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The proton transfer process mediated by water molecules adsorbed in an aluminosilicate framework was studied using ab initio molecular dynamics simulations. The investigation was conducted using a quasi-one-dimensional model simulating the mesoporous aluminosilicate channel structures.

A novel three-step assembly pathway is reported for the formation of a mesostructured alumina with framework pore walls made of crystalline, lathlike gamma-Al203 nanoparticles. The high surface areas (300-350 m2/g) and pore volumes (0.45-0.75 cm3/g) provided by these mesostructured forms of gamma-Al203 are useful in materials and catalytic applications where the availability of surface Lewis acid sites and the dispersion of supported metal centers govern reactivity.

A grafting process has been found to be effective in producing sieves that bind quantitatively more heavy metal ions than standard techniques. The sieves were made using covalent grafting of 3-mercaptopropylsilyl groups MCM-41 and HMS to the framework pore walls. The functionalized HMS derivative has found to bind more mercury (II) ions than the initially anionic MCM-41 derivative.

A novel assembly approach was used to prepare a porous lamellar silica with a hierarchical structure (MSU-V). This involved the cooperative formation of multilamellar vesicular surfactant-silica complexes, through the H-bondong interactions between H2N(CH2)12-NH2 as products of the tetraethylorthosilicate. Sorption properties of the lamellar MSU-V silica were similar to pillared lamellar clays.

The physical and catalytic properties of two titanium-substituted mesoporous catalysts prepared at ambient temperatures via electrostatic and neutral assembly pathways were compared. Specifically, Ti-MCM-41 and Ti-HMS molecular sieves were characterized with respect to their catalytic function in the liquid phase peroxide oxidations of methyl methacrylate, styrene, and 2,6-di-tert-butylphenol. The results demonstrated their superior catalytic efficiency over other titanium silicates.

X-ray diffraction, TGA-DTA, and (super 7)Li and (super 23)Na NMR data is presented for PEO nanocomposites made with natural and synthetic montmorillonite clays that provide new insight into interlayer structure. (super 23)Na NMR shows that PEO intercalculation results in the conversation of the multiple Na(super +) hydration states observed for the prostine clay into inner sphere sites most likely formed through coordination with the basal oxygens of the clay.

The mercury-binding mechanism for representative thiol-functionalized mesostructures by atomic pair distribution function analysis of synchroton X-ray powder diffraction data and by Raman spectroscopy is investigated. The Raman results indicate that the complexation of mercury centers by thiolate depends on the mercury loading.

The density functional theory (DFT) method is used to investigate the structure and bonding of silica and aluminosilicate nanoclusters containing five- and six-membered oxygen rings. The results reveal that an excitation energy at least 18 times larger than the room-temperature thermal energy is needed to break the stable five-membered ring structure, implying a high hydrothermal stability and acidity for this aluminosilicate structure.

The structure determination and an extensive exploration of the opportunities in the pore structure tailoring for a prominent member of ordered silicas with cage-like mesoporous structure (OSCMS) family are reported. It is shown that the temperature and time control during the synthesis allows one to gradually change cage-like pores of FDU-1 to a highly open and accessible porous system with narrow pore size distribution.

Two-dimensional, hexagonally ordered silicas with large uniform mesopores are assembled through a nonionic supramolecular assembly pathway using sodium silicate as a silica source and the triblock copolymer pluronic as a structure-directing agent. The materials exhibited adsorption properties highly similar to silica assembled through an electrostatic pathway under strongly acidic conditions, indicating the framework structure of analogues and consist of ordered large pores connected by micropores in the pore walls.

Thiol moieties which were grafted to the pore channel walls of mesoporous silica molecular sieves produced very effective heavy metal ion adsorbents which poses opportunities for operators of waste treatment and cleanup campaigns. Heavy metals such as lead and mercury are known to pollute the environment significantly to the detriment of natural ecosystems and human communities. Framework mesostructures that have many surface hydroxyl groups and huge pore channel parameters help develop framework channels which maintain appreciable open-framework features and various functional locations.

