Search

A comparative evaluation of ten catalysts for biomass pyrolysis was performed using poplar (DN-34) as the feedstock. Five of the catalysts consisted of HZSM-5 with different silica:alumina ratios (SAR, 23, 30, 55, 80 and 280). The other five catalysts were sulfated zirconia (SO4 2− ZrO 2 ), 20% SO4 2− ZrO 2 dispersed on a mesoporous MCM-41 silica support, Al–MSU–S alumnosilicate exhibiting a foam-like mesopore structure, Al–MSU–S aluminosilicate exhibiting wormhole mesopores, and a bauxite waste product known as red mud. Analytical pyrolysis in tandem with GC/MS showed that all of the catalysts except for HZSM-5 resulted in low aromatic chemical production. Highly acidic sulfated zirconia catalysts were not selective to aromatics and produced significant coke and non-condensable gases. Mesoporous MSU–S catalysts exhibiting high pore volume and acidity also gave high gas and coke yields. Among the HZSM-5 catalysts evaluated, those with the lowest SAR provided the highest yields of total aromatics and the lowest levels of undesired coke. [ABSTRACT FROM AUTHOR]

Abstract: Polymeric mesocomposite membranes were prepared via wet phase inversion processes by incorporating surfactant-templated mesoporous silica particles, denoted MSP-1, into polysulfone matrices formed with and without PEG as a molecular porogen. Transmission electron microscopy and N2 adsorption–desorption measurements showed higher surface area (354m2/g), smaller average pore size (53nm), and larger pore volume (2.92cm3/g) with a narrower pore size distribution (26nm width at half-maximum) for surfactant-templated mesoporous silica particles compared to those of precipitated commercially available mesoporous silica, HiSil. The distinct morphological changes induced by PEG and by MSP-1 were redundant from the membrane performance point of view as they translated into similar performance gains that were not additive, pointing to the potential use of mesoporous additive as an alternative porogen. The higher hydrophilicity and unique structural features of MSP-1 resulted in enhanced performance of the prepared membranes compared to MSP-free controls and HiSil-based mesocomposites. Mechanical properties of mesocomposites and neat polysulfone membranes were comparable. Electron microscopy coupled with flux and rejection measurements were used to investigate the influence of polymer content, MSP loading, and the presence of porogen on the structure and separation properties of mesocomposite membranes. Mesocomposite membranes showed increased water flux and dextran rejection. For ultrafiltration membranes the figure of merit, operationally-defined as the product of water flux and rejection of 12kDa dextran, increased by the factor of 2.8 (for membranes cast with a porogen) and 6.3 (in the absence of porogen) upon incorporation of the mesoporous additive at the loading of 10wt%. Enhancement factors were 3.7 and 11.2 for less permeable membranes cast from mixtures with higher (20wt%) polymer content. Fouling tests with humic acid solutions demonstrated that mesocomposite membranes experienced lower flux decline and showed higher rejections. [Copyright &y& Elsevier]

Zeolites with uniform intracrystal mesopores, designated MSU-MFI, were prepared using silane-modified polymers as mesopore-generating agents. X-ray diffraction analysis of this catalyst showed Braggs peaks representative of MFI structure. Catalyst characterization by nitrogen physisorption revealed a mesoporous structure with high surface area, pore size and volume. The MSU-MFI catalysts developed in this study were selective toward aromatic chemical production from poplar pyrolysis vapour. Yields of generalized products and aromatics were comparable to those obtained from conventional microporous ZSM-5 analogs as demonstrated by pyroprobe-gas chromatography/mass spectrometry and thermogravimetric analysis. While ZSM-5 was more selective to smaller C6 aromatics and naphthalenes, MSU-MFI catalysts were more selective to C8 and C9 monoaromatics. The incorporation of gallium(III) ions in MSU-MFI using the incipient wetness method increased aromatic yields by up to 15% over Ga-free catalysts and decreased the coke production by up to 6% (p < 0.05). Due to high yields and low coke formation, Ga-MSU-MFI offers an improved option for making non-oxygenated aromatic chemicals from photosynthetic biomass. [ABSTRACT FROM AUTHOR]

