Tailoring the acid strength of microporous silicoaluminophosphates through the use of mixtures of templates: Control of the silicon incorporation mechanism

SAPO-5 samples have been synthesized with triethylamine (TEA), benzylpyrrolidine (BP) and mixtures of them as structure directing agents (SDAs). It has been observed that in the as-synthesised materials the concentration of SDAs (molecules per unit cell) and the Si content are similar. According to the different molecular size of both SDAs, the samples exhibit higher organic weight and lower water content as the molar fraction of BP in the synthesis gel increases. These differences in selectivity for organic/water incorporation influences the mechanism of Si substitution in the AlPO lattice: the higher organic content obtained at higher BP/TEA ratio leads to the formation of large Si islands, while the higher water content of the sample obtained with TEA enhances the formation of isolated Si(OAl)4 environments. Interestingly, it has been found that these two opposite trends can be tailored to a certain point by using mixtures of both SDAs, TEA and BP, in the required ratio. The catalytic activity of the samples has been tested in the isomerisation of m-xylene. It has been observed a higher activity of samples obtained with BP as the main SDA, thus evidencing the better performance of large Si islands in this reaction.MEC (CTQ2006-06282)Peer reviewe

Simulaciones Moleculares Aplicadas al Estudio de la Dirección de Estructura de Materiales Microporosos

Trabajo presentado en el 2º Ciclo de Palestras sobre Peneiras Moleculares, celebrado en Natal (Brasil) del 13 al 14 de noviembre de 2014.Peer Reviewe

Efecto director de estructura de moléculas fluoradas en la síntesis de aluminofosfatos microporosos cristalinos

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Química-Física Aplicada. Instituto de Catálisis y Petroleoquímica (ICP-CSIC).--Fecha de lectura 10-01-2006El objetivo general de esta tesis doctoral consiste en realizar un estudio sobre el efecto de las moléculas orgánicas que actúan como agentes directores de estructura (ADEs) en la síntesis de aluminofosfatos microporosos cristalinos. Puesto que no existe enlace entre ellos, la capacidad de una molécula orgánica para dirigir la síntesis de una determinada estructura zeolítica depende fundamentalmente de las interacciones intermoleculares que se establezcan entre ambas. El llenado de los poros y cavidades de la zeolita por parte de estos agentes orgánicos, así como el estrecho ajuste que se establece entre ellos, implica que las interacciones químicas intermoleculares que se establecen entre estas moléculas orgánicas y las estructuras zeolíticas tienen lugar, fundamentalmente, a través de los átomos de hidrógeno terminales de las moléculas orgánicas. El tipo de moléculas más utilizado como agentes directores de estructuras zeolíticas han sido aminas terciarias y sales de amonio cuaternario. En este tipo de moléculas, todos los átomos de hidrógeno están enlazados a átomos de carbono; de este modo, las interacciones que se establezcan siempre serán a través de esos átomos de hidrógenos enlazados a átomos de carbono. Por tanto, la aparentemente amplia diversidad de agentes directores de estructura que se ha usado hasta hoy en la síntesis de materiales zeolíticos se refiere sólo a la forma y al tamaño de las moléculas. Sin embargo, el carácter químico de esas interacciones ha permanecido inalterado, pues éstas siempre han tenido lugar a través de esos átomos de hidrógeno enlazados a átomos de carbono. Por ello, el objetivo principal de este trabajo consiste en tratar de modificar el carácter químico de esas interacciones intermoleculares, en un intento por obtener nuevos materiales zeolíticos, tanto nuevas estructuras como nuevas composiciones, así como por entender el significado y función de las moléculas orgánicas en la síntesis de estas estructuras.Peer reviewe

accordion-like effect of flexible organic structure-directing agents in the synthesis of ferrierite zeolite

Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.micromeso.2020.110149[EN] Ferrierite zeolite was synthesized by a co-structure-directing route using a highly flexible diquaternary ammo-nium cation (N,N0-bis-triethylpentanediyldiammonium) as a structure directing agent in combination with tet-ramethylammonium as a small co-structure-directing agent. Strong alterations of the 13C NMR bands of the bulky organic dication upon confinement within the ferrierite framework suggest a change of conformation driven by host-guest interactions. A combination of molecular mechanics and DFT calculations of the theoretical 13C NMR chemical shifts allowed to explain the observed differences in the NMR bands of the dication in solution and when hosted in ferrierite: upon confinement, the flexible dication needs to squeeze through the flexible pentyl chain which locates along the 10 MR ferrierite channels in order to host the two bulky triethyl ammonium groups in adjacent intersections with 8 MR channels. Our work suggests that highly flexible cations, usually considered as less convenient organic structure-directing agents because of low specificity, have the advantage of being able to properly fit with different zeolite cell dimensions through an accordion-like effect by squeezing or stretching their flexible chains.This work has been partially financed by the Spanish State Research Agency (Agencia Española de Investigación, AEI) and the European Regional Development Fund (Fondo Europeo de Desarrollo Regional, FEDER) through the Project MAT2016-77496-R (AEI/FEDER, UE), and by Consejo Superior de Investigaciones Científicas (CSIC) through project 201780I043. R.K.S.A. is grateful to Fundação de Amparo à Pesquisa do Estado de São Paulo – FAPESP (Process nº 2014/10609-5) for the scholarship and financial support during post-doctoral internship at Instituto de Catálisis y Petroleoquímica (CSIC). Secretaría General Adjunta de Informática-CSIC is acknowledged for running the calculations, and BIOVIA for providing the computational software.Peer reviewe

