Quantum Chemical and FTIR Spectroscopic Studies on the Linkage Isomerism of Carbon Monoxide in Alkali-Metal-Exchanged Zeolites: A Review of Current Research

International Journal of Molecular Sciences

C. Otero Areán²  G. Turnes Palomino²  A. A. Tsyganenko¹ 

[1] Institute of Physics, St. Petersburg University, 198504 St. Petersburg, Russia;Departamento de Química, Universidad de las Islas Baleares, 07071 Palma de Mallorca, Spain

关键词: Alkali metal carbonyls;    CO adsorption;    FTIR spectroscopy;    Linkage isomerism;    Zeolites;   

DOI  :  10.3390/i3070764

来源: mdpi

【 摘 要 】

When adsorbed (at a low temperature) on alkali-metal-exchanged zeolites, CO forms both M(CO)⁺ and M(OC)⁺ carbonyl species with the extra-framework alkali-metal cation of the zeolite. Both quantum chemical and experimental results show that C-bonded adducts are characterized by a C−O stretching IR band at a frequency higher than that of 2143 cm^-1 for free CO, while for O-bonded adducts this IR band appears below 2143 cm^-1. The cation-CO interaction energy is higher for M(CO)⁺ than for M(OC)⁺ carbonyls, although the corresponding difference decreases substantially when going from Li⁺ to Cs⁺. By means of variable-temperature FTIR spectroscopy, this energy difference was determined for several alkali-metal cations, and the existence of a thermal equilibrium between M(CO)⁺ and M(OC)⁺ species was established. The current state of research in this field is reviewed here, with a view to gain more insight into the thermal isomerization process.

【 授权许可】

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