Abstract: 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), the prototypical aryl hydrocarbon receptor (AhR) ligand, exhibits immune suppression in vivo and in vitro. Suppression of primary humoral immune responses in particular has been well characterized as one of the most sensitive functional immune endpoints in animals treated with TCDD. Previous studies have used purified TCDD to elucidate the mechanisms by which TCDD and dioxin-like compounds (DLC) impair IgM production by B cells, but did not represent the route by which animals and humans are likely to be exposed environmentally. In the studies reported here, mice were treated with TCDD adsorbed onto a well-defined synthetic silica phase of known purity and physical properties, followed by sensitization with sheep erythrocytes to initiate a humoral immune response. We found that surfactant-templated mesoporous forms of amorphous silica provided an ideal combination of purity, dispersibility and textural properties for immobilizing TCDD. TCDD-adsorbed silica distributed to the spleen and liver after oral administration as assessed by induction of cyp1a1 gene expression. Most notably, TCDD delivered in the adsorbed state on amorphous silica and as a solute in corn oil (CO) produced similar suppression of the anti-sheep red blood cell immunoglobulin M antibody forming cell (sRBC IgM AFC) response at equivalent doses of TCDD. These results suggest that TCDD immobilized on silicate particles found in soils distributes to the spleen and suppresses humoral immunity. [Copyright &y& Elsevier]

Abstract: The complete understanding of the properties of a material goes in close relationship with a correct description of their structure. This is particularly true for mesoporous silica that exhibits different shapes and sizes of the porous framework as well as different degrees of crosslinking of the silica network itself. These variations can affect drastically the specific properties of these materials as well as their hydrothermal resistance. Hydrothermal resistance and adsorption properties are governed by the surface structure, but the later parameter is not frequently studied because it can be difficult to characterize. Therefore a simple parameter such as surface roughness could be helpful in relating the properties of materials with their surface structure. The direct determination of surface roughness is impossible, but it has been demonstrated that a single mathematical parameter, the surface fractal dimension Ds, can be related within a certain limit with surface roughness. Here we demonstrate using nitrogen adsorption data that a correlation can be drawn between the values of the surface fractal dimension Ds used as a gauge of the surface roughness and the structural evolution of a series of mesoporous silicas. Among the different adsorption models for obtaining Ds that are available nowadays, we selected the one proposed by Avnir and Jaroniec. We demonstrate in this report that there exists a real correlation between the evolution of Ds, when applied to a series of samples prepared under different synthesis conditions, with the evolution of their structure and properties. By example, this study allowed us to link the range of hydrothermal resistance of different mesoporous silicas (e.g. the HMS, MSU, MCM, SBA families of silicas) with their surface roughness. Moreover, we found that HMS silica, a very resistant material toward hydrothermal treatment, exhibits actually the lowest surface roughness. We could demonstrate too how different synthesis parameters such as temperature, can modify this surface roughness, hence the final properties of the mesoporous silica. Finally, we show that this method can even be applied to water ellipsoporometry and help to follow the crystallization of thin layers of metal oxide. Bearing in mind that Ds is a parameter that can readily be determined using the existing software – based on different models – associated with most commercial adsorption equipment, we urge the broader use of the Ds parameter for the structural characterization of surface roughness in mesoporous materials and metal oxide thin layers. [Copyright &y& Elsevier]

