Raquel Martínez-Franco

Synthesis of an extra-large molecular sieve using proton sponges as organic structure-directing agents

The synthesis of crystalline microporous materials containing large pores is in high demand by industry, especially for the use of these materials as catalysts in chemical processes involving bulky molecules. An extra-large–pore silicoaluminophosphate with 16-ring openings, ITQ-51, has been synthesized by the use of bulky aromatic proton sponges as organic structure-directing agents. Proton sponges show exceptional properties for directing extra-large zeolites because of their unusually high basicity combined with their large size and rigidity. This extra-large–pore material is stable after calcination, being one of the very few examples of hydrothermally stable molecular sieves containing extra-large pores. The structure of ITQ-51 was solved from submicrometer-sized crystals using the rotation electron diffraction method. Finally, several hypothetical zeolites related to ITQ-51 have been proposed.

Efficient One‐Pot Preparation of Cu‐SSZ‐13 Materials using Cooperative OSDAs for their Catalytic Application in the SCR of NOx

The cooperative use of the Cu‐tetraethylenepentamine complex and N,N,N‐trimethyl‐1‐adamantammonium as organic structure‐directing agents (OSDAs) enabled the rationalized “one‐pot” preparation of Cu‐containing SSZ‐13 zeolites. A detailed study of different synthetic variables permitted the control of the Si/Al and Cu/(Si+Al) ratios in the final solids. Cu‐SSZ‐13 molecular sieves synthesized in alkaline media demonstrate excellent catalytic activities and good hydrothermal stabilities for the selective catalytic reduction of NOx. Finally, the effect of synthesis media on the catalytic active sites is also demonstrated and a remarkable activity loss for samples synthesized in fluoride media is observed.

Improving the catalytic performance of SAPO-18 for the methanol-to-olefins (MTO) reaction by controlling the Si distribution and crystal size

The physico-chemical properties of the small pore SAPO-18 zeotype have been controlled by properly selecting the organic molecules acting as organic structure directing agents (OSDAs). The two organic molecules selected to attempt the synthesis of the SAPO-18 materials were N,N-diisopropylethylamine (DIPEA) and N,N-dimethyl-3,5-dimethylpiperidinium (DMDMP). On the one hand, DIPEA allows small crystal sizes (0.1–0.3 μm) to be attained with limited silicon distributions when the silicon content in the synthesis gel is high (Si/TO2 ∼0.8). On the other hand, the use of DMDMP directs the formation of larger crystallites (0.9–1.0 μm) with excellent silicon distributions, even when the silicon content in the synthesis media is high (Si/TO2 ∼0.8). It is worth noting that this is the first description of the use of DMDMP as OSDA for the synthesis of the SAPO-18 material, revealing not only the excellent directing role of this OSDA in stabilizing the large cavities present in the SAPO-18 structure, but also its role in selectively placing the silicon atoms in isolated framework positions. The synthesized SAPO-18 materials have been characterized by different techniques, such as powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), N2 adsorption, solid state NMR, and ammonia temperature programmed desorption (NH3-TPD). Finally, their catalytic activity has been evaluated for the methanol-to-olefin (MTO) process at different reaction temperatures (350 and 400 °C), revealing that the SAPO-18 catalysts with optimized silicon distributions and crystal sizes show excellent catalytic properties for the MTO reaction. These optimized SAPO-18 materials present improved catalyst lifetimes compared to standard SAPO-34 and SSZ-39 catalysts, even when tested at low reaction temperatures (i.e. 350 °C).

Supra-molecular assembly of aromatic proton sponges to direct the crystallization of extra-large-pore zeotypes.

The combination of different experimental techniques, such as solid 13C and 1H magic-angle spinning NMR spectroscopy, fluorescence spectroscopy and powder X-ray diffraction, together with theoretical calculations allows the determination of the unique structure directing the role of the bulky aromatic proton sponge 1,8-bis(dimethylamino)naphthalene (DMAN) towards the extra-large-pore ITQ-51 zeolite through supra-molecular assemblies of those organic molecules.

Synthesis of highly stable metal-containing extra-large-pore molecular sieves.

The isomorphic substitution of two different metals (Mg and Co) within the framework of the ITQ-51 zeotype (IFO structure) using bulky aromatic proton sponges as organic structure-directing agents (OSDAs) has allowed the synthesis of different stable metal-containing extra-large-pore zeotypes with high pore accessibility and acidity. These metal-containing extra-large-pore zeolites, named MgITQ-51 and CoITQ-51, have been characterized by different techniques, such as powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectrometry, UV–Vis spectroscopy, temperature programmed desorption of ammonia and Fourier transform infrared spectroscopy, to study their physico-chemical properties. The characterization confirms the preferential insertion of Mg and Co atoms within the crystalline structure of the ITQ-51 zeotype, providing high Brønsted acidity, and allowing their use as efficient heterogeneous acid catalysts in industrially relevant reactions involving bulky organic molecules.