Water Sorption on Mesoporous Aluminosilicate MCM-41

Llewellyn, Philip L.; Schüth, Ferdi; Grillet, Y.; Rouquérol, F.; Rouquérol, J.; Unger, Klaus K.

doi:10.1021/la00002a036

Cited by 187 publications

(114 citation statements)

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“…10, Table 4). It might be expected that adsorption of water should be higher for the samples with a larger amount of the Al centers located in the much less hydrophilic silica walls of MCM-41 (Branton, 1995;Llewellyn, 1995). At the same time, the heights of the isotherm steps increased in the same sequence, which meant that the smallest amount of condensed water occurred in the sample with the largest content of Al.…”

Section: Sorption Properties Of the Materialsmentioning

confidence: 98%

Mesoporous Molecular Sieves Modified with Carbonaceous Deposits

2005

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There were investigated aluminosilicate MCM-41 samples in the as-prepared form and those modified by the deposition of carbonaceous compounds during conversion of cyclohexene for 12 h. The amount of the deposits decreased with the rising reaction temperature and increased with the Al content of the samples. The cyclohexene conversion followed mainly two mechanisms: cyclohexene skeletal isomerization and hydrogen transfer. The products with 6 carbon atoms in a molecule prevailed in all cases. The process of conversion, proceeding on the Brønsted acid sites, resulted in formation of both coke deposits and volatile products. The creation of coke caused a decrease in the effective concentration of both the Brønsted and the Lewis acid sites. Thermodesorption of pyridine showed that (i) the concentration of these sites before and after the conversion differed only slightly and (ii) the acidic strength of the Brønsted sites was practically independent of their concentration and the sample Si/Al ratio. The chemical composition of the deposits was insignificantly affected by the Al content of the materials and depended mostly on the temperature and duration of the reaction. At relatively low temperatures, both aliphatic and aromatic compounds were formed, being rather weakly bound to the surface of the material. After a longer (55 h) reaction period, some deposits appeared that were strongly bound to the surface. Isotherms of adsorption of water, benzene, and nitrogen were determined, from which a mechanism of this process was derived. It included most probably multilayer adsorption at lower relative pressures, followed by capillary condensation. The sorption capacities of the uncoked samples for benzene and nitrogen were relatively high and independent of the sample Al content. In the case of water, however, an observed reduction in the sorption capacity with the increasing Al content suggested that clusters of the adsorbed molecules formed around the Al centers and caused partial clogging of the material pores. The deposited coke strongly decreased both the surface area and the sorption capacity of the materials.

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Section: Sorption Properties Of the Materialsmentioning

confidence: 98%

Mesoporous Molecular Sieves Modified with Carbonaceous Deposits

2005

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“…[1][2][3] In particular, hydroxylated mesoporous oxides and silicates exhibit moderate to high hydrophilicity, and so the interactions and the phase behavior of water in these materials have been the target of numerous studies. [6][7][8][9][10][11][12][13][14][15] Sorption-desorption isotherms of water and the associated gas-liquid equilibrium on highly ordered mesoporous solids as MCM-41 and FSM-16 silica and silicates, with pores ranging from 1 to 5 nm, have been characterized experimentally by several authors. [6][7][8][9]11,12,16 These isotherms are usually plotted in terms of water content as a function of vapor pressure and typically exhibit three regimes: the surface adsorption plateau, the capillary condensation branchwhere the content of water jumps abruptly-and the final high pressure plateau corresponding to the material mostly filled with liquid.…”

Section: Introductionmentioning

confidence: 99%

Water filling of hydrophilic nanopores

Llave

Molinero

Scherlis

2010

The Journal of Chemical Physics

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Phase diagram of supercooled water confined to hydrophilic nanopores J. Chem. Phys. 137, 044509 (2012) Molecular dynamics simulations of water in cylindrical hydrophilic pores with diameters of 1.5 and 3 nm were performed to explore the phase behavior and the nucleation dynamics of the confined fluid as a function of the percentage of volume filled f. The interactions of water with the pore wall were considered to be identical to the interactions between water molecules. At low water contents, all the water is adsorbed to the surface of the pore. A second phase consisting of a liquid plug appears at the onset filling for capillary condensation, f onset = 27% and 34% for the narrow and wide pores, respectively. In agreement with experimental results for silica pores, the liquid phase appears close to the equilibrium filling f eq in the 1.5 nm pore and under conditions of strong surface supersaturations for the 3 nm pore. After condensation, two phases, a liquid plug and a surface-adsorbed phase, coexist in equilibrium. Under conditions of phase coexistence, the water surface density ⌫ coex was found to be independent of the water content and the diameter of the pore. The value of ⌫ coex found in the simulations ͑ϳ3 nm −2 ͒ is in good agreement with experimental results for silica pores, suggesting that the interactions of water with silica and with itself are comparable. The surface-adsorbed phase at coexistence is a sparse monolayer with a structure dominated by small water clusters. We characterize the density and structure of the liquid and surface phases, the nucleation mechanism of the water plug, and the effect of surface hydrophilicity on the two-phase equilibrium and hysteresis. The results are discussed in light of experiments and previous simulations.

