Entirely monodisperse clusters of oxides are critically important model systems for catalysis studies because they allow the rigorous analysis of reaction mechanisms, and variations at the single-atom level can be already reflected in their reactivity. The generation and intact immobilization on a suitable substrate of such clusters is quite challenging, and usually requires mass spectrometric size selection and sophisticated soft landing protocols. As an example, tungsten(VI) oxide as a promising visible-light photocatalyst is very reactive and difficult to immobilize in a well-defined manner in vacuum. Here, we demonstrate that the boron nitride nanomesh, an atomically thin layer of hexagonal boron nitride on Rh(111) with strong corrugation, is a promising substrate for self-assembly of monodisperse cyclic tris(tungsten(VI)trioxide) clusters in solution. The triangular WO3 clusters adsorb in the pores of the nanomesh, where they were imaged with submolecular resolution using electrochemical scanning tunneling microscopy. The decorated surface was transferred to vacuum where the chemical identity of the clusters was confirmed with X-ray photoelectron spectroscopy. To our knowledge, this is the first successful example of self-assembly on the nanomesh from solution. We expect that proper control over deposition conditions will allow tuning of the number of clusters per pore, making this a promising model system for on-surface catalysis studies of oxide clusters. We contrast this finding with deposition of the same clusters on rutile TiO2(110) in liquid, on which the clusters appear to react and form chains, similar to observations of sublimated WO3 in vacuum. Even though the clusters are very likely hydroxylated in aqueous solution, this behavior indicates surprising parallels with ultrahigh vacuum and suggests that in many cases solution-based procedures may complement or even replace vacuum methods.

Boron nitride nanomesh: a robust template for monodisperse oxide cluster adsorption

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.