CO Oxidation on Au/TiO2: Condition-Dependent Active Sites and Mechanistic Pathways

Area of Science:

• Heterogeneous catalysis
• Surface science
• Computational chemistry

Background:

• CO oxidation over gold (Au) nanocatalysts supported on titanium dioxide (TiO2) is a critical reaction in environmental catalysis.
• Understanding the reaction mechanism is essential for designing efficient catalysts.

Purpose of the Study:

• To elucidate the CO oxidation mechanism on TiO2-supported Au nanocatalysts using advanced computational methods.
• To investigate the influence of temperature and oxygen partial pressure on catalytic activity and active sites.

Main Methods:

• Ab initio electronic structure calculations
• Ab initio molecular dynamics simulations (AIMD)
• Coverage-dependent microkinetic modeling based on density functional theory (DFT) energetics

Main Results:

• The dominant kinetic pathway, active oxygen species, and catalytic sites are strongly dependent on temperature and oxygen partial pressure.
• At T < 400 K, a dynamic single-atom mechanism involving Au-CO migration and Mars-van-Krevelen pathway is prevalent.
• At 300 ≤ T ≤ 600 K, synergistic catalysis occurs between single Oad-Au(+)-CO sites and Au nanoparticle perimeter sites.
• Above 600 K, multiple pathways involving both single-atom and perimeter sites become active.
• Low oxygen pressures can lead to catalyst deactivation via Oad-Au(+)-CO species, favoring perimeter site pathways.

Conclusions:

• The study resolves inconsistencies in previous mechanistic interpretations by providing a comprehensive model.
• Catalyst performance and mechanism are highly tunable by controlling reaction conditions (temperature and pressure).
• The findings offer crucial insights for the rational design of Au/TiO2 catalysts for CO oxidation.