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The location of aluminum in a zeolite framework structure defines the accessibility and geometry of the catalytically active sites, but determining this location crystallographically is fraught with difficulties. Typical zeolite catalysts contain only a small amount of aluminum, and the X-ray scattering factors for silicon and aluminum are very similar. To address this problem, we have exploited the properties of resonant X-ray powder diffraction across the Al K edge, where the aluminum scattering factor changes dramatically. By combining conventional synchrotron powder diffraction data with those collected at energies near the X-ray absorption edge, aluminum is highlighted. In this way, the different distributions of aluminum in two FER-type zeolites with identical chemical compositions but different catalytic properties could be determined unambiguously. The results are consistent with previous studies, but quantitative. This approach constitutes a major advance in our fundamental understanding of the relationship between zeolite structure and catalytic activity.

Direct methane functionalization and, in particular, the selective partial oxidation to methanol, remains an eminent challenge and a field of competitive research. The conversion of methane to methanol over transition-metal-containing zeolites using molecular oxygen is a promising and extensively studied process. Herein, we scrutinize some oft-cited assumptions in this topic—which include the labelling of the process as biomimetic, the debate regarding the industrial viability of direct methane-oxidation systems and the claim that methane is difficult to activate—and delineate the extent to which these are scientifically robust. We highlight both the merits and pitfalls of such statements and point out the hazards associated with their improper use. By examining these misconceptions, we build an outlook for future research, highlighting the need to optimize materials and process conditions for the stepwise approach and to further explore catalytic processes that explicitly employ strategies for the preservation of methanol. While converting methane to methanol is an attractive process, making a catalytic—and commercially viable—route has presented severe difficulties. Here van Bokhoven and co-workers discuss the successes, problems and misconceptions in the field, focusing on the reaction with molecular oxygen over zeolites.

The isothermal, low-temperature stepwise conversion of methane to methanol over copper-exchanged zeolites eliminates the time-consuming heating and cooling steps of the conventional high temperature activation approach. To better understand differences between the two approaches, a series of zeolites were screened, of which omega zeolite (MAZ) showed superior performance in both the isothermal and conventional approaches.

Methane is often flared due to the heavy economic burden of transportation, particularly at rural petroleum extraction sites. Directly converting methane to methanol is possible through a stepwise process with copper- exchanged zeolites. Factors affecting this conversion are not yet fully understood. Omega zeolite ( MAZ) can yield 197 mu mol per gram- zeolite, the highest reported thus far. Here we show that the synthesis and resulting morphology of the zeolite play an enormous role in the yield of methanol. High yields are only achieved when the zeolite has a longer stick- like bundled morphology ( 2- 4 mu m by 100 nm). When the zeolite forms small spherulitic aggregates, the methanol yield is severely diminished ( 60- 97 mu molmethanol per gram- zeolite). This difference originates from minute changes in the synthesis procedure, emphasizing the extreme sensitivity of zeolite properties towards synthesis conditions. This work shows that selecting a parent zeolite is crucial and is an opportunity for process optimization to achieve high and industrially- relevant methanol yields.

Zeolite mordenite (MOR) is one of the most studied zeolites for the stepwise direct conversion of methane to methanol, but it also can exist in two forms: large port and small port. Here we report that the synthesis and selection of the parent mordenite is critical for optimizing productivity, and that large-port mordenite outperforms small-port mordenite for the stepwise conversion of methane to methanol.

In the search for a commercially viable process to convert methane directly to methanol, the low-temperature isothermal process represents a promising new reaction pathway, because of its easier operation at lower temperatures than previously proposed processes with a high activation temperature. Isothermal methane to methanol conversion on copper-exchanged mordenite was examined by in situ XAS and compared to the conventional high-temperature activation procedure. Despite the copper remaining partially hydrated during the isothermal procedure, methanol can form when elevated pressures are applied. By observing the reduction of copper during reaction at elevated pressures, the mechanism was found to be a two-electron reduction–oxidation reaction for the isothermal procedure, as in the high-temperature activation case.

International audience; A family of Al-rich ZSM-5 zeolites with Si / Al = 8 ± 0.5 was prepared according to a biomass-mediated supramolecular approach. A combination of advanced characterisation techniques and periodic density functional theory (DFT) calculations unraveled the purity and stability of unexpected Al-enriched ZSM-5 structures, hence allowing to cross the frontier of Si / Al lower limit. In addition, these Al-rich ZSM-5 zeolites demonstrated high catalytic activity in n-hexane cracking and methanol conversion into hydrocarbons, being in line with the presence of numerous BrØnsted acid sites.

