Origin of highly active metal-organic framework catalysts: defects? Defects!
Résumé
This article provides a comprehensive review of the nature of catalytic
sites in MOFs. In the last decade, a number of striking studies have
reported outstanding catalytic activities of MOFs. In all cases, the
authors were intrigued as it was unexpected from the ideal structure. We
demonstrate here that (surface) defects are at the origin of the
catalytic activities for the reported examples. The vacancy of ligands
or linkers systematically generates (surface) terminations which can
possibly show Lewis and/or Bronsted acido-basic features. The
engineering of catalytic sites at the nodes by the creation of defects
(on purpose) appears today as a rational approach for the design of
active MOFs. Similarly to zeolite post-treatments, post-modifications of
MOFs by linker or metal cation exchange appear to be methods of choice.
Despite the mild acidity of defective MOFs, we can account for very
active MOFs in a number of catalytic applications which show higher
performances than zeolites or benchmark catalysts.