Search

One of the pioneering metal organic framework material, called MOF-2 and having the formula [Zn2(BDC)2], still continues awakening interest amongst the scientific community in spite of its layered character. However, the synthesis methods are either experimentally complicated or in two steps through the transformation of MOF-1. Here, we describe the preparation of a high-quality MOF-2 under more sustainable conditions, including room temperature, absence of any amine or any other pH-controller, partial substitution of the harmful organic solvent (N,N-dimethylformamide) by water, and by simply mixing linker and metal sources, the latter being zinc acetate, carefully selected as a function of their solubility in the solvent mixture. The optimum ratio of Zn(OAc)2·4H2O to terephthalic acid (H2BDC) is 1.74 and H2O to DMF is 3. MOF-2 [Zn2(BDC)2] has been characterized using powder X-ray diffraction, thermogravimetric analysis, N2 adsorption/desorption and scanning electron microscopy, all of them supporting the good quality of the material.

Different TAPO-5 materials, prepared from Ti(III) chloride, have been tested as catalysts in the oxidation of cyclohexene with hydrogen peroxide under anhydrous conditions. Solid TiCl3 was shown to render better synthesis reproducibility and higher catalytic activity of the resultant materials compared to TiCl3 aqueous solution. The synthesis of these materials was carried out under N2 atmosphere to preserve the initial oxidation state of Ti during the crystallization process. As a consequence, the so-called Ti(III)APO-5 materials have Ti environments different to those found in conventional TAPO-5 (Ti(IV)APO-5). Indeed, their catalytic activity in the oxidation of cyclohexene markedly overcomes that of the Ti(IV)APO-5 at any Ti content and after any reaction time. Turnover number (TON) of Ti(III)APO-5 samples exponentially increases as Ti content decreases, the Ti-poorer sample (Ti/(Ti + Al + P) molar ratio of 0.003) reaching TON values higher than 200 after 6 h of reaction at 343 K and higher than 550 after 24 h. The interest of Ti(III)APO-5 catalysts lies on their high selectivity to products formed through allylic oxidation of cyclohexene. The main product of this reaction, 2-cyclohexenyl hydroperoxide, was obtained with more than 80% selectivity over Ti(III)APO-5 catalysts. This behavior is in contrast with the well-known strong tendency of the more active Ti-zeolites to epoxidize the double bond.

A new M-MOF-74 material, with M being cadmium, is described. The so-called Cd-MOF-74 material was prepared under solvothermal conditions using cadmium acetate as metal source. It was characterized by a variety of physico-chemical techniques including PXRD, TGA, N2 adsorption–desorption isotherms, SEM, IR and multinuclear solid-state NMR. Although the quality and/or the size of the afforded crystals did not allow us solving the structure by single-crystal X-ray diffraction, the information given by different characterization techniques is enough to confirm that the sample is indeed a Cd-based MOF-74-like material. Fingerprint-based PXRD and FTIR techniques showed a good matching between the Cd-MOF-74 and the well-known Zn-MOF-74 samples. Likewise, TGA and N2 adsorption–desorption at 196 °C gave expected values of Cd/linker ratio and textural properties, respectively. SEM certified the homogeneity of crystals and the absence of impurities. Among the divalent metal ions capable to produce MOF-74 materials, Cd2+ presents some singularities: (i) it is the first metal of the second transition metal row able to led to a M-MOF-74 material; (ii) due to reasonably good magnetic properties of the diamagnetic non-quadrupolar 113Cd and 111Cd nuclei, metal-adsorbate interactions can be studied from a metal point of view by means of NMR techniques.

This paper describes the preparation and characterization of nanoscaled M-MOF-74/CPO-27-M (M = Mg, Mn, Co, Ni, and Zn) materials at room temperature. Some of the so-formed crystals are the smallest ones of any metal−organic framework (MOF) material (and, to the best of our knowledge, of any microporous material) ever reported. They are at the limit of being able to diffract, particularly those forming the Co- and Ni-MOF-74 samples. Consequently, unequivocal identification as the crystalline MOF-74 phase was deduced by combining other characterization techniques rather than powder X-ray diffraction. These small crystals are unstable as isolated ones, so they form steady and robust aggregates, whose mechanical properties strongly depend on the crystal size. The particles that result from the “fusion” of nanocrystals smaller than 10 nm (more properly denoted as nanodomains) could not be disaggregated by conventional ultrasonic and graining techniques. On the contrary, agglomerates of crystals larger than 10 nm are dissociable in discrete crystals. It allows characterizing Zn-MOF-74 nanocrystals by advanced electron microscopy methods. Cs-corrected scanning transmission electron microscopy (STEM) provided, for the first time, “quasi” atomic resolution images of MOFs, which are especially unstable under electronic radiation. The magnitude of the crystal size of M-MOF-74 is tentatively associated with the solubility of the metal source.