Ferrierite zeolite was synthesized in fluoride medium using dicationic 1,6-bis(N-methylpyrrolidinium)hexane (MPH) as a bulky structure directing agent (SDA) in combination with tetramethylammonium (TMA) as a small co-structure-directing agent (co-SDA). When trimethylamine, pyrrole or tert-butylamine were used as co-SDA, amorphous and beta zeolite (BEA framework type) were obtained, suggesting that these amines do not play a strong role as co-SDA. Only when TMA was used as co-SDA in synthesis gels with moderate pH, ferrierite is obtained; in fact, we have found a dramatic influence of the pH of the synthesis gel on the ferrierite crystallization, since even using TMA as co-SDA, ferrierite was only obtained under moderate pH values. Interestingly, ICP and CHN chemical analyses suggest that the Al content is driven by the amount of SDAs able to be hosted within the ferrierite framework, more specifically, by the nitrogen (positive charge) content available to charge-balance the negative charge associated to the incorporation of Al. A computational study showed that the most stable configuration of the ferrierite system corresponds to the occupation of the FER cages by TMA, while MPH accommodates in the 10-membered ring channels of the FER structure; the packing arrangement of MPH determines the density of positive charges, and hence the Al incorporation. Moreover, the unit cell parameters of the as-made ferrierite samples indicate that the structure is slightly expanded along the [100] direction in order to accommodate the bulky MPH dication.

A study exploring the use of ionic liquid reactions based on imidazolium halides in molecular sieve synthesis has produced a novel zincoaluminophosphate material with an open DFO-type framework structure. This framework structure had only been observed previously in the magnesioaluminophosphate system (Mg-DAF-1) where decamethonium was used as the structure directing agent. The new Zn-DAF-1 material has been characterized using chemical and thermogravimetric analysis and ^(13)C, ^(19)F, ^(27)Al and ^(31)P MAS NMR techniques. Structure analysis (P6/mcc, a = 22.2244(1) Å, c = 42.3293(3) Å) using synchrotron powder diffraction data not only confirmed the framework structure, but also revealed the locations of the Al, P and Zn atoms in the framework, the N,N′-di-isopropyl-imidazolium (DIPI) ions in the pores, some fluoride ions associated with double 4-rings, and some water molecules and anions filling the remaining space. This level of structural detail had not been possible in the Mg-DAF-1 material. Four different locations for the DIPI cation were found in the two 12-ring channels and Zn was found to substitute for only one of the six crystallographically distinct Al sites to yield the approximate crystal chemical formula |(DIPI)_(17)(OH,F)_(11)(H2O)_(23)|[Zn_6Al_(126)P_(132)O_(528)]-DFO.

Using heavy-atom labeling in conjunction with electron microscopy, we here visualize the distribution of point defects, i.e. internal silanol groups, in silicalite-1 zeolites at the single crystal level., Chemical Communications, 55 (4), ISSN:1359-7345, ISSN:1364-548X

A literature survey reveals a prominent reduction in the concentration of Brønsted acid sites in hierarchically organized zeolites with increasing mesoporous or external surface area independent of the framework type or synthesis route; this suggests a common fundamental explanation. To determine the cause, nature, and impact of the underlying changes in aluminum speciation, this study combines a multitechnique analysis that integrates basic characterization, a detailed synchrotron XRD and multiple-quantum NMR spectroscopy assessment, and catalytic tests to correlate evolution of the properties with performance during successive steps in the preparation of hierarchical MFI-type zeolites by desilication. The findings, subsequently generalized to FAU- and BEA-type materials, identify the crucial impact of calcination on the protonic form, which is an integral step in the synthesis and regeneration of zeolite catalysts; on aluminum coordination; and the associated acidity trends.

The synthesis of the ether-substituted group 4 metallocene complexes [Ti(η5-C5H5)(η5-C5H4{CMeRCH(OMe)2})Cl2] (R = Me (4), Ph (5)) and [M(η5-C5H4{CMeRCH(OMe)2})2Cl2] (M = Ti, R = Me (6), Ph (7); M = Zr, R = Me (8), Ph (9)) is reported. In addition, the titanocene derivatives 4–7 have been supported on the mesoporous silica-based material KIT-6, giving the functionalized materials K4–K7, respectively. All compounds and materials have been characterized by different analytical techniques such as solution NMR spectroscopy, mass spectrometry, elemental analysis, solid-state multinuclear NMR spectroscopy, IR spectroscopy, N2 adsorption–desorption isotherms, X-ray fluorescence and diffraction, SEM, and TEM. Additionally, the molecular structures of the zirconocene derivative 8 and the hydrolysis product [Ti(η5-C5H5)(η5-C5H4{CMe2COO})Cl] (4a) of titanocene complex 4 have been determined by X-ray diffraction studies. The structure of 4a reveals a five-membered metallacyclic arrangement. The ether-substituted titan...

The potential of valence to core Al X-ray emission spectroscopy to determine aluminum distribution in ferrierite zeolites was investigated. The recorded emission spectra of four samples prepared with different structure directing agents exhibit slight variations in the position of the main emission peak and the intensity of its low energy shoulder. Theoretical calculations indicate that an increased intensity of the Kβx shoulder in the Al emission spectra can be linked to a predominant occupation of the T3 site by a single aluminum atom. This study thus suggests that valence to core X-ray emission spectroscopy can be applied to help determine the occupation of aluminum at crystallographic T-sites in zeolites.