The replacement of amorphous aluminosilicated by derivatives of zeolite Y in gas oil cracking catalysts 40 years ago resulted in better product distribution, less coke formation, better stability, and lower catalyst consumption rates. Nanosized MSU-AS compositions possess the unique combination of mesoporosity, hydrothermal stability, acidity, and longevity that is desired for the efficient cracking of high molecular weight hydrocarbons.

A general route to mesostructured alumina containing transition alumina phase is reported. The study shows that surface areas are compatible with the values expected for a mesostructure with thick walls.

Aluminosilicate mesostructures that are steam stable were assembled from zeolite type Y seeds.

A novel three-step assembly pathway is reported for the formation of a mesostructured alumina with framework pore walls made of crystalline, lathlike γ-Al[sub 2]O[sub 3] nanoparticles, in the initial supramolecular assembly step of the pathway a mesostructured alumina with a wormhole framework morphology and amorphous pore walls is assembled through the hydrolysis of Al[sub 13] oligocations and hydrated aluminum cations in the presence of a nonionic diblock or triblock poly(ethylene oxide) surfactant as the structuredirecting porogen. The walls of the initial mesostructure are then transformed in a second hydrolysis step at a higher temperature to a surfactant-boehmite mesophase, denoted MSU-S/B, with a lathlike framework made of boehmite nanoparticles. A final thermal reaction step topochemically converts the intermediate boehmitic mesophase to a mesostructure with crystalline γ-Al[sub 2]O[sub 3] pore walls, denoted MSU-γ, with retention of the lathlike framework morphology. The boehmitic MSU-S/B intermediates formed from the chloride salts of aluminum incorporate chloride anions into the mesostructure. Chloride ion incorporation tends to disorder the nanoparticle assembly process, leading to a broadening of the slit-shaped framework pores in the final MSU-γ phases and to the introduction of intra- and inter-particle textural mesopores. However, the well-ordered MSU-γ phases made from aluminum nitrate as the preferred aluminum reagent exhibit narrow framework pore size distributions and average pore sizes that are independent of the surfactant size and packing parameter, in accord with a lathlike framework assembled from nanoparticles of regular size and connectivity. The high surface areas (∼300-350 m²/g) and pore volumes (∼0.45-0.75 cm³/g) provided by these mesostructured forms of γ-Al[sub 2]O[sub 3] should be useful in materials and catalytic applications where the availability of surface Lewis acid... [ABSTRACT FROM AUTHOR]

A novel three-step assembly pathway is reported for the formation of a mesostructured alumina with framework pore walls made of crystalline, lathlike γ-Al[sub 2]O[sub 3] nanoparticles. In the initial supramolecular assembly step of the pathway a mesostructured alumina with a wormhole framework morphology and amorphous pore walls is assembled through the hydrolysis of Al[sub 13] oligocations and hydrated aluminum cations in the presence of a nonionic diblock or triblock poly(ethylene oxide) surfactant as the structure-directing porogen. The walls of the initial mesostructure are then transformed in a second hydrolysis step at a higher temperature to a surfactant-boehmite mesophase, denoted MSU-S/B, with a lathlike framework made of boehmite nanoparticles. A final thermal reaction step topochemically converts the intermediate boehmitic mesophase to a mesostructure with crystalline γ-Al[sub 2]O[sub 3] pore walls, denoted MSU-γ, with retention of the lathlike framework morphology. The boehmitic MSU-S/B intermediates formed from the chloride salts of aluminum incorporate chloride anions into the mesostructure. Chloride ion incorporation tends to disorder the nanoparticle assembly process, leading to a broadening of the slit-shaped framework pores in the final MSU-γ phases and to the introduction of intra- and interparticle textural mesopores. However, the well-ordered MSU-γ phases made from aluminum nitrate as the preferred aluminum reagent exhibit narrow framework pore size distributions and average pore sizes that are independent of the surfactant size and packing parameter, in accord with a lathlike framework assembled from nanoparticles of regular size and connectivity. The high surface areas (∼300-350 m²/g) and pore volumes (∼0.45-0.75 cm[sup 3]/g) provided by these mesostructured forms of γ-Al[sub 2]O[sub 3] should be useful in materials and catalytic applications where the availability of surface Lewis acid... [ABSTRACT FROM AUTHOR]

