CO2-Induced Displacement of Na+ and K+ in Zeolite |NaK|-A

Adsorption technologies offer opportunities to remove CO2 from gas mixtures, and zeolite A has good properties that include a high capacity for the adsorption of CO2. It has been argued that its abilities to separate CO2 from N2 in flue gas and CO2 from CH4 in raw biogas can be further enhanced by replacing Na+ with K+ in the controlling pore window apertures. In this study, several compositions of |Na12–xKx|-A were prepared and studied with respect to the adsorption of CO2, N2, and CH4, and the detailed structural changes were induced by the adsorption of CO2. The adsorption of CO2 gradually decreased on an increasing content of K+, whereas the adsorption of N2 and CH4 was completely nulled already at relatively small contents of K+. Of the studied samples, |Na9K3|-A exhibited the highest CO2 over N2/CH4 selectivities, with α(CO2/N2) > 21 000 and α(CO2/CH4) > 8000. For samples with and without adsorbed CO2, analyses of powder X-ray diffraction (PXRD) data revealed that K+ preferred to substitute Na+ at t...