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Through density functional theory (DFT) calculations, we show that, in contrast to terrace sites of Pt(211) and Pt(111), on steplike sites of Pt(211) and Pt(110)-(2 × 1), methylene is more stable than methyl. The resulting site-dependent product selectivity for methane dissociation allows us to conciliate between theory and recent reflection absorption infrared spectroscopy (RAIRS) experiments, which might open a door to new applications of vicinal surfaces of Pt in heterogeneous catalysis and as templates for nanoscale patterning of self-assembled monolayers.

Adsorption dynamics of N2on the W(100) surface is studied by means of quasi-classical trajectories making use of a six-dimensional potential energy surface obtained from density functional theory calculations. In our simulations, van der Waals (vdW) interactions are accounted for by using the vdW-DF2 functional. In view of the comparison with experiments, we show that this leads to a good description of the adsorption dynamics, providing a significant improvement with respect to semi-local exchange–correlation functionals used in the past. Particular emphasis is placed on the description of nonactivated pathways, leading to either dissociation or molecular adsorption. Dynamics calculations are performed within the generalized Langevin oscillator (GLO) model in order to simulate the energy exchange between molecule and surface atoms. Electron–hole (e–h) pair excitations are also implemented in the dynamics via the local density friction approximation (LDFA). Overall adsorption probability, including dissociative and nondissociative mechanisms, is enhanced when molecules can lose energy through surface phonons and electronic excitations. However, the energy exchange with phonons has a larger influence in the adsorption probability than e–h pair excitations. Nondissociative molecular adsorption only takes place when such energy dissipation channels are included in the simulations, underlying the importance of GLO and LDFA models in such theoretical studies.

The reaction of diatomic molecules on bimetallic surfaces, formed by one to few monolayers of a metal adsorbed on a different metal substrate, is relevant to understand the role of surface strain and substrate chemical binding in catalysis, which is interesting for industrial applications, challenges existing state-of-the-art theoretical methods, due to the additional complexity associated with having a molecule with triplet spin multiplicity. Here, we have studied the interaction of O2with CuxML/Ru(0001) (xbeing the number of Cu monolayers), for which experimental data are available, by means of multidimensional classical dynamics simulations based on first-principles potential energy surfaces. Our results show, on the one hand, that the inclusion of the surface temperature on the simulations is essential to reproduce the experimental observations, and therefore, to analyze the physical mechanisms behind these observations, and, on the other hand, that electronic effects due to the binding between the two metallic species are only relevant for one Cu monolayer, whereas strain is responsible for the observed reactivity in O2interacting with Cu(x≥2)ML/Ru(0001).

We present a theoretical study of the dissociative adsorption of molecular hydrogen on PtRu bimetallic surfaces based on density functional theory (DFT) calculations. We focus on the reactivity of a pseudomorphic Pt monolayer deposited on Ru(0001), Pt1ML/Ru(0001), for which we have obtained a minimum activation energy barrier for H2dissociation, Eb= 0.32 eV, i.e., ∼0.3 and 0.26 eV higher than on Ru(0001) and Pt(111), respectively. Accordingly, the initial sticking probability for low energy impinging molecules (Ei≲ 0.1 eV) derived from classical trajectory calculations is various orders of magnitude smaller than on Ru(0001) in apparent contradiction with available experimental data. However, undercoordinated Pt atoms in the borders of Pt pseudomorphic islands and isolated Ru atoms or small Ru aggregates in a Pt-rich two-dimensional PtxRu1–xsurface alloy provide active sites allowing nonactivated H2dissociative adsorption. These two possible defects in a full pseudomorphic Pt monolayer deposited on Ru(0001) might be responsible for the relatively high initial sticking probabilities obtained experimentally for ∼1.0–1.2 ML of Pt evaporated over Ru(0001), only ∼30–65% smaller than on Ru(0001).

Formation of formate species on oxide surfaces plays a role in reactions for hydrogen production such as the water–gas shift and the steam-reforming of alcohols. It has been suggested that bridge formates are the most common and stable configuration on metal oxides. Ceria-based catalysts are important for these reactions where ceria is a “non-innocent” support. In this work, the nature of the formate species that are formed during decomposition and reaction of methanol on ceria surfaces have been studied using a combination of infrared temperature-programmed surface reaction (TPSR-IR) on a real powder catalyst support and density functional theory (DFT) together with statistical thermodynamics for model CeO2(111) surfaces. The influence of surface oxygen vacancies, hydroxyl groups, and water has been considered. Three different formate species have been identified (450–550 K). Initially, formates are adsorbed on the oxidized surface that is gradually hydroxylated by the release of hydrogen from methoxy groups (>500 K), which leads to a partially reduced surface. On the former, one kind of species is observed, whereas on the latter, the other two kinds appeared. We provide computational evidence that the bonding is only initially of the bridge type but becomes of the monodentate type as the surface concentration of hydroxyl groups rises. The calculated frequencies of the O–C–O symmetric and asymmetric stretching modes for the three structures are in good agreement with those experimentally observed. The existence of monodentate species is discussed in terms of a stabilizing effect of hydrogen bonds. The combined experimental and theoretical results on real and model systems, respectively, thus provide important insights on the reaction of methanol on ceria surfaces.

