A Study of Nanostructuring Effects on Model Heterogeneous Catalysts

• Autores: Sergey Kozlov
• Directores de la Tesis: Frances Illas Riera (dir. tes.), Konstantin Neyman (dir. tes.)
• Lectura: En la Universitat de Barcelona ( España ) en 2015
• Idioma: inglés
• Tribunal Calificador de la Tesis: Roy Johnston (presid.), Carmen Sousa Romero (secret.), Piero Ugliengo (voc.)
• Materias:
  • Física
    • Óptica
      • Radiación visible
    • Física del estado sólido
      • Superficies
• Enlaces
  • Tesis en acceso abierto en: Dipòsit Digital de la UB
• Resumen

  • The role of heterogeneous catalysts in modern society is immense. The majority of catalysts are nanostructured solely in order to increase the fraction of atoms on their surface. The nanostructuring, however, introduces important changes in properties of the catalysts. Since commercial heterogeneous catalysts have a very complex hierarchical structure many academic studies are performed on so-called model catalysts. The latter are simplified systems that have a realistic degree of nanostructuring, but lack complexity on micrometer and millimeter scales. This thesis summarizes results of computational investigations of different ways how nanostructuring may affect properties and activity of model heterogeneous catalysts. Among various forms of model catalysts this thesis considers supported and unsupported transition metal nanoparticles, steps on surfaces and nanometer thick films. In all cases computational models were designed to be as similar as possible to respective experimental systems. Since these models often contain hundreds of atoms they were investigated with density functional theory methods that yield a good compromise between accuracy and computational cost for systems of this size. In particular, the following studies were performed: ¿ Adsorption and infrared spectroscopy properties of CHxOy (x=1-3, y=0-1) species on Pd nanoparticles were characterized. ¿ The activity of edges Pd nanoparticles in methane dissociation was critically analyzed compared to that of Pd(111). ¿ The activity of {111} terraces of Pd, Pt, Ni, and Rh nanoparticles in ethyl hydrogenation was compared to the activity of respective (111) single crystal surfaces. ¿ A new method to optimize chemical ordering in bimetallic nanoparticles was proposed and applied to catalytically active PdAu, PdAg, PdCu and PdZn alloy particles. ¿ The effect of MgO(100) support on physical and adsorptive properties of Pd and Pt nanoparticles was quantified. ¿ H absorption into Pd and Pt nanoparticles supported on MgO(100) was simulated. ¿ Atomic and electronic structure of steps on CeO2(111) was determined. ¿ Two novel methods to calculate specific energy of steps on a surface were proposed and applied to steps on CeO2(111) ¿ The ability of steps on CeO2(111) to form O vacancies was investigated using a newly proposed prescreening procedure. ¿ Structure of ~1 nm thick Ce2O3 films was investigated by means of the simulated mechanical annealing method. ¿ Reconstructrion of PdZn films on Pd(111) for monolayer thick films or under CO atmosphere was characterized. This diverse list of studies fulfills the goal of exploring various effects of different forms of nanostructuring on heterogeneous catalysts. Many of these studies are one-of-a-kind investigations describing certain effects induced by the nanostructuring on catalytically active materials for the first time. Another part of these studies describe novel simulation and analysis techniques that advance the methodology of computational investigations of nanostructured solid state systems.