Host–Guest and Guest–Guest Interactions of P- and N-Containing Structure Directing Agents Entrapped inside MFI-Type Zeolite by Multinuclear NMR Spectroscopy

Abstract

Highly crystalline pure silica MFI zeolites have been synthesized using tetraethylammonium (TEA), tetraethylphosphonium (TEP) or a mixture of both cations in different proportions as organic structure directing agents (OSDAs). The zeolites have been deeply characterized in order to get insight about the guest-guest interactions involving the OSDAs and the guesthost interactions involving the OSDAs and the inorganic framework, as well as the main features of the resulting materials. The results show that the average size of the MFI crystals decreases when TEP is present within the zeolite and that this cation is homogeneously distributed throughout the crystallites. The multinuclear NMR investigation (1 H, 13 C, 14 N, 19 F, 29 Si, 31 P) indicates that TEP interacts with the zeolite host creating higher heterogeneity of the SiO4 crystallographic sites and a diminution on the mobility of fluorine atoms incorporated into the zeolite. Moreover, the presence of TEP influences the dynamics of the nitrogen atoms of the TEA molecules and 2D heteronuclear correlation experiments give evidence on the spatial proximity of the TEA and TEP molecules in the MFI samples. Then, it is concluded that TEA and TEP are intimately mixed within the zeolites voids of the pure silica MFI samples synthesized by the dual template route using TEP and TEA.

Influence of Organic Structure-Directing Agents on Fluoride Dynamics in As-Synthesized Silicalite-1

“…It has been established experimentally that MFI_(TEA,F) and MFI_(TPA,F) exhibit dynamic disorder of the uoride anions at room temperature. 19,21,22 Whereas the former system…”

“…Very recently, it was also shown that the replacement of tetraethylammonium (TEA) by tetraethylphosphonium (TEP) slows down the uoride motion. 22 Electronic structure calculations in the framework of DFT have been widely used to study zeolite structures and properties. 23 With regard to uoride-containing zeolites, several authors have used DFT methods to investigate the local uoride environment, 16,17,24,25 to predict 19 F NMR shifts or vibrational spectra, 2629 and to study the stability of dierent possible uoride positions.…”

Recent Advances of Solid‐State NMR Spectroscopy for Microporous Materials

“…[44] The full characterization of Ti species in zeolites is essential to understand the detailed property of the Ti active center in heterogeneous catalysis and photocatalysis. 47 Ti/ 49 Ti SSNMR has been applied to uncover the titanium environment of fresh and reused titanium-immobilized mesoporous silica nanoparticles. [45] Additionally, 47,49 Ti SSNMR has been employed to probe the location and chemical environment of Ti in Ti-substituted USY and MFI-type TS-1 zeolites although the spectra featured low resolution because of the low gamma nature and low natural abundance of the NMR-active 47,49 Ti nucleus.…”

“…47 Ti/ 49 Ti SSNMR has been applied to uncover the titanium environment of fresh and reused titanium-immobilized mesoporous silica nanoparticles. [45] Additionally, 47,49 Ti SSNMR has been employed to probe the location and chemical environment of Ti in Ti-substituted USY and MFI-type TS-1 zeolites although the spectra featured low resolution because of the low gamma nature and low natural abundance of the NMR-active 47,49 Ti nucleus. [46] It was found that Ti in a TS-1 framework was essentially tetrahedrally coordinated and became octahedrally coordinated in the presence of water.…”

Elucidating Zeolite Channel Geometry–Reaction Intermediate Relationships for the Methanol‐to‐Hydrocarbon Process

“…These materials exhibit comparable physicochemical properties,asdemonstrated by scanning electron microscope (SEM, Figures S5c-d) as well as MAS 29 Si and 27 Al ssNMR (Figures S6 and S7, Table S3). [47] Importantly,a sshown in Figure 1, qualitative analysis of the diffusion behaviors in zeolite channels using molecular dynamics (MD) simulations exhibited that the channels with short dimensions (SD) were preferentially filled with methanol molecules at the early stage of diffusion, although both channel dimensions were equivalently filled with the molecules eventually (t = t5 in Figure 1). Furthermore,n oa pparent diffusion of the molecules from the SD channels into the channels in long dimensions (LD) was observed ( Figure 1a nd movie S1).…”