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Activation and adsorption of multiple H2 molecules on a Pd5 cluster: a density functional study.
Autorzy
Rok wydania
2003
Czasopismo
Journal of Physical Chemistry A
Numer woluminu
107
Strony
4929-4939
DOI
10.1021/jp0343436
Kolekcja
Język
Angielski
Typ publikacji
Artykuł
The density functional study of the activation and adsorption of several H2 molecules on Pdn clusters is extended to n = 5. Detailed mechanisms of H−H activation by the trigonal bipyramidal (tbp) Pd5 cluster are described. They encompass various reaction pathways initiated by binding the first and second H2 to the axial/equatorial atoms of the Pd5 core, leading to the formation of Pd5(H)2 and Pd5(H)4 activation products, respectively. The Pd5 + H2 → Pd5(H)2 reaction involves spin crossing, and the most stable product, which is a singlet, prefers both hydrogens at cap sites of the nonadjacent faces of Pd5. By contrast to the cases for n = 3 and 4 studied previously, the activation of the second H2 through the reaction Pd5(H)2 + H2 → Pd5(H)4 is found to be exothermic with an associated barrier (ΔH (298.15 K)) lying below the Pd5(H)2 + H2 asymptote. The subsequent steps of the hydrogenation of Pd5 take place via molecular adsorption onto the Pd5(H)4 dissociative complex, ultimately giving the hydrogen-rich cluster Pd5(H)4(H2)5, consistent with experiment. A comprehensive set of the non-hydrogen-saturated species that contain the Pd5(H)4 core structure have also been predicted. The thermodynamic stabilities of the Pd5(H)4(H2)m (m = 1−5) hydrogenated clusters are discussed in terms of ΔH and ΔG values at T = 298.15 and 70 K.
Słowa kluczowe
Molecular structure, Palladium, Cluster chemistry, Chemical reactions, Chemical structure
Adres publiczny
https://doi.org/10.1021/jp0343436
Strona internetowa wydawcy
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