Detecting Lewis acid sites in metal-organic frameworks by density functional theory

Metal organic framework is one of the heterogeneous solid catalysts that has been exploited for wide range of applications in the past decades, next to zeolites. Amongst many applications offered by MOFs, heterogeneous catalysis is one such field attracted many researchers from catalysis and materials chemistry fields. This is due to the presence of broad range of active sites in MOFs like Lewis acids, Bro center dot nsted acid/base, host for metal nanoparticles/metal complexes. These active sites are homogeneously distributed within the framework and thus, behaving as superior heterogeneous catalysts compared to other related solids. Amongst these different active sites in MOFs, the use of Lewis acids as active sites has been well studied for many types of organic reactions. Although the presence of these sites is proved experimentally by appropriate characterization, experimental evidences are also provided in some cases. In the present review, we aim to present the importance of density functional theory (DFT) calculations to complement the experimental evidences in elucidating the presence of Lewis acids as well as their role in the catalytic reactions. This minireview is organized with a brief introduction on MOFs in catalysis which is followed by some selected MOFs and categorized based on the nature of metal ions. The presence of Lewis acids in MOFs in these selected examples are nicely proved with the assistance of DFT calculations which are considered as supporting evidences to experimental data. Also, emphasis is given to illustrate the importance of theoretical evidences to clearly understand the role of MOFs in promoting the reactions and providing convincing evidences to support the proposed reaction mechanism. Furthermore, our views in this area are summarized in conclusion section at the end of this review.