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 N₂ and CO₂ 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 K₂O 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 Ca²⁺ (10 h to full crystallinity) and similar rates in the presence of Ba²⁺ (4 h to full crystallinity); the crystallite size and morphology remained similar. The presence of Ca²⁺ or Ba²⁺ extra‐framework cations leads to N₂ uptake values of 290 and 169 mmol g⁻¹ (−196 °C, 100 kPa), respectively, while at low CO₂ pressure (<1 kPa, 25 °C), the physisorbed CO₂ 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 CO₂ species.