Studies the pillaring of Mg3Al layered double hydroxides (LDHs) by the title polyoxometalates (POMs) through the use of ion exchange reaction of LDH-hydroxide and -adipate precursors with the POM anion at ambient or refluxing temperatures. Pillaring reaction, formation of a poorly ordered impurity phase.

Examines the properties of and composition of a series of Mg2+1-xAl3+x layered double hydroxide (LDH) intercalated by carbonate, hydroxide, chloride, and sulfate anions. Thermal properties; Structural properties; Basic properties.

Reports on an example of nanosized mesoporous aluminosilicate with the hydrothermal stability and acidity needed for the cracking of high molecular weight hydrocarbons. Use of protozeolitic aluminosilicate nanoclusters in the construction of acidic pore walls and starch as a porogen.

Examines the effectiveness of framework sodium and local framework structure in determining the hydrothermal stability of MCM-41 mesostructures. Role of sodium ions in limiting the hydrothermal stability of the mesostructure; Device used in analyzing the MCM-41 mesostructures; Retention of residual sodium in the sodium silicate MCM-41.

Mesoporous gamma-alumina with precisely controlled mesoporosity is synthesized through the scaffolding of pseudoboehmite nanoparticles in the presence of a nonionic surfactant as the porogen. In the initial step of the synthesis, a colloidal suspension of pseudoboehmite is prepared by peptizing pseudoboehmite in dilute acidic solution. The nanoparticles in the peptizate are then assembled into a scaffold structure using nonionic Tergitol 15-S-7 (C(15)H(33)(OC(2)H(4))(7)OH) as the surfactant porogen. Calcination of the resulting surfactant-containing composites at 500 degrees C removes the surfactant and concomitantly converts the pseudoboehmite crystallites to gamma-alumina through topochemical transformation with the retention of the scaffold structure. Depending on the surfactant to alumina ratio used to form the scaffold structures, the average pore size can be precisely controlled over the range of 3.5-15 nm. Also, the BET surface areas of the scaffold structures are substantially larger in comparison to the gamma-alumina formed from pseudoboehmite at the same calcination temperature in the absence of surfactant (296-321 vs 238 m(2) g(-1)). The substantial improvement in surface area provided by the scaffold structures, together with the ability to provide narrow pore size distributions over a wide range of average pore sizes by simply adjusting the surfactant content, should substantially improve the effectiveness of this oxide as an adsorbent and as a catalyst or catalyst support.

The proton transfer process mediated by water molecules adsorbed in an aluminosilicate framework has been studied using ab initio molecular dynamics simulations. This investigation has been carried out using a quasi-one-dimensional model simulating the mesoporous aluminosilicate channel structures. The effects of both the water loading and temperature of the system have been considered. At low coverage (one water molecule per acid site), the hydroxonium ion (H(3)O)(+) is found to be a transition state, in agreement with earlier studies on zeolites. At a higher water coverage (two water molecules per acid site), the (H(5)O(2))(+) species and the hydrogen bonded "neutral complex" structure are both found to be stable complexes at finite temperatures. The vibrational frequency spectrum is simulated by performing a Fourier transform of the velocity autocorrelation function (VAF), and the peak positions in the VAF are compared with IR measurements and zero-temperature calculations.

