Comparative isotope-aided investigation of electrochemical promotion and metal–support interactions 1. 18O2 TPD of electropromoted Pt films deposited on YSZ and of dispersed Pt/YSZ catalysts

The adsorption of 18O2 on porous electropromoted Pt films deposited on Y2O3-stabilized ZrO2 (YSZ) and on nanodispersed Pt catalysts deposited on YSZ powder was investigated via TPD. The TPD spectra are very similar for both systems: When 18O2 adsorption takes place above 200 °C, two O adsorption states (β2 and β3 states) form, which desorb at 425 and 500 °C, respectively. The latter is always occupied by lattice oxygen. For 18O2 adsorption temperatures below 100 °C a weakly bonded state (β1 state) forms in addition to the β2 and β3 states. It desorbs at 100–160 °C and is occupied exclusively by 18O. Both the Pt film and the nanodispersed Pt catalyst act as oxygen portholes and mediate, via O spillover and backspillover, respectively, the incorporation of gaseous 18O2 into the YSZ lattice during adsorption as well as the desorption of lattice 16O during TPD. The excess oxygen stored in YSZ plays a key role in interpreting the TPD spectra. The observed very strong similarity between the O2 TPD spectra of electrochemically promoted Pt/YSZ films and nanodispersed Pt/YSZ powder catalysts corroborates the mechanistic equivalence of electrochemical promotion and metal–support interactions (MSI) with O2−-conducting supports.