Zeolite cage-lock strategy for in situ synthesis of highly nitrogen-doped porous carbon for selective adsorption of carbon dioxide gas

Abstract

Nitrogen-doped porous carbon (NPC) was prepared by directly carbonizing zeolite ZSM-39 containing a structure-directing agent, tetramethylammonium chloride (TMACl), which also acted as a source of C and N for NPC. The cage-like pore of zeolite ZSM-39 acted as an ideal space for immobilizing the C and N species. The obtained NPCs have a high N content up to 18.14%. The quaternary N of template TMACl was transformed into pyridinic and pyrrolic/pyridonic N during the carbonization. NPCs were suitable for selective adsorption of CO₂ because of their unique ultra-micropores and abundant basic sites. The adsorption selectivity of CO₂ over N₂ was more than 12.1 (molar ratio). The CO₂ adsorption capacity of the unit surface area for a NPC-723 sample was calculated as 26.6 μmol m⁻² at 0.93 bar and 273 K, which is one of the highest values among carbon adsorbents. Its excellent selectivity makes the NPC a good candidate for separating low concentrations of CO₂ in the purification of gas mixtures.