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Hydrolytically stable mesostructured aluminosilicates assembled from protozeolitic precursors are examined as acid catalysts in the isobutene oligomerization reaction. Steady state conversions as high as 80% at 60 °C are achieved, depending on the isobutene:butane feed composition and space velocity. Most notably, the product selectivity to dimeric C8=and trimeric C12=olefins is readily fine-tuned simply by changing the feed composition. Undesirable high molecular weight oligomers are not produced in any case. The superior catalytic performance of the mesostructured aluminosilicates in comparison to commercial USY and BEA zeolites is clearly established. The improvement in catalytic performance is attributed to a combination of textural and acidic properties, as judged by N2adsorption and pyridine adsorption studies.

A surfactant‐templated routeto mesostructured forms of the transition alumina phases η‐Al2O3and χ‐Al2O3is described. The surface areas and pore‐size distributions of these novel forms of alumina are substantially improved with respect to those of conventional forms of these phases. Wormholelike pores are visible in the TEM image shown of mesostructured η‐Al2O3.

The use of homoionic organic clays and mixed‐ion organic/inorganic clays modified by di‐ or triamines (Jeffamines), which are being used as epoxy resin curing agents, in the synthesis of polymer nanocomposites has been studied in this work. Our aim is to enhance polymer crosslinking and interfacial adhesion in the nanocomposite structure by utilizing the functionality of the di/triamines on the surface of clay nanolayers and by reducing the organic modifier via formation of homostructured mixed‐ion organic/inorganic clays. The results show that the use of homoionic organic clays exchanged with relatively short chain di‐ or triamines and mixed‐ion organic/inorganic clays partially exchanged (ca. 35%) with long chain diamines resulted in intercalated structures with enhanced thermo‐mechanical properties (Young's Modulus, Storage Modulus). On the other hand, homoionic organic clays exchanged with long chain diamines and triamines resulted in exfoliated nanocomposites but with compromised mechanical properties due to the plasticizing effect of the long chain amine modifiers.

Mesostructured forms of silica (denoted MSU‐J) and aminopropyl‐functionalized silica (denoted AP‐MSU‐J) with wormhole framework structures are effective reinforcing agents for a rubbery epoxy polymer. At loadings of 2.0–10 wt %, MSU‐J silica with an average framework pore size of 14 nm (65 °C assembly temperature) provides superior reinforcement properties in comparison to MSU‐J silica with a smaller average framework pore size of 5.3 nm (25 °C assembly temperature), even though the surface area of the larger pore mesostructure (670 m2g−1) is substantially lower than the smaller pore mesostructure (964 m2g−1). The introduction of 5.0 and 10 mol % aminopropyl groups in the wormhole framework walls decreases the textural properties in comparison to the pure silica analogs. AP‐MSU‐J organosilicas increase the tensile strength as well as the strain‐at‐break of the rubbery epoxy mesocomposites in comparison to MSU‐J silica as a reinforcing agent. The improved toughness provided by the aminopropyl functionalized mesostructures is attributable in part to covalent bond formation between the mesostructured silica walls and the cured epoxy matrix and to a more ductile mesostructure framework in comparison to a pure silica framework. An organosilica derivative containing 20 mol % aminopropyl groups, but lacking a mesostructured framework, provides little or no improvement in polymer tensile properties, demonstrating that an ordered porous network is essential for polymer reinforcement. In general, the reinforcement benefits provided by mesostructures with larger framework pores are superior to those provided by smaller pore derivatives, most likely because of more efficient polymer impregnation of the particle mesopores. The presence of a mesostructured form of the organosilica is essential for improving the mechanical properties of the epoxy polymer.

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Aluminosilicate mesostructures SiAl 1.6–49 with wormhole framework structures were assembled from protozeolitic nanoclusters zeolite seeds that normally nucleate the crystallization of faujasite FAU, zeolite ZSM-5 MFI and zeolite Beta BEA. The cationic surfactant cetyltrimethylammonium, the electrically neutral surfactant dodecylamine and the small molecule triethanolamine all are effective structure directors for the assembly of wormhole frameworks from zeolite seeds. The resulting aluminosilicate mesostructures exhibit high textural porosity, hydrothermal stability toward boiling water and 20 steam at 800 °C, and acidity for catalytic cumene cracking. That is, the amine and onium ion structure directors used to template a wormhole framework structure do not compromise the benefits provided by the zeolite seeds.

