Abstract
The formation of adsorbed O (O-ad) species and their reactivities in CO oxidation on BaO/Pt(111) (at two BaO coverages) were studied with temperature programmed desorption (TPD), infrared reflection absorption (IRA), and X-ray photoelectron (XP) spectroscopies. In neither of these two systems was the Pt(111) surface completely covered with BaO. On the system with lower BaO coverage (similar to 45% of the Pt(111) surface is covered by BaO), two different O-ad species form following the adsorption of O-2 at 300 K: O adsorbed on the BaO-free Pt(111) sites (O-Pt) and at the Pt-BaO interface (O-int). On the system with higher BaO coverage (similar to 60% of the Pt(111) surface is covered by BaO), two types of O-int are seen at the Pt-BaO interface. The desorption of O-Pt from the BaO-free portion of the Pt(111) surface gives an O-2 desorption peak with a maximum desorption rate at similar to 690 K. Migration of O-int to the Pt(111) sites and their recombinative desorption give two explosive desorption features at similar to 760 and similar to 790 K in the TPD spectrum. The reactivities of these O-ad species with CO to form CO2 follow their sequence of desorption; i.e., the O-Pt associated with the BaO-free Pt(111) surface, which de:;orbs at 690 K, reacts first with CO, followed by the O-int species at the Pt-BaO interface (first the one that desorbs at similar to 760 K and finally the one that is bound the most strongly to the interface, and desorbs at similar to 790 K).