Investigations into Li and Na Metal Oxide Carbon Capture Materials at High Temperatures

Abstract

The work undertaken in this thesis has led to deeper insight into the chemistry that occurs during the use and cycling of Li and Na based CO2 capture materials. A combination of techniques rigorously examined Li and Na based metal oxides already known to show significant CO2 capture capacity. The CO2 capture mechanism is explained through a core-shell model. Detailed studies into this mechanism and the layers shed more information used to fine tune the materials for CO2 capture. The initial candidate material was Na2ZrO¬3. TGA was combined with XRD to measure changes in physical mass and composition with successive cycles. The stability of the mass of the material over 1-, 2- and 5 cycles proved promising with only slight losses observed. X-ray spectroscopy (XAS) and particle size measurements revealed evidence of preferential reaction with smaller particles. NPD and SXRD identified and quantified all the possible products from the carbon capture process, including low temperature tetragonal-ZrO2 phase, both ex situ and in situ. Using the above knowledge, focus shifted to other materials to selectively apply the relevant techniques and expand on previous observations. The mechanism postulated for Li4SiO4 while Li2ZrO3 revealed an interesting increase in capacity with cycling, leading to the hypothesis that the process cracked the particles and increased their reactivity. XAS again revealed evidence for the particle effect, postulated for the Na2ZrO¬3. Ex situ studies were performed using NPD and quantified all the reaction products of Li4SiO4, Li2ZrO3, Li5AlO4 and Li6Zr2O7. Li6Zr2O7 was observed in a single space group setting, proving a group of studies correct, and was also observed to regenerate in a way that had not been observed which served to explain its mechanism for capacity loss. In situ SXRD studies investigated in detail Li4SiO4 and Li2ZrO3, supporting the previous observations in an experiment that more accurately modelled its real world application.