Synthesis of Discrete CHA Zeolite Nanocrystals without Organic Templates for Selective CO 2 Capture

Small‐pore zeolites such as chabazite (CHA) are excellent candidates for the selective separation of CO 2 ; however, the current synthesis involves several steps and the use of organic structure‐directing agent (OSDA), increasing their cost and energy requirements. We report the synthesis of small‐pore zeolite crystals (aluminosilicate) with CHA‐type framework structure by direct synthesis in a colloidal suspension containing a mixture of inorganic cations only (Na + , K + , and Cs + ). The location of CO 2 molecules in the host structure was revealed by 3D electron diffraction (3D ED). The high sorption capacity for CO 2 (3.8 mmol g −1 at 121 kPa), structural stability and regenerability of the discreate CHA zeolite nanocrystals is maintained for 10 consecutive cycles without any visible degradation. The CHA zeolite (Si:Al=2) reaches an almost perfect CO 2 storage capacity (8 CO 2 per unit cell) and high selectivity (no CH 4 was adsorbed).