The modularity and synthetic flexibility of metal–organic
frameworks (MOFs) have provoked analogies with enzymes, and even the
term MOFzymes has been coined. In this review, we focus on molecular
catalysis of energy relevance in MOFs, more specifically water oxidation,
oxygen and carbon dioxide reduction, as well as hydrogen evolution
in context of the MOF–enzyme analogy. Similar to enzymes, catalyst
encapsulation in MOFs leads to structural stabilization under turnover
conditions, while catalyst motifs that are synthetically out of reach
in a homogeneous solution phase may be attainable as secondary building
units in MOFs. Exploring the unique synthetic possibilities in MOFs,
specific groups in the second and third coordination sphere around
the catalytic active site have been incorporated to facilitate catalysis.
A key difference between enzymes and MOFs is the fact that active
site concentrations in the latter are often considerably higher, leading
to charge and mass transport limitations in MOFs that are more severe
than those in enzymes. High catalyst concentrations also put a limit
on the distance between catalysts, and thus the available space for
higher coordination sphere engineering. As transport is important
for MOF-borne catalysis, a system perspective is chosen to highlight
concepts that address the issue. A detailed section on transport and
light-driven reactivity sets the stage for a concise review of the
currently available literature on utilizing principles from Nature
and system design for the preparation of catalytic MOF-based materials.