The Nature of Chemisorption and Physisorption of CO2 on Zeolite A

Title: The Nature of Chemisorption and Physisorption of CO₂ on Zeolite A

Speaker: Niklas Hedin, Stockholm University

Venue: Lecture Room, 3^rd floor, College of Chemistry and Chemical Engineering

Time: 16.00, Sept. 16, 2019

Abstract:

Zeolites are candidate materials for CO₂ capture from gas mixtures, and the traditional zeolite A seems to be a good model system to study the interactions occurring on adsorption and desorption of CO₂. Recently We have studied |Na_12-x K_x|-A compositions that displayed a maximally enhanced CO₂ – over – N₂, and CO₂ - over CH₄ selectivity when x≈3. With in-situ X-ray diffraction studies, we determined that the cations were displayed into the a-cavities of the zeolite during adsorption of CO₂. Additional in-situ neutron diffraction studies during the adsorption of CO₂ allowed us to determine three site-specific adsorption isotherms of the physisorbed CO₂, and an approximate position of the CO₂ that had chemisorbed. More details of the chemical nature of the chemisorbed CO₂ in zeolite |Na₁₂K|-A were revealed by in-situ solid state NMR methods and in-situ IR spectroscopy. In contrast to what has sometimes been argued for, we showed that CO₂ chemisorbed as mainly HCO₃ - species without the involvement of the framework oxygen atoms. Under some conditions CO₃^2- formed as well. About 6% of the adsorbed CO₂ was chemisorbed at 1 bar and 273K.