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Activation of alkanes on zeolites: A DFT study of hydride abstraction and dehydrogenation on extra‐framework aluminum species
Author(s) -
Mota Claudio J. A.,
Bhering Daniel L.,
RamírezSolís Alejandro
Publication year - 2005
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.20668
Subject(s) - dehydrogenation , isobutane , chemistry , hydride , endothermic process , propene , alkene , enthalpy , activation energy , hydrogen atom abstraction , catalysis , computational chemistry , photochemistry , inorganic chemistry , hydrogen , adsorption , organic chemistry , thermodynamics , physics
An AlOH 2+ · T 6 cluster was used to represent, at zeroth order, an extra‐framework aluminum species coordinated with the zeolite Y structure. This cluster was used to study the hydride abstraction from alkanes, at B3LYP/6‐311++G(d,p)//B3LYP/6‐31G(d,p) level, to form an alkoxide and an Al‐hydride · T 6 species. It was found that all reactions were endothermic with respect to the isolated reactants and presented high activation energy. The endothermicity and activation energy depend on the type of hydride being abstracted. Methane showed the highest values (Δ H = +41.5 kcal/mol and Δ H ‡ = 91.7 kcal/mol); isobutane has the lowest (Δ H = +36.8 kcal/mol and Δ H ‡ = 46.7 kcal/mol). Dehydrogenation to form an alkene and an adsorbed hydrogen molecule on the AlOH 2+ · T 6 cluster was also investigated and computed slightly more endothermic than the respective hydride abstraction. However, dehydrogenation showed a significantly lower activation enthalpy, especially for linear alkanes. For isobutane the results indicated a similar energy barrier for hydride abstraction and dehydrogenation. Larger, more realistic clusters and periodic reactivity studies are nevertheless needed to describe, in a more refined way, the energetics of these relevant catalytic reactions in zeolitic systems. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005