Quantum Chemical and FTIR Spectroscopic Studies on the Linkage Isomerism of Carbon Monoxide in Alkali-Metal- Exchanged Zeolites: A Review of Current Research
نویسندگان
چکیده
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 for free CO, while for O-bonded adducts this IR band appears below 2143 cm. 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.
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