The influence of extraframework aluminum on H-FAU catalyzed cracking of light alkanes

Narbeshuber, Thomas; Brait, Axel; Seshan, Kulathuiyer; Lercher, Johannes A.

doi:10.1016/0926-860x(96)00289-x

Cited by 41 publications

(29 citation statements)

References 21 publications

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“…A further finding is that intrinsic kinetics has a larger influence than adsorption thermodynamics on the chain length dependence of the rate of alkane cracking. 27 Babitz et al, 19 Narbeshuber et al, 25,73 and Xu et al 29 The value of k app from Xu et al is extrapolated from k app and E a measured for 823 K.…”

Section: Resultsmentioning

confidence: 99%

“…As discussed below and determined experimentally, this change in potential is small, typically 10 kJ/mol. 72,73 The activation barrier for cracking is then the distance from the bottom of the well for alkane association with the acid site to the top of the transition state. Because the energy of association of an alkane with a Brønsted-acid site is small at temperature where cracking occurs (>773 K) only a small fraction of the molecules adsorbed within the zeolite will be in the reactant state (i,j).…”

Section: Theorymentioning

confidence: 99%

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Theoretical Simulation of n-Alkane Cracking on Zeolites

et al. 2010

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The kinetics of alkane cracking in zeolites MFI and FAU have been simulated theoretically from first principles. The apparent rate coefficient for alkane cracking was described as the product of the number of alkane molecules per unit mass of zeolite that are close enough to a Brønsted-acid site to be in the reactant state for the cleavage of a specific C-C bond and the intrinsic rate coefficient for the cleavage of that bond. Adsorption thermodynamics were calculated by Monte Carlo simulation and the intrinsic rate coefficient for alkane cracking was determined from density functional theory calculations combined with absolute rate theory. The effects of functional, basis set, and cluster size on the intrinsic activation energy for alkane cracking were investigated. The dependence of the apparent rate coefficient on the carbon number for the cracking of C 3 -C 6 alkanes on MFI and FAU determined by simulation agrees well with experimental observation, but the absolute values of the apparent rate coefficients are a factor of 10 to 100 smaller than those observed. This discrepancy is attributed to the use of a small T5 cluster representation of the Brønsted-acid site. Limited calculations for propane and butane cracking on MFI reveal that significantly better agreement between prediction and observation is achieved using a T23 cluster for both the apparent rate coefficient and the apparent activation energy. The apparent rate coefficients for alkane cracking are noticeably larger for MFI than FAU, in agreement with recent findings reported in the experimental literature.

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Section: Resultsmentioning

confidence: 99%

Section: Theorymentioning

confidence: 99%

Theoretical Simulation of n-Alkane Cracking on Zeolites

et al. 2010

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“…Several theories have been postulated in the literature concerning the influence of EFAl. It has been proposed that these EFAL species provide a more favorable reaction pathway to initiate the cracking cycle or that they interact with the Brønsted acid sites creating sites with higher strength and thus higher activity 4, 8, 9…”

Section: Introductionmentioning

confidence: 99%

Catalytic cracking of alkanes on FAU: Single‐event microkinetic modeling including acidity descriptors

2012

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Single‐event microkinetic (SEMK) modeling is applied to catalytic cracking of 2,2,4‐trimethylpentane on a series of faujasites with Si/Al ratio ranging from 2.6 to 30. Standard activation entropies of the various elementary reaction families are calculated a priori from transition state theory and statistical thermodynamics, while activation energies are estimated on a reference faujasite by regression to experimental kinetic data. The SEMK model is then extended with two acidity descriptors. The concentration of active sites is available from independent NH3‐TPD measurements, while the change in standard protonation enthalpy, relative to the reference faujasite, is obtained by regression to experimental kinetic data. The latter parameter accounts for the effect of the zeolite average acid strength both on the stability of the intermediates and on the activation energies of the protonation and protolytic scission reactions. For these five commercially available faujasites, a variation in standard protonation enthalpy of 29 kJ mol−1 was found. © 2012 American Institute of Chemical Engineers AIChE J, 2012

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“…It has been observed that extra framework alumina (EFAL) promotes inductive effects with respect to Lewis acid sites present around the Brønsted acid sites. These two sites are the active sites that determine the reactivity of zeolites [33]. While the former is related to the EFAL, the latter is connected to aluminium located in the framework of zeolites.…”

Section: Effects Of Catalyst Typementioning

confidence: 99%