Influence of a Confined Methanol Solvent on the Reactivity of Active Sites in UiO‐66

• Published in: Chemphyschem Vol. 19; no. 4; pp. 420 - 429
• Main Authors: Caratelli, Chiara, Hajek, Julianna, Rogge, Sven M. J., Vandenbrande, Steven, Meijer, Evert Jan, Waroquier, Michel, Van Speybroeck, Veronique
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 19.02.2018; John Wiley and Sons Inc
• Subjects: ab initio calculations; Atomic structure; Binding Sites; Chemical bonds; Computer simulation; Density functional theory; Hydrogen Bonding; Hydrogen storage; hydrogen transfer; Lewis acid; Metal-organic frameworks; Metal-Organic Frameworks - chemistry; Metals; Methanol; Methanol - chemistry; Modelling; Models, Chemical; Molecular dynamics; Molecular Dynamics Simulation; Monte Carlo Method; Porosity; Protons; Quantum Theory; solvent effects; Solvents; Solvents - chemistry; Terephthalate; UiO-66; Water - chemistry; Zirconium oxides; solvent effects; UiO-66; ab initio calculations; molecular dynamics; hydrogen transfer
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.201701109

UiO‐66, composed of Zr‐oxide bricks and terephthalate linkers, is currently one of the most studied metal–organic frameworks due to its exceptional stability. Defects can be introduced in the structure, creating undercoordinated Zr atoms which are Lewis acid sites. Here, additional Brønsted sites can be generated by coordinated protic species from the solvent. In this Article, a multilevel modeling approach was applied to unravel the effect of a confined methanol solvent on the active sites in UiO‐66. First, active sites were explored with static periodic density functional theory calculations to investigate adsorption of water and methanol. Solvent was then introduced in the pores with grand canonical Monte Carlo simulations, followed by a series of molecular dynamics simulations at operating conditions. A hydrogen‐bonded network of methanol molecules is formed, allowing the protons to shuttle between solvent methanol, adsorbed water, and the inorganic brick. Upon deprotonation of an active site, the methanol solvent aids the transfer of protons and stabilizes charged configurations via hydrogen bonding, which could be crucial in stabilizing reactive intermediates. The multilevel modeling approach adopted here sheds light on the important role of a confined solvent on the active sites in the UiO‐66 material, introducing dynamic acidity in the system at finite temperatures by which protons may be easily shuttled from various positions at the active sites. Move those hydrogens! Methanol solvent in the pores of UiO‐66 has a remarkable influence on the active sites. Simulations show that it forms a dynamic hydrogen‐bond network anchored on the defective site and aids in proton‐transfer mechanisms, both within the active site and from the solvent (see picture). These extra interactions can be beneficial for catalysis and in modulating the properties of the material, such as in the linker exchange process.