Advanced Solid-State NMR Techniques for the Study of Molecular Sieves

Determining the location and nearest neighbours of aluminium in zeolites with atom probe tomography

“…The major drawback of bulk characterization methods is the averaging over the whole crystalline bulk, while any atomic-scale variation in the distribution of Al goes undiscovered. For example, solid-state 27 Al MAS NMR can provide detailed information about T–O–T angle and chemical nature of Al species 27 ; however, the signal is averaged over the crystalline bulk and the analysis of T-site distribution still remains a difficult task. Furthermore, X-ray and electron probe-based techniques give no distinguishable contrast between Si and Al making high-resolution analysis very challenging.…”

Recent developments in solid-state NMR spectroscopy of crystalline microporous materials

“…Readers are referred to more comprehensive recent reviews for more detail. [4][5][6][7][8][9][10] The structures of microporous materials can generally be considered as nets, with cationic vertices and anionic links between the vertices, as shown schematically in Fig. 1(a) for the sodalite (SOD) net.…”

“…45 This has generally limited its application in comparison to MQMAS, although it has been applied to phosphate-based frameworks. 4,5,46 Although useful structural information can be obtained from high-resolution spectra, more detailed information can be obtained by exploiting the interactions between nuclei, through experiments that "recouple" a particular interaction or that transfer magnetisation between nuclear species. 29 Experiments that use the dipolar coupling enable internuclear distances or proximities to be probed, while those that use the scalar coupling provide information on covalent connectivity.…”

“…Comparison of experimental lineshapes (often acquired as a function of temperature) to those from simulation is able to provide information both on the rate and type of dynamic process. Many early examples focused on the study of loaded zeolites, 5 including, more recently, the study of methanol-d 4 within NaX and NaY zeolites. 106 In this latter example, variable temperature NMR was able to identify gas phase, liquid-like and immobilised methanol in both zeolites over a temperature range of 20 to 300 K. Two modes of methanol binding were identified -one involving interaction with the Na + cation and the second an interaction with the framework O in Al-O-Si linkages.…”

“…Readers are referred to more comprehensive recent reviews for more detail. [4][5][6][7][8][9][10] The structures of microporous materials can generally be considered as nets, with cationic vertices and anionic links between the vertices, as shown schematically in Figure 1(a) for the sodalite (SOD) net. 11 The nature of the vertices and links depends on the class of material in question, and the same underlying topology (i.e., network connectivity) can be constructed from many chemically-distinct species.…”