways proposed in prior mechanistic studies
of several oxide-supported atomically dispersed catalysts, we identify
the most active metal–support combinations for low-temperature
CO oxidation.