Electron-diffraction data on the zeolites Silicalite-1 and ZSM-5 (both MFI framework type) were collected from individual grains of about 150×100×50 nm3 . Crystals were synthesized with tetrapropylammonium as structure-directing agent. The resolution extended to about 0.8 A for Silicalite-1 and about 0.9-1.0 A for ZSM-5 crystals. Analysis of several data sets showed that at the nanometre-scale, these zeolite crystals are single crystals and not intergrown.

Large ZSM-5 zeolite crystals synthesized in fluoride medium show an astonishing activity, stability as well as selectivity towards light olefins in the Methanol-To-Olefins (MTO) reaction. By proper control of the synthesis parameters, ZSM-5 single crystals of unprecedented high quality are produced. The absence of usually uncontrollable variables such as structural defects, external non selective surface acid sites and extra-framework aluminium (EFAl) species was evidenced by SEM, HRTEM, CO-FTIR, 27Al and 19F MAS-NMR, Rietveld structure refinement and N2- and Ar-gas sorption measurements. Interestingly, diffusivity evaluation of different probe molecules (toluene, benzene and neopentane) has been carried out with PFG-NMR, allowing casting light on an interesting structure-diffusion-activity relationship. A “levitation” effect could be experimentally demonstrated and its impact on catalysis is highlighted in a rationalization attempt: Maxwell-Boltzmann based diffusion models properly predict product distributions for this counter-intuitively outstanding Methanol-To-Propylene (MTP) catalyst.

Funding: Royal Society for provision of an industry fellowship and the EPSRC for funding (EP/K025112/1 and EP/L014475/1) (R.E.M.); Czech Science Foundation for (P106/12/G015) (J.Cˇ.); European Community under a Marie Curie Intra-European Fellowship (A.B.P.). Zeolites are important materials whose utility in industry depends on the nature of their porous structure. Control over microporosity is therefore a vitally important target. Unfortunately, traditional methods for controlling porosity, in particular the use of organic structure-directing agents, are relatively coarse and provide almost no opportunity to tune the porosity as required. Here we show how zeolites with a continuously tuneable surface area and micropore volume over a wide range can be prepared. This means that a particular surface area or micropore volume can be precisely tuned. The range of porosity we can target covers the whole range of useful zeolite porosity: from small pores consisting of 8-rings all the way to extra-large pores consisting of 14-rings. Publisher PDF

A preliminary inspection of natural zeolites samples in the north east of Ethiopia showed a large deposit of highly pure stilbite (hereafter called |CaNa|-STI). Rietveld refinement of synchrotron powder diffraction data (C2/m, a = 13.62(1) Å, b = 18.2563(1) Å, c = 11.28(1) Å, β = 127.8(2)°) has shown that both Ca2+ and Na+ ions reside at the intersection of the ten- and eight-ring channels, and are completely surrounded by H2O molecules that make close contacts with the zeolite framework. Therefore, no coordination of the cations with framework oxygen atoms is observed. In an attempt to improve the defluoridation capacity, |CaNa|-STI was subjected to a NH4+ and subsequent Ca2+ ion-exchange treatment. Analysis of the diffraction pattern of the |Ca–NH4|-STI sample revealed the presence of a mixture of crystals with monoclinic and orthorhombic symmetry. This double-exchange treatment notably improved the ability of this material to remove fluoride from water, what is probably related to the formation of connectivity defects that are generated during the exchange treatments., The financial support from the Spanish Ministry of Foreign Affairs-Spanish Agency for Cooperation and Development through the Scientific Cooperation Program project number A1/035517/11 is acknowledged.

Hydrolysis of germanosilicate zeolites with the IWW structure shows two different outcomes depending on the composition of the starting materials. Ge-rich IWW (Si/Ge=3.1) is disassembled into a layered material (IPC-5P), which can be reassembled into an almost pure silica IWW on treatment with diethoxydimethylsilane. Ge-poor IWW (Si/Ge=6.4) is not completely disassembled on hydrolysis, but retains some 3D connectivity. This structure can be reassembled into IWW by incorporation of Al to fill the defects left when the Ge is removed., Angewandte Chemie, 53 (27), ISSN:1521-3757, ISSN:0044-8249