Aluminosilicate mesostructures (Si/Al = 1.6–49) with wormhole framework structures were assembled from protozeolitic nanoclusters (zeolite seeds) that normally nucleate the crystallization of faujasite (FAU), zeolite ZSM-5 (MFI) and zeolite Beta (BEA). The cationic surfactant cetyltrimethylammonium, the electrically neutral surfactant dodecylamine and the small molecule triethanolamine all are effective structure directors for the assembly of wormhole frameworks from zeolite seeds. The resulting aluminosilicate mesostructures exhibit high textural porosity, hydrothermal stability toward boiling water and 20% steam at 800 °C, and acidity for catalytic cumene cracking. That is, the amine and onium ion structure directors used to template a wormhole framework structure do not compromise the benefits provided by the zeolite seeds.

Metakaolin, formed through the thermal de-hydroxylation of kaolin clay, has been shown to be an effective reagent for the preparation of faujasitic zeolite nanoclusters for framework incorporation into hexagonal, cubic and wormhole aluminosilicate mesophases with Si/Al ratios in the range 5.6–1.6. Single tetrahedral aluminum sites with 27Al NMR chemical shift of 60 ppm are observed for each mesostructure, which is indicative of the incorporation of the protozeolitic nanoclusters into the framework walls. Unlike aluminosilicate mesostructures assembled from conventional precursors, no framework de-alumination was observed for the mesostructures upon calcination at 550 °C. The results suggest that metakaolin is a promising low-cost precursor for the industrial scale production of high quality aluminosilicate mesophases.

The synthetic layered silicates Na+-ilerite (Na₂Si₈O₁₇·nH2O), Na+-magadiite (Na₂Si₁₄O₂₉·nH₂O), and K+-kenyaite (K₂Si₂₀O₄₁·nH₂O) were converted to the corresponding layered silicic acids (silicas) through the stoichiometric replacement of the gallery alkali metal ions with protons. The protonated derivatives were subsequently used as hosts for the intercalation of poly(propyleneoxide) amines that are normally used as curing agents for thermoset polymers. The amines of interest were the commercially available α,ω-diamines known as Jeffamine D-series amines and Jeffamine T-series glycolitic triamines with molecular weights in the range 400–5000. Low molecular weight Jeffamines (MW~400) intercalate in all three layered silicas as lateral monolayers in which the PPO chains are oriented parallel to the silica sheets and the gallery heights are restricted to values of 4.0–4.9 Å. Amines with MW values of 1000–5000 afford intercalates in which the gallery heights are 2.6–9.0 times as large as the thickness of the host layers and the PPO chains adopt coiled conformations in the galleries. Substantial de-intercalation of the high MW amines occurs upon mild extraction with ethanol–water mixtures, as expected for an intercalation mechanism that involves hydrogen bonding between the amine head groups and silanol groups on the basal surfaces of the host silicas. The ability to control the amine to silica ratios in these intercalates should prove to be advantageous in applying these materials for the preparation of epoxy-layered silicates nanocomposites and other thermoset nanocomposites derived from amine monomers.

The synthetic layered silicates Na-ilerite Na2Si8O17·nH2O, Na-magadiite Na2Si14O29·nH2O, and K-kenyaite K2Si20O41·nH2O were converted to the corresponding layered silicic acids silicas through the stoichiometric replacement of the gallery alkali metal ions with protons. The protonated derivatives were subsequently used as hosts for the intercalation of polypropyleneoxide amines that are normally used as curing agents for thermoset polymers. The amines of interest were the commercially available α,ω-diamines known as Jeffamine D-series amines and Jeffamine T-series glycolitic triamines with molecular weights in the range 400–5000. Low molecular weight Jeffamines MW∼400 intercalate in all three layered silicas as lateral monolayers in which the PPO chains are oriented parallel to the silica sheets and the gallery heights are restricted to values of 4.0–4.9 Å. Amines with MW values of 1000–5000 afford intercalates in which the gallery heights are 2.6–9.0 times as large as the thickness of the host layers and the PPO chains adopt coiled conformations in the galleries. Substantial de-intercalation of the high MW amines occurs upon mild extraction with ethanol–water mixtures, as expected for an intercalation mechanism that involves hydrogen bonding between the amine head groups and silanol groups on the basal surfaces of the host silicas. The ability to control the amine to silica ratios in these intercalates should prove to be advantageous in applying these materials for the preparation of epoxy-layered silicates nanocomposites and other thermoset nanocomposites derived from amine monomers.