Abstract: In the present study two synthetic mesoporous carbons, a highly ordered CMK-3 sample with hexagonal structure and a disordered mesoporous carbon (denoted DMC) were investigated for the sorption of Remazol Red 3BS (C.I. 239) dye in comparison to three commercial activated carbons and a HMS mesoporous silica with a wormhole pore structure. The structural, porosity and surface characteristics of the materials were evaluated using XRD, TEM, N2 porosimetry, FT-IR spectroscopy and zeta-potential measurements. Optimal dye sorption occurred at pH ∼2. Equilibrium sorption data followed the Langmuir model and showed that the two synthetic mesoporous carbons exhibit higher sorption capacities (q max ∼500–580mg/g at 25°C) in comparison to the commercial activated carbons which possessed either microporous (Takeda 5A and Calgon carbon) or combined micro-/mesoporous (Norit SAE-2) structures and to the HMS mesoporous silica. Thermodynamic parameters as the change in free energy, enthalpy, and entropy of sorption were also estimated. Kinetic studies were carried out and showed a rapid sorption of dye in the first ca. 30min while equilibrium was reached after ca. 3h. The sorption kinetics of dye was best described by a second-order kinetic model. A surfactant enhanced carbon regeneration (SECR) technique was used to regenerate the dye-loaded carbon sorbents. [Copyright &y& Elsevier]

Abstract: Ti(IV)-functionalized derivatives of mesostructured HMS and MCM-41 silica with 3D wormhole and 1D hexagonal framework structures, respectively, were examined as catalysts for the oxidation of 4-tert-butyltoluene to 4-tert-butylbenzaldehyde using tert-butylhydroperoxide (TBHP) and aqueous hydrogen peroxide as oxidizing agents in acetonitrile solution. In an effort to achieve optimal site-isolation of reactive Ti(IV) centers, functionalization was carried out through the grafting of titanocene dichloride to the framework walls of the pre-assembled mesostructures, followed by calcination. Clear evidence for the undesirable clustering of Ti(IV) centers with increasing Ti(IV) loading was obtained by UV–Vis spectroscopy. Thus, the Ti(IV)-loading in the silica framework was limited to values below 8mol%. Maximal 23.6% and 21.8% conversions of 4-tert-butyltoluene to 4-tert-butylbenzaldehyde with >99% selectivity were observed for 4.8% Ti-HMS and 4.8% Ti-MCM-41 catalysts using TBHP as the oxidant. Substantially lower conversions were obtained with H2O2 as the oxidant due to clustering of Ti(IV) centers under reaction conditions and the catalyzed disproportionation of H2O2 by those clusters. A 2.0% Ti-HMS derivative prepared by direct assembly from tetraethylorthosilicate and tetraisopropylorthotitanate, denoted Ti-HMS(DS), was less active than Ti(IV)-functionalized mesostructures prepared by post-assembly grafting reaction with titanocene dichloride. Direct assembly places too much Ti(IV) at inaccessible positions within the framework walls, whereas grafting ensures optimal access to site-isolated Ti(IV) sites at the pore surfaces. [Copyright &y& Elsevier]

Abstract: Advanced heterogeneous catalysts for olefin metathesis were prepared by supporting Re(VII) oxide on (i) mesostructured γ-aluminas with lath-like and scaffold-like morphologies and (ii) organized mesoporous alumina with wormhole-like pore structure. The thermal spreading method was found to be very suitable technique for preparation of a highly active catalyst. In the case of dec-1-ene metathesis, Re(VII) oxide catalysts supported on mesoporous aluminas exhibited a high activity and selectivity independently of the type of catalyst support. For metathesis of olefin functional derivatives, namely p-allylanisole and diethyl diallylmalonate, the activity of Re(VII) catalysts with optimum amount of Re(VII) being 9.0wt% (with Me4Sn as co-catalyst) was found to depend on the catalyst pore size. Catalyst prepared from mesoporous aluminas with pore sizes at least 4.0nm exhibited much higher conversions of substrates compared with catalysts of 3.5nm pores. [Copyright &y& Elsevier]

