ZnO is a high-band gap semiconductor material important for microelectronic and catalytic applications, such as water splitting among others. Although the nonpolar face of ZnO has been well-studied, its polar faces (Zn- and O-terminated) are less studied because of intrinsic difficulties to the model. Here, we combine density functional theory calculations and analytical modelling to determine the thermodynamics of the water molecule interaction with perfect ZnO polar model surfaces, (0001) and (0001̅) surfaces (p-Zn and p-O). Defects (oxygen vacancies, pits, and missing oxygen rows) are also investigated. Adsorption, dissociation, surface migration, and agglomeration are considered. We find that H2O preferentially adsorbs and dissociates on Zn atoms on p-Zn and at defects on p-O. At room temperature, water is found to spontaneously dissociate, except for p-O, in which dissociation is endothermic. After dissociation, the resulting protons either bind to surface oxygen atoms or to zinc atoms to form hydrides. Migration of H and OH is limited on p-Zn with moderate barriers and absent on p-O. Interestingly, further agglomeration or islanding of OH species is inhibited by repulsive OH–OH electrostatic forces. Consequently, although polar surfaces are highly reactive with water, they cannot sustain high OH coverages, unless highly defective. This limitation is one obstacle to ZnO catalytic activity, pointing to the need to tune temperature and pressure conditions.

The understanding and quantification of the CO adsorption modes and strength on ultradispersed platinum catalysts supported on γ-Al2O3 is of prominent importance for analytic and catalytic purposes. We report a multiscale experimental (AEIR, CO-TPD) and theoretical approach to provide vibrational properties, adsorption enthalpies, and desorption behaviors. First principles calculations on Pt13(CO) m /γ-Al2O3 and Pt(111) surface models (using various exchange-correlation functionals) provide a complementary view to experimental approches. Adsorption enthalpies computed with the RPBE functional appear to be the most compatible with the AEIR results. The occupation of top sites by CO dominates the behavior of supported Pt clusters. CO coverage reaches higher values in comparison to Pt(111) for similar operating conditions, and considerable cluster reconstruction is observed at high coverage. First principles calculations also confirm the IR assignment related to the various adsorption modes on top and bridge sites and demonstrate a particle size effect, lowering the frequency of linear adsorption at top sites with respect to extended Pt(111) surfaces. Finally, first principles-based microkinetic modeling of CO-TPD experiments shows that the adsorption strengths predicted on the small-size cluster by DFT are compatible with the experimental values. We discuss possible reasons for the experimental desorption pattern to be much broader than the computed pattern.

Statistical mechanics and transition-state theory have been used to investigate the diffusion kinetics of gold and copper atoms on pristine and various reduced surfaces of rutile TiO2 (110). A DFT+U approach has been employed to calculate potential energy maps and to evaluate the required diffusion activation barriers. The role of the support reducibility has been examined on the adsorption properties (optimal structures, energetics, and spin polarization) and diffusion kinetics, especially for the reduced support presenting a single subsurface oxygen vacancy. This approach has allowed us to demonstrate key discrepancies between Au and Cu atoms and to sketch out a comparative scenario for the early-stage nucleation of Au and Cu nanoparticles on the various surface states of TiO2 (110).