NH₃ adsorption on anatase-TiO₂(101).

Area of Science:

• Surface Science
• Materials Chemistry
• Catalysis

Background:

• Ammonia adsorption on anatase titanium dioxide (TiO₂) is crucial for TiO₂ catalytic applications.
• Understanding acid-base interactions on TiO₂ surfaces is essential for catalysis.

Purpose of the Study:

• To identify the adsorption mode of ammonia on the anatase TiO₂(101) surface.
• To quantify the adsorption strength and interactions at various coverages.

Main Methods:

• High-resolution scanning tunneling microscopy (STM).
• Synchrotron X-ray photoelectron spectroscopy (XPS).
• Temperature-programmed desorption (TPD).
• Density functional theory (DFT) calculations.

Main Results:

• Ammonia (NH₃) adsorbs non-dissociatively on five-fold coordinated titanium sites (5f-Ti).
• Isolated ammonia exhibits an exothermic adsorption energy of 1.2 eV.
• Repulsive intermolecular interactions reduce adsorption energy at higher coverages, quantified by DFT and STM.

Conclusions:

• Ammonia adsorption on anatase TiO₂(101) is primarily governed by 5f-Ti sites.
• Adsorbate-adsorbate repulsion significantly impacts binding energy, especially at monolayer coverage.
• Findings align with experimental TPD data, validating the adsorption model.