Copper sites in Cu-ZSM-5 zeolites.: Part II.: An identification of defective AlOCu+ sites by FTIR

被引：12

作者：

Chen, L ^{[1
]}

Chen, HY ^{[1
]}

Lin, J ^{[1
]}

Tan, KL ^{[1
]}

机构：

[1] Natl Univ Singapore, Dept Phys, Surface Sci Lab, Singapore 119260, Singapore

来源：

INORGANIC CHEMISTRY | 1998年 / 37卷 / 20期

关键词：

D O I：

10.1021/ic980298i

中图分类号：

O61 [无机化学];

学科分类号：

070301 ; 081704 ;

摘要：

By in-situ FTIR study using CO as a probe molecule, a new type of Cu+ site, identified as defective (AlOdelta-)Cu+, was found to exist mainly in activated solution-exchanged Cu-ZSM-5, and was thought to derive from mixed ore-bridged Cu+ ions, (SiAlO)Cu+, due to high-temperature (400 degrees C) calcination. At room temperature the CO adsorption on this sample produced three infrared carbonyl bands at 21761 2156, and 2138 cm(-1). The first two bands, previously ascribed to the CO adsorbed at CU2+ sites and mixed ore-bridged (SiAlO)Cu+ ions, respectively, Vanished upon Ar purge at room temperature whereas the last band remained unaffected. The 2138 cm(-1) band was assigned to the CO adsorbed at defective (AlOdelta-)Cu+ site, and its desorption energy was higher than those at ore-bridged Cu+ and Cu2+ sites. The stronger Cu+-CO bonding and weaker C-O stretching are explained by a stronger pi back-donation due to the defective structure. The 2138 cm(-1) band was found to convert to the 2156 cm(-1) band during heating between 100 and 280 degrees C, with an estimated activation energy of the transition approximately equal to 4.8 kcal/mol. A reaction scheme is proposed to depict the mechanism of this transition.

引用

页码：5294 / 5298

页数：5

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