Energetics of<i>n</i>-Alkanes in Zeolites:  A Configurational-Bias Monte Carlo Investigation into Pore Size Dependence

Bates, SP Simon; Well, van Wjm Willy; Santen, van Ra Rutger; Smit, Berend

doi:10.1021/ja953856q

Cited by 115 publications

(109 citation statements)

References 43 publications

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“…Eder and Lercher 26 have reported that the enthalpy of adsorption, measured at ~340 K for alkanes in several zeolites, generally became less negative with an increase in the "average pore diameter." Similar findings have also been reported by Savitz et al 27 and by Gribov et al 28 In addition, Bates et al 29 have…”

Section: Introductionsupporting

confidence: 86%

Effects of Pore and Cage Topology on the Thermodynamics of n-Alkane Adsorption at Brønsted Protons in Zeolites at High Temperature

et al. 2017

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Monte Carlo simulations are used to systematically investigate the effects of structural topology on the thermodynamics of n-alkanes adsorbed at Brønsted protons in zeolites having one-dimensional channel systems. In zeolites without cages, the enthalpy and entropy of adsorption (∆H ads-H+ and ∆S ads-H+ ) at fixed pore-limiting diameter (PLD) generally increase (become less negative) as the ratio of the minimum to maximum channel diameter decreases, and are lowest when this ratio equals 1 (corresponding to approximately circular cross-sections). The effect of a change in diameter ratio on the free energy of adsorption (∆A ads-H+ ) is weak because the changes in ∆H ads-H+ and T∆S ads-H+ largely cancel. The addition of cages having a largestcavity diameter (LCD) greater than the PLD increases both ∆H ads-H+ and ∆S ads-H+ . Replacing channels with cages of the same diameter does not change ∆S ads-H+ significantly when the PLD is similar to the alkane length, but decreases both ∆H ads-H+ and ∆A ads-H+ because of the greater surface area of cages relative to channels. The selectivity to adsorption via a central C-C bond vs. a terminal bond when cages are absent is smallest for PLDs near the alkane length, and when cages are present, is even lower when the LCD exceeds the alkane length. This effect is attributed to more rotation of the alkane in cages vs. channels. The results show that ∆A ads-H+ at 773 K can be tuned by manipulating a characteristic dimension (LCD, PLD) and topology (e.g., adding cages) simultaneously, in order to circumvent the compensating changes in T∆S ads-H+ and ∆H ads-H+ that occur upon changing only one structural parameter.3

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Section: Introductionsupporting

confidence: 86%

Effects of Pore and Cage Topology on the Thermodynamics of n-Alkane Adsorption at Brønsted Protons in Zeolites at High Temperature

et al. 2017

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“…The trend of lower heats in larger cavities is apparent in this series of zeolites. Bates et al 21 showed that for pore openings larger than 5 Å, heats of adsorption decrease as the opening of the pore increases. The subtler competition between energetic heterogeneity and cooperative interactions mentioned previously causes the relative strength of cooperative interactions to increase with pore size.…”

Section: Results Of Experimentsmentioning

confidence: 99%

“…It is interesting that the increase in heat of adsorption per additional carbon atom in the alkane chain is a strong function of the size of the micropore. It has been reported from experimental measurements 7,8,11,13 and from computer simulations [21][22][23][24][25][26] that heats of adsorption in MFI increase approximately 10 kJ/mol with each carbon atom in the alkane chain. Table 5 confirms these results: the incremental increase in heat of adsorption per carbon atom is about 10 kJ/mol for MFI but increases in smaller pores (FER) and decreases in larger pores (UTD-1).…”

Section: Results Of Experimentsmentioning

confidence: 99%

Calorimetric Study of Adsorption of Alkanes in High-Silica Zeolites

et al. 1998

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Isosteric heats and adsorption isotherms were measured for combinations of three alkanes (methane, ethane, propane) on a series of six high-silica zeolites (TON, MTW, UTD-1, MFI, FER, FAU). Three of these zeolites (TON, MTW, UTD-1) have one-dimensional channels, two (MFI, FER) have two-dimensional intersecting channels, and FAU has spherical cavities. Since the adsorbate molecules are nonpolar and the zeolites possess a high Si/Al ratio, electrostatic energies are small in comparison to van der Waals energies. Heats of adsorption of methane at the limit of zero coverage are 27.2, 20.9, and 14.2 kJ/mol in TON, MTW, and UTD-1, respectively. This homologous series of zeolites has one-dimensional channels composed of 10-, 12-, and 14-membered rings of average effective diameter 5.0, 5.9, and 8.8 Å, respectively. Short-range gas-solid interactions between spherical methane molecules and the oxygen atoms composing the pore walls are explained by a smoothed integration of the Lennard-Jones 12-6 potential for cylindrical pores.

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“…12 It is particularly interesting as it yields large heats of adsorption for straight chain alkanes, as we have discussed in a previous publication. 6 For the sorption of butane in ferrierite, approximately onethird of the butane molecules are found to be parallel to the [010] direction, which is the direction of the smaller 8-ring channel. The remaining butane molecules adsorb parallel to the [001] direction, the direction of the larger 10-ring channel.…”

Section: Resultsmentioning

confidence: 99%

Location and Conformation of n-Alkanes in Zeolites: An Analysis of Configurational-Bias Monte Carlo Calculations

et al. 1996

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Results from calculations using a novel Monte Carlo method to simulate the sorption of n-butane to n-decane in various all-silica zeolites are analyzed to obtain information on the location and the conformation of the sorbed molecules. In general, the framework topology determines the conformation of the sorbed molecules. In mordenite, we find that butane is able to adsorb relatively unhindered, whereas longer chains are oriented parallel to the main channel direction and become less kinked with increasing carbon number. In ferrierite, butane molecules are distributed over both the 8-and 10-ring channels, while pentane and longer molecules are restricted to an all-trans conformation in the larger 10-ring channel. Faujasite appears to only slightly perturb the distribution of alkane conformations, compared to those found for gas phase alkanes. In zeolites rho and A, all alkanes are sorbed in a highly coiled conformation inside the R-cages of these structures.

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

Cited by 115 publications

References 43 publications

Effects of Pore and Cage Topology on the Thermodynamics of n-Alkane Adsorption at Brønsted Protons in Zeolites at High Temperature

Effects of Pore and Cage Topology on the Thermodynamics of n-Alkane Adsorption at Brønsted Protons in Zeolites at High Temperature

Calorimetric Study of Adsorption of Alkanes in High-Silica Zeolites

Location and Conformation of n-Alkanes in Zeolites: An Analysis of Configurational-Bias Monte Carlo Calculations

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