Theoretical Simulation of n-Alkane Cracking on Zeolites

Swisher, Joseph A.; Hansen, Niels; Maesen, Theo L. M.; Keil, Frerich J.; Smit, Berend; Bell, Alexis T.

doi:10.1021/jp101262y

Cited by 78 publications

(135 citation statements)

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“…37 and ΔS ads-H+ (i) at 773 K determined for each cell were found to be within ~2 kJ mol -1 and ~1 J mol -1 K -1 , respectively, for all three zeolites. The ratio of equilibrium constants K ads-H+ (j) for adsorption to form a central (j=2) vs. a terminal (j=1) cracking reactant state were within ~0.02.…”

Section: Configurational-bias Monte Carlo Simulationsmentioning

confidence: 75%

“…Each of these zeolites has one Al atom per unit cell. 33,37,39 Several million Widom insertions were carried out to ensure statistically accurate ensemble averages. To avoid insertions occurring within inaccessible pore space, regions of the zeolite that are inaccessible to methane were first identified using Zeo++.…”

Section: Configurational-bias Monte Carlo Simulationsmentioning

confidence: 99%

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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: Configurational-bias Monte Carlo Simulationsmentioning

confidence: 75%

Section: Configurational-bias Monte Carlo Simulationsmentioning

confidence: 99%

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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“…As ambition grows toward treating the catalysis of larger organic molecules, for example, the inclusion of van der Waals interactions becomes important (74,75). Although steps have already been taken in that direction (76)(77)(78), it appears that further improvements are needed.…”

Section: Challenges In Theoretical Surfacementioning

confidence: 99%

Density functional theory in surface chemistry and catalysis

Nørskov

Abild‐Pedersen

Studt

et al. 2011

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

1,963

1,342

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Recent advances in the understanding of reactivity trends for chemistry at transition-metal surfaces have enabled in silico design of heterogeneous catalysts in a few cases. The current status of the field is discussed with an emphasis on the role of coupling theory and experiment and future challenges. S urface chemistry is interesting and challenging for several reasons. It takes place at the border between the solid state and the liquid or gas phase and can be viewed as a meeting place between condensed-matter physics and chemistry. The phenomena at the solid-gas or solid-liquid interface are complicated for this reason. A chemical reaction at a metal surface, for instance, has all of the complexity of ordinary gas-phase reactions, but in addition the usual electron conservation rules do not apply because the metal provides a semi-infinite source of electrons at the Fermi level. A new set of concepts therefore needs to be developed to describe surface chemistry.An understanding of surface chemical reactions is necessary to describe a large number of surface phenomena including semiconductor processing, corrosion, electrochemistry, and heterogeneous catalysis. Heterogeneous catalysis alone has been estimated to be a prerequisite for more than 20% of all production in the industrial world (1), and it will most likely gain further importance in the years to come. The development of sustainable energy solutions represents one of the most important scientific and technical challenges of our time, and heterogeneous catalysis is at the heart of the problem. Most sustainable energy systems rely on the energy influx from the sun. Sunlight is diffuse and intermittent, and it is therefore essential to be able to store the energy, for example chemically as a fuel or in a battery. Such storage can then provide energy for the transportation sector and in decentralized applications, as it evens out temporal variations (2, 3). The key to providing an efficient transformation of energy to a chemical form or from one chemical form into another is the availability of suitable catalysts. In essentially all possible sustainable energy technologies, the lack of efficient and economically viable catalysts is a primary factor limiting their use (3, 4).In the present paper, we will discuss the status of the development of an understanding of surface chemistry. We will do this from a theoretical perspective, but it is important to stress that it is a close coupling between theory and experiment which has enabled the developments thus far. Surface science experiments have been invaluable in providing a quantitative description of a range of surface phenomena (5-14). This has been essential in benchmarking computational surface science based on density functional theory (DFT) calculations and in providing experimental guidance and verification of the concepts developed. This forms a good background for the development of an understanding of heterogeneous catalysis, which is the other part of this paper. We will show how the concepts dev...

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“…We showed in previous work that this assumption is a strong simplification because the probability of being in the reaction state decreases with increasing temperature. 9 Bucǩo et al showed that at 800 K the calculated likelihood to form an adsorption complex for propane in chabazite has decreased to 18% compared to 68% at 300 K (see Figure 4 in ref 30 and Figures 5 and 6 in ref 124). However, the present analysis focuses on the influence of the selected adsorption parameters on the extracted intrinsic entropy of activation and therefore neglects the lower probability, also to be comparable with ref 31.…”

Section: −35mentioning

confidence: 99%

Combined Density Functional Theory and Monte Carlo Analysis of Monomolecular Cracking of Light Alkanes Over H-ZSM-5

et al. 2012

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Density functional calculations applying periodic boundary conditions have been performed to investigate adsorption and cracking of light alkanes (C 3 −C 6 ) on zeolite H-ZSM-5. Intrinsic energy barriers were obtained from singlepoint calculations by applying the revised form of the PBE functional (RPBE) to structures optimized on the PBE potential energy surface. Dispersion interactions were accounted for by adding a damped dispersion term to the PBE energies. The dependence of the adsorption enthalpy on the carbon number is in agreement with experimental observation. From intrinsic energy barriers, intrinsic rate coefficients were calculated by means of transition state theory. The dependence of the intrinsic enthalpy and entropy of activation on the carbon number is discussed and compared to experimental observations. Transition path sampling was employed to unravel qualitatively the reaction mechanism for cracking of butane. Monte Carlo simulations in the canonical ensemble were conducted to estimate the temperature dependence of the adsorption enthalpy and entropy of propane to nhexane. These quantities are not constant, as is often assumed in the interpretation of experimental data but become less negative with increasing temperature. It is shown how the selection of adsorption parameters influences the extraction of intrinsic rate parameters from experimental rate data. Based on the present analysis, an alternative partitioning of the experimentally accessible apparent entropy of activation into contributions from adsorption and intrinsic reaction is proposed.

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Theoretical Simulation of n-Alkane Cracking on Zeolites

Cited by 78 publications

References 78 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

Density functional theory in surface chemistry and catalysis

Combined Density Functional Theory and Monte Carlo Analysis of Monomolecular Cracking of Light Alkanes Over H-ZSM-5

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