Abstract: The in situ upgrading of biomass pyrolysis vapors with two mesoporous aluminosilicate materials (MSU-SBEA) assembled from zeolite Beta (BEA) seeds was tested in the present study, in comparison to conventional Al-MCM-41 and to non-catalytic biomass pyrolysis. The first sample (MSU-S/HBEA) exhibited an hexagonal mesopore structure while the second one (MSU-S/WBEA) possessed a wormhole-like mesopore structure with high textural porosity. The catalytic tests were performed on a fixed-bed reactor, the reaction temperature was 500°C and the feed was a lignocellulosic biomass based on beech wood. The use of the MSU-S catalytic materials led to significantly lower organic phase in the produced bio-oil and also to higher coke and char yields, compared to non-catalytic pyrolysis and to the use of Al-MCM-41 which induced a small increase in the yields of liquid oil and coke. Pyrolysis gases were also affected by all mesoporous catalysts. The MSU-S catalytic materials were very selective towards polycyclic aromatic hydrocarbons (PAHs) and heavy fractions, while they produced negligible amounts of acids, alcohols and carbonyls, and very few phenols. The MSU-S materials appeared to possess stronger acid sites than Al-MCM-41, resulting in enhanced yields of aromatics, PAHs and coke, as well as propylene in the pyrolysis gases. [Copyright &y& Elsevier]

Thiol-functionalized mesostructured silica with anhydrous compositions of (SiO2)1-x(LSiO1.5)x, where L is a mercaptopropyl group and x is the fraction of functionalized framework silicon centers, are effective trapping agents for the removal of mercuric(II) ions from water. In the present work, we investigate the mercury-binding mechanism for representative thiol-functionalized mesostructures by atomic pair distribution function (PDF) analysis of synchrotron X-ray powder diffraction data and by Raman spectroscopy. The mesostructures with worm hole framework structures and compositions corresponding to x = 0.30 and 0.50 were prepared by direct assembly methods in the presence of a structure-directing amine porogen. PDF analyses of five mercury-loaded compositions with Hg/S ratios of 0.50-1.30 provided evidence for the bridging of thiolate sulfur atoms to two metal ion centers and the formation of chain structures on the pore surfaces. We find no evidence for Hg-O bonds and can rule out oxygen coordination of the mercury at greater than the 10% level. The relative intensities of the PDF peaks corresponding to Hg-S and Hg-Hg atomic pairs indicate that the mercury centers cluster on the functionalized surfaces by virtue of thiolate bridging, regardless of the overall mercury loading. However, the Raman results indicate that the complexation of mercury centers by thiolate depends on the mercury loading. At low mercury loadings (Hg/S ≤ 0.5), the dominant species is an electrically neutral complex in which mercury most likely is tetrahedrally coordinated to bridging thiolate ligands, as in Hg(SBut)2. At higher loadings (Hg/S 1.0-1.3), mercury complex cations predominate, as evidenced by the presence of charge-balancing anions (nitrate) on the surface. This cationic form of bound mercury is assigned a linear coordination to two bridging thiolate ligands. [ABSTRACT FROM AUTHOR]

A mesostructured γ-alumina with a lathlike framework morphology, denoted MSU-γ, has been prepared according to previously described methods through the reassembly and crystallization of a mesostructured alumina precursor with initially amorphous framework walls and used as a support for the catalytic hydrodesulfurization (HDS) of dibenzothiophene (DBT). The alumina support was loaded with molybdenum and cobalt ions via incipient wetness impregnation methods and then converted to the active sulfide form by reaction with H2S. HDS reactions of DBT were carried out at 400 °C and 400 psi to achieve a DBT conversion of 69–77% and a biphenyl (BP) product selectivity of 60–64% after a reaction time of 3 h, indicating that most of the DBT could undergo desulfurization while limiting excessive hydrogen consumption through aromatic hydrogenation. Although the dispersion of the active Mo/Co sulfide phase supported on lathlike MSU-γ alumina remained very high after several hours on stream, the conversions most likely were limited by a loss of surface area and porosity under HDS conditions. [Copyright &y& Elsevier]

