Adsorption of CO on NaY Faujasite: A Revisited FT-IR Study

The interaction between carbon monoxide (CO) and Na+ extra-framework cations has been studied at low temperature (80 K) by two adsorption procedures. Besides the classic one, CO adsorption on pyridine precovered NaY zeolite has been investigated and allows new IR spectral features to be assigned. Depending on the different pyridine precoverage level, three distinct C-O stretch vibrational bands of varying intensity and with maxima at 2175, 2163, and 2149 cm(-1) have been observed. Beyond the CO equilibrium pressure introduced, the bands' appearance and intensities depend on the amounts of preadsorbed pyridine. At low pyridine coverage, only the classical, prominent band at 2175 cm(-1) is present, while increasing pyridine coverage causes the appearance of the two additional bands. Furthermore, at higher pyridine coverage, the prominent band at 2175 cm(-1) completely vanishes. After recalling the different spread of experimental results and their assignments, arguments are presented to show that these three distinct C-O stretch vibrational bands result from the formation of weakly bound (CO)(n) complexes, n = 1-3 through a C-end interaction. Moreover, this study provides the first experimental evidence of the formation of tricarbonyl Na+(CO)(3) after CO adsorption at low temperature on NaY. This last result would confirm the three coordinative vacancies of Na+ cations in S-II positions. These carbonyl adducts are stabilized and underwent specific conditions that are discussed.