The alkenyl substituted zirconocene complexes, [Zr(η5-C5H4{CMeRCH2CH2CH = CMe2})2Cl2] (R = Me (1), Ph (2) were prepared from the reaction of the lithium derivative Li(C5H4{CMeRCH2CH2CH = CMe2}) (R = Me, Ph) with zirconium tetrachloride. The bulky alkyl substituted cyclopentadienyl ligand precursor was prepared as its fulvene derivative (C5H4) = CMeCH2CHMe2 (3) via the reaction of cyclopentadiene with 4-methyl-2-pentanone and then converted to Li(C5H4{CMe2CH2CHMe2}) (4) via nucleophilic attack of LiMe. The reaction of 4 with [TiCl4(THF)2] and ZrCl4 gave the metallocene complexes [M(η5-C5H4{CMe2CH2CHMe2})2Cl2] (M = Ti (5), Zr (6)), respectively. The ansa-ligand precursor, SiMe2(C5HMe4)(C5H4{CMe2CH2CHMe2}) (7), was prepared via the reaction of 4 with SiMe2(C5HMe4)Cl and subsequently converted to its dilithium derivate, Li2(Me2Si(C5Me4)(C5H3{CMe2CH2CHMe2})) (8), using n-butyllithium. The ansa-zirconocene complex, [Zr{Me2Si(η5-C5Me4)(η5-C5H3{CMe2CH2CHMe2})}Cl2] (9), was synthesized by the reaction of 8 with zirconium tetrachloride. Compounds 1–9 were characterized by 1H and 13C{1H} NMR spectroscopy. In addition, the molecular structures of 5, 6 and 9 were determined by single crystal X-ray diffraction studies. The metallocene complexes have been tested as catalyst (with co-catalyst MAO) in the polymerization of ethylene where the substituents on the cyclopentadienyl ligand have a direct influence on the catalytic activity.

Herein, the first comparison of the mechanisms of glucose-to-fructose isomerization in aqueous media enabled by homogeneous (CrCl3 and AlCl3 ) and heterogeneous catalysts (Sn-beta) by using isotopic-labeling studies is reported. A pronounced kinetic isotope effect (KIE) was observed if the deuterium label was at the C2 position, thus suggesting that a hydrogen shift from the C2 to C1 positions was the rate-limiting step with the three catalysts. (13) C and (1) H NMR spectroscopic investigations confirmed that an intra-hydride-transfer reaction pathway was the predominant reaction channel for all three catalysts in aqueous media. Furthermore, the deuterium atom in the labeled glucose could be mapped onto hydroxymethylfurfural and formic acid through reactions that followed the isomerization step in the presence of Brønsted acids. In all three catalysts, the active site appeared to be a bifunctional Lewis-acidic/Brønsted-basic site, based on a speciation model and first-principles calculations. For the first time, a mechanistic similarities between the homogeneous and heterogeneous catalysis of aldose-to-ketose isomerization is established and it is suggested that learning from homogeneous catalysis could assist in the development of improved heterogeneous catalysts.

Copper-containing zeolites exhibit high activity in the direct partial oxidation of methane into methanol at relatively low temperatures. Di- and tricopper species have been proposed as active catalytic sites, with recent experimental evidence also suggesting the possibility of the formation of larger copper oxide species. Using density functional theory based global geometry optimization, we were able to identify a general trend of the copper oxide cluster stability increasing with size. For instance, the identified ground-state structures of tetra- and pentamer copper clusters of CunOn2+ and CunOn−12+ stoichiometries embedded in an 8-ring channel of mordenite exhibit higher relative stability compared to smaller clusters. Moreover, the aluminium content and localization in the zeolite pore influence the cluster's stability and its geometrical motif, which offers a perspective of tuning the properties of copper-exchanged zeolites by creating copper oxide clusters of a given structure and size. With the activity of the cluster towards methane being connected to its stability, such tuning will potentially allow the design of catalysts with engineered properties.

The Authors would like to thank: The EPSRC (grant EP/K025112/1) and the Czech Science Foundation grant no. P106/12/G015 (Centre of Excellence) for funding opportunities and beam lines I15 and I11 at the Diamond Light Source. Nicola Casati and Antonio Cervelino from the MS Powder beamline at the Swiss Light Source are acknowledged for their support in the data collection. A.B.P. acknowledges the support of the European Community under a Marie Curie Intra-European Fellowship for Career Development. The disordered intermediate of the ADORable zeolite UTL has been structurally confirmed using the pair distribution function (PDF) technique. The intermediate, IPC-1P, is a disordered layered compound formed by the hydrolysis of UTL in 0.1M hydrochloric acid solution. Its structure is unsolveable by traditional X-ray diffraction techniques. The PDF technique was first benchmarked against high-quality synchrotron Rietveld refinements of IPC-2 (OKO) and IPC-4 (PCR) – two end products of IPC-1P condensation that share very similar structural features. An IPC-1P starting model derived from density functional theory was used for the PDF refinement, which yielded a final fit of Rw = 18% and a geometrically reasonable structure. This confirms the layers do stay intact throughout the ADOR process and shows PDF is a viable technique for layered zeolite structure determination. Postprint

A procedure to enable the use of the very open framework Zn-STA-1 as catalyst, based on in situ calcination in a water-free environment, has been developed. The material shows a remarkable performance in the m-xylene isomerization test reaction, comparable to that of USY zeolite. The reported experimental procedure avoids the collapse of the SAO structure upon calcination, which has prevented the use of this very open framework structure in catalytic applications, and provides a promising new microporous catalyst for processing bulky molecules.

