Figure 1

There are structural changes in a 2 wt% platinum on Al₂O₃ catalyst during the switch from carbon monoxide to the catalytic mixture of carbon monoxide and oxygen as observed by transient quick XANES and EXAFS at the Pt L₃ edge. (A) Whiteline intensity of normalized Pt L₃ XANES spectra versus time during the switch indicates that right after the switch, starting from a carbon monoxide-poisoned surface, a short-lived phase forms, as indicated by a temporary decrease in whiteline intensity followed by a rapid increase. This rapid increase is indicative of the formation of a surface oxide³⁶. (B) Corresponding XANES spectra at 0 s (green), 31 s (blue), and 43 s (red). (C) Spectra of the carbon monoxide-covered platinum (green), surface platinum oxide (red) and the intermediate (blue) determined by the genetic algorithm procedure. (D) Fractions of the surface occupied by carbon monoxide (green), the intermediate species (blue) and a surface oxide (red) as determined by linear combination fitting of the spectra in (C) (crosses) as a function of time. The estimated error was 5% based on a systematic analysis of the sensitivity of the fit towards variation in relative amounts of each component.