MP2 study on decomposition of nitrous oxide on the Ga-ZSM-5статья

Статья опубликована в высокорейтинговом журнале

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[1] Solkan V. N., Zhidomirov G. M. Mp2 study on decomposition of nitrous oxide on the ga-zsm-5 // International Journal of Quantum Chemistry. — 2008. — Vol. 108, no. 14. — P. 2732–2743. The reaction mechanism for nitrous oxide decomposition has been studied on gallium site in Ga-ZSM-5 using the MP2/6-31 +G(d) method. The active centers were taken to be mononuclear [Ga] +, [Ga=O] +, and [GaO 2] + and the surrounding portion of the zeolite was represented by a 3T cluster, namely [AlSi 2O 4H 8] -. The first elementary step of N 2O decomposition involves the formation of [GaO] + and the release of N 2. The metal-oxo species produced in this step then reacts with N 2O again, to release N 2 and form [GaO 2] +. The calculated activation energies at MP2 level for N 2O dissociation on Ga-ZSM-5 and GaO-ZSM-5 are 15.7 and 26.5 kcal/mol at 298 K, respectively. The third elementary step of N 2O decomposition on GaO 2-ZSM-5 involves the formation of [GaO 3] + and the release of N 2. The calculated activation energy at MP2 level for N 2O dissociation on GaO 2-ZSM-5 is 43.7 kcal/mol. Four-order perturbation theory (MP4//MP2) predicts that the activation barriers for nitrous oxide dissociation at 298 K on Ga-ZSM-5, GaO-ZSM-5, and GaO 2-ZSM-5 are 13.9, 13.0, and 34.4 kcal/mol, respectively. The calculated energy for desorption of singlet O 2 from the 3T -[Ga(O) 3] + cluster at MP2 level is 33.4 kcal/mol. When one takes into account the entropy gained on desorption of singlet O 2, the contribution of entropy to the free energy of desorption is TΔS = 12.3 kcal/mol at 298 K. The calculated energy of the singlet oxygen desorption from 3T -[OGaO 2] + cluster ΔH (298 K) = +43.57 kcal/mol and ΔG(298 K) = 30.13 kcal/mol is significantly higher than the barriers of the singlet molecular oxygen desorption from 3T -[Ga(O) 3] + cluster. © 2008 Wiley Periodicals, Inc. [ DOI ]

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