Quantum mechanical modeling of the chemical reactivity of metal surfaces: two case studies involving water formation and dissociation (original) (raw)

We could naively think that the best catalyst is the one that makes the reaction as fast as possible but this is not the case. The best catalyst is the one that works the way we expect, at the speed we need: an explosive reaction can be less interesting than a slow one. Also, a catalyst that accelerates unwanted reactions that may spoil (poison) the catalytic device is certainly noxious. Schematically, a reaction catalyzed by a solid surface can be described by three elementary processes: adsorption of the reactants, formation of the products on the catalyst's surface, and desorption of the products. Reactants form an activated complex, called the transition state, that decomposes into products. Transition state corresponds to a maximum in the energy profile plot from initial to final state. The height of the energy gap between transition state and initial state is called energy barrier and is equal High Resolution Scanning Electron Microscopy, Field Ion Microscopy (FIM), Scanning Tunnelling Microscopy (STM). In figure I.2 we can see a practical example of STM utility in understanding microscopic details of a reacting surface. These different types of experiments have provided us with a wealth of detailed information about surface structures, adsorption geometries, bond strengths and elementary reactions steps. A realistic heterogeneous catalyst consists in a disordered surface with many facets, defects, terraces with different behaviors among the various Theoretical modeling of surfaces At the present time theoretical study of surface properties is achieved mainly through computational methods that practically consist in large-scale computer simulations of a set of atoms interacting and positioned in a defined space at our will. The choice of the parameters and conditions determin-Water on transition metals Water is perhaps the most important and most pervasive chemical of our planet. The influence of water permeates virtually all areas of biochemical, chemical and physical importance, and is especially evident in phenomena occurring at the interfaces of solid surfaces. The progress in understanding the properties of water on solid surfaces is evident both in areas for which surface science methodology has traditionally been strong (catalysis and electronic materials) and also in new areas not traditionally studied by surface In this thesis we will present two different studies involving water reactions on transition metal surfaces. The first one involves study of water dissociation on flat and stepped platinum surfaces through the estimate of energy barriers for different reaction pathways. Data at the present time published