  Understanding the fundamental mechanisms of single-atom catalysis (SAC) is
important to design systems with improved performance and stability. This is
problematic, however, because single-atom active sites are extremely difficult
to characterize with existing experimental techniques. Over the last 40 years,
surface science has provided the fundamental insights to understand
heterogeneous catalysis, but model systems in which metal atoms are stable on
well-characterized metal-oxide substrates at reaction temperatures are scarce.
In this perspective, I discuss what is already known about isolated metal atoms
adsorbed on model metal-oxide surfaces, and how this information can be used to
understand SAC. A key issue is that, although the highly-idealised model
systems studied in surface science may not be representative of a real working
catalyst, they do very much resemble what can be calculated using
state-of-the-art theoretical modelling. Thus, surface science offers an
opportunity to rigorously benchmark the theoretical approach to modelling SAC
in future. Perhaps more excitingly, several groups have developed model systems
where metal adatoms remain stable at elevated temperatures. To date however,
there has been no clear demonstration of catalytic activity. The perspective
closes with a brief discussion of the prospect for STM experiments under
realistic reaction conditions.