Metal-organic frameworks (MOFs) have been postulated for years as industrially achievable materials for CO2 capture and H2 storage. However, a great leap forward their real applications is still pending. This article details the design of a MOF material, including the reasoned choices of metal ion, organic linker, and even the structural subunits, as efficient adsorbent of both CO2 and H2. In particular, it was planned (i) to raise the polarizability of the framework by using a highly N-rich organic linker and (ii) to favor the formation of nanocavities with suitable size to confine small molecules. The resultant tetrazole-imidazole- based ITF-1 material containing nanocubes certainly achieved all these aimed premises. Nevertheless, such structural and compositional distinctiveness was reflected in some noteworthy adsorption features. CO2 adsorption was highly remarkable, and it was characterized by a wide hysteresis loop along the whole studied range of pressures. H2 molecules totally filled the nanocavities under only 0.1 bar at 77 K, and at 273 K, H2 uptake became tens of times higher than expected according to their textural properties. These unique adsorption results, together with the discussed relationship between structure/composition of ITF-1 and their adsorption features, underline the importance of a tailored MOF materials for particular applications.

This work focuses on the synthesis and characterization of a conceptually innovative series of TAPO materials, particularly centered in the AFI-structured TAPO-5. Unlike the conventional TAPOs, the so-called Ti(III)APO-5 are prepared by using Ti(III) sources. This strategy aims to avoid the presence of both Ti–O–Al and Ti–O–Ti bonds in TAPOs, undesired for catalytic purposes. The thermodynamic stability of this oxidation state of Ti in water and in the presence of air is low, but the preparation of the gel and the filling of the autoclaves under N2 atmosphere allowed Ti to maintain its 3+ oxidation state in a considerable proportion in the hydrothermally-crystallized solids. The materials were characterized by powder XRD, ICP chemical analysis, SEM, DR-UV–visible spectroscopy, TGA and 31P and 27Al MAS NMR. DR-UV–visible spectroscopy certified the presence of Ti(III) in both tetrahedral and octahedral environments in the as-made samples before being exposed to air, whereas 31P MAS NMR indicated the vicinity of Ti in the second coordination sphere of P in the already oxidized sample. Although once dried and calcined in air Ti(III) is entirely oxidized to Ti(IV), Ti(III)APO-5 materials present key singularities against conventional TAPO-5. Thus, apart from the presence of Ti(OP)4 environments, the charge transfer transition detected by DR-UV–vis appears at lower wavelength, whereas both TGA and 27Al NMR indicates a peculiar hydration of the as-prepared samples, which is unprecedented in conventional TAPO-5. Based on these characterization features, the possible nature of the Ti centers generated by this synthesis approach is discussed.

Uno de los principales retos que debe afrontar la industria química es satisfacer las continuas exigencias a las que está sometida para incrementar su eficiencia en la utilización de materias primas y energía, con la finalidad de disminuir la cantidad de productos secundarios característicos de todo proceso, así como sus costes de fabricación. Ello significa en la práctica la implementación de procesos cada vez más selectivos hacia el producto deseado, al menor consumo energético posible. Por esa razón, existe una marcada tendencia a sustituir esquemas de producción tradicionales por otros que emplean catalizadores, de manera que según estimaciones de la Unión Europea, al menos el 80% de todos los procesos químicos utilizan al menos un catalizador en una u otra etapa. Las ventajas de utilizar un catalizador provienen de su capacidad para favorecer una ruta particular de transformación de un compuesto químico determinado en otro, frente a otras posibles rutas alternativas, y ello lo realiza además disminuyendo la energía de activación del camino de reacción favorecido. Por lo tanto, se economiza materia prima y se disminuye en gran medida tanto la producción de compuestos no deseados como el consumo de energía, ya que la reacción transcurre por lo general a temperaturas menores que las requeridas en ausencia de catalizador.

