Date of Degree
PhD (Doctor of Philosophy)
Vicki H. Grassian
In this study, CO2 adsorption in the presence and absence of co-adsorbed H2O was investigated on different nanomaterials including nanocrystalline NaY zeolite (nano NaY), ZnO, MgO and λ-Al2O3 nanoparticles as well as mixed phase aluminum nanowhiskers. In the case of nano NaY, FTIR spectra show that a majority of CO2 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 CO2 adsorption on the surface of these small nanomaterials. Adsorption of 18O-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, CO2 reacts with surface hydroxyl groups to yield adsorbed bicarbonate as well as some carbonate. C18O2 adsorption confirms these assignments. In the case of nanoparticulate ZnO, CO2 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. 18O-labeled carbon dioxide adsorption and theoretical quantum chemical calculations confirm the vibrational assignment for these different species. Mixed isotope studies with H216O + C18O2 and H218O + C16O2 suggest that there is extensive exchange between oxygen in adsorbed water and oxygen atoms in gas-phase carbon dioxide. CO2 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.
Copyright 2010 Pragati Galhotra