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.