Segregation dynamics of a Pd-Ag surface during CO oxidation investigated by NAP-XPS

• CO oxidation over Pd 75% Ag 25% (100) studied by NAP-XPS. Reversed hysteresis in 2 formation during heating and cooling ramps observed. Hysteresis behaviour depends on exposure, rate, maximum temperature, sample history. Dynamic changes Pd/Ag surface composition cycling to 450 °C or 600 Relatively facile kinetics of segregation that proceeds even at ambient temperature. The dynamic the near-surface region a single crystal were monitored using near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) under oxygen rich conditions total 1.1 mbar. Six temperature cycles investigated different rates temperatures °C. It was found history bimetallic plays an important role, as profile varies depending initial conditions, previous temperatures. In terms coverage effects, normal, reversed no all agreement with modelling predictions, NAP-XPS data confirm upon heating/cooling where amount decreases increasing Nevertheless, 3d 5/2 core level relative area assessment is not fully capable capturing dynamics inferred from dependent profiles, due probing depth. While residing reaction mixture, however, there build-up adsorbed showing induces topmost layer these conditions. total, this suggests kinetically relatively cycling, adsorbate main controlling factor for termination.