Molecular models for single cobalt ions supported on cerium dioxide nanoparticles: Heterometallic Ce/Co-oxo clusters

Doory Dan, Khalil A. Abboud, Lukasz Wojtas, George Christou

University of Florida, University of South Florida

Cerium dioxide (CeO₂, ceria) nanoparticles (CNPs) have gained substantial interest in a wide range of fields including industrial catalysis and, more recently, biomedical applications. In addition, ceria-containing materials have often been used as redox support materials, solid oxide fuel cells, UV filters, and three-way catalysts (TWCs) for the control of auto-exhaust pollutants. This outstanding versatility is partially due to the significant natural abundance of cerium and its facile Ce³⁺/Ce⁴⁺redox capability.

Despite the widespread use of nanoceria, the current synthetic procedures suffer from poor size control (i.e., polydispersity) and require extreme reaction conditions. In addition, the detailed structural analysis of nanoparticles to atomic resolution remains a massive challenge. Therefore, we have developed molecular ‘bottom-up’ routes to molecular cerium-oxo-carboxylate clusters that are ultra-small (1–3 nm) CNPs. These bring all the advantages of molecular chemistry to the area, including monodispersity (single-size), solubility, and crystallinity, the latter enabling structural characterization to atomic resolution by single-crystal X-ray crystallography. Given their strong resemblance to the bulk material, we classify these clusters as “molecular nanoparticles” (MNPs).

More recently, we have extended this approach towards using CeO₂ MNPs as supports for 3d transition metals such as Mn^III on their surface. Co ions supported on traditional CNPs exhibit enhanced catalytic activity such as dehydrogenation of ethane and low temperature methanation at low partial pressure of CO₂. However, there are no reports to date of molecular Ce/Co-oxo clusters that can be described as models of ceria-supported Co^III ions. We have therefore taken on the synthetic challenge of attaining such compounds, and this presentation will describe the structures of a family of novel Ce/Co-oxo clusters that represent molecular models of Co^III ions on CNP surfaces.