CO2 Adsorption Behavior of Nanosized CHA Zeolites Synthesized in the Presence of Barium or Calcium Cations

Abstract Alkaline‐earth metal cations impact the rate of crystallization and the adsorption of N 2 and CO 2 on nanosized chabazite zeolites. In this study, either calcium or barium is added to precursor mixtures containing alkali‐metal cations (Na + , K + , Cs + ) to prepare chabazite (labeled Ca‐CHA and Ba‐CHA), and are compared to a reference sample (Ref‐CHA) synthesized using exclusively Na + , K + , and Cs + . Partial substitution of the Na + and the pore‐blocking Cs + extra‐framework cations is observed for Ca‐CHA depending on the molar ratio of K 2 O used in the synthesis, while a change to the amount of Na + cations only is observed for Ba‐CHA. The type of alkaline‐earth metal cation affects the crystallization rate; slower in the presence of Ca 2+ (10 h to full crystallinity) and similar rates in the presence of Ba 2+ (4 h to full crystallinity); the crystallite size and morphology remained similar. The presence of Ca 2+ or Ba 2+ extra‐framework cations leads to N 2 uptake values of 290 and 169 mmol g −1 (−196 °C, 100 kPa), respectively, while at low CO 2 pressure (<1 kPa, 25 °C), the physisorbed CO 2 capacity for Ref‐CHA, Ca‐CHA, and Ba‐CHA zeolites is 0.63, 0.66, and 0.59 mmol g −1 , respectively. Interestingly, an opposite effect is observed for the amount of chemisorbed CO 2 species.