| This work examines the nature of the adsorption of carbon dioxide onto calcined Layered Double Hydroxides (LDHs) of the magnesium/aluminum/gallium type. Additionally, this work investigates the effects of the gallium content of the LDHs as well as the effects of the potassium carbonate promotion of the LDHs on the carbon dioxide adsorption onto the calcined LDHs.; It was found that the addition of small amounts of gallium (<10% of M(III) cations) to the synthesis products used to construct the LDHs as well as the promotion of the LDHs with potassium carbonate increased the dry carbon dioxide adsorption capacity of the calcined LDH nearly threefold in comparison to the native unpromoted calcined hydrotalcite. The LDHs were characterized using Inductively Coupled Plasma Atomic Emission Spectroscopy, X-Ray Powder Diffraction, BET Surface Area techniques, Thermal Gravimetric Analysis, Scanning Electron Microscopy, Transmission Electron Microscopy, Infrared Spectrometry, and Temperature Programmed Carbon Dioxide Desorption. The reconstruction kinetics were also examined at ambient conditions, to identify the effects of gallium as well as potassium carbonate on the time needed to reconstruct the samples. Similarly, the decomposition of the various LDHs was investigated using controlled heating and off gas analysis using an Infrared Carbon Dioxide Detector. Finally, the carbon dioxide capacity as a function of the number of reversible carbon dioxide adsorption/desorption cycles was determined when the cycling gas contained water vapor. Using these techniques, several factors were identified which gave clues to the nature of the effects of potassium carbonate as well as gallium addition to the LDH. Expansion of the calcined lattice structure, as well as subtle changes in the thermal gravimetric analysis scans were noted. The combined effects of gallium addition and potassium carbonate promotion sufficiently change the decomposition and desorption profiles of these LDHs, with the decomposition profiles shifting to lower temperatures upon potassium carbonate promotion, and additional high strength base sites arising during carbon dioxide desorption for those sample containing potassium carbonate. |