Synthesis of a germanosilicate zeolite HPM-12 using a short imidazolium-based dication: Structure-direction by charge-to-charge distance matching

[EN] A short imidazolium based dication, with only three methylene units in the spacer linker, selectively directs the crystallization of zeolite HPM-12 (?UOE) as long as there is enough germanium present in the synthesis gel. The integrity of the dication is proved by dissolution of the zeolite and H and C NMR spectroscopy, where significant effects of organic dication concentration and the presence and concentration of HF need to be taken into account. For the as-made HPM-12 zeolite, a large shift of 9 ppm of one resonance in the C MAS NMR spectrum is due to the particular conformation of the dication imposed by confinement in the zeolite framework, as found by DFT calculations. The structure-directing ability of this kind of dication with varying length of the linker suggests that matching of the distance between positive charges (imidazolium moieties) and negative charges (double four rings in which fluoride resides) plays a crucial role during crystallization.The authors acknowledge financial support from the Spanish Ministerio de Economía y Competitividad, the Spanish Agencia Estatal de Investigación and the EU's Fondo Europeo de Desarrollo Regional under projects MAT2016-77496-R (AEI/FEDER, UE) and MAT2015-71117-R (MINECO/FEDER, UE). We acknowledge the support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI). P.L. is grateful to the China Scholarship Council (CSC) for a fellowship and to the Dalian Institute of Chemical Physics for permission to leave. Centro Técnico Informático-CSIC is acknowledged for running the calculations and Biovia for providing the computational software. We also thank L. A. Villaescusa for helpful comments

Material compuesto de estilbita-nanohidroxiapatita, procedimiento de preparación y utilización para la eliminación de fluoruro del agua

La presente invención se refiere a un material compuesto basado en una zeolita natural rica en Calcio, estilbita, en cuya superficie se hace crecer de manera controlada hidroxiapatita de tamaño nanométrico, al procedimiento mediante el cual se obtiene dicho material compuesto, así como a su aplicación en la eliminación de fluoruro del agua con fines de potabilización. Como consecuencia de las citadas características particulares de los cristales de hidroxiapatita, ésta posee una capacidad intrínseca (en base a peso de hidroxiapatita) de eliminación de fluoruro extremadamente elevada lo cual, unido al bajo coste y fácil accesibilidad de los materiales empleados en su preparación, así como a la facilidad del procedimiento, convierte estos materiales en candidatos idóneos para su empleo en la eliminación de fluoruro de aguas ricas en este contaminante.Peer reviewedConsejo Superior de Investigaciones Científicas, Addis Ababa UniversityB1 Patente sin examen previ

Zeolite structure direction by simple bis(methylimidazolium) cations: The effect of the spacer length on structure direction and of the imidazolium ring orientation on the 19F NMR resonances

[EN] A series of doubly charged structure-directing agents based on two methylimidazolium moieties linked by a linear bridge of n = 3,4,5, or 6 methylene groups has been used in the synthesis of pure silica zeolites in the presence of fluoride. All of them yielded zeolite TON while only the one with n = 4 was able to produce also zeolite MFI at highly concentrated conditions. In this MFI zeolite, two distinct 19F MAS NMR resonances with about equal intensity were observed, indicating two different chemical environments for occluded fluoride. With the singly charged 1-ethyl-3-methylimidazolium cation, which can be formally considered as the "monomer" of the bis-imidazolium cation with n = 4, TON and MFI were also obtained, and again two 19F MAS NMR resonances now with largely dissimilar intensities were observed in MFI. Molecular mechanics simulations support a commensurate structure-direction effect for n = 4 in MFI, with each imidazolium ring, in two different orientations, sitting close to the [4 15 26 2] cage. Periodic DFT calculations suggest that F in MFI resides always in the [4 15 26 2] cages, with the different 19F resonances observed being due to the different orientation of the closest imidazolium ring. © 2012 American Chemical Society.Financial support by the Spanish CICYT, MAT2009-09960 is gratefully acknowledged. AR thanks CSIC for a JAE-predoc fellowship. LGH acknowledges the Spanish Minister of Science and Innovation for a Juan de la Cierva contract. Accelrys is acknowledged for providing the software, and Centro Técnico de Informática-CSIC for running the calculations.Peer reviewe

Synthesis of pure silica MFI zeolites using imidazolium-based long dications. A comparative study of structure-directing effects derived from a further spacer length increase

