Using a combination of modeling and experiment, we have developed and studied nanoporous catalysts that control the alignment of reactant molecules in ways that can be used to tune catalytic activity and selectivity. In the first example, metal nanoparticles (NP) are encapsulated by metal–organic frameworks (MOFs) for regioselective catalysis. The regioselectivity in these materials arises from steric constraints imposed by the porous MOF structure, which limit the way molecules approach and interact with the metal surface. We have introduced a conceptually simple DFT approach to model reactions under such steric constraints and used this method to understand the potential of Pd NPs encapsulated in MOFs for the oxidation of n-butane to 1-butanol. We also used a combination of DFT calculations and DRIFTS for adsorbed CO to characterize the nanoparticle-MOF interface. These studies reveal that in Pt@ZIF-8, the ZIF linkers donate electron density to the Pt NPs, affecting their electronic structure. DRIFTS measurements also show that the MOF linker can undergo an unexpected reaction with the Pt NPs during the encapsulation process. In the second example, the catalytic activity for acyl transfer from N-acetylimidazole (NAI) to different pyridylcarbinol (PC) regioisomers (2-PC, 3-PC, and 4-PC) was studied in a set of zirconium-based (porphinato)zinc MOFs of different topologies. The experimentally obtained reaction kinetics can be understood with the help of molecular modeling. The catalytic activity is shown to vary across the series of MOFs due to the different extent to which each topology facilitates reactant preconcentration and alignment of PC and NAI via coordination to framework porphyrin sites (orientation effects). The work shows how the proper alignment of catalytic linkers can enhance reaction rates in MOFs.

Design of metal-organic framework catalysts beyond the active site

255th National Meeting (2018)

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