Theoretical study of protonation of butene isomers on acidic zeolite: the relative stability among primary, secondary and tertiary alkoxy intermediates

Correa, Rodrigo; Mota, Cláudio J. A.

doi:10.1039/b104837f

Cited by 36 publications

(35 citation statements)

References 31 publications

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“…The energy barrier and apparent activation energy for this step are calculated to be 30.06 and 21.33 kcal mol À1 , respectively. The computed apparent activation energy is in agreement with the experimental estimates of the apparent activation energy for isotope exchange of ethylene in zeolites of 15-20 kcal mol À1 [17] and the computed values also compare well with other theoretical calculations [8,20,21] at different levels of theory. Herein, the resulting ethoxide is as reactive as the adsorbed ethylene and the protonation process is almost thermoneutral (only exothermic by 0.24 kcal mol À1 ).…”

Section: Stepwise Mechanismsupporting

confidence: 82%

“…However, most quantum cluster calculations reported that the ethoxide species in zeolites were significantly more stable than the adsorbed p adduct and the reactions were significantly exothermic. [20][21][22] Recent studies [23][24][25] using large quantum clusters, QM/MM, or periodic DFT calculations have concluded that stability of alkoxide intermediates formed in the zeolite structure is very sensitive to the geometry of the active site, in that the steric constraints of the zeolite pore walls can weaken the covalent bond between the alkoxide and the zeolite and thus destabilize the alkoxide intermediates. In this study, the formation of the ethoxide species is associated with significant structural changes of the zeolite.…”

Section: Stepwise Mechanismmentioning

confidence: 99%

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Investigation of Ethylene Dimerization over Faujasite Zeolite by the ONIOM Method

2005

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Ethylene dimerization was investigated by using an 84T cluster of faujasite zeolite modeled by the ONIOM3(MP2/6-311++G(d,p):HF/6-31G(d):UFF) method. Concerted and stepwise mechanisms were evaluated. In the stepwise mechanism, the reaction proceeds by protonation of ethylene to form the surface ethoxide and then C--C bond formation between the ethoxide and the second ethylene molecule to give the butoxide product. The first step is rate-determining and has an activation barrier of 30.06 kcal mol(-1). The ethoxide intermediate is rather reactive and readily reacts with another ethylene molecule with a smaller activation energy of 28.87 kcal mol(-1). In the concerted mechanism, the reaction occurs in one step of simultaneous protonation and C--C bond formation. The activation barrier is calculated to be 38.08 kcal mol(-1). Therefore, the stepwise mechanism should dominate in ethylene dimerization.

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Section: Stepwise Mechanismsupporting

confidence: 82%

Section: Stepwise Mechanismmentioning

confidence: 99%

Investigation of Ethylene Dimerization over Faujasite Zeolite by the ONIOM Method

2005

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“…Calculation of the relative stability of butoxide isomers 16 afforded a comparison among the primary, secondary and tertiary alkoxides. Table 2 shows the energy difference indicating the lower stability of the tert-butoxide, which is due to the steric repulsion between the methyl groups and the framework atoms.…”

Section: Early Theoretical Studies Using Finite Clustersmentioning

confidence: 99%

Carbocations on zeolites: quo vadis?

Mota

Rosenbach

2011

J. Braz. Chem. Soc.

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A natureza dos carbocátions adsorvidos na superfície da zeólita é discutida neste artigo, destacando estudos experimentais e teóricos. A adsorção de halogenetos de alquila sobre zeólitas trocadas com metais tem sido usada para estudar o equilíbrio entre alcóxidos, que são espécies covalentes, e carbocátions, que têm natureza iônica. Cálculos teóricos indicam que os carbocátions são mínimos (intermediários) na superfície de energia potencial e estabilizados por ligações hidrogênio com os átomos de oxigênio da estrutura zeolítica. Os resultados indicam que zeólitas se comportam como solventes sólidos, estabilizando a formação de espécies iônicas.The nature of carbocations on the zeolite surface is discussed in this account, highlighting experimental and theoretical studies. The adsorption of alkylhalides over metal-exchanged zeolites has been used to study the equilibrium between covalent alkoxides and ionic carbocations. Theoretical calculations indicated that the carbocations are minima (intermediates) on the potential energy surface and stabilized by hydrogen bonds with the framework oxygen atoms. The results indicate that zeolites behave like solid solvents, stabilizing the formation of ionic species.

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“…There are several studies that report DFT calculations on protonation of isobutene employing rather small cluster models to mimic local surrounding Brønsted acid site in a zeolite (see e.g., [33,34]). A very strong dependency of the relative stabilities of the protonated products on the level of computations and more importantly on the size of the cluster model was found.…”

Section: Activation Of Hydrocarbons In Zeolites: the Role Of Dispersimentioning

confidence: 99%

“…Indeed, applying DFT under periodic boundary conditions to the realistic system containing isobutene adsorbed in ferrierite a rather different picture was observed [37] as compared to the situation when a small cluster model was used to mimic the zeolite active site [34]. Only the π-complex of butane (1) with the Brønsted acid site of the zeolite was found to be more stable than the isolated alkene separated from the zeolite [37].…”

Section: Activation Of Hydrocarbons In Zeolites: the Role Of Dispersimentioning

confidence: 99%

Theoretical Chemistry of Zeolite Reactivity

Pidko

Santen

2010

Zeolites and Catalysis

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IntroductionNowadays, advances in chemical theory rely to a significant extent on computations. Novel theoretical concepts arising directly from experiments usually require further investigations using computational modeling. This is necessary to develop a conclusive molecular-level picture of the observed phenomenon. As a result, computational methods are nowadays widely and extensively applied in the chemical, physical, biomedical, and engineering sciences. They are used in assisting the interpretation of experimental data and increasingly in predicting the properties and behavior of matter at the atomic level.Computational simulation techniques can be divided into two very broad categories. The first is based on the use of interatomic potentials (force fields). These methods are usually empirical and do not consider explicitly any electron in the system. The system of interest is described with functions (normally analytical), which expresses its energy as a function of nuclear coordinates. These are then used to calculate structures and energies by means of minimization methods, to calculate ensemble averages using Monte Carlo simulations, or to model dynamic processes via molecular dynamics simulations using classical Newton's law of motion. The current capabilities and challenges for the corresponding computational methods have been recently reviewed in excellent papers by Woodley and Catlow [1] and by Smit and Maesen [2, 3].The second category includes quantum chemical methods based on the calculation of the electronic structure of the system. Such methods are particularly important for processes that depend on bond breaking or making, which include, of course, catalytic reactions. Hartree Fock (HF), Density Functional Theory (DFT), and post-HF ab initio approaches have been used in modeling zeolites, although DFT methods have predominated in recent applications.This chapter focuses on illustrating the power and capabilities of modern quantum chemical techniques, and aims at highlighting the key areas and challenges

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Theoretical study of protonation of butene isomers on acidic zeolite: the relative stability among primary, secondary and tertiary alkoxy intermediates

Cited by 36 publications

References 31 publications

Investigation of Ethylene Dimerization over Faujasite Zeolite by the ONIOM Method

Investigation of Ethylene Dimerization over Faujasite Zeolite by the ONIOM Method

Carbocations on zeolites: quo vadis?

Theoretical Chemistry of Zeolite Reactivity

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