Theoretical study of hydrogen dissociation on dialuminum oxide clusters and aluminum–silicon–oxygen clusters, as models of extraframework aluminum species and zeolite lattice

Lukinskas, Povilas; Fǎrcaşiu, D.

doi:10.1016/s0926-860x(00)00752-3

Cited by 23 publications

(27 citation statements)

References 46 publications

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“…43 Similar cluster models and theoretical approach in the literature have been used to simulate reactions on oxides. 17,32,[44][45][46] All reaction pathways were first mapped by scanning the potential energy surface of the reaction coordinate. The energy maximum that was found along the reaction coordinate was fully relaxed to a saddle point to locate the actual transition state (TS).…”

Section: Methodsmentioning

confidence: 99%

Structure–activity relationships on metal-oxides: alcohol dehydration

Kostestkyy

Yü

Gorte

et al. 2014

Catal. Sci. Technol.

113

142

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Section: Methodsmentioning

confidence: 99%

Structure–activity relationships on metal-oxides: alcohol dehydration

Kostestkyy

Yü

Gorte

et al. 2014

Catal. Sci. Technol.

113

142

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“…In some cases, such sites are able to dissociate dihydrogen or alkanes, sometimes forming metal hydrides. While framework aluminum atoms in proton- or metal-exchanged zeolites react sparingly with dihydrogen, DFT calculations suggest that extraframework aluminum species can. − Such species are formed during partial dealumination of zeolites and consist of mono- or oligomeric octahedral aluminum complexes bearing water or hydroxyl ligands. Due to their being less covalent than framework aluminum atoms, they are more Lewis acidic …”

Section: Hydrides In Zeolitesmentioning

confidence: 99%

Isolated Surface Hydrides: Formation, Structure, and Reactivity

et al. 2016

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Surface hydrides are ubiquitous in catalysis. However, their structures and properties are not as well-understood as those of their molecular counterparts, which have been extensively studied for the past 70 years. Hydrides isolated on surfaces have been characterized as stable entities on oxide surfaces or in zeolites. They have also been proposed as reaction intermediates in numerous catalytic processes (hydrogenation, hydrogenolysis, etc.). They have also been prepared via surface organometallic chemistry. In this review, we describe their key structural features and spectroscopic signatures. We discuss their reactivity and stability and also point out unexplored areas.

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“…MO calculations, both semiempirical and ab initio without electron correlation, following this postulated reaction pathway, were conducted. , We noted, however, deficiencies in those calculations and conducted a computational study of the dissociative chemisorption of hydrogen on coordinatively unsaturated aluminum centers. In it, standard ab initio and DFT calculations were conducted with large basis sets (6-31G* to 6-311++G**) and electron correlation (MP2 and B3LYP, respectively) . They showed that the chemisorption occurs through the interaction of H 2 with the aluminum until both hydrogen atoms are bonded to Al, after which one hydrogen migrates to an adjacent oxygen atom.…”

Section: Introductionmentioning

confidence: 99%

“…They showed that the chemisorption occurs through the interaction of H 2 with the aluminum until both hydrogen atoms are bonded to Al, after which one hydrogen migrates to an adjacent oxygen atom. Thus, the reaction is better described as metal ion catalysis, rather than acid−base catalysis …”

Section: Introductionmentioning

confidence: 99%

Mechanism and Reactivity of Alkane C−H Bond Dissociation on Coordinatively Unsaturated Aluminum Ions, Determined by Theoretical Calculations

and

Lukinskas

2002

J. Phys. Chem. A

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DFT calculations at the B3LYP/6-31G** level were conducted on the reaction of the propane molecule with the aluminum hydroxide clusters (HO) 3 Al(OH 2 ) x (x ) 0,1). Weak, physisorbed (van der Waals) complexes were identified. Chemisorption does not involve the Brønsted acidity of the catalyst, as no hydron transfer occurs. Instead, the reaction involves insertion of the aluminum atom into a C-H bond, followed by the migration of the hydrogen atom from aluminum to oxygen, to form the chemisorbed intermediate, (H 2 O) x+1 (HO) 2 Al-CH 2 Et or (H 2 O) x+1 (HO) 2 Al-CHMe 2 , with the latter having a higher energy barrier. The elimination of hydrogen from Cβ and oxygen gives then H 2 and propene, which forms a strong π complex with the aluminum cluster for x ) 0. The first step, chemisorption, has a lower energy barrier than the second, elimination, but still higher than the hydrogen dissociation on the same clusters. Thus, the rate relationship H 2 /D 2 exchange > H 2 /RH exchange > RH dehydrogenation is predicted, as was experimentally observed. The tetracoordinated aluminum cluster (x ) 1) reacts with the hydrocarbon by the same pathway as the tricoordinated aluminum cluster (x ) 0) but with higher barriers for both steps; the barriers are reduced for the larger cluster (HO) 2 (H 2 O)Al-O-Al(OH) 2 (H 2 O). The alternative pathway, forming the alkyl-oxygen adduct (HO) 2 Al(OH 2 ) x (H)-O(R)H is too high in energy to compete. Examination of butane and isobutane establishes the reactivity order: prim C-H > sec-C-H > tert-C-H. For isobutane, essentially only methyl C-H cleavage should occur in the common first step for hydrogen exchange and dehydrogenation. In the second step, i.e., the β C-H cleavage in the Al-alkyl intermediate, the reactivity order is tert-C-H > sec-C-H > prim C-H. "Broken lattice" zeolites and especially extraframework aluminum species present in steamed zeolites should be more reactive than the intact zeolite lattices. Thus, the mechanism is relevant for the activation of alkanes for acid-catalyzed conversions on these catalysts, which have insufficient acid strength to cleave C-H and C-C bonds by hydron transfer.

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Theoretical study of hydrogen dissociation on dialuminum oxide clusters and aluminum–silicon–oxygen clusters, as models of extraframework aluminum species and zeolite lattice

Cited by 23 publications

References 46 publications

Structure–activity relationships on metal-oxides: alcohol dehydration

Structure–activity relationships on metal-oxides: alcohol dehydration

Isolated Surface Hydrides: Formation, Structure, and Reactivity

Mechanism and Reactivity of Alkane C−H Bond Dissociation on Coordinatively Unsaturated Aluminum Ions, Determined by Theoretical Calculations

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