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[EN] The nature of organic structure directing agents (OSDAs) is of paramount importance in the final properties of zeolites, particularly the framework and porosity. Recently, the use of P-containing OSDAs has been employed for new zeolites, but there is little discussion compared to their analogues N-OSDAs. The main objective of this work is the characterization of pure silica MFI zeolite (silicalite-1) prepared by the dual-template route with tetrapropylammonium (TPA), tetrapropylphosphonium (TPP) cations, and mixtures thereof aiming to understand by advanced NMR methods how the nature of the organic influences the physico-chemical properties of the zeolite. Silicalite-1 has been successfully synthesized using the dual-template procedure with TPA and TPP molecules. Both OSDAs are incorporated into the zeolite without any specific preference, differently to that observed before for the TEA/TEP system, and homogenously mixed inside of the zeolite voids. The presence of TPP leads to the incorporation of less F, raising the concentration of Q(3)-defective sites in the silicalite-1 zeolites. Detailed NMR results indicate that those structural defects are close to the -CH3 group of the entrapped OSDAs in the zeolite and these defects consist of at least two silanol groups stabilizing the Si-O- species, which is responsible for the charge balancing.

The nature of organic structure directing agents (OSDAs) is of paramount importance in the final properties of zeolites, particularly the framework and porosity. Recently, the use of P-containing OSDAs has been employed for new zeolites, but there is little discussion compared to their analogues N-OSDAs. The main objective of this work is the characterization of pure silica MFI zeolite (silicalite-1) prepared by the dual-template route with tetrapropylammonium (TPA), tetrapropylphosphonium (TPP) cations, and mixtures thereof aiming to understand by advanced NMR methods how the nature of the organic influences the physico-chemical properties of the zeolite. Silicalite-1 has been successfully synthesized using the dual-template procedure with TPA and TPP molecules. Both OSDAs are incorporated into the zeolite without any specific preference, differently to that observed before for the TEA/TEP system, and homogenously mixed inside of the zeolite voids. The presence of TPP leads to the incorporation of less F, raising the concentration of Q-defective sites in the silicalite-1 zeolites. Detailed NMR results indicate that those structural defects are close to the –CH group of the entrapped OSDAs in the zeolite and these defects consist of at least two silanol groups stabilizing the Si-O species, which is responsible for the charge balancing.

Expanding the previously known family of -onium (ammonium, phosphonium, and sulfonium) organic structure-directing agents (OSDAs) for the synthesis of zeolite MFI, a new member, the arsonium cation, is used for the first time. The new group of tetraalkylarsonium cations has allowed the synthesis of the zeolite ZSM-5 with several different chemical compositions, opening a route for the synthesis of zeolites with a new series of OSDA. Moreover, the use of As replacing N in the OSDA allows the introduction of probe atoms that facilitate the study of these molecules by powder X-ray diffraction (PXRD), solid-state nuclear magnetic resonance (MAS NMR), and X-ray absorption spectroscopy (XAS). Finally, the influence of trivalent elements such as B, Al, or Ga isomorphically replacing Si atoms in the framework structure and its interaction with the As species has been studied. The suitability of the tetraalkylarsonium cation for carrying out the crystallization of zeolites is demonstrated along with the benefit of the presence of As atoms in the occluded OSDA, which allows its advanced characterization as well as the study of its evolution during OSDA removal by thermal treatments.

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 guest-host 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 (H, C, N, F, Si, P) indicates that TEP interacts with the zeolite host creating higher heterogeneity of the SiO 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 zeolites. Then, it is concluded that TEA and TEP are intimately mixed within the zeolite voids of the pure silica MFI samples synthesized by the dual template route.

In this work a new ultrafast data collection strategy for electron diffraction tomography is presented that allows reducing data acquisition time by one order of magnitude. This methodology minimizes the radiation damage of beam-sensitive materials, such as microporous materials. This method, combined with the precession of the electron beam, provides high quality data enabling the determination of very complex structures. Most importantly, the implementation of this new electron diffraction methodology is easily affordable in any modern electron microscope. As a proof of concept, we have solved a new highly complex zeolitic structure named ITQ-58, with a very low symmetry (triclinic) and a large unit cell volume (1874.6 Å), containing 16 silicon and 32 oxygen atoms in its asymmetric unit, which would be very difficult to solve with the state of the art techniques.