Abstract
The development of model catalyst systems for heterogeneous catalysis going beyond the metal single crystal approach, including phenomena involving the limited size of metal nanoparticles supported on oxide surfaces, as well as the electronic interaction through the oxide-metal interface, is exemplified on the basis of two case studies from the laboratory of the authors. In the first case study the reactivity of supported Pd nanoparticles is studied in comparison with Pd single crystals. The influence of carbon contaminants on the hydrogenation reaction of unsaturated hydrocarbons is discussed. Carbon contaminants are identified as a key parameter in those reactions as they control the surface and sub-surface concentration of hydrogen on and in the particles. In the second case study, scanning probe techniques are used to determine electronic and structural properties of supported Au particles as a function of the number of Au atoms in the particle. It is demonstrated how charge transfer between the support and the particle determines the shape of nanoparticles and a concept is developed that uses charge transfer control through dopants in the support to understand and design catalytically active materials.
Highlights
The factors addressed above influence, decisively, the reactivity of the catalytic system, and one may hope that by considering a finite number of factors, a detailed understanding of the complexity of the reacting system, at least in the static limit, may be approached
In our recent studies we investigated the hydrogenation activity of a Pd(111) single crystal surface and Pd nanoparticles supported on Fe3O4/Pt(111) model catalyst using a combination of isothermal pulsed molecular beam (MB) methods, vibrational spectroscopy and resonant nuclear reaction analysis for hydrogen depth profiling to further clarify the microscopic mechanisms active for hydrogenation over Pd catalysts.[13,14,15,16,17,18]
The nearly 100% increase of the overall reaction rate arises from modification of only B20% of the surface sites constituting edges and corners of Pd nanoparticles
Summary
Carbon contaminants are identified as a key parameter in those reactions as they control the surface and sub-surface concentration of hydrogen on and in the particles. In the second case study, scanning probe techniques are used to determine electronic and structural properties of supported Au particles as a function of the number of Au atoms in the particle. It is demonstrated how charge transfer between the support and the particle determines the shape of nanoparticles and a concept is developed that uses charge transfer control through dopants in the support to understand and design catalytically active materials
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