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

被引:27
|
作者
Morpurgo, Simone [1 ]
Moretti, Giuliano [1 ]
Bossa, Mario [1 ]
机构
[1] Univ Roma La Sapienza, Dipartimento Chim, I-00185 Rome, Italy
关键词
DFT; Zeolites; Cu-ZSM-5; NO decomposition; Reaction mechanism; Energetic span model; DENSITY-FUNCTIONAL THEORY; EXCHANGED ZSM-5 ZEOLITE; ZETA VALENCE QUALITY; GAUSSIAN-BASIS SETS; N-2; ADSORPTION; NITRIC-OXIDE; ROOM-TEMPERATURE; QUANTUM-MECHANICS; ION-EXCHANGE; COPPER IONS;
D O I
10.1016/j.molcata.2012.03.008
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
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 O-2 + N-2. 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. (C) 2012 Elsevier B.V. All rights reserved.
引用
收藏
页码:134 / 144
页数:11
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