Operando hysteresis of a palladium surface during high-frequency gas-pulsing of ethylene into oxygen

Catalytic active phases are often separated from inactive ones by their appearance/removal in heating/cooling experiments. Such experiments can reveal ignition, extinction, and often an associated hysteresis. The corresponding behavior and hysteresis under rapid gas composition changes in the milliseconds regime remain largely unexplored. However, such experiments can potentially be highly rewarding as catalytic properties of surfaces that have not yet equilibrated to the gas phase can be studied. Here, we use time-resolved Ambient Pressure X-ray Photoelectron Spectroscopy (tr-APXPS) to study ethylene oxidation on polycrystalline Pd during modulation of the C 2 H 4 :O 2 ratio. By combining 10 Hz gas pulsing with 25 kHz spectral acquisition, we track both gas phase and surface chemistry under non-equilibrium conditions and reveal and discuss a pronounced hysteresis. • Study of surface coverage hysteresis during fast gas pulsing (bistability). • Discussion of adsorption mechanism with a time resolution of 40 µs. • Study of the ethylene oxidation reaction during fast pulsing of ethylene over Pd.