Estudio teórico de la adsorción y reactividad de especies nitrogenadas sobre superficies metálicas

Identifier:  TDX:852

Handle: https://hdl.handle.net/20.500.11797/TDX852

Authors:  Ample Navarro, Francisco

Abstract:
Heterogeneous catalysis has been used in a lot of industrial processes since more than a century; nevertheless, the experimental research at atomic level has not been developed until 25 years ago. These studies are relatively young and many of the mechanisms that are used in the industry are still unknown. To know these mechanisms is indispensable for the design of new catalyst and to increase its effectiveness. The theoretical simulation of chemical processes over surfaces is an alternative to obtain information that it is not easily accessible by means of experimental techniques. The great increase of the computational power in the last years and the development of efficient theoretical codes is making that the computational chemistry is an area of increasing importance in surface science and heterogeneous catalysis. The objective of this thesis was the study of the adsorption and reactivity of small N-containing molecules over transition metallic surfaces by means of theoretical methods. This study was focused over the adsorption and reactivity of the cyanide (CN), cyanhydric acid (HCN), isocyanhydric acid (HNC), molecular nitrogen (N2) and nitrous oxide (N2O) over metallic surfaces. The obtained conclusions can be used as basis for the adsorption and reactivity of more complex molecules. This thesis has allowed to obtain the different adsorption modes of CN, HCN, HNC, N2 and N2O over metallic surfaces of (111) type. The obtained adsorption energies and vibrational frequencies can be compared with the experimental data. The analysis of the density of states, projection of molecular orbitals and the topologic study of the electronic localization function (ELF) have allowed to explain the bonding mechanisms of these molecules with the metal surface. The diffusion of the molecules and of the implicated atoms over the surface has been studied. The reactivity has been studied obtaining the energetic formation barriers for CN, N2, HCN and N2O starting from his adsorbed fragments. The obtained values for these barriers can explain experimental results.