This work presents a study on the chemisorption of CO2 by a bed of Ca(OH)(2) powder subjected to the flow of a dry CO2/N-2 gas mixture (1 vol.% CO2) at ambient temperature and atmospheric pressure. The amount of CO2 and vapor water in the effluent gas from the fluidized bed is analyzed by means of FTIR spectrophotometry. The results obtained indicate that, even in an almost dry atmosphere (RH <= 0.01%), CO2 capture in the fluidized bed occurs by chemisorption on Ca(OH)(2), as inferred from the rise of vapor water at the end of the fast carbonation phase. The use of nanosilica as an additive increases the gas-solids contact efficiency and, therefore, enhances CO2 chemisorption on Ca(OH)(2) particles. This process is initially activated by free molecular water physisorbed on the material and becomes autocatalyzed by water produced from Ca(OH)(2) carbonation. Accordingly, the addition of hydrophilic nanosilica, capable of retaining higher amounts of free molecular water, yields a further enhancement of the CO2 fast sorption capacity. (C) 2013 Elsevier B.V. All rights reserved.