In Situ Studies of Carbon Monoxide Oxidation on Platinum and Platinum–Rhenium Alloy Surfaces

CO oxidation has been investigated by near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) on Pt(111), Re films on Pt(111), and a Pt–Re alloy surface. The Pt–Re alloy surface was prepared by annealing Re films on Pt(111) to 1000 K; scanning tunneling microscopy, low energy ion scattering, and X-ray photoelectron spectroscopy studies indicate that this treatment resulted in the diffusion of Re into the Pt(111) surface. Under CO oxidation conditions of 500 mTorr O2/50 mTorr CO, CO remains on the Pt(111) surface at 450 K, whereas CO desorbs from the Pt–Re alloy surface at lower temperatures. Furthermore, the Pt–Re alloy dissociates oxygen more readily than Pt(111) despite the fact that all of the Re atoms are initially in the subsurface region. Mass spectrometer studies show that the Pt–Re alloy, Re film on Pt, and Pt(111) all have similar activities for CO oxidation, with the Pt–Re alloy producing ∼10% more CO2 than Pt(111). The Re film is not stable under CO oxidation conditions at temperatures ≥450 K due to the formation and subsequent sublimation of volatile Re2O7. However, the Pt–Re alloy surface is more resistant to oxidation and therefore also more stable against Re sublimation.