Unusual Carbonyl-Nitrosyl Complexes of Rh2+ in Rh-ZSM-5: A Combined FTIR Spectroscopy and Computational Study
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- 作者：Elena Ivanova ; Mihail Mihaylov ; Hristiyan A. Aleksandrov ; Marco Daturi ; Frederic Thibault-Starzyk ; Georgi N. Vayssilov ; Notker Rö ; sch ; Konstantin I. Hadjiivanov
- 刊名：Journal of Physical Chemistry C
- 出版年：2007
- 出版时间：July 19, 2007
- 年：2007
- 卷：111
- 期：28
- 页码：10412 - 10418
- 全文大小：191K
- 年卷期：v.111,no.28(July 19, 2007)
- ISSN：1932-7455
文摘
Adsorption of CO on Rh-ZSM-5 leads to the formation of the well-known Rh+(CO)2 gem-dicarbonyls, withvibrational frequencies 
rs/nu.gif" BORDER=0 >s(CO) at 2114 cm-1 and rs/nu.gif" BORDER=0 >as(CO) at 2048 cm-1, and the Rh2+(CO)2 species (2176 and2142 cm-1). The dicarbonyl structures have been proven by 12CO-13CO co-adsorption. The Rh2+(CO)2 speciesare not able to accommodate a third CO ligand even at 100 K, but in the presence of NO, they form Rh2+(CO)2(NO) complexes. These are characterized by rs/nu.gif" BORDER=0 >s(CO) at 2181 cm-1, rs/nu.gif" BORDER=0 >as(CO) at 2153 cm-1, and rs/nu.gif" BORDER=0 >(NO)at 1890 cm-1. The composition of the species is established using isotopic labeled molecules 13CO and 15NO.In excellent agreement with the values derived with an approximate force-field model, the Rh2+(12CO)(13CO)(NO) species have been found to display rs/nu.gif" BORDER=0 >(12CO) at 2168 cm-1 and rs/nu.gif" BORDER=0 >(13CO) at 2116 cm-1. Co-adsorption ofCO and a 14NO-15NO mixture reveals the existence of only one NO ligand in the complex. Complementarydensity functional modeling of both supported and isolated model complexes suggests the dicarbonyl complexesof Rh+ and Rh2+ to be planar and bound close to Al centers of the zeolite framework. While the location ofthe dinitrosyl complex of Rh+ in the zeolite framework is similar to that of dicarbonyls, the Rh2+(CO)2(NO)complex is considerably distorted in this position, and the simulated N-O frequencies differ strongly fromthe experimental ones. The vibrational frequencies of the ligands in the mixed complex are determined to besimilar to the experimental values only when the complex is bound to one zeolite oxygen center or when thecomplex is isolated inside the zeolite cavity. On this basis, it is concluded that insertion of a NO moleculein the Rh2+(CO)2 complex is accompanied by the breaking of one or two bonds between the Rh2+ cation andzeolite oxygen atoms.
rs/nu.gif" BORDER=0 >s(CO) at 2114 cm-1 and rs/nu.gif" BORDER=0 >as(CO) at 2048 cm-1, and the Rh2+(CO)2 species (2176 and2142 cm-1). The dicarbonyl structures have been proven by 12CO-13CO co-adsorption. The Rh2+(CO)2 speciesare not able to accommodate a third CO ligand even at 100 K, but in the presence of NO, they form Rh2+(CO)2(NO) complexes. These are characterized by rs/nu.gif" BORDER=0 >s(CO) at 2181 cm-1, rs/nu.gif" BORDER=0 >as(CO) at 2153 cm-1, and rs/nu.gif" BORDER=0 >(NO)at 1890 cm-1. The composition of the species is established using isotopic labeled molecules 13CO and 15NO.In excellent agreement with the values derived with an approximate force-field model, the Rh2+(12CO)(13CO)(NO) species have been found to display rs/nu.gif" BORDER=0 >(12CO) at 2168 cm-1 and rs/nu.gif" BORDER=0 >(13CO) at 2116 cm-1. Co-adsorption ofCO and a 14NO-15NO mixture reveals the existence of only one NO ligand in the complex. Complementarydensity functional modeling of both supported and isolated model complexes suggests the dicarbonyl complexesof Rh+ and Rh2+ to be planar and bound close to Al centers of the zeolite framework. While the location ofthe dinitrosyl complex of Rh+ in the zeolite framework is similar to that of dicarbonyls, the Rh2+(CO)2(NO)complex is considerably distorted in this position, and the simulated N-O frequencies differ strongly fromthe experimental ones. The vibrational frequencies of the ligands in the mixed complex are determined to besimilar to the experimental values only when the complex is bound to one zeolite oxygen center or when thecomplex is isolated inside the zeolite cavity. On this basis, it is concluded that insertion of a NO moleculein the Rh2+(CO)2 complex is accompanied by the breaking of one or two bonds between the Rh2+ cation andzeolite oxygen atoms.