Separation of CO2 from light gas mixtures using nanoporous silicoaluminophosphate sorbents: Effect of multiple-step ion exchange and adsorption mechanism via computational studies

1H and 23Na MAS NMR spectroscopy of cationic species in CO2 selective alkaline earth metal porous silicoaluminophosphates prepared via liquid and solid state ion exchange

“…A detailed description of the synthesis is available elsewhere [5,7,34]. Detemplation was performed in partial or complete fashion via calcination in a computer controlled muffle furnace [35,36].…”

“…The resulting sample was denominated NH 4 þ -SAPO-34. Alkaline earth metals (Sr 2 þ or Ba 2 þ ) were introduced onto a fully detemplated SAPO-34 framework via LSIE using SrCl 2 Á 6H 2 O or BaCl 2 salts using the procedures described elsewhere [5,7]. The resulting samples were identified as either Sr 2 þ -SAPO-34 LSIE or Ba 2 þ -SAPO-34 LSIE.…”

“…The incorporation of alkaline earth metal cations into the framework of silicoaluminophosphate-34 (SAPO-34) has resulted in promising materials for the selective removal of CO 2 at temperatures and pressures that approach ambient conditions [1][2][3], particularly the variants containing Sr 2 þ and Ba 2þ extra-framework cations [3][4][5]. The sorbent is synergistically functionalized by the exposed Sr 2 þ or Ba 2 þ species and the small dimensions of the SAPO-34 cages, which when combined still do not provide transport resistance or pore blocking to the structure.…”

“…The sorbent is synergistically functionalized by the exposed Sr 2 þ or Ba 2 þ species and the small dimensions of the SAPO-34 cages, which when combined still do not provide transport resistance or pore blocking to the structure. Since the adsorption interactions are in the physisorption range, these sorbents can be fully regenerated by simple engineering methods (i.e., lowering pressure) [5][6][7].…”

“…Techniques such as conventional and multi step liquid state ion exchange [5,7], wetness impregnation [8] as well as solid state ion exchange [4,[9][10][11] have been studied to attain full exchange of the original charge-balancing species. However, full knowledge of the location and distribution of the charge-compensating cations inside zeolitic structures is of utmost importance to optimize ion exchange procedures and promote the occupancy of sites available for interaction with other extra-framework guest molecules or adsorbates (i.e., CO 2 ).…”