Spectroscopic Evidence for the Involvement of Interfacial Sites in O-O Bond Activation over Gold Catalysts

Catalytic functions at interfaces between oxides and Au nanoparticles assist the activation of O2 and H2O2 during selective oxidations. We use in situ surface-enhanced Raman spectroscopy to reveal the differences in the types and distributions of reactive oxygen species (ROS) derived from H2O2 on Au catalysts that reflect interactions at nanoparticle-support interfaces. The pristine Au(111) does not activate H2O2 to form detectable surface intermediates, whereas Au nanoparticles on SiO2 bind small amounts of diatomic oxygen intermediates. In comparison, nanoparticles of Au on γ-Al2O3 bind significant coverages of diatomic and monoatomic oxygen species formed by activation processes that appear to involve hydroxyl (OH*) functions present on the support. Electrochemically roughened Au(111) activates O-O bonds in H2O2 by interactions with OH∗ groups to produce high atomic oxygen coverages. These observations appear consistent with comparisons between oxidation rates and barriers for supported Au catalysts and provide direct evidence for the involvement of interfacial sites and OH∗ groups in elementary steps that determine the distribution of ROS upon surfaces.