Kommensurables Einfrieren von <i>n</i>‐Alkanen im Silicalit

Well, Willy J.M. van; Wolthuizen, J.P.; Smit, Berend; Hooff, J.H.C. van; Santen, Rutger A. van

doi:10.1002/ange.19951072234

Cited by 10 publications

(4 citation statements)

References 6 publications

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“…Experimentally, it is found that, from C 14 to C 22 , the number of −CH x groups adsorbed per unit cell remains at a constant value of 53−54. Some older studies report adsorption capacities of 51−52 −CH x groups adsorbed per unit cell for C 7 3,19 and for C 10 , obtained with gas-phase adsorption measurements. A particular study reports a value of even 55.3 −CH x groups adsorbed per unit cell for C 7 .…”

Section: Resultsmentioning

confidence: 99%

“…Generally, it is found that the adsorption capacity, expressed in molecules adsorbed per unit cell, decreases with carbon number. A steep drop in adsorption capacity is observed between C 6 and C 8 . ,, The most probable explanation for this less efficient packing of C 7 and C 8 molecules compared to shorter ones is that C 6 molecules fit nicely within the sinusoidal channel segment, while longer molecules protrude into the intersections and thus partially obstruct filling of adjacent sections . No attention has been paid in the literature to the packing of long-chain alkanes.…”

Section: Introductionmentioning

confidence: 99%

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Packing Effects in the Liquid-Phase Adsorption of C₅_-C₂₂ n-Alkanes on ZSM-5

et al. 2003

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The liquid-phase adsorption of C5 -C22 linear alkanes on ZSM-5 was studied using a batch adsorption technique. Saturation capacities of the alkanes depend strongly on the chain length. The number of −CH x groups adsorbed per unit cell drops steeply between C7 and C8 and then increases steadily to reach a plateau of 53−54 for C14−C22. In this plateau region, the pores of ZSM-5 are densely packed with alkane molecules. The mechanisms of packing in liquid-phase adsorption were studied using configurational-bias grand canonical Monte Carlo simulations. These simulations revealed that the probability of bending and crossing in the intersections increases with chain length, explaining the very good packing of long-chain alkanes. Short alkanes tend to stay away from the intersections, resulting in a lower packing density.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Packing Effects in the Liquid-Phase Adsorption of C₅_-C₂₂ n-Alkanes on ZSM-5

et al. 2003

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“…The excess of sorbate was used in order to ensured that the maximum loading (8 molecules/u.c. ) was achieved. The Silicalite-I/ n- hexane mixture was kept in a sealed glass tube at 353 K for 6 h. Thermogravimetric measurements were carried out heating the sample up to 650 K in a Linseis L81/075 thermobalance to verify the loading.…”

Section: Methodsmentioning

confidence: 96%

Structural Investigation of Silicalite-I Loaded with n-Hexane by X-ray Diffraction, ²⁹Si MAS NMR, and Molecular Modeling

et al. 2002

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The room temperature (298 K) structure of zeolite Silicalite-I loaded with approximately eight n-hexane molecules per unit cell was solved from twinned single-crystal X-ray diffraction (XRD) data in the monoclinic space group P121/n1 with a = 19.8247(2) Å, b = 20.1292(2) Å, c = 13. 4510(2) Å, and β = 90.29(8)°. At this temperature, the guest molecules are dynamically disordered and distributed throughout the entire channel system. The structure determined from a Rietveld refinement of room-temperature powder XRD data, which is not affected by the twinning, confirmed this. A twinned crystal refinement was also carried out for data collected at 180 K (P121/n1, a = 19.9310(2) Å, b = 20.1730(3) Å, c = 13.4191(3) Å, β = 90.20(5)°). At 180 K, the sorption sites of the n-hexane molecules are well-defined within the channel system, being located only in the straight and sinusoidal channels, leaving the intersections unoccupied. This ordering is commensurate with the framework structure of Silicalite-I. 29Si HPDEC MAS NMR shows that the loading of n-hexane induces a phase transition to an orthorhombic space group (most likely Pnma) only above 340 K. Force field simulations confirm that the absorption of n-hexane molecules occurs only inside the straight and sinusoidal channels and leads to an energetically minimized host−guest structure. By optimizing the van der Waals interactions between the n-hexane molecules and the silica host framework, the nonbonding energy is minimized, leading to a general minimization of the total potential energy, and the energetically most favorable structure is obtained.

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“…It is most probable that the presence of aluminium is responsible for the difference. (It has been found that the heats of adsorption of n -pentane and n -hexane in ZSM-5silicalite with framework aluminiumare increased by some 10 kJ/mol compared to silicalite …”

Section: Energetics Of N-alkane Sorptionmentioning

confidence: 99%

Energetics ofn-Alkanes in Zeolites: A Configurational-Bias Monte Carlo Investigation into Pore Size Dependence

et al. 1996

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Abstract:A recently-developed Monte Carlo method is used to simulate the energetics of n-alkanes from butane to decane in a variety of different all-silica zeolite structures (MFI, MOR, FAU, RHO, LTA, and FER). Where possible, the predicted values of the heat of adsorption are compared to experimental data and are generally found to be in good agreement. On the basis of the energetic data, the graphs of heat of adsorption as a function of mean pore diameter appear to show a maximum between 4 and 5 Å. However, close inspection of the location and conformation of the alkanes in small pore zeolites reveals that the molecules adopt highly coiled conformations localized exclusively in regions of maximum void volume. In the case of the small pore zeolites studied heresRHO and LTAsthese maximum void volumes are the R-cages and the alkanes "feel" a larger pore diameter than that generally used to characterize the zeolite (that of the channels). It is necessary to obtain information on the location and conformations of sorbed molecules to fully understand the trends in the heat of adsorption as a function of pore diameter.

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Kommensurables Einfrieren von n‐Alkanen im Silicalit

Cited by 10 publications

References 6 publications

Packing Effects in the Liquid-Phase Adsorption of C₅_-C₂₂ n-Alkanes on ZSM-5

Packing Effects in the Liquid-Phase Adsorption of C₅_-C₂₂ n-Alkanes on ZSM-5

Structural Investigation of Silicalite-I Loaded with n-Hexane by X-ray Diffraction, ²⁹Si MAS NMR, and Molecular Modeling

Energetics ofn-Alkanes in Zeolites: A Configurational-Bias Monte Carlo Investigation into Pore Size Dependence

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Kommensurables Einfrieren von n‐Alkanen im Silicalit

Cited by 10 publications

References 6 publications

Packing Effects in the Liquid-Phase Adsorption of C5-C22 n-Alkanes on ZSM-5

Packing Effects in the Liquid-Phase Adsorption of C5-C22 n-Alkanes on ZSM-5

Structural Investigation of Silicalite-I Loaded with n-Hexane by X-ray Diffraction, 29Si MAS NMR, and Molecular Modeling

Energetics ofn-Alkanes in Zeolites: A Configurational-Bias Monte Carlo Investigation into Pore Size Dependence

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Packing Effects in the Liquid-Phase Adsorption of C₅_-C₂₂ n-Alkanes on ZSM-5

Packing Effects in the Liquid-Phase Adsorption of C₅_-C₂₂ n-Alkanes on ZSM-5

Structural Investigation of Silicalite-I Loaded with n-Hexane by X-ray Diffraction, ²⁹Si MAS NMR, and Molecular Modeling