Adsorption of CO on LTA zeolite adsorbents: An IR investigation

The low temperature adsorption of CO on the zeolites K-LTA (3A) Na-LTA (4A) and Ca,Na-LTA (5A) has been investigated by IR spectroscopy. For comparison, the adsorption of CO on K-MOR, Na-MOR and Ca-MOR has also been studied. CO adsorption on K-LTA zeolite is mostly limited at the external surface. In the case of Na-LTA zeolite, terminal Na+ carbonyls are formed. In the case of Ca,Na-LTA zeolite, Ca2+ polycarbonyls and monocarbonyls are observed. In both Na-LTA and Ca,Na-LTA zeolites strongly bonded CO characterized by low CO stretching frequencies (2112 and 2107–2099 cm−1) are also observed. These have been identified as CO interacting with more than one cation, through both the C atom and the O atom. Ca2+ ions in Ca,Na-LTA zeolite are also bonded to extraframework hydroxyl and carbonate ions, which modify their coordination sphere. These results may be relevant in relation to the use of these zeolites as adsorbents for the removal of CO from fuel gases, such as hydrogen.