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A series of monoquaternary and diquarternary benzyl-imidazolium derivatives are prepared and used as organic structure direction agents (OSDAs) in germanosilicate syntheses. The goal of this work is to create new multidimensional large pore zeolites. For the OSDA made and tested, we looked for relationships based upon stereochemistry from the benzyl ring as part of each structure. Several known molecular sieves with the *BEA, BEC, IWS, or LTA topologies are obtained. Molecular modeling is carried out with the goal of understanding: (a) the product selectivity correlation with the OSDA and the zeolite obtained, and (b) why differential rates of crystallization are observed for isomers that lead to different zeolite products. Additionally, a new molecular sieve denoted CIT-13 is prepared and shown to possess intersecting 14- and 10-membered ring pores, which gives confidence to the soundness of this approach for OSDA construction to yield new multidimensional large pore zeolites. CIT-13 is the first molecul...

The aluminosilicate molecular sieve with the AEI framework topology (SSZ-39) is currently of great interest for use in a number of important applications such as exhaust gas NO_x reduction and the methanol-to-olefins reaction. It is likely that advances in the synthesis of this molecular sieve will be needed for applications to proceed. Here, dimethylpiperidine based organic structure directing agents (OSDAs) are used to prepare SSZ-39, and the influence of diastereo- and structural isomeric mixtures on the synthesis of SSZ-39 is reported. Although differences in the rates of molecular sieve formation as well as preferential isomer incorporation occur, the synthesis of SSZ-39 is possible over a wide range of isomeric mixtures. These findings demonstrate that the synthesis of SSZ-39 can be accomplished with OSDA isomer mixtures that naturally occur from the synthesis of the organic precursors used to prepare the OSDAs.

RTH type zeolite (aluminosilicate) is a potentially useful catalytic material that is limited by the inability to easily prepare the material over a wide composition range. Here, we report the use of pentamethylimidazolium to prepare aluminosilicate RTH across a wide range of compositions in both fluoride and hydroxide inorganic systems. RTH type zeolites are crystallized with a calcined product Si/Al of 7–27 from fluoride media and 6–59 from hydroxide media. The use of this new, simple organic structure-directing agent that can be prepared in one step allows for dramatic improvement in the compositional space where aluminosilicate RTH can be formed. RTH is tested as a catalyst for the methanol-to-olefins reaction and at complete conversion shows a high propylene/ethylene ratio of 3.9 at a propylene selectivity of 43%.

Zeolites and zeolite-like materials are continually finding new applications. Because of the uniformity of these solids, the expression of macroscale materials properties that are controlled by the materials chemistry at the atomic/molecular scale are achievable. In this Perspective, I discuss the following areas of current interest in zeolites and zeolite-like materials that rely on manipulation of the materials chemistry for their preparation and provide new opportunities for application: (i) exploitation of organic structure-directing agents (SDAs) for new materials, (ii) the synthesis of zeolites without SDAs, (iii) the synthesis of very hydrophobic materials, (iv) conversions of two-dimensional (2D) to 3D materials and vice versa, (v) hierarchically organized materials, (vi) chiral materials, and (vii) direction of tetrahedral atoms to specific framework positions.

A manganese oxide-based, thermochemical cycle for water splitting below 1000 °C has recently been reported. The cycle involves the shuttling of Na+ into and out of manganese oxides via the consumption and formation of sodium carbonate, respectively. Here, we explore the combinations of three spinel metal oxides and three alkali carbonates in thermochemical cycles for water splitting and CO_2 reduction. Hydrogen evolution and CO_2 reduction reactions of metal oxides with a given alkali carbonate occur in the following order of decreasing activity: Fe_(3)O_4 > Mn_(3)O_4 > Co_(3)O_4, whereas the reactivity of a given metal oxide with alkali carbonates declines as Li_(2)CO_3 > Na_(2)CO_3 > K_(2)CO_3. While hydrogen evolution and CO_2 reduction reactions occur at a lower temperature on the combinations with the more reactive metal oxide and alkali carbonate, higher thermal reduction temperatures and more difficult alkali ion extractions are observed for the combinations of the more reactive metal oxides and alkali carbonates. Thus, for a thermochemical cycle to be closed at low temperatures, all three reactions of hydrogen evolution (CO_2 reduction), alkali ion extraction, and thermal reduction must proceed within the specified temperature range. Of the systems investigated here, only the Na_(2)CO_3/Mn_(3)O_4 combination satisfies these criteria with a maximum operating temperature (850 °C) below 1000 °C.