We report the first study of the hydrolysis of tetraethyl orthosilicate (TEOS) in an aqueous solution of N,N,N-trimethyl-1-adamantammonium (TMAda) hydroxide, the clear sol precursor for the preparation of the high-silica zeolite SSZ-13 (CHA). The initial stages of the hydrolysis of TEOS were monitored by quantitative 29Si and 27Al nuclear magnetic resonance (NMR) and small-angle X-ray scattering (SAXS). 29Si NMR allowed quantitative characterization of Si in nanoparticles and dissolved oligomers and measuring the average Si–O–Si connectivity. The average Si connectivity increases when hydrolysis advances, and at a [Si]/[TMAdaOH] ratio of one, nanoparticles are detected. The average connectivity of nanoparticles reached 3.1. This is similar to what has been observed during TEOS hydrolysis with other organic bases, i.e., tetrapropylammonim hydroxide (TPAOH) and tetrabutylammonium hydroxide (TBAOH) used for silicalite-1 and silicalite-2 syntheses, confirming that it is a general phenomenon independent of the...

A nonenzymatic route for xylose isomerization in an aqueous medium using zeolite Sn-beta as a catalyst is demonstrated. Xylulose and lyxose are the primary and secondary products. The maximum yield to xylulose is 27%, with an 11% yield to lyxose at ∼60% xylose conversion at 100 °C. When the Sn-beta zeolite is combined with a Bronsted acid catalyst, furfural forms in a single pot from xylose in an aqueous medium at much lower temperatures than typically employed for this reaction.

Three bulky organic cations, benzylmethylpyrrolidinium (BMP), (S,S)-2-hydroxymethyl-1-benzyl-1-methylpyrrolidinium (BML) and benzylmethylhexamethyleniminium (BMH), were used in combination with the small cation tetramethylammonium (TMA) in the synthesis of zeolite materials. Two of them are distinguished by the number of carbon atoms forming the cyclic amine, which varies from 4 in BMP to 6 in BMH. In addition, a –CH2–OH group has been introduced in the carbon atom belonging to the amine ring next to the nitrogen atom, to originate a chiral molecule, BML, the third SDA used in this work. It has been found that the combination of the small TMA with those three bulkier SDAs, promotes the crystallization of zeolite structures that contain cages and channels. BMP leads to the crystallization of the 10-ring zeolite ferrierite, where TMA is located inside the ferrierite cage. If the size of the N-cyclic amine moiety increases, the resulting cation cannot be accommodated in the relatively narrow 10-ring channels of ferrierite, and in these cases the zeolite MCM-22 crystallizes. This zeolite contains large cages whose cross section is delimited by a 12-ring, where both BMH and BML can be easily accommodated. In this system, cage-like, chlatrasil type structures often co-crystallize with the open structures, evidencing that an appropriate balance between TMA and the bulky SDA is required to achieve the crystallization of open-frameworks. When BMP is used, mixtures of structurally related ferrierite and cage-like RUB-10 are obtained if an excess of TMA is present in the synthesis gel, while MCM-22 crystallizes together with the structurally related cage-like MTN phase.

The zeolite ferrierite has been synthesized in fluoride medium in the presence of pyrrolidine as structure directing agent (SDA). The templating role of pyrrolidine molecules in the crystallization process has been studied by combining X-ray Rietveld refinement and computational calculations. Pyrrolidine molecules are accommodated in two sites, one within the ferrierite cavity, and another in the widest section of the 10-ring channel, with the plane of the molecule perpendicular to the first. Both molecules show well-defined positions, with little freedom to move away from its most stable location, indicating the good fit of pyrrolidine to the ferrierite topology. This implies a strong templating role played by pyrrolidine in the crystallization of ferrierite, acting as a true template rather than a mere pore-filling agent as previously proposed due to its ability to act as structure directing agent for more than one structure.

We propose a new computational model to study structure direction in nanoporous materials that takes into account the stability of the guest species in solution as well as the possibility of occluding solvent molecules in the nanopores. The model is applied to study the structure directing effect of (S)-(-)-N-benzylpyrrolidine-2-methanol (BPM) and benzylpyrrolidine (BP) in the synthesis of the nanoporous STA-1 material (SAO framework type), and compare results with experimental characterization. Despite the fact that up to 8 BP or BPM molecules can be loaded within the nanoporous framework, the relative stability of the SDA molecules in solution and the simultaneous incorporation of water limit the amount of organic content. The most stable arrangements correspond to the occlusion of 6 BPM or 5 BP molecules per SAO unit cell, accompanied respectively by 9 and 22 water molecules in order to complete space filling, leading to a cooperative structure-directing action between organic SDA and water molecules during crystallization. The organic molecules act as primary structure-directing agents, and the water molecules as secondary space-filling species whose role is to completely fill the void space of the pore system and provide further stabilization to the nanoporous framework. We demonstrate the necessity of including in the computational models the occlusion of water molecules as well as to account for the stability of SDA and water molecules in solution for realistically studying the structure-directing effect of organic molecules in the synthesis of hydrophilic aluminophosphate nanoporous frameworks. We therefore provide a useful computational tool for studying the occlusion of guest species in host-guest systems, an issue which is essential for controlling the potential applications of these materials.

