Platinum particles supported on graphite have been investigated by scanning tunneling microscopy (STM). For one monolayer thick Pt particles the individual Pt atoms form a characteristic intensity pattern due to a mismatch between the Pt and graphite lattice. Based on density functional theory calculations and model structures of Pt on graphite it is argued that the observed STM imaging contrast has its origin in the tip induced elastic deformation of the graphite underneath the Pt particle. The Pt–graphite potential is much stiffer than the graphite–graphite potential. The calculations furthermore indicate that Pt adsorption is favored over top rather than hole sites and that the barrier for diffusion is very low.

The adsorption of ethyl pyruvate on Pt(111) has been studied by in situ XANES measurements in the presence and absence of hydrogen. Depending on the hydrogen and ethyl pyruvate pressure, the C and O K�edge spectra exhibit distinctly different angular dependence. Without hydrogen ethyl pyruvate is oriented preferentially perpendicular to the surface, indicating bonding via the O lone pairs. In the presence of hydrogen the mean orientation is more tilted towards the surface. Likely, ethyl pyruvate also interacts with Pt via its π system under these conditions. The observed angle�dependent shift of the energy of the π* and σ* resonances indicates the coexistence of differently adsorbed ethyl pyruvate species. The experimental findings demonstrate the importance of the in situ approach for unraveling the adsorption mode of ethyl pyruvate in the enantioselective hydrogenation over cinchona�alkaloid�modified Pt.

The adsorption of ethyl pyruvate on Pt(111) at low temperature was investigated by XP and UP spectroscopy. The assignment of the photoelectron spectra was assisted by calculation of correlated ionization potentials. Comparison of the XP and UP spectra of the condensed and chemisorbed layer indicates a strong ethyl pyruvate adsorption bond in the latter. Upon chemisorption, the HOMO of ethyl pyruvate, which is a lone-pair orbital delocalized over both C=O groups, is stabilized by about 0.7 eV with respect to the other orbitals, which is characteristic for a lone-pair bonding mechanism. The same bonding mechanism was found for coverages far below saturation. The XP spectra further indicate that the ketone C=O is more strongly involved in the chemisorption bond than the carboxyl C=O of ethyl pyruvate. The packing density of the saturated chemisorbed ethyl pyruvate layer, as determined by XPS, is high. This points toward an upright or tilted orientation of ethyl pyruvate in this layer, in line with the observed bonding mechanism.