Breakdown of the Structure–Function Relationship on a Polycrystalline Pd Catalyst Surface Illustrated by Dynamic CO Oxidation

Real catalysts consisting of nanoparticles host many nanofacets. Each nanofacet changes its structure and function in response to its local environment but is also affected by neighboring nanofacets. Time-resolved operando experiments close to realistic conditions at polycrystals mimicking real catalyst particles are unfortunately challenging but could be highly rewarding. Here, we demonstrate how such studies can be performed with time-resolved ambient pressure X-ray photoelectron spectroscopy in the millibar regime and how the local surface composition/adsorbates and gas composition can be measured simultaneously for grains on a Pd polycrystal. For the CO oxidation reaction, we demonstrate how the ignition and extinction are gas-phase-driven and grain-independent, while the surface structure near the extinction point is highly grain-dependent.