Surface Modification of Catalytic Materials

This thesis is a summary of my work on the following systems: Pt alloys for Oxygen Reduction Reaction (ORR) and CO oxidation, Ru for methanation and finally CuZn for methanol synthesis. An important subject throughout the thesis is gas induced surfaces changes. This has been investigated on single crystals as well as nanoparticles on planar surfaces as a model system.
The model system consisting of planar supports and mass selected nanoparticles has been investigated in a series of Ultra High Vacuum (UHV) compatible chambers. The nanoparticles were produced in a UHV setup by magnetron sputter gas aggregation techniques. With the use of two different filter mechanisms, the Quadrupole and the Lateral Time Of Flight, the nanoparticles were mass selected. This was done to correlate nanoparticle size with reactivity.
Selected key findings can be summarized as: 1) CO induced surface changes of Pt based system from 3 different views: morphology, reactivity and surface alloy composition, 2) A correlation and understanding of the size dependency of PtX nanoparticles for the Oxygen Reduction Reaction (ORR), 3) Size dependency of Ru nanoparticles for methanation and iv) The presence of metallic Zn during methanol synthesis.
The importance of conducting well controlled UHV experiments and characterization in combination with experiments at higher pressures to span the pressure gap between UHV and operando conditions is definitely highlighted in this thesis.