One of the pioneering metal organic framework material, called MOF-2 and having the formula Zn(bdc) 1 still continues awakening interest amongst the scientific community2·3 in spite of its layered character. However, their synthesis methods are either experimentally complicated' or in two steps through the transformation of MOF-12• Here, we describe the preparation of a high-quality MOF-2 under environmentally friendly conditions, including room temperature, absence of any amine or any other pH-controller, partially substitution of the harmful organic solvent (N,N-dimethylformamide) by water, and by simply mixing linker and metal sources, the latter being zinc acetate, carefully selected as a function of their solubility in the solvent mixture. The effect of the ratio of the two solvents and the different parameters that determine the preparation of MOF-2 have been studied. The optimum ratio of the Zn(OAc)z.4H 20 to H2bdc is 1.74 and the DMF to H20 is 3. The so-synthesized MOF-2 has been characterized using powder X-ray difftaction (Fig. la), thermal gravimetric analysis (Fig. lb), N2 adsorption/desorption and scanning electron microscopy (Fig. 1c), all of them supporting the good quality of the material.

This work studies the influence of the amount of water accompanying and stabilizing the conventional oxidant agent H2O2 on the activity of different TAPO-5 materials in cyclohexene oxidation, in comparison to that of the par excellence large-pore Al-free Ti-beta zeolite. It was proved that the catalytic activity of a TAPO-5 markedly and systematically increases as the amount of the oxidant H2O2 (30 wt.% in aqueous solution) decreases, suggesting the strong inhibitor role of water in the catalytic activity of TAPOs. Following this noteworthy result, we have developed a method for removing water from the mixture solvent (acetonitrile)/H2O2 30 wt.% (aqueous solution) based on a Soxhlet extraction. Water content was quantified by FTIR, which certified the reproducible reaching of a nearly anhydrous system (5 mg H2O/g CH3CN). Under these conditions, TAPO-5 catalysts were able to convert cyclohexene in an extension higher that half of that given by Ti-beta. The product selectivity given by TAPOs and Ti-beta is completely different, as the former favors the cyclohexene reaction through radicalary mechanism and Ti-beta almost exclusively gives epoxidation products. The catalytic features of the conventional Ti(IV)APO-5 is improved by the new so-called Ti(III)APO-5 catalyst, synthesized from gels containing Ti(III).

Commercial mesopores-containing carbon (carbon black BP2000) has been used as crystallization host as well as hard template of intracrystalline mesopores in CoAPO-5 materials prepared with N-methyldicyclohexylamine as specific structure-directing agent. As a result, micrometer-sized AFI-structured terminated-tip (pencil-like) hexagonal prims have been obtained. Despite the appearance of single crystals, the crystals are actually composites formed by a large number of elongated-shape CoAPO-5 and carbon nanodomains. Indeed, the removal of carbon by calcination leaves an inorganic Co-doped AlPO 4-based material having a complex hierarchical pore system, formed by the expected microporosity for an AFI-structured material and both intra- and intercrystalline mesoporosity. In good agreement with the nanocomposite nature of these micrometer-sized crystals, the size of their fibers generated by burning the carbon matrix can be relatively controlled by the conditions of the calcination processes. Under optimized synthesis and calcination conditions, AFI-structured materials with high mesoporous surface area and pore volume can be afforded. © 2013 American Chemical Society.

The generation of mesoporosity in microporous materials has been postulated as a valid strategy to limit the diffusional problems of organic substrates within the pores of these materials, without affecting their intrinsic catalytic behavior. This article shows the effect of systematic variations of different synthesis parameters on the nature of the intercrystalline mesoporosity in CoAPO-5 materials. The hard impositions of this approach, including a structure-directing agent (SDA) possessing enough structural specificity towards AFI materials under a very wide range of synthesis conditions, and at the same time having the ability of generating intercrystalline mesoporosity, severely reduces the possible choices. Fortunately, N-methyldicyclohexylamine (MCHA) simultaneously obeys both conditions. We have examined some parameters conventionally affecting the crystallization process such as time, temperature and dilution, and some other parameters with particular effect on the results of the crystallization of microporous materials such as heteroatom content, heteroatom source, pH of the starting gel and heating source (conventional or assisted by microwave radiation). Except Co source, the rest of the parameters did have a significant influence on the nature and/or magnitude of intracrystalline mesoporosity. The effect of pH and dilution was particularly relevant, so that ordered intracrystalline mesoporosity is favored when CoAPO-5 is crystallized from relatively diluted and acidic gels. In addition, high Co content produces a higher and better-defined mesoporosity, although it implies a modification of the catalytic activity as the number of active centers is inherently varied. Finally, a relevant improvement in the mesoporosity is obtained when heating is assisted by microwave radiation, since the resultant CoAPO-5 is composed by smaller crystals efficiently and orderly agglomerated in pseudospherical particles with a well-defined mesoporosity of narrower pores.

