K. Hadjiivanov et al., FTIR study of low-temperature CO and N-15(2) adsorption on a CaNaY zeolite: formation of site-specified Ca2+(CO)(3) and Ca2+(N-15(2))(3) complexes, PHYS CHEM P, 3(12), 2001, pp. 2531-2536
Adsorption of CO at room temperature on a CaNaY zeolite results in formatio
n of several species: Ca2+(CO) (2198 cm(-1)); Ca2+(CO)(2) (2188 cm(-1)), Ca
2+(OC) (2094 cm(-1)), Na+(CO) (2172 cm(-1)) and Na+(OC) (2119 cm(-1)). At 8
5 K no O-bonded CO is observable but, in addition to the C-bonded complexes
found at room temperature, two additional species have been detected: Ca2(CO)(3) (2185 cm(-1)) and Na+(CO)(2) (2167 cm(-1)). At high CO coverages (e
quilibrium CO pressures above ca. 100 Pa), the Ca2+(CO)(3) and Na+(CO)(2) s
pecies are predominant. The Ca2+(CO)(3) complexes are decarbonylated stepwi
se and first converted into Ca2+(CO)(2) and then into Ca2+(CO) species with
decreasing coverage. The latter are quite stable at 85 K. The Na+(CO)(2) s
pecies stepwise lose the two CO ligands. Adsorption of a (CO)-C-12-(CO)-C-1
3 mixture reveals that the CO ligands in the di- and tri-carbonyls behave a
s independent oscillators. Low temperature N-15(2) adsorption can also be e
xplained in terms of formation of Ca2+(N-15(2))(n)(n = 1-3) and Na+(N-15(2)
)(m) (m = 1-2) species. A theoretical model of the process is proposed and
adsorption isotherms well describing the experimental results are derived.