Hybrid organic−inorganic solids featuring millimolar/gram concentrations of intracrystalline organic moieties and shape-selectivity are synthesized. Pure-silica zeolite beta crystals are coated with zirconia and treated in aqueous sodium hydroxide to create defects and mesoporosity within the crystalline structure. Aminopropyl organic groups are subsequently grafted onto the generated intracrystalline silanol groups. After grafting, characterization data indicate a high organic concentration localized primarily within the intracrystalline voids. Specifically, thermogravimetric analysis shows an organic loading of 0.7 mmol of NH_2/g, ^(29)Si solid-state nuclear magnetic resonance (NMR) spectra display a quantitative decrease in Q^3 silicon atoms with a corresponding resharpening of the Q^4 resonances, and N_2 adsorption data show a decrease in micropore volume to 0.10 cm^3/g. Knoevenagel condensation reactions are catalyzed by the aminopropyl-functionalized materials using differently sized aldehydes and the results show that the zirconia-protected functionalized solid have shape selective properties.

Direct methanol fuel cells (DMFCs) and hydrogen proton exchange membrane fuel cells (PEMFCs) are two types of fuel cells where commercial products have been developed, but have yet to find widespread deployment. Although these devices are compact, easily refuelable, and operate at comparatively low temperatures, problems such as catalyst poisoning, methanol crossover, and water management exist and are current topics of research. One important component of both the DMFC and PEMFC is a protonically conducting but electronically insulating membrane placed between the anode and cathode. To minimize internal ohmic losses, the membrane must possess a high proton conductivity, and is commonly formed from Nafion or other perfluorosulfonic acid polymers. When fully hydrated, these polymers exhibit proton conductivites on the order of 1 × 10^(-1) to 1 × 10^(−2) S/cm. For hydrogen PEMFC without active humidification, proton conductivity decreases rapidly with increasing temperaure. For DMFC, membrane swelling allows methanol diffusion directly from anode to cathode decreasing cell efficiency.

The formation of precursor particles in the crystallization of zeolites from gelating systems has been studied using X-ray scattering at small angles. The crystallization of Si−MFI using trimethylene-bis(N-hexyl, N-methyl-piperidinium) as the structure-directing agent shows the formation of two categories of precursors: gel particles and nanometer-scaled primary units. The size of the primary units for the crystallization of Si−MFI is found to be 2.8 nm both for gelating and nongelating systems using different structure-directing agents. Zeolites Si−BEA and Si−MTW have been prepared using the same organic (trimethylene-bis(N-benzyl, N-methyl-piperidinium)) at different concentrations. Primary units with a size of 2.6 nm are found to be present in the synthesis of Si−BEA, while their size is 1.5 nm in the synthesis mixture directing to Si−MTW. Our data suggest that the nanometer-scaled primary units are specific for the zeolite topology formed.

A functional polymerizable surfactant has been synthesized and used as a template to prepare MCM-41. Ozonolysis of the olefin functional group in the composite material generates a nonporous proton-conducting solid acid that has a conductivity of ca. 6 mS cm^(-1) at 95 °C and an activation energy of 14.2 kJ/mol.

Alumina mesophases have been synthesized by reacting aluminum alkoxides and carboxylic acids with controlled amounts of water in low-molecular-weight alcoholic solvents. Calcination of these materials yields aluminas that are thermally stable to 1073 K and contain randomly ordered pores. Specific surface areas as high as 710 m2/g and narrow pore size distributions centered at 20 A that do not contain “zeolitic” micropores are exhibited by the calcined solids.

Progress on the use of imprinting (templating) for the synthesis of nanostructured catalysts is reviewed. In the context of providing a foundation for synthetic mimics, the basic principles of enzyme catalysis are enumerated. With these paradigms in mind, catalytic antibodies, imprinted polymers, imprinted amorphous metal oxides, and zeolites are discussed with respect to their preparation procedures and catalytic properties. These synthetic catalysts are contrasted to one another in order to highlight the advantages and disadvantages of each system. Suggestions for future work on preparing enzyme-mimicking materials by imprinting are provided.

Zeolite L (structure code LTL) crystals are synthesized starting from homogeneous potassium aluminosilicate solutions. Particle size and shape of the formed zeolite L are examined by high-resolution transmission electron microscopy, field emission-scanning electron microscopy, X-ray diffraction, and dynamic light scattering. The synthesis conditions reported lead to nanoclusters of aligned zeolite crystalline domains of dimensions {approximately}40 nm in the channel direction and {approximately}15 nm in the direction perpendicular to the zeolite channels. The nanoclusters have sizes of {approximately}60 nm. Electron microscopy of the nanoclusters reveals the presence of inhomogeneities (intercrystalline porosity) on length scales ranging from 2 to 60 nm. The N{sub 2} and cyclohexane adsorption capacities and the thermal stability of the crystals synthesized are correlated with their microstructure. The preparation of colloidal suspensions of the zeolite L nanoclusters in water is described along with their use in seeded growth and film formation. 16 refs., 12 figs.

