Shedding light on light-off: Photoemission electron microscopy, DFT, and microkinetic modeling were used to examine the local kinetics in the CO oxidation on individual grains of a polycrystalline sample. It is demonstrated that catalytic ignition (“light-off”) occurs easier on Pd(hkl) domains than on corresponding Pt(hkl) domains. The isothermal determination of kinetic transitions, commonly used in surface science, is fully consistent with the isobaric reactivity monitoring applied in technical catalysis.

The locally resolved kinetics of CO oxidation on individual (111), (110) and (100) domains of a polycrystalline Pt foil were obtained by intensity analysis of video-PEEM images (see picture), and are compared to the global kinetics determined simultaneously by mass spectroscopy. The individual domains behave independently, with the propagating reaction fronts being confined within the grain boundaries

The role of artificially created defects and steps in the local reaction kinetics of CO oxidation on the individual domains of a polycrystalline Pd foil was studied by photoemission electron microscopy (PEEM), mass spectroscopy (MS), and scanning tunneling microscopy (STM). The defects and steps were created by STM-controlled Ar+ sputtering and the novel PEEM-based approach allowed the simultaneous determination of local kinetic phase transitions on differently oriented μm-sized grains of a polycrystalline sample. The independent (single-crystal-like) reaction behavior of the individual Pd(hkl) domains in the 10–5 mbar pressure range changes upon Ar+ sputtering to a correlated reaction behavior, and the reaction fronts propagate unhindered across the grain boundaries. The defect-rich surface shows also a significantly higher CO tolerance as reflected by the shift of both the global (MS-measured) and the local (PEEM-measured) kinetic diagrams toward higher CO pressure.

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In this contribution we present ab initio density-functional-theory (DFT) calculations for CeO 2 monolayers on the Pt(111) surface. The ceria surface and ceria-metal interface are of great interest because of the oxygen-storage and release capabilities of ceria, which are widely utilized in catalysis. Both the experimentally reported 3 : 4 [(4 × 4)] and 5 : 7 [(1.4 × 1.4)] matching geometries of the CeO 2 /Pt(111) system are studied using the GGA + U exchange-correlation scheme. Geometry optimizations of the structures are performed, resulting in a significant corrugation of both the Pt surface as well as the ceria adlayer surface. The total energies and adsorption energies of three different adsorption geometries for the 3 : 4 type are compared to the 5 : 7 structure in terms of stability. The electronic properties and the bonding character are studied by analysis of the density of states (DOS) and of the electron density. The charge transfer occurring during adsorption is calculated using the atoms-in-molecules (AIM) method. Strong interactions are detected, which are mainly based on electrostatic interactions between the topmost Pt layer and the oxygen atoms at the interface, but also include small contributions from hybridization.