Structure, stability, and mobility of small Pd clusters on the stoichiometric and defective TiO$_2$ (110) surfaces

TL;DR

This study investigates how small Pd clusters interact with and behave on TiO2 (110) surfaces, revealing how surface defects influence their stability, electronic properties, and sintering behavior through computational simulations.

Contribution

It provides detailed insights into the structure, electronic effects, and sintering processes of Pd clusters on both perfect and defective TiO2 surfaces using density functional theory and Monte Carlo simulations.

Findings

Pd clusters prefer binding near subsurface Ti-interstitials or on stoichiometric surfaces.

Oxygen vacancies reduce charge localization and ferromagnetic states in Pd-adsorbed surfaces.

Oxygen vacancies promote Pd cluster dissociation, while other defects support cluster stability below 600 K.

Abstract

We report on the structure and adsorption properties of Pd$_n$ ($n=1-4$) clusters supported on the rutile TiO$_2$ (110) surfaces with the possible presence of a surface oxygen vacancy or a subsurface Ti-interstitial atom. As predicted by the density functional theory, small Pd clusters prefer to bind to the stoichiometric titania surface or at sites near subsurface Ti-interstitial atoms. The adsorption of Pd clusters changes the electronic structure of the underlying surface. For the surface with an oxygen vacancy, the charge localization and ferromagnetic spin states are found to be largely attenuated owing to the adsorption of Pd clusters. The potential energy surfaces of the Pd monomer on different types of surfaces are also reported. The process of sintering is then simulated via the Metropolis Monte Carlo method. The presence of oxygen vacancy likely leads to the dissociation of Pd clusters. On the stoichiometric surface or surface with Ti-interstitial atom, the Pd monomers tend to sinter into larger clusters, whereas the Pd dimer, trimer and tetramer appear to be relatively stable below 600 K. This result agrees with the standard sintering model of transition metal clusters and experimental observations.