FDU-1 silicas with large cage-like pores (diameter about 10 nm) were synthesized under acidic conditions from tetraethyl orthosilicate in the presence of a poly(ethylene oxide)-poly(butylene oxide)-poly(ethylene oxide) triblock copolymer template B50-6600 (EO[sub 39]BO[sub 47]EO[sub 39]). High-resolution transmission electron microscopy and small-angle X-ray scattering provided strong evidence that FDU-1 silica synthesized under typical conditions is a face-centered cubic Fm3m structure with 3-dimensional hexagonal intergrowth and is not a body-centered cubic lm3m structure, as originally reported. Samples synthesized in a wide range of conditions (initial temperatures from 298 to 353 K; hydrothermal treatment at 333-393 K) exhibited similar XRD patterns and their nitrogen adsorption isotherms indicated a good-quality cage-like pore structure. The examination of low-pressure nitrogen adsorption isotherms for FDU-1 samples, whose pore entrance diameters were evaluated using an independent method, allowed us to conclude that low-pressure adsorption was appreciably stronger for samples with smaller pore entrance sizes. This prompted us to examine low-pressure adsorption isotherms for a wide range of samples and led us to a conclusion that the FDU-1 pore entrance size can be systematically enlarged from about 1.3 nm (perhaps even lower) to at least 2.4 nm without an appreciable loss of uniformity by increasing the temperature of the hydrothermal treatment or the initial synthesis. Further enlargement of pore entrance size was achieved for sufficiently long hydrothermal treatment times at temperatures of 373 K or higher, as seen from the shape of nitrogen desorption isotherms. This allowed us to obtain samples with uniform pore sizes, high adsorption capacity, and with pore entrances enlarged so much that their size was similar to the size of the pore itself, resulting in a highly open porous structure. However, in the latter case, there was evidence that the pore... [ABSTRACT FROM AUTHOR]

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.

The low-temperature synthesis (90°C) of nanoparticle forms of a pure phase smectic clay (saponite) and zeolite (cancrinite) is reported, along with phase mixtures thereof. A synthesis gel corresponding to the Si:Al:Mg unit cell composition of saponite (3.6:0.40:3.0) and a NaOH/Si ratio of 1.39 affords the pure phase clay with disordered nanolayer stacking. Progressive increases in the NaOH/Si ratio up to a value of 8.33 results in the co-crystallization of first garronite and then cancrinite zeolites with nanolath morphology. The resulting phase mixtures exhibit a compound particulate structure of intertwined saponite nanolayers and cancrinite nanolaths that cannot be formed through physical mixing of the pure phase end members. Under magnesium-free conditions, pure phase cancrinite nanocrystals are formed. The Si/Al ratio of the reaction mixture affects the particle morphology as well as the chemical composition of the cancrinite zeolite. Ordinarily, cancrinite crystallizes with a Si/Al ratio of 1.0, but a silicon-rich form of the zeolite (Si/Al=1.25) is crystallized at low temperature from a silica rich synthesis gel, as evidenced by (29)Si NMR spectroscopy and XEDS-TEM. Owing to the exceptionally high external surface areas of the pure phase clay (875 m(2)/g) and zeolite end members (8.9 - 40 m(2)/g), as well as their unique mixed phase composites (124 - 329 m(2)/g), these synthetic derivatives are promising model nanoparticles for studies of the bioavailability of poly-aromatic hydrocarbons immobilized in silicate bearing sediments and soils.

