Catalysis in frequency space: Resolving hidden surface structure and activity oscillations

In situ catalysis studies typically correlate catalytic function and majority surface structures, but neglect that difficult-to-detect minority structures might govern catalysis. Here we use an oscillating CO:O ₂ gas composition to drive structural oscillations on a catalytically active Pd(100) surface and collect photoelectron spectroscopy data at high measurement frequency to demonstrate that the Fourier-transformed data selectively probe oscillations of minority surface structures and of the gas phase. Using the Fourier transform phase as well as work function shifts in the Fourier-transformed photoemission signal, we synchronize all signals and prove an asymmetric CO ₂ production above the minority CO- and majority oxide-covered surface areas, without imaging. The methodology is easy to use with other experimental techniques, which enables a wide range of future investigations into minority structure catalysis.