Normal incidence scattering of hydrogen atoms off a H-covered tungsten W(110) surface is simulated via quasiclassical trajectories. A density functional theory (DFT) based multiadsorbate potential is developed to model a wide range of surface coverages, θ = 0.25–1 monolayer (ML), reproducing the surface arrangements observed at low temperature. The competition between hot-atom (HA) and Eley–Rideal (ER) abstraction mechanisms is studied for collision energies of the projectile atom in the range Ep= 0.1–5.0 eV (Ep= 0.1–2.0 eV) for θ = 0.25 ML (θ = 0.5, 0.75, and 1 ML) coverage. Cross sections, final energies of the recombination products, and reaction times are analyzed. At low coverage and low collision energy, HA dominates the abstraction, whereas HA and ER cross-sections become similar when collision energy increases. The vibrational distribution of recombined H2molecules at finite coverage is found to be in better agreement with experiments than the one computed within the single adsorbate limit. At high surface coverage, ER dominates abstraction but the dynamical observables highlight the similarity between both reaction mechanisms, thus suggesting that abstraction may be considered as a unique process.

Through a systematic analysis based on DFT calculations, we have studied the adsorption of S atoms on Au(111) at low and intermediate coverages (θ ≤ 1/3). Our calculations predict ground state structures characterized by two periodicities: (5 × 5) and (√3 × √3)R30°. In line with experiments, the (5 × 5) periodicity seems to dominate in a much larger coverage range than the (√3 × √3)R30° one, which should be only observable in a narrow coverage window close to 1/3. In addition, our results unambiguously reveal the crucial role of S-induced substrate relaxation. Using a first-principles parametrized lattice-gas Hamiltonian approach, we determine lateral interactions between S atoms which allow us to provide a sound explanation for the relative stability of ground state structures.

We have constructed first principle based six-dimensional (6D) potential energy surfaces (PESs) describing the interaction of H2with Cu(111) obtained by interpolation of a set of density functional theory (DFT) total energy data. The DFT calculations have been performed within the generalized gradient approximation (GGA) framework. In applying the GGA we have tested the two exchange−correlation (XC) functionals most popular in surface science, i.e., the PW91 and RPBE functionals. The interpolation of the PW91 PES has been performed using two different methods, the corrugation reducing procedure (CRP), which has been proven to be one of the most successful interpolation methods to build 6D PESs, and the modified Shepard (MS) interpolation method, a very promising method to build high dimensional (nD) PESs, which is computationally cheaper than the CRP. We show that, in spite of the difference between the CRP-PES and the MS-PES and the inaccuracies found in the latter, quantum and classical reaction and scattering probabilities obtained for both PESs are very similar. We also show that PW91 predicts higher reactivity than RPBE, due to the presence of lower energy dissociation barriers in the PW91-PES. The differences between the PW91-PES and the RPBE-PES are also reflected in the vibrational excitation and rotational excitation probabilities, and the diffraction patterns.

In this work, we revisit the dissociative sticking of methane on Pt(110)-(2×1) using quasi-classical trajectory (QCT) calculations and supersonic molecular beam (SMB) experiments. Experimentally, we apply the King and Wells method and the reflection absorption infrared spectroscopy (RAIRS) technique to measure the initial dissociative sticking probability, S0. Our QCT calculations make use of a reactive force field (RFF) based on density functional theory (DFT) total energy results. We compare our QCT results for S0with experiments and with density functional molecular dynamics (DFMD) data available for CHD3(v= 0). The fact that our QCT RFF-based approach is computationally much cheaper than DFMD allows us to integrate a much larger number of trajectories for longer interaction times. Thus, we can significantly extend the previously reported comparison of QCT-DFMD and experimental results, for CHD3(v= 0), CH4(v= 0), and CH4(ν3= 1) to lower incident energies, Ei(≥ 0.2 eV), and surface temperatures, Ts(down to 120 K). Our QCT results and the SMB experimental data agree qualitatively with theory, underestimating the experimental results by a factor of ∼2–3. Our calculations shed light on the fate of the surprisingly large fraction of methane molecules, which remain trapped on the surface for much more than 1 ps (and therefore can hardly be studied using DFMD) for Eivalues as large as ∼1 eV. We show that the contribution of trapped molecules to S0is negligible over a wide range of initial conditions, due to two reasons: (i) the barrier for dissociation is larger than that for desorption on all surface sites and (ii) trapped molecules spend most of the time on top of the valley Pt atoms, where the physisorption well is the deepest but the energy barrier for dissociation is the highest.