In Situ Ambient Pressure XPS Study of CO Oxidation Reaction on Pd(111) Surfaces

Abstract

The CO oxidation reaction on the Pd(111) model catalyst at various temperatures (200–400 °C) under hundreds mTorr pressure conditions has been monitored by in situ ambient pressure X-ray photoelectron spectroscopy and mass spectroscopy. In situ observation of the reaction revealed that the Pd(111) surface is covered by CO molecules at a lower temperature (200 °C), while at higher temperatures (300–400 °C) several oxide phases are formed on the surface. We found that the reactivity is enhanced in the presence of a surface oxide and significantly suppressed by formation of a cluster oxide and the PdO bulk oxide. CO titration experiments suggest that less coordinated oxygen atoms are more reactive for CO oxidation.

Chemical states of surface oxygen during CO oxidation on Pt(1 1 0) surface revealed by ambient pressure XPS

“…The specifications of beamline and endstation can be found elsewhere [24,25]. A well-ordered Pt (1 1 0) single crystal, provided by Princeton Scientific Corp., was prepared with the repeated cleaning cycles of annealing and Ar ion sputtering process.…”

Insights into Electrochemical Reactions from Ambient Pressure Photoelectron Spectroscopy

“…[18][19] A typical instrument (Figure 1) consists of a highpressure cell/chamber, separated from the electron analyzer-which remains in high vacuum-by a differentially pumped electrostatic lens system and series of apertures. [20][21] Such instruments are found at synchrotrons around the world [22][23][24][25][26][27] and are being increasingly used with lab X-ray sources as well, which will further empower the field in the years to come. AP-XPS probes the surface chemistry of catalysts at elevated pressures, 29 identifying and quantifying adsorbates in equilibrium with the gas.…”

Reversed Hysteresis during CO Oxidation over Pd75Ag25(100)

“…[30][31][32][33][34][35][36][37][38][39][40] In the case of Pd(100), it has been shown experimentally that the higher activity of this surface towards CO oxidation at these conditions coincides with the presence of the √ 5 surface oxide. 30,32,35,38,39,41 Kinetic Monte-Carlo simulations support the view that a surface oxide on Pd(100) could be responsible for increased reactivity.…”