Highly Stable and Low-Cost Pure-Silica Zeolite with Narrow 8-Ring Pores: Unlocking Exclusive Carbon Dioxide...

The similar molecular sizes and physicochemical properties of carbon dioxide (CO₂) and hydrocarbons like methane (CH₄), acetylene (C₂H₂), ethylene (C₂H₄), and ethane (C₂H₆) make their separation a major industrial challenge. Here, we develop a low-cost, easily regenerable, pure-silica zeolite adsorbent "Instituto de Tecnología Química-55" (ITQ-55) capable of exclusively recognizing CO₂ over these hydrocarbons. Guided by three-dimensional electron diffraction (3D ED) and density functional theory calculations, we identified commercially available and cost-effective diquaternary ammonium compounds as alternative organic structure-directing agents (OSDAs), partially replacing the previously expensive and complex ones for the synthesis of pure-silica ITQ-55. The calcined ITQ-55 features narrow 8-ring pores that enable selective CO₂ adsorption while minimizing the uptake of CH₄, C₂H₂, C₂H₄, and C₂H₆. Notably, the uptake ratio of CO₂/C₂H₂ is much higher than that of currently reported CO₂-selective adsorption materials. Dynamic breakthrough tests reveal that ITQ-55 exhibits excellent separation performance for CO₂/C₂H₂, CO₂/CH₄, CO₂/C₂H₄, and CO₂/C₂H₆. In addition, the spent ITQ-55 adsorbent can be easily regenerated at 80 °C. Furthermore, theoretical calculations confirm that the separation mechanism of ITQ-55 for CO₂/hydrocarbons is a size-exclusion mechanism.