The density functional theory (DFT) method is used to investigate the structure and bonding of silica and aluminosilicate nanoclusters containing five- and six-membered oxygen rings. The clusters, which are derived from the BEA zeolite structure, are considered as models of the protozeolitic clusters that are incorporated into the pore walls of steam stable aluminosilicate mesostructures assembled from zeolite seeds. Two locally different Brønsted acid sites in the aluminosilicate structure are identified for the adsorption of a water molecule. The sterically more open acid site is favored for water binding. The stability of the aluminosilicate structure in the presence of H2O molecule is studied by breaking an Al-O bond and inserting a water molecule into the five-membered ring structure. We find that an excitation energy at least 18 times larger than the room-temperature thermal energy is needed to break the stable five-membered ring structure, implying a high hydrothermal stability and acidity for this aluminosilicate structure.

Directly assembled wormhole mesostructures with high level functionalized mercaptan (MP-HMS) have been shown to be effective mercury(II) (Hg2+) trapping agents. Sorption of Hg2+ onto MP-HMS was investigated using X-ray absorption spectroscopy (XAS) to identify the structural coordination of the adsorbed Hg. Samples with different fractions of mercaptan functionalized groups (i.e., x = 0.1 and 0.5) with various Hg/S molar ratios ranging from 0.05 to 1.4 were investigated. XAS analysis indicates that adsorbed Hg first coordination shell is best fitted with an Hg-O path and an Hg-S path. The Hg-S atomic distance (R(Hg-S)) remained relatively constant while the Hg-S coordination numbers (CN) decreased as Hg/S loading increased. For the Hg-O path, both the CN and the R(Hg-O) increased with increasing Hg loading. XAS results suggest that at low Hg loadings, adsorbed Hg2+ forms mostly monodentate sulfur complexes (-S-Hg-OH) with the sulfur functional groups on the MP-HMS surfaces. At high Hg loadings, the Hg coordination environment is consistent with the formation of a double-layer structure of Hg attached to sulfur binding sites (-S-Hg-O-Hg-OH).

Aluminosilicate nanoparticles containing 9.0-20 nm mesopores were prepared through the use of protozeolitic nanoclusters as the inorganic precursor and starch as a porogen. The calcined, porogen-free composition containing 2 mol % aluminum exhibited the porosity, hydrothermal stability, and acidity needed for the cracking of very large hydrocarbons. In fact, the hydrothermal stability of the nanoparticles to pure steam at 800 degrees C, along with the cumene cracking activity, surpassed the analogous performance properties of ultrastable Y zeolite, the main catalyst component of commercial cracking catalysts. The remarkable hydrothermal stability and catalytic reactivity of the new nanoparticles are attributable to a unique combination of two factors, the presence of protozeolitic nanoclusters in the pore walls and the unprecedented pore wall thickness (7-15 nm). In addition, the excellent catalytic longevity of the nanoparticles is most likely facilitated by the small domain size of the nanoparticles that greatly improves access to the acid sites on the pore walls and minimizes the diffusion length of coke precursors out of the pores.

gamma-Al2O3 is one of the most extensively utilized metal oxides in heterogeneous catalysis. Conventional forms of this oxide typically exhibit a surface area and pore volume less than 250 m2/g and 0.5 cm3/g, respectively. Previous efforts to prepare mesostructured forms of alumina resulted only in structurally unstable derivatives with amorphous framework walls. The present work reports mesostructured aluminas with walls made of gamma-Al2O3, denoted MSU-gamma. These materials are structurally stable and provide surface areas and pore volumes up to 370 m2/g and 1.5 cm3/g, respectively. The key to obtaining these structures is the formation of a mesostructured surfactant/boehmite precursor, denoted MSU-S/B, assembled through the hydrolysis of an aluminum cation, oligomer, or molecule in the presence of a nonionic surfactant. Mesostructured, gamma-aluminas offer the possibility of improving the catalytic efficiency of many heterogeneous catalytic processes, such as petroleum refining, petrochemical processing, and automobile exhaust control.