Computational catalysis of homogeneous and heterogeneous systems: new insights into the activation of small molecules
- Autores: Julen Munárriz Tabuenca
- Directores de la Tesis: Victoriano Polo Ortiz (dir. tes.)
- Lectura: En la Universidad de Zaragoza ( España ) en 2019
- Idioma: español
- Tribunal Calificador de la Tesis: Manuel Yáñez Montero (presid.), Gregori Ujaque Pérez (secret.), Mónica Calatayud Antonino (voc.)
- Programa de doctorado: Programa de Doctorado en Química Física por la Universidad de Zaragoza
- Materias:
- Enlaces
- Tesis en acceso abierto en: Zaguán
- Resumen
This Ph.D. Thesis is devoted to the theoretical and computational study of homogeneous and heterogeneous catalysts for the activation of small molecules, namely N2, O2, CO, NH3, HCOOH and hydrosilanes, by means of DFT methodologies. These processes have a great interest in current chemical research, as their in-depth knowledge paves the way to the rational design of new environmentally respectful and active catalysts. A summary of the different reactions considered is presented below. Within the field of homogeneous catalysis, four different chemical processes catalysed by Rh- or Ir-based organometallic complexes were considered:
(i) Ammonia fixation by Ir-complexes that bear different pincer ligands. In particular, we studied the thermodynamic and kinetic factors that can affect the catalytic activity. For that, different methods for the study of chemical bonds, such as IQA and the ELF, were applied.
(ii) The silylation of aromatic C–H bonds by means of a well-defined and highly active Ir(III)-NHC catalyst. A detailed computational study of the reaction mechanism was performed. This mechanism was experimentally supported by different stoichiometric experiments. The results revealed the key role of the substrate directing groups in the reaction selectivity.
(iii) The use of molecular hydrogen as an energy vector. In particular, we considered the formic acid dehydrogenation process to yield H2 catalysed by a highly active Ir-NHO complex. The performed studies allowed to propose a plausible reaction mechanism that is in agreement with the activation energy experimentally determined.
(iv) The alcoxycarbonylation of alcohols and amines with CO to yield carbamates. The process is catalysed by a Rh-complex and requires the presence of an oxidant (KHSO5). The theoretical study allowed to propose a reaction mechanism, as well as to unravel the role of the oxidant.
With respect to heterogeneous catalysis, we addressed the proposal of new catalytic descriptors on the basis of the magnetic properties of the catalyst and the reactants. The considered processes are the following:
(v) The oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) catalysed by perovskite-based materials. Specifically, the magnetic features of different catalysts based on LaMnO3 were analyzed. The results showed the importance of taking into account the electronic entropy and the catalyst magnetic phase. On the basis of these results, a set of rules for the design of heterogeneous catalysts for ORR and OER based on magnetic metal oxides was proposed. Finally, these guidelines were applied to the design of new catalysts for OER based on a LaFeO3 composition.
(vi) The previous principles were extended to N2 fixation catalysed by different Mo-based nitrides. The results provided strong evidence on the application of the Mo magnetic moment as a descriptor of the catalytic activity towards N2 fixation.
