H2 reduction of surface oxides on Pd-based membrane model systems – The case of Pd(100) and Pd75Ag25(100)

•H2 reduction of the surface oxide is significantly slower for Pd75Ag25(100) compared to Pd(100).•The reduction behavior shows complex temperature dependence, not well described by Avrami kinetics.•Oxygen spillover effects during the surface oxide reduction are observed for Pd(100).•For Pd(100) the observed reduction rate is rather independent of temperature.•For Pd75Ag25(100) the reduction rate displays a non-monotonic variation with temperature. Reduction of the (5×5)R27° surface oxide on Pd(100) and Pd75Ag25(100) surfaces by H2 has been studied using high-resolution photoelectron spectroscopy in situ at H2 pressures 5×10−9mbar and 5×10−8mbar and selected temperatures in the range 30°C to 170°C. The reduction is slower on Pd75Ag25(100) compared to Pd(100) for all temperatures and pressures investigated. For Pd(100), the surface oxide reduction rate is rather independent of temperature, while for Pd75Ag25(100) a non-monotonic variation is observed. As indicated by kinetic analysis, the complex reduction behavior is not well described by Avrami kinetics. Oxygen spillover effects contribute to this picture for Pd(100), while surface compositional effects appear to dominate the performance for Pd75Ag25(100). These findings may have implications for understanding the oxidation, reduction and hydrogen transport properties of Pd–Ag membranes.