Hydrogenation Size-Selective Pt/Hollow Beta Catalysts.

The aim of the present work is to synthesize a zeolite-based catalyst with a hollow morphology and highly dispersed metal nanoparticles (NPs) encapsulated inside the zeolite micropores. For this purpose, we have studied a treatment using tetraalkylammonium (TAA) bromides for the selective removal of a large Pt particle from the outer surface of a hollow Beta zeolite. TEM analysis reveals that we succeeded in the synthesis of a hollow beta zeolite single crystal with encapsulated particles, with a high dispersion of 50-60 %. The molecular-sieve-type mechanism of the obtained catalysts was evaluated in the model reaction of toluene and mesitylene catalytic hydrogenation. Thanks to the high dispersion. a 10-fold activity enhancement has been obtained with respect to hollow beta zeolites with encapsulated NPs recently described in the literature.

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.

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.

Unusually Low Heat of Adsorption of CO2 on AlPO and SAPO Molecular Sieves.

The capture of CO2 from post-combustion streams or from other mixtures, such as natural gas, is an effective way of reducing CO2 emissions, which contribute to the greenhouse effect in the atmosphere. One of the developing technologies for this purpose is physisorption on selective solid adsorbents. The ideal adsorbents are selective toward CO2, have a large adsorption capacity at atmospheric pressure and are easily regenerated, resulting in high working capacity. Therefore, adsorbents combining molecular sieving properties and low heats of adsorption of CO2 are of clear interest as they will provide high selectivities and regenerabilities in CO2 separation process. Here we report that some aluminophosphate (AlPO) and silicoaluminophosphate (SAPO) materials with LTA, CHA and AFI structures present lower heats of adsorption of CO2 (13-25 kJ/mol) than their structurally analogous zeolites at comparable framework charges. In some cases, their heats of adsorption are even lower than those of pure silica composition (20-25 kJ/mol). This could mean a great improvement in the regeneration process compared to the most frequently used zeolitic adsorbents for this application while maintaining most of their adsorption capacity, if materials with the right stability and pore size and topology are found.

High-silica nanocrystalline Beta zeolites: efficient synthesis and catalytic application.

An efficient synthesis methodology to obtain homogeneous nanosized high-silica Beta zeolites (∼10-20 nm) with high solid yields (above 95%) using simple alkyl-substituted flexible dicationic OSDAs is described. These dicationic OSDAs allow the synthesis of nanosized Beta zeolites with different Si/Al ratios (15-30) in alkaline and fluoride media, resulting in nanocrystalline materials with different physico-chemical properties. These nanosized Beta zeolites show better catalytic behavior towards the industrially-relevant alkylation of benzene with propylene to obtain cumene compared with other commercially available nanosized Beta zeolites.

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.