Significant improvements in both the hydrothermal stability and the acidity of mesostructured aluminosilcates have been reported recently. New assembly pathways, along with post-synthesis treatment methods, have made it possible to form structures with thick and more highly crosslinked framework walls. The resulting structures are slow to degrade under hydrothermal conditions in comparison to conventional analogs. Also, improved methodologies for grafting Al centers into the walls of pre-assembled frameworks have afforded aluminosilicate mesostructures with enhanced acidity. The most promising strategy for improving the hydrothermal stability and acidity of aluminosilicate mesostructures, however, is based on the use of protozeolitic nanoclusters. These so-called “zeolite seeds” can be directly assembled into hexagonal, cubic, wormhole, and foamlike framework structures under a variety of assembly conditions. They also can be grafted into the walls of pre-assembled frameworks to form more stable acidic derivatives.

A mesoporous MSU-G molecular sieve silica, prepared through a H bonding assembly mechanism in the presence of a C12H25NH(CH2)2NH2gemini surfactant as the structure director, is shown on the basis of N2and XRD measurements to be substantially more stable to calcination at 1000°C and to hydrothermal treatment at 100°C than electrostatically assembled MCM-41, KIT-1 and SBA-3 silicas. Also, 2%Al-MSU-G derivatives as prepared through grafting reactions with aluminum nitrate, aluminum iso-butoxide or sodium aluminate, are far more efficient acid catalysts than 2%Al-MCM-41 for the conversion of 2,4-di-tert-butylphenol and cinnamyl alcohol to a bulky flavan as the primary alkylation product. The exceptional stability of MSU-G mesostructures is consistent with the very high degree of framework cross-linking (Q4/Q3=6.2) and thick framework walls (∼25 Å). The improved catalytic activity of MSU-G mesostructures is attributable to the vesicular particle morphology, which facilitates reagent access to catalytic centers in the lamellar framework.

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The cationic metal cage complex (1,3,6,8,10,13,16,19-octaazabicyclo[6.6.6]cicosane)cobalt(III), Co(sep)3+ has been investigated as a potential pillaring reagent for Na+-magadiite (Na1.7Si14O27.9(OH)1.9 · 7.6 H2O) a synthetic layered sodium silicate. Reaction of Na+-magadiite with aqueous solutions of Co(sep)Cl3 at 25°C resulted in the binding of Co(sep)3+ cations to the external crystalline surface of the layered silicate. In contrast, an intercalated product exhibiting a 17.6 Å basal spacing was generated by reaction at 100°C.29Si MAS NMR and FT-IR spectroscopy indicate that Co(sep)3+ intercalated reaction products retain the magadiite layer structure. Moreover, scanning electron micrographs of the reaction products showed retention of the original particle morphology, suggesting a topotactic intercalation. However, during intercalation, some of the Co(sep)3+ was found to undergo an unusual demetalation reaction leaving a combination of Co(II) and Co(sep)3+ between the layers. Nitrogen surface area analysis showed that only a small amount of microporous surface existed in the Co(sep)3+ intercalated derivative, suggesting that most of the interlayer space is ‘stuffed’ with cobalt species.

An amorphous zinc-aluminium oxide solid solution, Zn0.67Al0.33O1.17, Prepared by the thermal decomposition of the acidic layered double hydroxide (LDH), [Zn0.67·Al0.33(OH)2](CO3)1.17·0.33H2O, was found to react with Keggin-like heteropolyoxometalate anions such as α-[Si·W11O39]8−and α-1,2,3-[SiV3W9O40]7−in acid solution to form pillared LDH structures with gallery heights of 9.9 Å.

