NO adsorption and diffusion on hydroxylated rutile TiO2(110)

Area of Science:

• Surface Science
• Computational Chemistry
• Materials Science

Background:

• Titanium dioxide (TiO2) is a crucial material in catalysis and environmental remediation.
• Understanding gas adsorption and diffusion on TiO2 surfaces is vital for optimizing its applications.
• Nitric oxide (NO) is a key molecule in atmospheric chemistry and industrial processes.

Purpose of the Study:

• To investigate the adsorption and diffusion mechanisms of nitric oxide (NO) on the hydroxylated rutile TiO2(110) surface.
• To elucidate the electronic structure changes upon NO adsorption.
• To propose and validate a novel diffusion pathway for NO on this surface.

Main Methods:

• Density Functional Theory (DFT) calculations.
• Inclusion of on-site Coulomb corrections (DFT+U) for accurate electronic structure.
• Consideration of long-range dispersion interactions.
• Comparison of calculated Scanning Tunneling Microscopy (STM) features with experimental data.

Main Results:

• Nitric oxide (NO) preferentially adsorbs with its nitrogen atom bonded to surface Ti5c sites.
• An excess electron from the hydroxylated surface localizes in the 2π* orbital of the adsorbed NO molecule.
• A new 'roll-over' diffusion mechanism involving multiple Ti5c sites and a hydroxyl group was identified.
• Calculated STM images exhibiting a 'bright-dark-bright' pattern correlate well with experimental observations of diffusing NO.

Conclusions:

• The N-end down adsorption configuration is energetically favorable for NO on hydroxylated rutile TiO2(110).
• The proposed 'roll-over' diffusion mechanism provides a detailed understanding of NO surface mobility.
• Computational results, particularly STM simulations, successfully explain experimental observations, validating the proposed mechanisms.