Catalytic Mechanisms of Nanoclusters

Atomically Precise Nanoclusters are Nanoparticles that can be synthesized with exact purity

Atomically-precise nanoclusters are valued as nanoparticles that can be isolated with exact compositional purity and often crystallized to determine their exact structures. They are tunable by size, metal doping, or exchange of some or all ligands, giving them great flexibility to be tuned for various applications in catalysis, sensing, or photonics.  

Several hundred of these nanoclusters have been reported in the last 18 years.  While gold is synthetically facile, clusters of silver, copper, and other metals are increasingly being reported as synthetic techniques mature.  Ligands such as halides, phosphines, thiolates, N-heterocyclic carbenes, and more, play a key role in stabilizing clusters and determinging their geometric and electronic structure.

Despite the excitement over their potential as "designer nanoparticles," understanding the properties of atomically-precise nanoclusters remains a challenge, and we lack quantitative intuitive frameworks to guide synthetic efforts to leverage their tunability to optimize their performance.  Our goal is to use precision measurements to create predictive models describing the electronic effects of doping, ligand exchange, and structural transformations.

Atomically-tailored nanocluster catalysts for CO₂  reduction

Nanoclusters have generated much excitement for their potential to serve as designer catalysts, essentially nanoclusters with optimized, reproducible active sites for efficient generation of products.  However, the necessity to separate and isolate nanoclusters from polydisperse synthetic mixtures makes it difficult to perform classic catalysis optimization studies, producing "volcano plots," and other systematic studies.  We use the mass spectrometric nature of our experiments as a shortcut: we can select specific cluster compositions out of a polydisperse mixture and probe elementary reactions critical for their mechanisms.  We hope to identify particularly promising compositions that are worth the effort to isolate and use as catalysis, as well as understand the underlying synthetic principles that can be used to tune their performance.

A major part of this effort is understanding the nature of species very transiently bound to the surface of clusters, most importantly, hydrogens.  These surface-bound hydrogens often formally appear as hydrides, but they strongly couple with the molecular orbitals delocalized across the gold cluster core.  However, their transient nature and the difficulty of observing them in x-ray crystal structures makes them hard to study.  We can straightforwardly isolate these species by mass spectrometry to probe their chemical nature and reactivity.