Models in Catalysis

Abstract

The paper discusses the hierarchy of model studies with increasing complexity towards an understanding of industrial catalysts under reaction conditions. We use three case studies to document the progress in systems complexity as well as the development of instruments that allow us to approach the study of acting catalysts: magnesium oxide clusters in the gas phase, gold nanoparticles on metal oxide surfaces, and palladium nanoparticles compared to crystal surfaces. While the examples are from the field of heterogeneous catalysis, we discuss the relation to homogeneous and enzymatic catalysis.

Gas phase structures and charge localization in small aluminum oxide anions: Infrared photodissociation spectroscopy and electronic structure calculations

“…60,61 The IR spectrum of SiO 3 is characterized by a dominant peak at high energies (1364 cm −1 ), 16 cm −1 below the corresponding intense absorption in SiO 2 (1380 cm −1 ), and two weaker absorptions roughly 500 cm −1 lower in energy at 877 and 855 cm −1 . This compares favorably with the present IRPD spectrum of AlO 3 − , which is characterized by a red shift of the most intense absorption (versus AlO 2 − ) of 36 cm −1 and considerably weaker features ∼420 cm −1 lower in energy, indicating a similar geometric arrangement as in SiO 3 . A C 2v structure with a peroxo-group as part of a threemembered ring has also been predicted for the ground state of GaO 3 − .…”

“…Experiments on these model systems thus provide insight into structure-reactivity correlations as well as the transition from molecular to condensed phase properties. [2][3][4] Small aluminum oxide cluster cations 5,6 and anions 7 containing oxygen-centered radicals have raised interest recently as models for understanding water chemisorption and C-H bond activation. There is also an astrochemical interest in the role that small aluminum oxide clusters play in the formation of circumstellar corundum (Al 2 O 3 ) grains.…”

“…There is also an astrochemical interest in the role that small aluminum oxide clusters play in the formation of circumstellar corundum (Al 2 O 3 ) grains. 8 In the present study, we use cryogenic ion trap vibrational spectroscopy of messenger-tagged, mass-selected anions in combination with density functional theory (DFT) to examine the geometric structure of AlO [1][2][3][4] − and Al 2 O 3-6 − ions formed by sputtering of elemental aluminum in the presence of oxygen. We are particularly interested in the identification of reactive oxygen species like O 2 −.…”

Models for heterogeneous catalysts: studies at the atomic level

“…Each level is evaluated with respect to experiment and theory and with respect to progress that has been made to achieve a proper representation/description of each level: green: yes, achieved; red: no, not achieved. In addition, it is indicated whether studies have been performed under UHV and under ambient condition (Sauer and Freund 2015) (color figure online)…”

Atomic Structure Control of Silica Thin Films on Pt(111)

“…Furthermore, it has been shown that the metal upon which thin films are grown can influence nanoparticle morphology by a charge transfer mechanism from the thin film/metal interface. [21][22][23] The ability to grow thin, closed silica films on Pt(111), allows for the investigation of these structure-property relationships with regards to to the underlying metal support. The change in work function between Mo, Ru and Pt, represents a decisive parameter governing surface charging effects, whose influence on nanoparticle morphology, and hence catalytic activity, can now be investigated.…”