Silvia González

Critical size for O(2) dissociation by au nanoparticles.

Density functional theory calculations predict that the presence of low-coordination Au atoms is not enough to dissociate O(2), that there is a common pathway for O(2) dissociation on Au nanoparticles and that there is critical size for Au nanoparticles to dissociate O(2) (see figure).Density functional theory calculations carried out for a series of Au nanoparticles as well as for extended systems containing low-coordinated sites show that the presence of low-coordinate Au atoms is not enough to dissociate O(2). Strong adsorption of molecular oxygen on Au nanoparticles is a necessary but not sufficient condition for O(2) dissociation, there is a common pathway for O(2) dissociation on these nanoparticles and there is critical size for Au nanoparticles to dissociate O(2).

On the activation of molecular hydrogen by gold: a theoretical approximation to the nature of potential active sites

The study of adsorption and dissociation of molecular hydrogen on single crystal Au(111) and Au(001) surfaces, monoatomic rows in an extended line defect and different Au nanoparticles by means of DF calculations allows us to firmly conclude that the necessary and sufficient condition for H2 dissociation is the existence of low coordinated Au atoms, regardless if they are in nanoparticles or at extended line defects.

Theoretical study of the chemisorption of CO on bimetallic RhCu surfaces and nanoparticles

Abstract The CO interaction with bimetallic RhCu surface models representing several compositions has been studied by first principles density functional theory calculations. The analysis of the bare bimetallic clusters Rh(4s) and Cu(3s) core-level binding energies indicates that is not possible to extract information about the oxidation state of the alloy components. The present calculations predict that CO does always sit on top sites, the influence of the alloy composition on the equilibrium geometry and vibrational frequency of CO chemisorbed at a given Rh or Cu site being very small. However, there is a large difference in the structural properties corresponding to CO chemisorption above either Rh or Cu. Therefore, the absolute value of the vibrational frequency of chemisorbed CO does not permit to extract any information about the alloy composition but afford to assign the chemisorption site. Finally, the CO adsorption energy does not follow a monotonic trend with composition. The use of the Constrained Space Orbital Variation analysis permits one to firmly establish that the difference in adsorption energy for different compositions cannot be explained through differences in the σ-donation and π-backdonation mechanisms.

Similarities and differences on the molecular mechanism of CO oxidation on Rh(111) and bimetallic RhCu(111) surfaces

The reaction between adsorbed CO and atomic O on various sites of Rh(111) and on the bimetallic RhCu(111) surface has been investigated by first principles density functional theory using slab models. The most likely reaction pathway for CO oxidation on Rh(111) involves probably migration of atomic oxygen from fcc to hcp sites. On the bimetallic surface the mechanism is similar, although depending on the type of bimetallic site a reduction of the energy barrier is predicted. Consequences for the NO reduction by CO reaction are analyzed.

Exploring the molecular mechanisms of reactions at surfaces

The study of the molecular mechanism of chemical reactions occurring at solid surfaces is of primary importance to understand heterogeneous catalysis from a microscopic point of view. The present paper reviews the state of the art methods of electronic structure and the surface models currently used in this type of studies by making use of three different examples. Those are the decomposition of azomethane on Pt(111), the study of the different selectivity of Cu(111) and Ag(111) towards ethene partial oxidation and the comparative study of NO dissociation on Rh(111) and bimetallic RhCu(111) surfaces. These examples illustrate the power of the electronic structure computational approaches to predict the structure and stability of different intermediates and to unravel the molecular mechanism of these surface reactions.

FEATURES AND CATALYTIC PROPERTIES OF RhCu: A REVIEW

The study of bimetallic catalysts has scientific and technologic importance because of special catalytic activity towards several reactions. RhCu is an interesting bimetallic system due to combination of the very different catalytic activities of Rh and Cu. The catalytic activity of this bimetallic does not result from simple interpolation of the constituents. In fact, at low Cu content, the catalytic activity of RhCu is superior to that of Rh but when the Cu content is higher the activity decays. This is a curious trend which theoretical works had attempted to explain. This paper reports an overview of the most recent research works about this bimetallic system with emphasis in its especial characteristics.