Several syntheses of zeolites that employ organic structure-directing agents are investigated via ^1H-^(29)Si CP MAS NMR spectroscopy. Inorganic-organic interactions in the tetrapropylammonium- and 1,6-hexanediamine-mediated syntheses of pure-silica ZSM-5 (Si-ZSM-5) are compared; these results are contrasted to those from the 1,6-hexanediamine-mediated synthesis of pure-silica ZSM-48 (Si-ZSM-48), in which the diamine serves as a pore-filling agent. Synthesis gels containing tetramethylammonium, tetraethylammonium, tetrabutylammonium, tetrapentylammonium, and tetraethanolammonium in lieu of tetrapropylammonium are evaluated by ^1H-^(29)Si CP MAS NMR to examine the significance of hydrophobic hydration behavior in structure direction. Finally, the effects of sodium, the silica source, and the substitution of D_2O for H_2O on the kinetics of nucleation and crystallization are discussed in terms of their mechanistic implications. A modified mechanism of structure direction in zeolite synthesis is proposed for which the formation of inorganic-organic composite structures is initiated by overlap of the hydrophobic hydration spheres of the inorganic and organic components, with subsequent release of ordered water to establish favorable intermolecular van der Waals interactions.

The role of tetrapropylammonium (TPA) as a structure-directing agent in the sodium-free synthesis of pure-silica ZSM-5 (Si-ZSM-5) is investigated by solid-state ^1H-^(29)Si CP MAS NMR. It has previously been proposed that the mechanism of structure direction in a sodium-containing system involves preorganization of silicate species around the TPA ions with subsequent assembly of these inorganic-organic composite structures to yield crystalline Si-ZSM-5 with occluded TPA molecules.l ^1H-^(29)Si CP MAS NMR results indicate that short-range intermolecular interactions, i.e., on the order of van der Waals contact distances, are established during heating of the zeolite synthesis gel prior to the development of long-range order indicative of the ZSM-5 structure. These interactions are independent of the presence of sodium in the gel or the silica source used. An attempt to isolate the composite species by trimethylsilylation of the synthesis mixture was partially successful. These results provide additional evidence for the existence of preorganized, inorganic-organic composite structures during the synthesis of Si-ZSM-5. A modified mechanism of structure direction and crystal growth of Si-ZSM-5 is proposed.

Sol-gel synthesis of aluminum oxide from mixtures containing Al(O-s-Bu)_3, acetic acid, and sec-butyl alcohol, whereby water was produced in situ, was characterized by infrared, ^1H NMR, ^(13)C NMR, and ^(13)C and ^(27)Al magic angle spinning NMR spectroscopies. The molar ratio (R) of acetic acid to Al(O-s-Bu)_3 strongly influenced the nature of the product. When R was < 2, the product was an opaque gelatinous precipitate, and when R was ≥ 2, transparent gels were formed. Acetic acid played crucial roles in both the hydrolysis and condensation reactions that constitute the essential chemistry of the sol-gel synthesis. Acetic acid influenced the rate of hydrolysis by (1) reacting rapidly with Al(O-s-Bu)_3 to give Al(O-s-Bu_2-OCOCH_3), which is much less reactive than Al(O-S-BU)_3 in hydrolysis, (2) catalyzing condensation reactions, and (3) catalyzing the dehydration of sec-butyl alcohol to give water. Acetic acid is involved in all the reactions of the sol-gel synthesis and thus provides a delicate control of the chemistry. The ratio R also influenced the morphology of the products formed as a result of drying at temperatures in the range 50-300 °C; these products were characterized by infrared spectroscopy, scanning electron microscopy, and surface area/pore volume measurements. Upon heating, the gelatinous precipitate was transformed into a dense material with a low surface area and low pore volume. Prior to drying, this material contained principally oligomeric species with few OH ligands and little unreacted acetic acid, thus favoring intermolecular condensation reactions and collapse of the structure during drying. In contrast, gels produced at values of R ≥ 2 gave materials with higher surface areas and higher pore volumes. Prior to drying, these materials contained principally polymeric species incorporating acetate and OH ligands located close to each other, thus favoring intramolecular condensation reactions during drying. Removal of unreacted acetic acid from the gel led to high-surface-area and high-pore-volume materials.

The incorporation of Zn^(2+) into tetrahedral framework positions of zeolites with the sodalite topology (SOD) is obtained by direct synthesis. The zincosilicates are characterized by thermal analyses, a Rietveld refinement of powder X-ray diffraction (XRD) data, and infrared (IR) and ^1H, ^(23)Na, ^(13)C, and ^(29)Si MAS NMR spectroscopies. A zinc substitution level as high as Si/Zn = 6-7 is achieved and constitutes by far the largest extent of isomorphous substitution by a doubly charged heteroatom in the framework of a zeolite. Two types of β-cage occupancies (TMA^+ and Na^+) are observed.

