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In this study, CO 2 adsorption in the presence and absence of co-adsorbed H 2 O was investigated in zeolite Y. Several different zeolite Y materials were investigated including commercial NaY, commercial NaY ion-exchanged with Ba 2+ and nanocrystalline NaY; herein referred to as NaY, BaY and nano-NaY. Following heating of these zeolites to 573 K and cooling to room temperature, CO 2 was adsorbed as a function of pressure. FTIR spectra show that a majority of CO 2 adsorbs in the pores of these three zeolites (NaY, BaY and nano-NaY) in a linear complex with the exchangeable cation, as indicated by the intense absorption band near 2350 cm À1 , assigned to the n 3 asymmetric stretch of adsorbed CO 2 . Most interestingly is the formation of carbonate and bicarbonate on the external surface of nano-NaY zeolites as indicated by the presence of several broad absorption bands in the 1200-1800 cm À1 region, suggesting unique sites for CO 2 adsorption on the surface of the nanomaterial. For the other two zeolite materials investigated, bicarbonate formation is only evident in BaY zeolite in the presence of co-adsorbed water. Adsorption of 18 O-labeled carbon dioxide and theoretical quantum chemical calculations confirm these assignments and conclusions.

In this study, CO 2 adsorption in the presence and absence of co-adsorbed H 2 O was investigated on different nanomaterials including nanocrystalline NaY zeolite (nano NaY), ZnO, MgO and γ-Al 2 O 3 nanoparticles as well as mixed phase aluminum nanowhiskers. In the case of nano NaY, FTIR spectra show that a majority of CO 2 adsorbs in the pores of these zeolites in a linear complex with the exchangeable cation. Most interesting is the formation of carbonate and bicarbonate on the external surface of nano NaY zeolites, suggesting unique sites for CO 2 adsorption on the surface of these small nanomaterials. Adsorption of 18 O-labeled carbon dioxide and theoretical quantum chemical calculations confirms the assignment of these different species. For aluminum oxyhydroxide nanowhiskers and gamma alumina in the absence of co-adsorbed water, CO 2 reacts with surface hydroxyl groups to yield adsorbed bicarbonate as well as some carbonate. C 18 O 2 adsorption confirms these assignments. In the case of nanoparticulate ZnO, CO 2 adsorption under dry conditions results in formation of carbonate, bicarbonates as well as carboxylates. However, in the presence of co-adsorbed water, only carbonate species is formed. 18 O-labeled carbon dioxide adsorption and theoretical quantum chemical calculations confirm the vibrational assignment for these different species. Mixed isotope studies with H 2 16 O + C 18 O 2 and H 2 18 O + C 16 O 2 suggest that there is extensive exchange between oxygen in adsorbed water and oxygen atoms in gas-phase carbon dioxide. CO 2 adsorption on MgO surfaces, under dry conditions results in formation of carbonate and bicarbonates. Implications for the use of these nanomaterials in carbon dioxide uptake and storage are discussed. vi