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 synthesis of saponite in the presence of bis(triethoxysilyl)methane (BTESM) as an organosilicon reagent results in the replacement of up to 33.3 % of the oxygen atoms in the tetrahedral sheet by bridging methylene groups. The methylene-functionalized saponites represent a new form of covalently-bonded organoclay that truly is isomorphic with purely inorganic saponite made under equivalent reaction conditions from sodium silicate as the silicon source. The isoelectronic and isolobal relationship between methylene and bridging oxygen centers is essential for methylene saponite formation. Bridging ethylene groups are not incorporated into the Kagome net of the basal surfaces due to a mismatch in bridging group size. The textural properties of the methylene saponites are similar to those for purely inorganic magnesium saponite made under equivalent synthetic conditions in the absence of BTESM. Layer stacking disorders afford large surface areas (~550 to 650 m(2)/g), making the methylene saponites attractive candidates for use as adsorbents and functional fillers for polymer composites.

Large-pore mesoporous silica with 3D wormhole framework structures (denoted MSU-J) are prepared through a supramolecular hydrogen-bonding assembly pathway from low-cost sodium silicate as the silica source and commercially available mono- and triamine Jeffamine and Surfonamine surfactants as structure-directing porogens. The calcined mesostructures exhibit large pore sizes (up to 8.2 nm), surface areas (632-1030 m(2)/g) and pore volumes (0.5-2.0 cm(3)/g), depending on the surfactant chain length and synthesis temperature (25-65 °C). The textural properties of these new wormhole mesostructures are comparable to those of hexagonal SBA-15 derivatives and large pore MCM-48. However, unlike the SBA-15 structure type, wherein the 3D pore network is formed by connecting 1D cylindrical mesopores through micropores, MSU-J mesophases have wormhole framework structures containing fully interconnected 3D mesopores that can minimize the diffusion limitations often encountered in adsorption and chemical catalysis. Also, unlike large pore MCM-48, which requires cost-intensive tetraethylorthosilicate as a silica source and the use of a co-surfactant as a pore expander under strong acid conditions, MSU-J mesostructures are assembled from low cost sodium silicate in the presence of a single Jeffamine or Surfonamine porogen at near-neutral pH.

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.

Clay-PEO nanocomposites can have large electrical conductivities that make them potential electrolyte materials for rechargeable lithium batteries, but the origin of these large conductivities, especially for Li-containing materials, is poorly understood. This paper presents X-ray diffraction (XRD), TGA-DTA, and (7)Li and (23)Na NMR data for PEO nanocomposites made with natural (SWy-1) and synthetic (MNTS) montmorillonite clays that provide new insight into interlayer structure. An increase in basal d(001)-spacings demonstrates successful intercalation of PEO in all samples, and X-ray line narrowing shows that this intercalation improves the layer stacking order. The basal spacings of 17.9-19.4 A are consistent with a helical or bilayer structure of PEO in the interlayer. TGA-DTA provides quantitative results for the hydration state of the nanocomposites, demonstrates PEO intercalation, and shows that the composites prepared from the synthetic montmorillonite are less stable than those made with SWy-1. (7)Li NMR shows that the nearest neighbor hydration state of Li(+) is unaffected by PEO intercalation and suggests weak interaction of Li(+) with PEO. (23)Na NMR shows that PEO intercalation results in the conversion of the multiple Na(+) hydration states observed for the pristine clay into inner sphere sites most likely formed through coordination with the basal oxygens of the clay. These differences between lithium and sodium suggested that tighter binding of the Na to the clay may be the origin of the conductivity of Li-montmorillonite-PEO nanocomposites being as much as 2 orders of magnitude larger than those of Na-montmorillonite-PEO nanocomposites. The results confirm the idea that polymer oxygen atoms do not participate in sequestering the exchangeable cations and agree with the jump process for cation migration advanced by Kuppa and Manias (Kuppa, V.; Manias, E. Chem. Mater. 2002, 14, 2171).

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

The direct supramolecular assembly of organofunctional mesostructures with a vesicular hierarchical morphology is reported for the first time for (SiO2)1-x(LSiO1.5)x compositions, where L is a mercaptopropyl group and x = 0.10-0.30.

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.