The Relation of Mononuclear Surface Oxygen Species to Electron Spectroscopic and Catalysis Studies

The Relation of Mononuclear Surface Oxygen Species to Electron Spectroscopic and Catalysis Studies 

XPS has been used by Inoue and Yasumori (425a) to study the surface of MgO, CaO, and BaO after exposure to water vapor followed by in situ dehydration at various temperatures. Signals attributed to O2- lattice ions were observed after all treatments with peaks at 531.6 (MgO), 529.6 (CaO), and 528.5 (BaO) eV. Immediately after hydration, a second series of peaks at 533.7 (MgO), 532.2 (CaO), and 532.1 (BaO) eV were observed, which progressively disappeared as the dehydration temperature increased these were assigned to OH- ions. In addition, peaks at 532.1 (CaO) and 530.6 (BaO) eV which appeared during dehydration were assigned to O- ions formed from the following reaction  

However, although the assignments to O2- and OH- are reasonably clear, the assignment to O- seems much less certain. For CaO, the peak cannot be 

In conclusion, although both the O2 lattice and the OH on the surface are well characterized by XPS, the evidence for O from XPS and UPS must be treated with considerable caution since it has proved very difficult to correlate the details of the Of 1 s) binding energy unambiguously with the charge and environment of the adsorbed oxygen and to distinguish clearly when OH- may be present as a contaminant. 

The oxidation of olefins has also been investigated on a-Mo03 supported on carbon the mild oxidation of propene into acrolein takes place mainly on the (100) face of a-Mo03 while total oxidation occurs on the (010) face (425fg). Similar results have been obtained for the oxidative dehydrogenation of 1-butene into butadiene (425h). 

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