Copper metal films were grown on single-crystal strontium titanate (100) by the thermal decomposition of copper dimethylamino ethoxide in inert atmosphere at temperatures between 150 and 270 °C. Films grown at 200 °C are copper metal, free from contaminants, while higher temperatures result in significant carbon and oxygen incorporation. Deposition products were identified by Fourier transform infrared spectroscopic analysis of the reactor gas phase in situ and by mass spectroscopic analysis of the reactor exit gas during deposition. At 200 °C, deposition occurs by interdependent β-hydride elimination and reductive elimination reactions which produce (dimethylamino)ethanal, (dimethylamino)ethanol, and copper metal. β-Hydride and reductive elimination reactions are also dominant at 250 "C; however, the competition of ligand fragmentation reactions with the whole-ligand eliminating reactions leads to carbon and oxygen contamination of the copper metal film.

The series of high-silica zeolites ZSM-5,ZSM-11,ZSM-12, SSZ-24, cubic and hexagonal faujasite has been studied to understand the relation between crystal structure and stability in open silicate frameworks. High-temperature solution calorimetry using lead borate (2PbO_2•B_2O_3) solvent at 977 K measured enthalpies of solution and transposed temperature drop calorimetry obtained heat contents at 977 K. Data have been compared with those for quartz and other “dense”, crystalline polymorphs of silica. The enthalpies of formation at 298 K are as follows: ZSM-12, -(902.0 ± 1.3); ZSM-5, -(902.5 ± 1.3); ZSM-11, (902.5 ± 1.4); SSZ-24, -(903.5 ± 1.3); hexagonal faujasite, -(900.2 ± 1.3); and cubic faujasite, -(897.1 ± 1.2) kJ/mol. The value for quartz is -(910.70 ± 1.00) kJ/mol. All zeolitic silicas are only 7-14 kJ/mol less stable in enthalpy than quartz. This implies an entropic or kinetic rather than a large stabilizing energetic role of the template in zeolite synthesis. The small variations in energy among these structures cannot be directly related either to the degree of ”openness” (framework density or molar volume) or to the mean Si-O-Si angle. Rather, the overall distribution of bond angles seems to dictate the energy of these structures, with Si-O-Si angles below 140° being the major destabilizing factor. On the other hand, heat contents, (H_(977)-H_(298), including those for “dense” crystalline polymorphs, show a linear dependence on the framework density or molar volume.

Zeolite and molecular sieve syntheses are reviewed. The synthesis of aluminum-rich zeolites, high-silica zeolites, and phosphate-based molecular sieves are evaluated. Unresolved mechanistic issues are outlined and areas for exploration suggested. The ability to plan zeolite and molecular sieve syntheses is discussed and a strategy for synthesizing a chiral zeolite is used to demonstrate the current limitations in "designing" new molecular sieves.

Synthetic cubic faujasite (FAU) has been known for several decades, and it is one of the most studied and commercially important zeolites. Recently, the hexagonal polytype of faujasite has been synthesized by Delprato et al. We have subsequently confirmed the synthesis procedures used to crystallize this new zeolite and have compared some of its physicochemical properties to those of FAU. Also, we have shown that the hexagonal polytype of faujasite (for our purposes denoted as hex) can be dealuminated by contact with SiCl_4 vapor in a manner similar to that used for the dealumination of FAU. The existence of the cubic and hexagonal polytypes of faujasite leads one to speculate on whether zeolites can be synthesized as intergrowths between these two end members at any ratio of two polytype contents. ZSM-20 is an intergrowth of cubic and hexagonal stackings of faujasite sheets, and ZSM-2, ZSM-3, and ZSM-19 may also be intergrowths. The purpose of our work is to explore the possibility of synthesizing zeolites that are comprised of intergrowths of cubic and hexagonal stackings of faujasite sheets and vary in the ratio of cubic/hexagonal content. From Delprato et al., pure hex and FAU can be synthesized from the reaction mixture R·2.4Na_2O·Al_O_3·10SiO_2·140H_2O, where R is 1,4,7,10,13,16-hexaoxacyclooctadecane (18- crown-6) and 1,4,7,10,13-pentaoxacyclopentadecane (15- crown-5), respectively. Thus, in this work we use the reaction mixture (1 - x)R_1·xR_2·2.4Na_2O·Al_2O_3·10SiO_2• 140H_2O, where R_1 = 18-crown-6, R_2 = 15-crown-5, and x is varied as 0 ≤ x ≤ 1.