[EN] Length-dependent structure direction of linear methylimidazolium-based dications towards MFI zeolite, previously known only for the tetramethylene spacer, has also been found for octamethylene and decamethylene spacers. This works only under highly concentrated conditions, whereas dilution always tends to favor TON, a default structure that is the only zeolite obtained with the other reported dications (with tri-, penta-, and hexamethylene spacers). The locations and conformations of the dications have been studied by molecular mechanics simulations. As longer dications introduce lower density of positive charges in the zeolite, the density of connectivity defects also decreases. Finally, these long dications cannot easily place each charged imidazolium ring in the two possible orientations (either parallel or perpendicular to 4MR close to F sites) found for the tetramethylene case. Hence, although the three MFI materials display two F NMR resonances at similar chemical shifts, their relative intensities strongly vary as a function of the spacer length.Financial support provided by the Spanish Ministry of Economy and Competitiveness (projects MAT2015-71117-R and MAT2016-77496-R) is acknowledged. P. L. is grateful to the China Scholarship Council (CSC) for a fellowship and to the Dalian Institute of Chemical Physics for permission to leave. Centro Técnico Informático-CSIC is acknowledged for running the calculations, and Biovia is acknowledged for providing the computational software

Benzylimidazolium cations as zeolite structure-directing agents. Differences in performance brought about by a small change in size

Two imidazolium cations containing a benzyl group, 1-benzyl-3- methylimidazolium and 1-benzyl-2,3-dimethylimidazolium, generally produce the large pore zeolite MTW when used as structure directing agents in the synthesis of pure silica zeolites by the fluoride route. When working at low water contents only the smallest of these cations is able to crystallize MFI, a zeolite with crossing medium pore channels. In that case, MFI is metastable towards MTW, but the in situ transformation slows down as the water content is decreased. Structure-direction is discussed in terms of hydrophobicity, flexibility and size of the cations. A conformational analysis shows that the bulkier 1-benzyl-2,3-dimethylimidazolium is slightly more rigid than the smaller 1-benzyl-3-methylimidazolium, and thus could have been expected to depart more easily from crystallizing a default structure such as MTW. The different performance of both cations is investigated by molecular mechanics and the simulations show that the small increase in size brought about by a methyl group at position 2 of the imidazolium ring prevents an adequate sitting of the cation at channel intersections with the imidazolium ring close to the small cavity in which fluoride resides in MFI. The calculated interaction energies help to understand the phase selectivity and time evolution experimentally observed with both cations. © 2013 The Royal Society of Chemistry.Financial support from the Spanish CICYT, MAT2009-09960, is gratefully acknowledged. AR thanks CSIC and Fondo Social Europeo (EU) for a JAE-predoc fellowship. LGH acknowledges the Spanish Minister of Economy and Competitivity for a Juan de la Cierva contract.Peer Reviewe

Synthesis of Pure Silica MWW Zeolite in Fluoride Medium by Using an Imidazolium-Based Long Dication

[EN] As the spacer length in 1,2-dimethylimidazolium-based dications increases beyond a specific point (six methylene units), they fail in structure-directing towards STW zeolites in any synthetic conditions. These dications can instead produce, under fluoride concentrated conditions, either *BEA [in the case of the eight-methylene-unit structure-directing agent (SDA)] or MWW (ten methylene units) zeolites. For any length of the dication, the default zeolite (MTW) is a relatively dense zeolite containing a unidimensional channel, whereas the zeolite demanding most specificity (STW, *BEA or MWW) is more porous, affording a larger concentration of the dication to be occluded. This work provides the first reported fluoride synthesis of pure silica MWW zeolites. Charge balance of the organic dications in this zeolite was achieved by combining “structural” silanolates, regular “connectivity defects” and occluded fluoride. Molecular mechanics calculations showed a perfect fit of the decamethylenebis(dimethylimidazolium) dication in the sinusoidal intralayer pore system of MWW. The calculations showed also that the dication is able to stabilize the interlayer space without disturbing the hydrogen-bonding system that holds the layers together in the as-made material. The F magic-angle spinning (MAS) NMR presented two distinct resonances at −71 and −83 ppm, which, on the basis of DFT calculations, we tentatively assigned to fluoride occluded in [46] and [456] cages of the MWW structure, respectively. The same DFT study determines a different chemical shift of one methyl C nuclear magnetic resonance according to the imidazolium ring residing in the sinusoidal channels or in the large cup cavities, thus explaining an experimentally observed splitting of that resonance.Financial support provided by the Spanish Ministry of Economy and Competitiveness (projects MAT2015-71117-R and MAT2016-77496-R) is acknowledged. P. L. is grateful to the China Scholarship Council (CSC) for a fellowship and to the Dalian Institute of Chemical Physics for permission to leave. Centro Técnico Informático-CSIC is acknowledged for running the calculations, and Biovia is acknowledged for providing the computational software