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“…Y mutinaite, as above, Y tschernichite, the Al-bearing analog of the Mobil high silica zeolite Beta (59-67), which has a remarkable polytypic domain structure with a 10-ring, three-dimensional channel system, Y boggsite, with a 10-to 12-ring, three-dimensional channel system, which occurs with tschernichite in Columbia basalt (68), Y faujasite, the natural analog of Linde Type Y, the main industrial catalyst with a 12-ring, three-dimensional channel system; can be de-aluminated by various processes (not referenced in detail); known only as a very rare mineral until discovery in sedimentary beds of diagenetic tuffs in Jordan (69), Y mordenite, an easily de-aluminated, common, high silica natural zeolite, with industrial analogs, whose one-dimensional channel can be blocked by either faulting or an Al-complex , Y mesoporous silicas with nanometer channels and mainly hydrophilic surfaces but some organophilic behavior (91)(92)(93)(94)(95)(96)(97)(98)(99)(100)(101)(102)(103), Y all-silica analog (Chevron SSZ-24) of Union Carbide aluminophosphate AlPO-5, for which one might envisage unipolar segments of aluminophosphate interleaved with nonpolar silica down the 12-ring cylindrical channel (104)(105), and Y theoretical chiral frameworks in the database of the Consortium for Theoretical Frameworks, University of Chicago, being prepared for publication.…”

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confidence: 99%

Biochemical evolution. I. Polymerization on internal, organophilic silica surfaces of dealuminated zeolites and feldspars

Smith

1998

Proc. Natl. Acad. Sci. U.S.A.

117

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Catalysis at mineral surfaces might generate replicating biopolymers from simple chemicals supplied by meteorites, volcanic gases, and photochemical gas reactions. Many ideas are implausible in detail because the proposed mineral surfaces strongly prefer water and other ionic species to organic ones. The molecular sieve silicalite (Union Carbide; ‫؍‬ Al-free Mobil ZSM-5 zeolite) has a three-dimensional, 10-ring channel system whose electrically neutral Si-O surface strongly adsorbs organic species over water. Three -O-Si tetrahedral bonds lie in the surface, and the fourth Si-O points inwards. In contrast, the outward Si-OH of simple quartz and feldspar crystals generates their ionic organophobicity. The ZSM-5-type zeolite mutinaite occurs in Antarctica with boggsite and tschernichite (Al-analog of Mobil Beta). Archean mutinaite might have become de-aluminated toward silicalite during hot/cold/wet/dry cycles. Catalytic activity of silicalite increases linearly with Al-OH substitution for Si, and Al atoms tend to avoid each other. Adjacent organophilic and catalytic Al-OH regions in nanometer channels might have scavenged organic species for catalytic assembly into specific polymers protected from prompt photochemical destruction. Polymer migration along weathered silicic surfaces of micrometer-wide channels of feldspars might have led to assembly of replicating catalytic biomolecules and perhaps primitive cellular organisms. Silica-rich volcanic glasses should have been abundant on the early Earth, ready for crystallization into zeolites and feldspars, as in present continental basins. Abundant chert from weakly metamorphosed Archaean rocks might retain microscopic clues to the proposed mineral adsorbent/catalysts. Other framework silicas are possible, including ones with laevo/dextro one-dimensional channels. Organic molecules, transition-metal ions, and P occur inside modern feldspars.

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Water Sorption on Mesoporous Aluminosilicate MCM-41

Cited by 187 publications

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Mesoporous Molecular Sieves Modified with Carbonaceous Deposits

Mesoporous Molecular Sieves Modified with Carbonaceous Deposits

Water filling of hydrophilic nanopores

Biochemical evolution. I. Polymerization on internal, organophilic silica surfaces of dealuminated zeolites and feldspars

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