Surface curvature effects in physisorption and catalysis by microporous solids and molecular sieves

Derouane, Éric G.; André, Jean‐Marie; Lucas, A. A.

doi:10.1016/0021-9517(88)90297-7

Cited by 391 publications

(203 citation statements)

References 25 publications

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“…Consistent with firstorder kinetics, the conversion is independent of the partial pressure of the individual n-alkanes (Table 4) [23][24][25]. First-order kinetics implies that the reaction rate is directly proportional to the n-alkane partial pressure, because the n-alkane loading of the zeolite pores is extremely low [7,13,15]. Molecular simulations on the adsorption of n-tridecane (n-C 13 , taken as representative for the n-C 10 -n-C 16 reactant slate) corroborate that ERI-type zeolites indeed require a significantly higher n-alkane pressure than, say, FER-type zeolites before they fill up with these relatively long n-alkanes (Fig.…”

Section: Diffusion and Adsorption Combine To Yield A Cage Effect For mentioning

confidence: 84%

“…because their Gibbs free energy of adsorption decreases linearly with their chain length and, by the same token, their adsorption constant increases exponentially with increasing chain length ( Fig. 1) [10][11][12][13][14][15][16][17][18][19][37][38][39]. ERI-type zeolites afforded the first example of the inverse order in reactivity, because in ERI-type zeolites the n-alkane reactivity decreases monotonically with increasing n-alkane length from n-decane (n-C 10 ) to n-hexadecane (n-C 16 ) (Fig.…”

Section: Diffusion and Adsorption Combine To Yield A Cage Effect For mentioning

confidence: 97%

“…Description of adsorption effects in catalysis usually uses the Langmuir-Hinshelwood-Hougen-Watson approach [7,[12][13][14][15][16][17]. This approach assumes that catalytic activity is directly proportional to the fractional loading of the acid sites.…”

Section: Appendix a Reaction Kinetics In The Henry And Langmuir Regimesmentioning

confidence: 99%

“…A window effect refers to the proportionality between the diffusion rate and the commensurateness of the shape of the adsorbent and the shape of the adsorbate [13,[49][50][51][52][53][54][55]. Such a phenomenon was already known as "incommensurate diffusion" in physics [56], but was renamed "resonance diffusion" in catalysis [51].…”

Section: Introductionmentioning

confidence: 99%

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Understanding cage effects in the n-alkane conversion on zeolites

Maesen

Beerdsen

Calero

et al. 2006

Journal of Catalysis

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Molecular simulations are used to provide insight into published catalytic reactivity data for zeolites that exhibit a cage effect, the selective and preferential conversion of short-chain rather than long-chain n-alkanes. This paper demonstrates that understanding cage effects for ERI-, AFX-, and FER-type zeolites requires consideration of four components: (1) adsorption thermodynamics, (2) adsorption kinetics, (3) conversion at the exterior surface of the catalysts, and (4) coke-induced modifications to the pore texture. By breaking down the Gibbs free energy of adsorption into its enthalpic and entropic contributions, we can further elucidate the influence of the zeolite topology on the adsorption of n-alkanes with different hydrocarbon chain lengths. This analysis indicates that zeolite topologies with cages accessible through windows <0.47 nm wide are particularly prone to exhibiting a cage effect, because they impose a high thermodynamic penalty on the adsorption of molecules that are too long to fit comfortably in a single cage. This improved understanding of the cage effect could facilitate its renewed use in commercial practice.  2005 Elsevier Inc. All rights reserved.

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Section: Diffusion and Adsorption Combine To Yield A Cage Effect For mentioning

confidence: 84%

Section: Diffusion and Adsorption Combine To Yield A Cage Effect For mentioning

confidence: 97%

Section: Appendix a Reaction Kinetics In The Henry And Langmuir Regimesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Understanding cage effects in the n-alkane conversion on zeolites

Maesen

Beerdsen

Calero

et al. 2006

Journal of Catalysis

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“…These geometric distortions become more prevalent as alkoxides become larger and more substituted, thus accounting for the unfavorable formation of bulkier alkoxides on TON relative to HPW measured experimentally. These crystalline framework distortions are likely to become more significant on nanometer-sized crystals and in near-surface regions, plausibly giving rise to observed diffusion and catalytic phenomena typically denoted as surface barriers (20)(21)(22) and pore mouth catalysis (23)(24)(25), respectively.…”

Section: Significancementioning

confidence: 99%

Stability of bound species during alkene reactions on solid acids

Sarazen

Iglesia

2017

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

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This study reports the thermodynamics of bound species derived from ethene, propene, n-butene, and isobutene on solid acids with diverse strength and confining voids. Density functional theory (DFT) and kinetic data indicate that covalently bound alkoxides form C-C bonds in the kinetically relevant step for dimerization turnovers on protons within TON (0.57 nm) and MOR (0.67 nm) zeolitic channels and on stronger acids HPW (polyoxometalate clusters on silica). Turnover rates for mixed alkenes give relative alkoxide stabilities; the respective adsorption constants are obtained from in situ infrared spectra. Tertiary alkoxides (from isobutene) within larger voids (MOR, HPW) are more stable than less substituted isomers but are destabilized within smaller concave environments (TON) because framework distortions are required to avoid steric repulsion. Adsorption constants are similar on MOR and HPW for each alkoxide, indicating that binding is insensitive to acid strength for covalently bound species. DFT-derived formation free energies for alkoxides with different framework attachments and backbone length/structure agree with measurements when dispersion forces, which mediate stabilization by confinement in host-guest systems, are considered. Theory reveals previously unrecognized framework distortions that balance the C-O bond lengths required for covalency with host-guest distances that maximize van der Waals contacts. These distortions, reported here as changes in O-atom locations and dihedral angles, become stronger for larger, more substituted alkoxides. The thermodynamic properties reported here for alkoxides and acid hosts differing in size and conjugate-anion stability are benchmarked against DFT-derived free energies; their details are essential to design hostguest pairs that direct alkoxide species toward specific products.zeolites | alkene adsorption | heterogeneous catalysis | density functional theory H ydrocarbon reactions on solid Brønsted acids often involve bound alkene-derived intermediates. Their reactivity and selectivity in C-C bond formation and cleavage and in hydrogen transfer reactions depend on their thermodynamic properties, which reflect, in turn, the properties of the conjugate anion and of the confining voids in microporous solid acids. Weakly bound adsorbed alkanes interact with void walls via dispersion forces at low temperatures without molecular transformations; their unreactive nature allows accurate assessments of their binding properties (1-4). Alkenes interact with protons via H bonding or π-interactions, as well as by proton transfer from strong acids to form alkoxides; the intermediate between these states is a positively charged carbenium ion. The thermodynamics of alkoxide formation remain uncertain because of their very fast oligomerization and β-scission reactions (5, 6), thus requiring indirect inferences from kinetic, spectroscopic, or theoretical methods. This uncertainty is particularly prevalent in isobutene-derived species, for which steric effects may disfavor the f...

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Reactions in Zeolites

Walspurger

Sommer

2010

Molecular Encapsulation

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Surface curvature effects in physisorption and catalysis by microporous solids and molecular sieves

Cited by 391 publications

References 25 publications

Understanding cage effects in the n-alkane conversion on zeolites

Understanding cage effects in the n-alkane conversion on zeolites

Stability of bound species during alkene reactions on solid acids

Reactions in Zeolites

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