Fig. 2: In situ ambient-pressure X-ray photoelectron spectroscopy.
From: Tracking the dynamics of catalytic Pt/CeO2 active sites during water-gas-shift reaction
a Pt 4f spectra of Pt/CeO2-rod catalyst; b Pt 4f spectra of Pt/CeO2-cube catalyst; c Pt 4f spectra of Pt/CeO2-oct catalyst; d oxidation state change of Pt on Pt/CeO2-rod catalyst; e oxidation state change of Pt on Pt/CeO2-cube catalyst; f oxidation state change of Pt on Pt/CeO2-oct catalyst. The solid peaks in a-c represent Pt0. A photon energy of 1100 eV was used. The spectra of fresh catalysts were collected at 400 °C under UHV (2 × 10−8 Torr) conditions. Then, the catalyst was pretreated under 0.40 Torr O2 at 400 °C for 30 min, followed by pretreatment under 0.40 Torr H2 at 300 °C for 30 min. To investigate the oxidation state change of Pt under reaction conditions, the spectra were collected at 300 °C in the presence of 0.35 Torr CO for 60 min. After further introducing 0.70 Torr H2O, another set of spectra were collected at 300 °C for 60 min. The pink solid peaks represent CO adsorption on Pt0 in the presence of CO (and H2O). The percentages of Ptδ+ and Pt0 were obtained from the peak areas of each species. The CO adsorption on Pt0 was included in the calculation of percentage of Pt0. Solid circles in d-f represent the fraction of Pt0, while the open circles represent the fraction of Ptδ+. The survey spectra of all the catalysts are summarized in Supplementary Fig. 5. The oxidation state changes of Pt, Ce and O with time for all the catalysts under different conditions are summarized in Supplementary Figs. 6–13.