The skeletal isomerization of n-butenes to isobutene has been carried out over ferrierite catalysts (Si/Al ~ 15) containing different acid sites distribution and different amount of defects. The zeolite crystals were synthesized under hydrothermal conditions in fluoride medium in the absence of alkaline cations by using suitable combinations of structure directing agents. Template-driven low density of acid sites in 10-membered-ring channels enhances the isobutene selectivity and decreases catalyst deactivation. The presence of high amount of silanol groups and Lewis acid sites increases the yields of by-products and catalysts decay., MICINN (CTQ2006-06282) CSIC (JAE-doc contract)

We report on the systematic exploration of zeolite synthesis using a combination of organic molecules of different size. The effect of changing the co-structure directing agent, co-SDA, (tetramethylammonium or quinuclidine) and its replacement by sodium cations, when used together with the bulky organic cation 1-benzyl-1-methylpyrrolidinium (bmp) is analyzed and compared with preparations where bmp is replaced by the related cation (S)-1-benzyl-2-hydroxymethyl-1-methylpyrrolidinium (bmprol). The tendency to direct the synthesis to ferrierite or ferrierite-like materials depending on the particular combination of bulky organic cation and co-SDA is discussed. The catalytic activity of some of the materials synthesized was tested in the isomerization of m-xylene.

Hydrothermal synthesis of zeolites often requires the presence of an organic molecule or structure directing agent (SDA), which participates in the organization of the inorganic tetrahedral units into a particular topology. Bulky molecules are frequently employed as SDAs in attempts to obtain large-pore zeolite structures. However, many open-framework zeolitic structures are composed of small cages apart from the wide channels, and only small SDAs can be accommodated within these cages. These observations leaded us to design a synthesis strategy based on the combination of small molecules with bulkier cations as SDAs. The simultaneous use of tetramethylammonium (TMA) and the bulkier benzylmethylpyrrolidinium (bmp) as SDAs has led to the crystallization of the zeolite ferrierite from gels having a Si/Al ratio in the range of 16−10, in fluoride medium and in the absence of inorganic cations. Molecular mechanics calculations revealed the templating role of both cations, as the most stable configuration of th...

Ceramic cements are good candidates for the stabilization of fractured bone due to their potential ease of application and biological advantages. New formulations of ceramic cements have been tested for their mechanical properties, including strength, stiffness, toughness and durability. The changes in the mechanical properties of a soluble cement (calcium sulfate) upon water-saturation (saturation) was reported in our previous study, highlighting the need to test ceramic cements using saturated samples. It is not clear if the changes in the mechanical properties of ceramic cements are exclusive to soluble cements. Therefore the aim of the present study was to observe the changes in the mechanical properties of soluble and insoluble ceramic cements upon saturation. A cement with high solubility (calcium sulfate dihydrate, CSD) and a cement with low solubility (dicalcium phosphate dihydrate, DCPD) were tested. Three-point bending tests were performed on four different groups of: saturated CSD, non-saturated CSD, saturated DCPD, and non-saturated DCPD samples. X-ray diffraction analysis and scanning electron microscopy were also performed on a sample from each group. Flexural strength, effective flexural modulus and flexural strain at maximum stress, lattice volume, and crystal sizes and shape were compared, independently, between saturated and non-saturated groups of CSD and DCPD. Although material dissolution did not occur in all cases, all calculated mechanical properties decreased significantly in both CSD and DCPD upon saturation. The results indicate that the reductions in the mechanical properties of saturated ceramic cements are not dependent on the solubility of a ceramic cement. The outcome raised the importance of testing any implantable ceramic cements in saturated condition to estimate its in vivo mechanical properties.

The germanosilicate ITQ-24 (IWR framework type) was synthesized in fluoride medium using 1,3,5-tris(1,2-dimethylimidazolium) benzene as the structure directing agent (SDA). A structure analysis of the as-synthesized ITQ-24 material using synchrotron powder diffraction data and difference electron density calculations have allowed the fluoride ions and the germanium atoms to be located and the conformation of the SDA to be determined. The benzyl ring is perpendicular to the b axis with the three imidazolium moieties forming a “T-shaped” arrangement. Ge atoms replace some of the Si in the double-4-ring (d4r) and in one of the single-4-rings (s4r). The other s4r contains only Si. Fluoride ions are in the d4r units. Initially, the space group Cmmm (highest possible symmetry) was assumed, but the framework geometry was strained. An independent evaluation of the symmetry using the powder charge flipping algorithm in Superflip led to a successful refinement with reasonable geometry and a refined composition of |[(C_6H_3)(C_7H_(10)N_2)_3]_2F_2|[Si_(40.2)Ge_(15.8)O_(112)] in the space group Pban.

