Synthesis of Discrete CHA Zeolite Nanocrystals without Organic Templates for Selective CO2 Capture

Abstract

Small-pore zeolites such as chabazite (CHA) are excellent candidates for the selective separation of CO₂ ; 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 CO₂ molecules in the host structure was revealed by 3D electron diffraction (3D ED). The high sorption capacity for CO₂ (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 CO₂ storage capacity (8 CO₂ per unit cell) and high selectivity (no CH₄ was adsorbed).

Keywords: CO2 adsorption; in situ PXRD; nanozeolites; precession-assisted 3D ED; template-free synthesis.