Catalyst Surface Species Imaged

Researchers at Pacific Northwest National Laboratory have imaged two never-before-seen chemical intermediates that have been proposed to play key roles in the interconversion of oxygen and water on catalyst surfaces (J. Phys. Chem. C, DOI: 10.1021/jp807030n). The study broadens understanding of surface reaction mechanisms in photocatalyzed H₂O splitting and other reactions of H₂O and O₂ on solids. Igor Lyubinetsky, Yingge Du, and coworkers prepared partially hydroxylated titania—a model photocatalyst—by exposing the crystal to H₂O, which dissociates at crystal defect sites. The group then treated the prepared surface with O₂. On the basis of scanning tunneling microscopy images recorded before and after O₂ exposure, along with calculations that aid in interpreting the images, the researchers report the first observation of adsorbed hydroperoxyl, HO₂, which they say forms directly upon reaction of O₂ with a single OH group that bridges two titanium atoms in the row beneath. HO₂ can then dissociate to form an adsorbed O atom and the other elusive species: a Ti-bound OH group.