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

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.