[EN] The invention relates to novel microporous crystalline aluminophosphate materials comprising Ti (TAPOs) based on gels containing Ti in a state of oxidation lower than (IV), preferably Ti(III). The invention also relates to the method for producing said materials. The resulting TAPO materials can comprise two types of cores, both non-described in aluminium phosphates, depending on the atmosphere to which they are exposed following the production thereof. In this way, if they are kept in the absence of oxygen, aluminophosphates will be produced, comprising Ti(III) (Ti(III) APOs) with redox properties for exploiting in catalysis, for example, in the production of plastics. The invention further relates to the first TAPO materials that do not contain Brönsted acid cores coexisting with the redox cores. On the other hand, if they are exposed to molecular oxygen, TAPO materials comprising Ti(IV) (Ti( IV) APOs ) are produced, but with an environment different from that of the known TAPOs in that, instead of Ti(OA1)4 o Ti (OA1)4-n (OTi)n (con 04, and therefore with a specific catalytic behaviour in acid and oxidation reactions, [ES] En esta patente se reivindica nuevos materiales aluminofosfatos microporosos cristalinos que comprenden Ti (TAPOs) partiendo de geles que contienen Ti en estado de oxidación inferior a (IV), preferentemente Ti(III). Asimismo, se reivindica el procedimiento de obtención de estos materiales. Los materiales TAPOs resultantes pueden comprender dos tipos de centros, ambos no descritos en aluminofosfatos, dependiendo de la atmósfera a la que se expongan tras su preparación. Así, si se mantienen en ausencia de oxigeno, se obtendrán materiales aluminofosfatos que comprenden Ti(III) (Ti(III) APOs) con propiedades rédox por explotar en catálisis, por ejemplo, en la producción de plásticos. Además, se trata de los primeros materiales TAPOs que no contienen centros ácidos de naturaleza Briinsted coexistiendo con los centros rédox. Por el contrario, si se exponen a oxigeno molecular, se obtienen materiales TAPOs que comprenden Ti(IV) (Ti( IV) APOs ), pero con un entorno diferente al de los TAPOs conocidos: en lugar de entornos Ti(OA1)4 o Ti (OA1)4.n (OTi)n (con O

Esta patente reivindica materiales aluminofosfatos microporosos cristalinos que comprenden Ti (TAPOs) partiendo de geles que contienen Ti en estado de oxidación inferior a (IV), así como el procedimiento de obtención de estos materiales. Los materiales pueden comprender dos tipos de centros dependiendo de la atmósfera a la que se expongan tras su preparación. Si se mantienen en ausencia de oxígeno, se obtendrán materiales aluminofosfatos que comprenden Ti(III) (Ti(III)APOs) con propiedades rédox por explotar en catálisis (por ejemplo, producción de plásticos). Se trata de los primeros materiales TAPOs que no contienen centros ácidos de naturaleza Brönsted coexistiendo con los centros rédox. Si se exponen a oxígeno molecular, se obtienen materiales TAPOs que comprenden Ti(IV) (Ti(IV)APOs), pero con un entorno diferente al de los TAPOs conocidos: en lugar de entornos Ti(OAl)4 o Ti(OAl)4-n(OTi)n (con 0<=4), sus entornos son exclusivamente Ti(OP)4, presentando así un comportamiento catalítico propio en reacciones ácidas y de oxidación.

Hay motivos y razones para la esperanza, pero sobre todo hay posibilidad de encontrar fundamentos para esta esperanza. La reedición de la obra insigne de enrst bloch por la editorial taurus1 nos permite la posibilidad de recuperar una mirada abierta por e, There are motives and reasons for a new hope, but most of all there is a possibility to find fundamentals for this hope. The reedition of bloch's distinguished work by taurus2 publishing house give us the opportunity to recover a wide glance by ernst bloc