Subtle and reversible interactions of ambient pressure H2 with Pt/Cu(111) single-atom alloy surfaces

Pt-Cu single-atom alloys (SAA) have been identified as promising hydrogenation catalysts with an ability to activate H-2 better than the individual metals alone. We studied the interaction between H-2 and Pt/Cu(111) SAA model surface using ambient pressure X-ray photoelectron spectroscopy (AP-XPS). A binding energy shift in the Pt 4f spectrum indicates the presence of adsorbed H at 350 K, occurring because of H-H bond activation. No evidence was found of either surface segregation, subsurface diffusion of Pt atoms, or any effects on the thermal stability of the surface, likely due to the subtle interaction between Pt and H. This shift is reversible upon evacuation of H-2, which is a sign of a weak interaction. In addition, we studied the effect of H-2 and CO co-adsorption and found that while the surface is unaffected by poisoning by a small amount of CO at 350 K, CO can displace adsorbed H on almost half of the surface Pt sites at 300 K. The susceptibility to CO poisoning increases after the surface was heated to 450 K due to changes in the structure of the subsurface layer that enhance the binding of CO to the surface Pt sites.