A computational study on the mechanism of NO decomposition catalyzed by Cu-ZSM-5: A comparison between single and dimeric Cu⁺ active sites

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• 作者：Simone Morpurgo ; ^{simone.morpurgo@uniroma1.it} ; Giuliano Moretti ; Mario Bossa
• 关键词：DFT ; Zeolites ; Cu-ZSM-5 ; NO decomposition ; Reaction mechanism ; Energetic span model
• 刊名：Journal of Molecular Catalysis A ; Chemical
• 出版年：2012
• 期刊代码：57_13811169
• 类别：ch
• 出版时间：June, 2012
• 卷：358
• 期：Complete
• 页码：134-144
• 文件大小：1327 K

摘要

The present computational study investigates the mechanism of NO decomposition catalyzed by Cu-ZSM-5. It was considered that the active site could be of two kinds: (i) pairs of Cu⁺ ions located at opposite sides of the ten-membered rings of the zeolite, in the region at the intersection of the linear and sinusoidal channels; (ii) isolated Cu⁺ ions. DFT calculations were performed by using the B3LYP functional on cluster models suited to reproduce the geometrical constraints of the ZSM-5 structure. It was shown that both the Cu⁺-pair mechanism and that catalyzed by a single-Cu⁺ site proceed through the formation of N₂O as a reaction intermediate, which further reacts with the oxygen atom of a ZCu-O-CuZ or ZCuO unit (Z = zeolite) to give O₂ + N₂. The latter step displayed a larger activation energy in the Cu⁺-pair mechanism, which is therefore unfavored although the pathway associated to Cu⁺-pairs occurs at lower energy than that associated to a single-Cu⁺ site. Such a large activation energy is associated to the stability of the ZCu-O-CuZ fragment. A quantitative analysis, performed by means of the energetic span model of Kozuch and Shaik, reinforced the just outlined observations.