A DFT study on the mechanism of NO decomposition catalyzed by short-distance Cu(I) pairs in Cu-ZSM-5

作者：Morpurgo Simone^*

来源：Molecular Catalysis, 2017, 434: 96-105.

DOI：10.1016/j.mcat.2017.01.028

• Zeolites
• Cu-ZSM-5
• DFT
• NO decomposition
• reaction mechanism

The complete NO decomposition catalyzed by short-distance Cu+ pairs in Cu-ZSM-5 was studied by means of DFT calculations. After adsorption of two NO molecules, an hyponitrite species is formed. Further decomposition of hyponitrite occurs with activation energies ranging from about 4 to 24 kcal mol(-1), depending on the initial geometry of the substrate-catalyst complex. An oxidized form of the catalyst, [Cu-O-Cu](2+) and a copper-coordinating N2O molecule are obtained. Further N2O decomposition may occur with oxygen transfer from N2O to [Cu-O-Cu](2+) and formation of N-2 and O-2, both adsorbed on the catalyst. Three different kinds of transition states were identified for the latter step, which appears to be rate-determining due to activation energies ranging from 39-40, to 44-45, and to 50-52 kcal mol(-1), respectively. After this, N-2 desorption occurs easily, whereas O-2 desorption is endothermic (from 28.8 to 36.5 kcal mol(-1)), the highest value being associated to reductive O-2 desorption from a peroxide-like complex. It turned out that the best way for N2O elimination is the direct, spin-forbidden decomposition on a reduced Cu+center dot center dot center dot Cu+ pair, with formation of [Cu-O-Cu](2+) and N-2, as already suggested in the literature. The problem of how the reduced catalyst may be regenerated is left open.

• 出版日期2017-6