Formation of several types of coordination complexes upon CO adsorption on the zeolite Li-ZSM-5

Carbon monoxide adsorbed at 77 K on Li-ZSM-5 gives Li+···CO and Li+(CO)2 adducts characterized by C–O stretching bands at 2195 and 2188 cm−1, respectively. Variable temperature FTIR spectroscopy has shown that, at a higher temperature, formation of Li+···OC and Li+(CO,OC) species also occurs; the corresponding C–O stretching mode of O-bonded carbon monoxide appears at 2100 and 2110 cm−1, respectively. The relative amount of O-bonded CO increases with increasing temperature, in agreement with the fact that cation–CO interaction energy is higher for C-bonded carbon monoxide.