Nichtionische Polyethylenoxid‐Detergentiensind vielseitige strukturdirigierende Agentien bei Synthesen mesoporöser Molekularsiebe. Ihr größter Nutzen könnte darin bestehen, daß sie zu mesoporösen Strukturen führen, deren Porengröße von der Synthesetemperatur abhängt. Für mesoporöse Silicate mit wurmlochartigen Strukturmotiven kann der durchschnittliche Porendurchmesser Rdurch Variation der Synthesetemperatur in einem engen Bereich unterhalb des Trübungspunktes des Detergens um bis zu 2.4 nm verändert werden; eine typische Größenverteilung ist rechts oben gezeigt.

A heavy metal ion adsorbent that binds Hg2+ ions from solution to a capacity of 0.74 mmol/g has been prepared by grafting 3-mercaptopropyltrimethoxysilane to the intragallery framework walls of a porous fluorohectorite clay heterostructure (PCH). Up to 67% of the immobilized thiol groups are accessible for Hg2+ trapping. This represents a significant improvement over previously reported clay-based ion adsorbents in which pore blockage limits the access of metal ions to fewer than 10% of the complexing sites. The uniform open-framework mesoporosity of PCH materials greatly facilitates access to most of the reactive sites attached to the pore walls. The possible use of PCH materials in future environmental remediation efforts is briefly discussed.

Heterostructured fluorohectorite clays with regularly alternating interlayers of inorganic and organic exchange cations have been prepared through ion exchange reaction of the sodium clay in aqueous suspension with half an equivalent of alkylammonium ions. In order to elucidate this staging-like behavior of the intercalates, the exchange process was examined for a series of onium ion surfactants of the type [CnH(2n+1)N(CmH(2m+1))3]+. One set of onium ions varied the alkyl chain length (n=4–22), while maintaining a constant onium head group size (m=4). A second set varied the head group size (m=1–5), while the chain length remained fixed (n=16). Two fundamental factors, namely, alkyl chain length and head group size determined staging behavior. The surfactant alkyl chain length determined the extent of Na+replacement by onium ions. Relatively little Na+exchange (∼10%) occurred for the short chain onium ions withn=4,m=4 andn=6,m=4. The replacement of Na+by onium ions became more favorable as the alkyl chain length was increased ton=8 or 10. For very hydrophobic surfactants withn≥12, onium ion uptake was essentially quantitative, affording 1:1 mixed Na+–onium ion intercalates. The “footprint” or area covered by the onium ion head group on the interlayer surface controlled heterostructure formation for the 1:1 intercalates. Form≥3 the head group footprint matched the clay surface charge density and precluded the mixing of organic and inorganic exchange cations within the same gallery. The segregation of the hydrophobic organic cations and the hydrophilic inorganic cations on the internal and external surfaces of two-nanolayer tactoids during the ion exchange process was proposed as the pathway for staging behavior in the heterostructured intercalates. The smaller footprints of trimethyl and triethyl onium ion head groups (m=1,2) allowed for comingling of the exchange ions on single-nanolayer tactoids and the formation of phase–segregated organic and sodium ion clays upon stacking of the tactoids.

The specific activities of catalysts formed by thermal activation of the layered double hydroxide [Mg2.34Al (OH)6.68] (CO3)0.5·2.6H2O have been determined using 2-methyl-3-butyn-2-ol (MBOH) as an acid/base-selective substrate. Acetone and acetylene were the only reaction products formed over the temperature range 80–150°C, demonstrating that all of the LDHderived catalysts have highly basic selectivities. Thermal activation below the structural decomposition point of the LDH (?250°C) afforded catalysts with specific activities approximately an order of magnitude larger than the amorphous metal oxides and crystalline MgAl2U4 spinel-MgO mixtures formed by thermal activation at 450 and 890°C, respectively. Even the remnant LDH structure formed by partial decarbonation/dehydroxylation at 350°C was substantially more active than the more commonly used metal oxide derivatives.

