The recent development
of high spatial resolution microscopy
and
spectroscopy tools enabled reactivity analysis of homogeneous and
heterogeneous (electro)catalysts at previously unattainable resolution
and sensitivity. These techniques revealed that catalytic entities
are more heterogeneous than expected and local variations in reaction
mechanism due to divergences in the nature of active sites, such as
their atomic properties, distribution, and accessibility, occur both
in homogeneous and heterogeneous (electro)catalysts. In this review,
we highlight recent insights in catalysis research that were attained
by conducting high spatial resolution studies. The discussed case
studies range from reactivity detection of single particles or single
molecular catalysts, inter- and intraparticle communication analysis,
and probing the influence of catalysts distribution and accessibility
on the resulting reactivity. It is demonstrated that multiparticle
and multisite reactivity analyses provide unique knowledge about reaction
mechanism that could not have been attained by conducting ensemble-based,
averaging, spectroscopy measurements. It is highlighted that the integration
of spectroscopy and microscopy measurements under realistic reaction
conditions will be essential to bridge the gap between model-system
studies and real-world high spatial resolution reactivity analysis.