Advances in materials synthesis bring about many opportunities for technological applications, but are often accompanied by unprecedented complexity. This is clearly illustrated by the case of hierarchically organized zeolite catalysts, a class of crystalline microporous solids that has been revolutionized by the engineering of multilevel pore architectures, which combine unique chemical functionality with efficient molecular transport. Three key attributes, the crystal, the pore and the active site structure, can be expected to dominate the design process. This review examines the adequacy of the palette of techniques applied to characterize these distinguishing features and their catalytic impact., Nature Communications, 6, ISSN:2041-1723

Adsorption of ethane in a slit shaped micropore system has been studied by Monte Carlo molecular simulation by considering this hydrocarbon as a two interacting sites molecule. Ethane adsorption in pore sizes from 0.41 to 1.66 nm was simulated at 303 K. Microscopic characteristics of the adsorbed phase have been studied for pores of different size, comparing two density profiles: the molecule centre of mass profile and the molecular interaction site profile. Averaged angle distribution of molecule positions with respect to the slit plane across the pore width has been also obtained by simulation. These results were related to ethane molecule packing efficiency, which is also related to the adsorption capacity in terms of the adsorbed phase density. Packing efficiency presents an oscillation shape as the result of the adsorbate disorder inside the pore. Pressure influence on the adsorption has been studied by following pore filling by simulation. When pore condensation takes place and for pressures above condensation, fluid-fluid interactions are determinant in molecule disorder observed between the two adsorbed layers.

© 2014 American Chemical Society, 1,3-Diphenylguanidine (DPG) has distinguishable polar and apolar groups, aromatic rings that can self-assemble through π-π type interactions, and high conformational flexibility. These features make it a potential self-assembling structure-directing agent in the synthesis of hybrid host-guest aluminophosphates. Computational simulations show that the molecule has a strong tendency to self-assemble in aqueous solution. Large supramolecular organic aggregates are produced, with the hydrophobic aromatic rings located in the center of the aggregates, stabilized by π-π type interactions, and the hydrophilic guanidine groups on the external surface in close contact with water molecules. With this organic molecule, a new 1-D AlPO framework material (ICP-1) was formed. Its structure, characterized by a combination of single-crystal and powder diffraction techniques, consists of AlP 2O8H chains connected to the polar groups of the organic DPG molecules through a complex H-bonding network. This material has an extremely high organic content, close to that of typical mesoporous materials. However, DPG molecules are part of the ICP-1 network, rather than guest molecules in the pores, so removal of DPG results in a collapse of the structure, limiting its potential applications. Nevertheless, this work demonstrates the potential of using self-assembling organic molecules for producing very open-framework materials., The research leading to these results has received funding from the Spanish Ministry of Science and Innovation MICINN (Projects MAT2009-13569 and MAT2012-31127) and the European Research Council, under the Marie Curie Career Integration Grant program (FP7-PEOPLE-2011-CIG), Grant Agreement PCIG09-GA-2011-291877. L.G.-H. acknowledges Ministerio de Economıa y Competitividad for a Ramón y Cajal ́ contract (RYC-2012-11794) A.B.P. acknowledges the support of the European Community under a Marie Curie IntraEuropean Fellowship for Career Development

The tailoring of the aluminum distribution over the various T sites in zeolites remains a major challenge. By using differing combinations of templating molecules, we managed to control the aluminum siting over the T sites as identified by 27Al MQ MAS NMR in samples of the same Si/Al ratio. This is unique evidence of a modified aluminum distribution in samples prepared following a strategy to tailor the location of aluminum in the zeolite ferrierite framework., A.B.P. is thankful for the support of the European Community under a Marie Curie Intra-European Fellowship for Career Development. Funding from the Spanish Ministry of Economy (project MAT2012-31127) is greatly acknowledged.

Analysis of the structure of the zeolite ferrierite (framework type FER) synthesized using a combination of tetramethylammonium (TMA) and pyrrolidine as organic structure-directing agents (|((CH3)4N) 0.4((CH2)4NH)3.6H 1.7|[Si33.9Al2.1O72]) has revealed that TMA ions reside exclusively in the [58668 2] cavities of the FER framework, whereas pyrrolidine species are found in both the [586682] cavities and the main 10-ring channel. A similar, but not identical, arrangement of pyrrolidine molecules was found for a sample synthesized with pyrrolidine as the only SDA (|((CH2)4NH)4.2H2.2|[Si 33.8Al2.2O72])). A comparison of the two structures shows the influence of TMA on the location of pyrrolidine and the framework Al. Pyrrolidine species establish stronger interactions with the zeolitic framework than does TMA, suggesting a different ability of the amine to exert an influence on the aluminum distribution of the zeolite. These findings have implications in the catalytic performance of the samples. © 2013 American Chemical Society., A.B.P. acknowledges the support of the European Community under a Marie Curie Intra-European Fellowship for Career Development. L.G.H. acknowledges the Spanish Ministry of Economy for a Juan de la Cierva contract. The Spanish Ministry of Economy has funded this work (project MAT2012–31127) .

