FTIR study of the low-temperature adsorption and co-adsorption of CO and N2 on NaY zeolite:: evidence of simultaneous coordination of two molecules to one Na+ site

Na+ cations in S-Pi positions in NaY zeolite are able, at 85 K, to coordinate two CO or N-2 molecules as well as to form mixed Na+(CO)(N-2) species. In all these complexes, the ligands behave as independent oscillators. The Na+(N-15(2))(2) species (IR band at 2255.5 cm(-1)) are typical at equilibrium pressures > 30 Pa, whereas the respective linear complexes (band at 2258.5 cm(-1)) prevail at lower pressures. The dicarbonyls (band at 2163 cm(-1)) are the principal complexes observed at CO pressures higher than ca. 0.1 Pa and evacuation converts them to linear carbonyls (band at 2174 cm(-1)). The mixed Na+(CO)(N-15(2)) complexes [nu(C-O) at 2167 cm(-1) and nu(N-15-N-15) at 2254 cm(-1)] are produced during CO and N-15(2) co-adsorption and easily lose one N-15(2) ligand, being thus converted to linear carbonyls. (C) 1999 Elsevier Science B.V. All rights reserved.