Utilising lone single atoms as model catalysts

Catalysis, the acceleration of chemical reactions using a catalyst, is used in the production of almost every manufactured product we interact with. Catalysts used industrially allow chemical reactions to happen using less energy and producing less waste, and the catalyst can be retrieved and reused almost endlessly. Understanding and improving catalyst materials are clearly, therefore, vital for current and future green economies. Catalysts can be grouped in to two distinct categories, homogenous catalysts and heterogenous catalysis. A homogenous catalyst shares the same physical state (solid, liquid or gas) as the reactants while heterogeneous catalysts exist in a different physical state to reactants. For example, a homogeneous catalyst could be dissolved in a solvent and help to join together small molecules in the same solvent, while a heterogenous catalyst could be a solid block of metal used to help gas phase molecules react. Homogenous catalysts commonly feature metal atoms as part of larger molecules and overall molecular shape and size has huge implications for their behaviour as catalysts. These catalysts are highly selective for specific reaction pathways from many that reactant molecules can undergo, and as such reduce waste from the unwanted pathways.
Homogenous catalysts can operate with very few expensive metal atoms but can be difficult to separate from the final products. This is problematic both because it is hard to achieve high purity for consumer goods likes pharmaceuticals (the catalyst is considered an impurity) and some valuable catalytic material is lost and cannot be reused for later batches. Heterogenous catalysts use small (over 10000 times smaller than the width of a human hair) clusters of very few metal atoms spread over a relatively inert, cheap support material. These catalysts are less selective, so produce more waste, and require larger quantities of expensive metals for the same amount of product. The huge advantage, compared...