Zn atoms have been incorporated into the STA-1 microporous framework (SAO framework type) for the first time. Pure Zn-containing STA-1 aluminophosphate has been obtained in the presence of either (S)-(-)-N-benzylpyrrolidine-2-methanol (BPM) or benzylpyrrolidine (BP) as structure-directing agent. Characterisation results have demonstrated that the organic molecules remain intact within the microporous framework after the hydrothermal treatment. The X-ray diffraction pattern has been indexed in the tetragonal space group I ̅4m2 (a = 13.7828(1) Å and c = 21.9444(4) Å). Chemical analysis and (31)P MAS NMR spectroscopy confirm the incorporation of ca. 4.5 Zn atoms per unit cell by isomorphous substitution of Al. This large-pore aluminophosphate has one of the lowest framework densities among the known zeolite structures, and is therefore of potential interest for applications in adsorption or catalytic processes involving bulky molecules.

A computational study is performed to rationalize the effect of the organic template molecules used in the synthesis of zeolites on their catalytic behaviour. Apart from being structure-directing, these molecules influence the location of heteroatoms. Molecules bearing acidic protons susceptible to forming H-bonds with framework oxygens show the strongest dopant-siting direction.

Fluorescence spectroscopy and a range of computer simulation techniques are used to study the structure directing effect of benzylpyrrolidine (BP) and (S)-(-)-N-benzylpyrrolidine-2-methanol (BPM) in the synthesis of nanoporous aluminophosphate frameworks with AFI (one-dimensional channels) and SAO (three-dimensional interconnected channels) topologies. We study the supramolecular chemistry of BP and BPM molecules in aqueous solution and compare it with the aggregation state of the molecules found when they are inside the AlPO nanopores after crystallization. The aggregation of the molecules within the structures can be explained by a combination of thermodynamic and kinetic effects. The former are given by the stability of the molecular species interacting with the oxide networks relative to their stability in solution; the latter depend on the aggregation behavior of the molecules in the synthesis gels prior to crystallization. Whereas BPM only forms one type of aggregate in solution, which has the appropriate conformation to match the empty channels of the forming nanoporous frameworks, BP forms aggregates with different molecular orientations, of which only one matches the framework interstices. This different supramolecular chemistry, together with the higher interaction of BPM with the oxide networks, makes BPM a better structure directing agent (SDA); it is also responsible for the higher incorporation of BPM as dimers in the frameworks, especially in the AFI structure, observed experimentally. The concentration of the SDA molecules in the gels, and so the density per volume of the SDAs, determines the exclusion zone from which the pores and/or cavities of the framework will arise, and so the porous network of the formed material. A clear relationship between the SDA density in solution and in the framework is observed, thus enabling an eventual control of the material density by adjusting the SDA concentration in the gels. The topological instability intrinsic to these open framework structures is compensated by a high host-guest interaction energy; the SAO topology is further stabilized by doping with Zn. Our computational results account for and rationalize all the effects observed experimentally, providing a complete picture of the mode of structure direction of these aromatic molecules in the synthesis of nanoporous aluminophosphates.

A synthesis strategy to tailor the acid sites location in ferrierite crystals has been developed. The zeolite catalysts were synthesised in fluoride medium using different combinations of organic structure directing agents (SDAs) in the absence of inorganic cations. Therefore, the negative charge associated to the incorporation of aluminium to the framework was compensated exclusively by the positive charge of the organic SDAs. In this way, Al sitting in the zeolite framework was driven by the specific location of the different SDA molecules within the zeolite void volume. Following this synthesis strategy, it has been found that the distribution of strongly acidic hydroxyl groups in the proton form of the zeolites obtained after removal of the organic templates was dependent on the combination of organic molecules used as SDAs. Moreover, the catalytic activity of the zeolites in m-xylene and 1-butene isomerisation increased as the relative population of strong Brönsted acid groups in sterically constrained sites inside the ferrierite cavity decreased., This work has been financially supported by the MICINN (project CTQ2006-06282).

1-benzyl-1-methyl-pyrrolidium and a chiral related molecule have been used together with several cage-forming organic molecules like TMA, TEA and quinuclidine, as well as with sodium cations, as structure directing agents (SDA) to crystallize different zeolite materials. Ferrierite, ferrierite-related layered compounds, ZSM-12 and MCM-22 were obtained from highly concentrated synthesis gels in fluoride medium. It has been found that the nature of the zeolite phase obtained is influenced by the specific combination of bulky and cage-forming cations and the synthesis temperature. Computational studies have been used to rationalize the experimental results, in terms of the relative trend for each SDA to occupy specific sites within each zeolite structure. Examples are provided on the influence of the synthesis procedure on the acidity and catalytic activity of the different synthesized materials in acid-catalyzed reactions.

Ferrierite synthesis from gels containing a mixture of two template molecules, in the absence of inorganic cations and in fluoride media, is described. One of them is a bulky structure-directing agent (SDA), 1-benzyl-1-methylpyrrolidinium cation (bmp), and the other one is a small organic cation acting as a co-template. We present here the results obtained with tetramethylammonium (TMA) and quinuclidinium (Qui) compounds as co-templates in a gel containing bmp cation as SDA. It has been observed that in both cases co-templates exert a marked effect on the nature of the synthesis products, This work has been financially supported by the CICYT (project CTQ2006-06282).