The carbon dioxide adsorption properties of zeolite Rho materials, containing various exchangeable cations have been investigated. All carbon dioxide adsorption properties were measured at a temperature of 25 degrees C over a pressure range of 0-100 kPa. The results show that the carbon adsorption properties are dependent on the cations present. The highest amount of CO2 absorbed, measured at 4.0 mmol g(-1), was obtained for a proton-exchanged zeolite Rho (H Rho), which was prepared by the calcination of NH4+-exchanged zeolite Rho at 350 degrees C.