Heats and entropies of adsorption of saturated hydrocarbons by zeolites X and Y

Atkinson, Dianne; Curthoys, Geoffrey

doi:10.1039/f19817700897

Cited by 34 publications

(27 citation statements)

References 3 publications

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“…There is a clear relationship between the strength of the adsorption site and the entropy change for pyridine adsorption on the site. A similar trend has been found previously for hydrocarbon adsorption on X and Y zeolites [5]. The agreement in the peak temperature is satisfactory, considering that no adjustable parameters were used.…”

Section: And 3 D I T Bsupporting

confidence: 71%

Thermodynamic and kinetic aspects of surface acidity

Dumesic¹

1992

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Our research funded by the Department of Energy in the general area of acid catalysis involves 1) the characterization of solid aadity, 2) the assessment of catalytic performance of acidic materials, and 3) the elucidation of possible relationships between surface thermodynamic and kinetic properties of acidic sites. During the past year we have focused on zeolitic acid catalysts and on methylamine synthesis from ammonia and methanol. Part of our work has also involved elucidation of the role of acidity in the selective catalytic reduction of nitric oxide over vanadia/ titania.Acidic zeolites find use in a wide variety of catalytic applicatione, ranging from large scale petrochemical processes to the synthesis of specialty chemicals. Quantitative characterization of catalyst acid properties is important for elucidation of the role of surface acidity in determining the catalytic activity and selectivity of these materials. However, solid acid catalysts have long posed a challenge for quantitative characterization. Accordingly, one aspect of our research addresses the problem of quantitative characterization of zeolite acidity.Dehydrative methylamine synthesis from ammonia and methanol is an important example of an acid catalyzed reaction for specialty chemicals production. Amines are used in a number of applications such as pharmaceuticals, herbicides, pesticides, solvents, surfactants and detergents [ 11. Production of methylamines in the US. is approximately 270 Mlb per year [2]. In addition to this commercial importance, the methylamine synthesis reaction is of scientific interest; it poses the classic problem of series selectivity combined with adsorption and readsorption phenomena for each intermediate species. An understanding of the mechanistic details of such a reaction would be of general interest and utility.The objectives of our acid characterization work are based in determining 1) the type of acid site, 2) the strength of the sites, 3) the number of sites of different strength, and 4) the mobility of molecules adsorbed on the acid sites. An accurate measure of acid strength is given by the heat of adsorption of a basic probe molecule on the acid site, AH&. In general, a catalyst may have sites of different strength and there will thus be a distribution of numbers of sites in strength. The mobility of a molecule adsorbed on an acid site is also an important probe of the site. A thermodynamic representation of this mobility is given by 1 * @ e !''%STRWT)ON OF THfS DOCUMENT IS UNLIMI'T'EB

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Section: And 3 D I T Bsupporting

confidence: 71%

Thermodynamic and kinetic aspects of surface acidity

Dumesic¹

1992

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“…We observed the expected linear relationship between the heat of adsorption and the adsorption entropy (see Fig. 12) when the Gibbs free energy is constant (Atkinson and Curthoys 1981).…”

Section: Preexponential Factormentioning

confidence: 82%

Adsorption of n-alkanes in faujasite zeolites: molecular simulation study and experimental measurements

et al. 2007

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We report an application of a previously developed force field for adsorption of hydrocarbons in silicalite (Pascual, P., et al. in Phys. Chem. Chem. Phys. 5:3684-3693, 2003), to the case of the linear alkane-sodium faujasite systems. In order to extend this force field from siliceous to cationic zeolites, we propose to take into account the polarization part of the zeolite-molecule interaction energy. A first order polarization term is explicitly considered for this purpose, using standard molecular polarizabilities. Polarization appears to amount to 30-40% of the zeolitealkane interaction energy, as a consequence of the strong electric field created by the sodium cation distribution and negatively charged framework. This approach is compared with experimental adsorption isotherms of ethane, propane, n-octane and n-decane in NaY from the literature and with original measurements of n-butane isotherms in NaY obtained by thermal gravimetry. Henry constants and heats of adsorption at zero coverage of n-alkanes (n = 6-10) are also compared with experimental measurements. Although no specific parameter has been calibrated for extending the force field, the general agreement between simulation results and experiments is satisfactory. Cation redistribution upon alkane adsorption is not observed in these simulations.

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“…For example, if localized adsorption on distinct adsorption sites is considered, then the following equation can be developed (Atkinson and Curthoys, 1981;Denayer et al, 1998): For example, if localized adsorption on distinct adsorption sites is considered, then the following equation can be developed (Atkinson and Curthoys, 1981;Denayer et al, 1998):…”

Section: Methodsmentioning

confidence: 99%