Near Ambient Pressure XPS Investigation of CO Oxidation Over Pd₃Au(100)

The CO oxidation behavior under excess oxygen and near stoichiometric conditions over the surface of Pd₃Au(100) has been studied by combining near-ambient pressure X-ray photoelectron spectroscopy and quadrupole mass spectrometry and compared to Pd(100). During heating and cooling cycles, normal hysteresis in the CO₂ production, i.e. with the light-off temperature being higher than the extinction temperature, is observed for both surfaces. On both Pd₃Au(100) and Pd(100) the (√5 × √5)R27° surface oxide structure is present during CO₂ production under excess oxygen conditions (O₂:CO = 10:1), while at near stoichiometric conditions (O₂:CO = 1:1) the surfaces are covered with atomic oxygen. Au as alloying element hence induces only minor differences in the observed hysteresis and the active phase compared to pure Pd. Alloying with Au thus yields a different behavior compared to Ag, where reversed hysteresis is observed for CO₂ production over Pd₇₅Ag₂₅(100) at similar conditions [Fernandes et al., ACS Catal. (2016) 4154].