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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