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题名: On configuration of exchanged La3+ on ZSM-5: A theoretical approach to the improvement in hydrothermal stability of La-modified ZSM-5 zeolite
作者: Yang, G;  Wang, Y;  Zhou, DH;  Zhuang, JQ;  Liu, XC;  Han, XW;  Bao, XH
刊名: JOURNAL OF CHEMICAL PHYSICS
发表日期: 2003-11-08
DOI: 10.1063/1.1615762
卷: 119, 期:18, 页:9765-9770
收录类别: SCI
文章类型: Article
部门归属: 502
项目归属: 502
产权排名: 1;1
WOS标题词: Science & Technology ;  Physical Sciences
类目[WOS]: Physics, Atomic, Molecular & Chemical
研究领域[WOS]: Physics
英文摘要: Density functional calculations have been employed to investigate the locating and binding of lanthanum cation, i.e., La(OH)(2)(+), on HZSM-5 zeolite. Through geometry optimization, it was determined that lanthanum ions are favorably accommodated in the two 6-T rings of the straight channels (Clusters 1 and 2, see Sec. III A for details). Cluster 1 was found to exist in prior to Cluster 2 due to the preference of Al substitution in the T11 site (Cluster 1) rather than in the T8 site (Cluster 2). Geometry-optimization of Cluster 1 containing another two lanthanide ions Nd3+ and Yb3+ was also carried out and it was found that a monotonic decrease in Ln-O bond length will take place as the atomic number increases, conforming well to the rule of lanthanide contraction. Some of the optimized parameters are comparable to the corresponding experimental values in Y zeolite, which confirms that the optimized configurations are acceptable. The average frequencies of hydroxyls attached to La3+ or Yb3+ in Cluster 1 fall at 3609.16 and 3579.76 cm(-1), respectively, with the gap of these two frequencies close to that in the sodalite cage of Y zeolite. Compared to H-form zeolite, the charges on both Al and O atoms in Ln-ZSM-5 zeolite show an obvious increase, which will undoubtedly lead to a stronger mutual interaction and hence enhance the stability of the [AlO4](-) anion. Moreover, the Ln(OH)(2)(+) seem to have thickened the zeolite framework, which can effectively retard the process of dealumination. Through the evaluation of the possibility for dimer formation, it turned out that when the exchange degree arrived to approximately 0.28, lanthanum monomers began to aggregate into dimers, and were completely converted into dimers when the exchange degree approached 0.60. (C) 2003 American Institute of Physics.
关键词[WOS]: DENSITY-FUNCTIONAL METHODS ;  Y-ZEOLITES ;  ION-EXCHANGE ;  LANTHANUM ;  CATIONS ;  ALUMINUM ;  EARTH ;  RELAXATION ;  REDUCTION ;  NONRANDOM
语种: 英语
原文出处: 查看原文
WOS记录号: WOS:000186138700050
Citation statistics: 
内容类型: 期刊论文
URI标识: http://cas-ir.dicp.ac.cn/handle/321008/83339
Appears in Collections:中国科学院大连化学物理研究所_期刊论文

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作者单位: 1.Chinese Acad Sci, Dalian Inst Chem Phys, State Key Lab Catalysis, Dalian 116023, Peoples R China
2.Liaoning Normal Univ, Dept Chem, Dalian 116029, Peoples R China

Recommended Citation:
Yang, G,Wang, Y,Zhou, DH,et al. On configuration of exchanged La3+ on ZSM-5: A theoretical approach to the improvement in hydrothermal stability of La-modified ZSM-5 zeolite[J]. JOURNAL OF CHEMICAL PHYSICS,2003,119(18):9765-9770.
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