Adsorption of CO at room temperature on a CaNaY zeolite results in formation of several species : Ca2`(CO) (2198 cm~1) ; (2188 cm~1), Ca2`(OC) (2094 cm~1), Na`(CO) (2172 cm~1) and Na`(OC) (2119 Ca2`(CO) 2 cm~1). At 85 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 : (2185 cm~1) and (2167 cm~1). Ca2`(CO) 3 Na`(CO) 2 At high CO coverages (equilibrium CO pressures above ca. 100 Pa), the and species are Ca2`(CO) 3 Na`(CO) 2 predominant. The complexes are decarbonylated stepwise and Ðrst converted into and Ca2`(CO) 3 Ca2`(CO) 2 then into Ca2`(CO) species with decreasing coverage. The latter are quite stable at 85 K. The Na`(CO) 2 species stepwise lose the two CO ligands. Adsorption of a 12COÈ13CO mixture reveals that the CO ligands in the di-and tri-carbonyls behave as independent oscillators. Low temperature adsorption can also be 15N 2 explained in terms of formation of (n \ 1È3) and (m \ 1È2) species. A theoretical Ca2`(15N 2 ) n Na`(15N 2 ) m model of the process is proposed and adsorption isotherms well describing the experimental results are derived.
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