Nuclear Magnetic Resonance Spectroscopy for In Situ Monitoring of Porous Materials Formation under Hydrothermal Conditions

Abstract

The employment of nuclear magnetic resonance (NMR) spectroscopy for studying crystalline porous materials formation is reviewed in the context of the development of in situ methodologies for the observation of the real synthesis medium, with the aim of unraveling the nucleation and growth processes mechanism. Both liquid and solid state NMR techniques are considered to probe the local environment at molecular level of the precursor species either soluble in the liquid phase or present in the reactive gel. Because the mass transport between the liquid and solid components of the heterogeneous system plays a key role in the synthesis course, the two methods provide unique insights and are complementary. Recent technological advances for hydrothermal conditions NMR are detailed and their applications to zeolite and related materials crystallization are illustrated. Achievements in the field are exemplified with some representative studies of relevance to zeolites, aluminophosphate zeotypes, and metal-organic frameworks.

On the Role of Enthalpic and Entropic Contributions to the Conformational Free Energy Landscape of MIL‐101(Cr) Secondary Building Units

“…[13] Also, Haouas compared MIL-101(Cr) synthesis in water against DMF and observed that solvent effects are key to determine the final MOF structure. [10,14] Taddei also described SBU formation as a key step in MOF synthesis. [10] Working on MIL-53 Embrechts et al identified the rearrangement of soluble MOF precursors as the rate-limiting step in MOF synthesis.…”

Application of Multinuclear MAS NMR for the in situ Monitoring of Hydrothermal Synthesis of Zeolites

“…Therefore, during the last years, many efforts have been focused on the development of different techniques for the investigation of hydrothermal synthesis in situ. [14][15][16][17][18][19][20] Among the in situ spectroscopic techniques, MAS NMR is one of the most informative, since it is based on the direct observation of atomic nuclei, which compose the frameworks of reagents, products and intermediates during the synthesis and therefore provides a unique advantage to probe the local structure at the molecular level and to access the crystallization process from the very beginning. Besides that, it allows distinguishing between different species in solution and solid state, which is not possible by other techniques.…”

Solid-state NMR spectroscopy: an advancing tool to analyse the structure and properties of metal–organic frameworks

“…41 The synthesis of various materials including MOFs can be monitored by in situ liquid-state and solid-state NMR spectroscopy as reviewed by Haouas. 42 An elegant combination of liquid-and solid-state NMR spectroscopy is denoted as CLASSIC (combined liquid-and solid-state in situ crystallization). It is performed on identical samples under MAS by interleaved detection of directly excited and crosspolarization spectra.…”