Propene alkylation of biphenyl was catalyzed by alumina pillared clays, and, for comparison, by several other oxide acids including an alumina delaminated clay, an acid washed clay (K-10 montmorillonite) and zeolites (USY and H-mordenite). Relationships between pore structures and catalytic properties were investigated. The microporous catalysts afforded high yields of meta- and para-alkylated isomers at the expense of the more spatially demanding ortho-alkylated isomer.

Although the layer charge in 2:1 phyllosilicate minerals is known to result from the replacement of tetrahedral Si or octahedral Al, Fe and Mg by ions of lower charge, there is only limited information concerning the distribution of layer charge from X-ray crystallographic data1–3. Here we use 29Si and 27Al magic angle spinning (MAS) NMR spectroscopy to examine the site distribution of tetrahedral Si and Al in a series of synthetic trioctahedral clays with (Si/Al)tetrvalues in the range 2.74–7.69. Analysis of the 29Si spectra shows that Loewenstein's rule for Al occupancy of the tetrahedral sheet is obeyed and that there is some short-range ordering for Al sites. The nature of the ordering is explained in part by the results of electrostatic potential energy calculations. In general, strong 27Al resonances are observed for Al in tetrahedral sites, but the resonances due to Al in octahedral sites are considerably weaker than would be expected on the basis of chemical analysis. Consequently, no quantitative analysis of the 27Al spectra is possible.

The direct supramolecular assembly of organofunctional mesostructures with a vesicular hierarchical morphology is reported for the first time for SiO21−xLSiO1.5xcompositions, where L is a mercaptopropyl group and x 0.10–0.30.

Thiol-functionalized mesostructured silica, prepared by direct assembly methods, is an effective trapping agent for the removal of arsenite from water.

An amphiphilic smectite clay, interlayered by regularly alternating galleries of organic [C₁₆H₃₃N(C₄H₉)₃⁺] and inorganic (Li⁺ ) exchange cations, is shown to be especially efficient for the removal of a chlorinated aromatic pollutant (2,4-dichlorophenol) from water in comparison to the fully-exchanged hydrophobic form of the same clay.

Nonionic polyethylene oxide surfactantsare versatile structure-directing agents for the assembly of mesoporous molecular sieves, but their greatest benefit may lie in their ability to control the pore size of the mesostructure by the assembly temperature (see dependence of pore diameter Ron temperature shown on the right). For mesostructured silicas with wormhole motifs, the average pore diameter can be altered by as much as 2.4 nm by varying the assembly temperature over a relatively narrow range below the cloud point temperature of the surfactant.

Silica mesostructures with well-expressed hexagonal and wormhole framework structures and up to 50% organo-functionalization of the framework silicon sites have been directly assembled from sodium silicate.

Silica mesostructures with well-expressed hexagonal and wormhole framework structures and up to 50 organo-functionalization of the framework silicon sites have been directly assembled from sodium silicate.

The in-situgraphitization of an as-made, large pore silica mesostructure templated by nonionic Pluronic 123 surfactant micelles provides a low cost pathway to the nanocasting of linear carbon nanotubes.

The in-situ graphitization of an as-made, large pore silica mesostructure templated by nonionic Pluronic 123 surfactant micelles provides a low cost pathway to the nanocasting of linear carbon nanotubes.

A mesoporous carbon molecular sieve with a hexagonal framework structure (denoted C-MSU-H) has been prepared using a MSU-H silica template that can be assembled from a low cost soluble silicate precursor at near-neutral pH conditions.

In contrast to earlier methods requiring the presence of organic modifiers for the preparation of cubic MCM-48 mesostructures from low cost sodium silicate, we show that this three dimensional framework structure can be readily assembled in the absence of co-surfactants simply by using the overall SiO₂/OH− ratio as a means of controlling the surfactant packing parameter.

Very large pore hexagonal and cellular foam-like molecular sieve silicas with well cross-linked framework walls (denoted MSU-H and MSU-F, respectively), have been prepared from soluble silicate precursors under neutral pH conditions.

Thermally stable mesoporous silica molecular sieves with wormhole framework structures, previously obtainable only from silicon alkoxides, have been prepared from low cost soluble silicate precursors in the presence of non-ionic surfactants as structure directors.

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ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.